Iptv Testing Book

Althos Publishing404 Wake Chapel RoadFuquay-Varina, NC 27526 USA

IPTV Service Quality explains how to identify, measure, and analyze the operation,performance and quality of IPTV systems and services.

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This Book Covers:

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For Updates and Resources Visitwww.AlthosBooks.com

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If you need to understand how to moni-tor, test, and diagnose IPTV systems andservices, this book is for you.

Lawrence Harte

IPTV TestingIPTV TestingService Quality Monitoring, Analysis,

and Diagnostics for IP Television Systemsand Services

IPTV Testing

Lawrence Harte

Althos PublishingFuquay-Varina, NC 27526 USATelephone: 1-800-227-9681Fax: 1-919-557-2261email: [email protected]: www.Althos.com

Althos

All rights reserved. No part of this book may be reproduced or transmitted in anyform or by any means, electronic or mechanical, including photocopying recordingor by any information storage and retrieval system without written permissionfrom the authors and publisher, except for the inclusion of brief quotations in areview.

Copyright c 2008 By Althos PublishingFirst Printing

Printed and Bound by Lightning Source, TN.

International Standard Book Number: 1-932813-88-8

Every effort has been made to make this manual as complete and asaccurate as possible. However, there may be mistakes both typographi-cal and in content. Therefore, this text should be used only as a generalguide and not as the ultimate source of information. Furthermore, thismanual contains information on telecommunications accurate only up tothe printing date. The purpose of this manual to educate. The authorsand Althos Publishing shall have neither liability nor responsibility toany person or entity with respect to any loss or damage caused, or allegedto be caused, directly or indirectly by the information contained in thisbook.

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About the Author

Mr. Harte is the president of Althos, an expert information providerwhich researches, trains, and publishes on technology and businessindustries. He has over 29 years of technology analysis, development,implementation, and business management experience.

Mr. Harte managed a repair and calibration laboratory, createdmany test and measurement procedures, and is the inventor of sev-eral patents on communication systems. Mr. Harte has appeared on

television as an industry expert and has been referenced in over 75 communicationsrelated articles in industry magazines. He has been a speaker and moderator atnumerous industry seminars and trade shows.

Mr. Harte has worked for leading companies including Ericsson/General Electric,Audiovox/Toshiba and Westinghouse and has consulted for hundreds of other com-panies. Mr. Harte continually researches, analyzes, and tests new communicationtechnologies, applications, and services.

Mr. Harte has instructed communication courses at The Billing College, WrayCastle, Nokia, MCI, Panasonic, Telcordia, and at many other companies. He hasreceived numerous certificates and diplomas including IPTV, VoIP/InternetTelephony, 3G wireless, wireless billing, Bluetooth technology, Internet billing,cryptograph, microwave measurement, calibration, radar, nuclear power, DaleCarnegie, 360 leadership, and public speaking.

As of 2008, he has authored over 100 books on telecommunications technologies andbusiness systems covering topics such as mobile telephone systems, data communi-cations, voice over data networks, broadband, prepaid services, billing systems,sales, and Internet marketing. Mr. Harte holds many degrees and certificatesincluding an Executive MBA from Wake Forest University (1995) and a BSET fromthe University of the State of New York, (1990).

Introduction to IPTV Testing

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Table of Contents

IPTV TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

IPTV CONNECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1IPTV LAYERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3QUALITY OF SERVICE (QOS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5QUALITY OF EXPERIENCE (QOE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

WHY TEST FOR IPTV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

CUSTOMER SATISFACTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5NETWORK UTILIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6FAILURE PREDICTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6OPPORTUNITY IDENTIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6SERVICE LEVEL AGREEMENT (SLA) . . . . . . . . . . . . . . . . . . . . . . . . . 6

IPTV TESTING CHALLENGES . . . . . . . . . . . . . . . . . . . . . . . . . 7

MIXED MEDIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7CONTENT DEPENDENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7MULTIPLE CONVERSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7CONTENT PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9ERROR CONCEALMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

TESTING TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

OPERATIONAL TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10FUNCTIONAL TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

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Feature Function Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11END TO END TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11MULTILAYER TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11ACCEPTANCE TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11FIELD TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11DIAGNOSTIC TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12LOOPBACK TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12LABORATORY TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13ALPHA TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13BETA TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14PERFORMANCE TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14INTEROPERABILITY TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14LOAD TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15STRESS TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15SERVICE CAPACITY TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

CONTENT FLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

MEDIA CAPTURING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16COMPRESSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16PACKETIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16PACKET TRANSMISSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17PACKET RECEPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17DECOMPRESSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17DECODING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

IPTV SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

CONTENT AGGREGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19HEADEND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19CORE NETWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19ACCESS NETWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20PREMISES NETWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20VIEWING DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

AUDIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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AUDIO COMPRESSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Waveform Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Perceptual Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

VIDEO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

VIDEO COMPRESSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Spatial Compression (Image Compression) . . . . . . . . . . . . . . . .27Time Compression (Temporal Compression) . . . . . . . . . . . . . . .30Coding Redundancy (Data Compression) . . . . . . . . . . . . . . . . .32

VIDEO ELEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Pixels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Macroblocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Slice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

FRAMES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Intra Frames (I-Frames) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35Predicted Frames (P-Frames) . . . . . . . . . . . . . . . . . . . . . . . . . .35Bi-Directional Frames (B-Frames) . . . . . . . . . . . . . . . . . . . . . .36

FRAME RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36GROUPS OF PICTURES (GOP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37QUANTIZER SCALING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

MPEG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

MEDIA STREAM (MS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43ELEMENTARY STREAM (ES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44PACKET ELEMENTARY STREAM (PES) . . . . . . . . . . . . . . . . . . . . . . . 44PROGRAM STREAM (PS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45TRANSPORT STREAM (TS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

QUALITY METRICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

OBJECTIVE QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Mean Square Error (MSE) . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Peak Signal to Noise Ratio (PSNR) . . . . . . . . . . . . . . . . . . . . .49

SUBJECTIVE QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

AUDIO QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

AUDIO FIDELITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51FREQUENCY RESPONSE (FR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52TOTAL HARMONIC DISTORTION (THD) . . . . . . . . . . . . . . . . . . . . . . 52NOISE LEVEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52SIGNAL TO NOISE RATIO (SNR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

VIDEO QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

TILING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54ERROR BLOCKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54JERKINESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55RINGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56QUANTIZATION NOISE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56ALIASING EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56ARTIFACTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57OBJECT RETENTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58BRIGHTNESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59CONTRAST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59SLICE LOSSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59BLURRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59COLOR PIXELATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

TESTING MODELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

FULL REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60REDUCED RATE REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61ZERO REFERENCE (NON REFERENCE) . . . . . . . . . . . . . . . . . . . . . . . 62

NETWORK MEASUREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . 63

PACKET LOSS RATE (PLR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63PACKET DISCARD RATE (PDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65PACKET LATENCY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65PACKET JITTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Packet Delay Variation (PDV) . . . . . . . . . . . . . . . . . . . . . . . . . .65OUT OF ORDER PACKETS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

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GAP LOSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Packet Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

ROUTE FLAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69LOSS OF SIGNAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69ERROR FREE SECONDS (EFS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70BIT ERROR RATE (BER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70CONNECTION SUCCESS RATE (CSR) . . . . . . . . . . . . . . . . . . . . . . . . 70LINE RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70STREAM RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

CONTENT QUALITY MEASUREMENTS . . . . . . . . . . . . . . . . 71

DELAY FACTOR (DF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71FRAME COUNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71FRAME LOSS RATE (FLR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71MEDIA LOSS RATE (MLR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72BUFFER TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72REBUFFER EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72REBUFFER TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72STREAM INTEGRITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73AUDIO VISUAL SYNCHRONIZATION OFFSET . . . . . . . . . . . . . . . . . . . . 73TRANSPORT STREAM RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73PROGRAM STREAM RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74CLOCK RATE JITTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74JITTER DISCARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74COMPRESSION RATIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74PROTOCOL CONFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74PROGRAM TRANSPORT STREAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Program Association Table Error (PAT Error) . . . . . . . . . . . . .75Continuity Count Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Program Map Table Error (PMT Error) . . . . . . . . . . . . . . . . . .75Packet Identifier Error (PID Error) . . . . . . . . . . . . . . . . . . . . .75Transport Stream Synchronization Loss (TS-Sync Loss) . . . . .75Transport Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76Program Clock Rate Error (PCR Error) . . . . . . . . . . . . . . . . . .76Presentation Time Stamp Error (PTS Error) . . . . . . . . . . . . . .76

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Cyclic Redundancy Check Error (CRC Error) . . . . . . . . . . . . . .76Channel Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

IMAGE ENTROPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77MISSING CHANNELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

COMMAND AND CONTROL MEASUREMENTS . . . . . . . . . . 77

CHANNEL CHANGE TIME (ZAP TIME) . . . . . . . . . . . . . . . . . . . . . . . . 77Multicast Join Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79

SET TOP BOX INITIALIZATION TIME . . . . . . . . . . . . . . . . . . . . . . . . . 79ENCODER INITIALIZATION TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79CONNECT TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

CONTENT QUALITY RATING SYSTEMS . . . . . . . . . . . . . . . . 79

MOVING PICTURE QUALITY METRICS (MPQM) . . . . . . . . . . . . . . . . 80MEDIA DELIVERY INDEX (MDI) . . . . . . . . . . . . . . . . . . . . . . . . . . . 81V FACTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82VIDEO SERVICE TRANSMISSION QUALITY (VSTQ) . . . . . . . . . . . . . . 84VIDEO SERVICE PICTURE QUALITY (VSPQ) . . . . . . . . . . . . . . . . . . . 84VIDEO SERVICE AUDIO QUALITY (VSAQ) . . . . . . . . . . . . . . . . . . . . 84PERCEPTUAL EVALUATION OF VIDEO QUALITY (PEVQ) . . . . . . . . . . 84MEAN OPINION SCORE (MOS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Video Mean Opinion Score (MOS-V) . . . . . . . . . . . . . . . . . . . . .86Audio Mean Opinion Score (MOS-A) . . . . . . . . . . . . . . . . . . . .86Audiovisual Mean Opinion Score (MOS-AV) . . . . . . . . . . . . . .86Gap Video Mean Opinion Score (Gap MOS-V) . . . . . . . . . . . . .86Burst Video Mean Opinion Score (Burst MOS-V) . . . . . . . . . . .86

SINGLE STIMULUS CONTINUOUS QUALITY EVALUATION (SSCQE) . . . 87

TEST EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

VIDEO ANALYZER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87MPEG GENERATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88PROTOCOL ANALYZER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88BUILT-IN TEST EQUIPMENT (BITE) . . . . . . . . . . . . . . . . . . . . . . . . 88IMPAIRMENT EMULATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

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NETWORK MONITORING . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

MIRROR PORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Active Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89In Line Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90Hierarchical Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90Alarm Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

NETWORK PROBES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90Measurement Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90Reference Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

TEST CLIENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91HEARTBEAT GENERATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

FAULT MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

FAULT PREDICTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93FAULT FINDER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93FAULT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

APPENDIX I - ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

APPENDIX II - IPTV TEST EQUIPMENTMANUFACTUERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

INDEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Table of Contents

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Copyright ©, 2008, ALTHOS, Inc

IPTV Testing

IPTV testing is the performing of measurements or observations of a device,system or service that provides television service through data networks tovalidate its successful operation and/or performance. IPTV testing can becomplicated because there are many interrelated processes which all canreduce the quality of the media and processes that are used to control themedia flow.

IPTV systems differ from broadcast television systems as they use trans-mission systems that provide varying levels of performance. Broadcast sys-tems are designed for controlled continuous transmission while IPTV sys-tems use packet transmission that is subject to varying transmission pat-terns and packet losses (burst errors).

IPTV Connection

IPTV systems use switched video service (SVS) that dynamically setup (ondemand) video signal connections between two or more points. SVS servicescan range from the setup of data connections that allow video transfer to theorganization and management of video content and the delivery of video pro-grams.

Figure 1.1 shows how a basic IP television system can be used to allow aviewer to have access to many different media sources. This diagram showshow a standard television is connected to a set top box (STB) that convertsIP video into standard television signals. The STB is the gateway to an IPvideo switching system. This example shows that the switched video service(SVS) system allows the user to connect to various types of television mediasources including broadcast network channels, subscription services, andmovies on demand. When the user desires to access these media sources, thecontrol commands (usually entered by the user with a television remote con-trol) are sent to the SVS and the SVS determines which media source theuser desires to connect to. This diagram shows that the user only needs onevideo channel to the SVS to have access to virtually an unlimited number of

video sources.

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Figure 1.1, IPTV Video Connection

IPTV Layers

IPTV systems can be divided into multiple layers ranging from a layer thatphysically transports data to the layer that presents the media to the view-er. The divisions of the hierarchy are referred to as layers or levels, witheach layer performing a specific task. In addition, each protocol layerobtains services from the protocol layer below it and performs services to theprotocol layer above it.

The physical layer is responsible for converting bits of information into datapackets that are transferred on a network. The MAC layer is responsible forrequesting and coordinating access to the physical channel. The Internetprotocol (IP) layer is responsible for adding the network address to packetsso they can travel through the network to reach their destination. The trans-port layer is responsible for transferring packets (such as UDP/RTP)between the sender and the receiver. The session layer coordinates andoversees that transfer of the media components for the program channel(such as MPEG). The packet elementary stream (PES) layer maps and coor-dinates the media components to the transport streams. The applicationlayer coordinates the information interface between the communicationdevice and the end user or the program they are using.

Figure 1.2 shows an IPTV system that has been divided into multiple lay-ers. The physical layer is responsible for converting bits of information intodata packets that are transferred on a network. The MAC layer is responsi-ble for requesting access and coordinating the flow of information. TheInternet protocol (IP) layer is responsible for adding the network address topackets. The UDP/RTP (transport layer) is responsible for transferringpackets between the sender and the receiver. The MPEG transport streamlayer combines multiple media streams (audio and video) into a single pro-gram transport stream. The PES layer assigns media components (such asaudio and video) to specific packet streams. The application layer presentsthe media to the viewer.

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The operation of IPTV systems is commonly measured by a combination ofobjective quality of service (QoS) and quality of experience (QoE) evaluationprocesses.

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Figure 1.2, IPTV Layers

Quality of Service (QoS)

Quality of service (QoS) is one or more measurements of desired perfor-mance and priorities of a communications system. QoS measures mayinclude service availability, maximum bit error rate (BER), minimum com-mitted bit rate (CBR) and other measurements that are used to ensure qual-ity communications service.

Quality of Experience (QoE)

Quality of experience (QoE) is one or more measurements of the total com-munications experience or the entertainment satisfaction from the perspec-tive of the end user. QoE measures may include service availability, audioand video fidelity, types of programming, ability to use and the value ofinteractive services.

Why Test for IPTV

The benefits of testing IPTV systems include customer satisfaction, networkutilization, failure prediction, opportunity identification, and validation ofperformance for service level agreement terms.

Customer Satisfaction

Customer satisfaction is the perceived value that a customer has that aproduct or service fulfills their needs or desires. Customer satisfaction forIPTV systems can be influenced by the content offered, quality of service,features, cost, and other factors.

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Network Utilization

Network utilization is a comparison of how many network resources arebeing used as compared to the total amount of availability of networkresources. Testing can be used to determine how network resources areassigned and when additional resources need to be acquired (reducing theneed to overbuild).

Failure Predictions

Fault predictions are estimated unwanted conditions that are likely to occuras a result of measured or observed conditions. Testing can be used to iden-tify potential areas of a system that may fail reducing the cost of emergencyservice.

Opportunity Identification

Opportunity identification is the awareness of services or products that maybe provided to earn additional revenue, reduce cost, or increase customersatisfaction. IPTV testing can be used to identify people or customers thathave specific types of needs or buying patterns.

Service Level Agreement (SLA)

Service level agreements are a set of terms between a customer and a ser-vice provider that defines the services provided by the carrier and the per-formance requirements of the customer. The SLA may include fees and dis-counts for the services based on the actual performance level received by thecustomer. IPTV testing can be used to monitor and adjust services to ensurethey meet customer SLA levels.

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IPTV Testing Challenges

IPTV testing involves multiple types of tests because IPTV systems trans-mit mixed media, the service can be content dependent, there are multiplemedia conversion (encoding) processes, an inability to measure the qualityof protected (encrypted) content, and hidden distortion due to error conceal-ment techniques.

Mixed Media

Mixed media is the combining of media of different types. An example ofmixed media is the combining of video, audio, and text graphics on a videoor television monitor. The challenge that this can cause is in the way eachmedia type is processed as it is distributed through the network. Video andaudio processing functions can result in different amounts of delay or qual-ity resulting in acceptable quality on one type of media while another typeof media has an unacceptable quality level.

Content Dependent

Content dependency factors are a set of conditions such as rapid motiongraphics that can influence the display or perception of media. Contentdependency causes some types of content to look good while other types ofcontent look bad given the same network performance impairments. Thismeans that the user’s perceived quality can vary on the same networkdepending on the content that is sent through the network.

Multiple Conversions

Media conversions are the process of changing information from one formatto another format. There may be several conversion processes along the con-tent flow path in IPTV systems and one or more of them may degrade thequality of the media.

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IPTV media conversion commonly uses lossy media compression. Lossy com-pression is a process of reducing an amount of information (usually in digi-tal form) by converting it into another format (such as MPEG) that repre-sents the initial form of information. Each time the media is converted, addi-tional distortion occurs.

The content producer (such as a studio) provides the media to a content dis-tribution system (such as a satellite distribution system) usually in high-quality uncompressed form. Content distributors may compress the mediaand send it to broadcasters (such as IPTV systems). When it is received bythe IPTV systems, it is decoded and re-encoded for local distribution. The re-encoding process may be in another compressed format (such as MPEG-4).The encoder may change the media format from variable bit rate (VBR) toconstant bit rate (CBR). Each of these conversions can add distortion to themedia signal.

Figure 1.3 shows how content may be converted multiple times between itshigh-quality format and when the media is received by the viewing device.This example shows that the media is compressed and encoded into MPEG-2 before it is distributed via a satellite system. When the satellite signal isreceived at the cable head end, it is decoded, switched with other videosources, and re-encoded into MPEG-4 before it is distributed to the viewer.

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Content Protection

Content Protection is the end-to-end encryption system that prevents con-tent from being pirated or tampered with in a communication network (suchas in a television system). Content protection involves uniquely identifyingthe content, assigning the usage rights, scrambling and encrypting the dig-ital assets prior to play-out or storage (both in the network or end userdevices) as well as the delivering the accompanying rights to allow legalusers to access the content. When content is encrypted or uniquely encoded,it is usually not possible to analyze the underlying media.

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Figure 1.3, IPTV Multiple Conversions

Error Concealment

Error concealment is a process that is used by a coding device (such as aspeech coder) to create information that replaces data that has beenreceived in error. Error concealment is possible when portions of the signaloutput of the coder have some relationship to other portions of the signaloutput and that relationship can be used to produce an approximated signalthat replaces the lost information period (lost bits). Error concealmentmethods (such as repeating the last frame of video when a frame is lost) caninfluence the ability to accurately measure the effects of distortion (such aspacket loss).

Testing Types

There are many types of testing ranging from simple operational testing tomultilayer testing. Each testing type may have a set of test procedures asso-ciated with it to allow customer support and test personnel to reliably per-form the tests.

Operational Testing

Operational testing is the configuring of system equipment, application oftest signals (if required) and measuring or observation of signals and testresponses that ensure a system is operating correctly.

Functional Testing

Functional tests are observations and/or measurements that are performedduring normal operating conditions of a device, service or system to deter-mine if it can perform its designed functions.

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Feature Function Testing

Feature function testing is the verification of the desired operation of fea-tures and functional operations they are supposed to perform. Feature func-tion testing may involve the combination of features to determine how theyinteract and influence each other.

End to End Testing

End to end testing is the process of verifying a communication transmissionor service from its source (origin) to its end (termination). End to end test-ing can be used to verify that all the paths and systems are operating.

Multilayer Testing

Multilayer testing is the performing of measurements or observations of anetwork or system which interact with different functional levels such asphysical, link, transport, and session to help understand the operation orperformance of a device, system or service.

Acceptance Testing

Acceptance testing is the performing of measurements that determine if theoperations and performance of a system, subsystem, or component partswithin systems meet the required performance characteristics.

Field Testing

Field testing is the process of testing a device, assembly, or system at a loca-tion that typically involves its normal operation. Field testing commonlyinvolves the use of portable test equipment that is used by qualified testtechnicians.

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Diagnostic Testing

Diagnostic testing is the process of gathering information or data that canbe used to identify parts of a device or system that are performing undesiredprocesses or functions.

Loopback Testing

Loopback testing is the process of testing the transmission capability andfunctioning of equipment within a system in which a signal is transmittedthrough a loop that returns the signal to the source. The test verifies thecapability of the source to transmit and receive signals. Failure of one ormore of these tests can be used to isolate and help diagnose problems with-in the system.

Loopback testing can be used to verify the operation or performance of thesystem. To verify the performance of the network, the error rate, packet lossrate, and other network parameters can be tested in loopback mode. Duringerror testing, error correction processes (such as FEC) may be disabled sothat the automatic error correction processes do not interfere with thecounting of errors in the test signals.

Figure 1.4 shows how loopback testing can be used in an IP television sys-tem to progressively test, confirm, and identify failed equipments in por-tions of a network such as the core network, the access network, and the enduser viewer device. To verify the core network, the test signal is sent to theONU at the access network connection point where it is returned (looped)back to the headend. If the core network is verified, the test signal can besent to the modem at the access connection point portion of the networkwhere it is looped back to the headend. If the access network is operatingcorrectly, the test signal can be sent to the viewing device where it is loopedback to the headend. This verifies that all the links in the network are oper-ating correctly.

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Laboratory Testing

Laboratory testing is the process of measuring the characteristics or opera-tion of a device, assembly, or system at a location that typically involves itsdesign, prototyping or performance certification.

Alpha Testing

Alpha testing is the first stage in testing a new hardware or software prod-uct, usually performed by the in-house developers or programmers. Alphatesting is the initial internal and possibly limited field testing process usedto confirm the operation and performance of new hardware or software prod-

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Figure 1.4, IPTV Loopback Testing

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ucts. The key purpose of Alpha testing is to identify basic problems duringtypical operating conditions. The typical number of Alpha test participantsis 10 to 50.

Beta Testing

Beta testing is the field testing process used to confirm the operation andperformance of new hardware or software products before a product is offi-cially released. Beta testing is the second stage for testing a new hardwareor software product, usually performed by friendly customers or affiliates ofthe manufacturer or developer. The key purpose of Beta testing is to identi-fy problems and the reliability of operation during normal field operatingconditions. The typical number of Beta test participants is 50 to several hun-dred.

Performance Testing

Performance tests are measurements of operational parameters during spe-cific modes of operation. Performance tests are used to determine if thedevice or service is operating within its designed operational parameters.Performance tests can be performed over time to determine if a system isdeveloping operational problems.

Interoperability Testing

Interoperability testing is the performing of measurements or observationsof a device, system or service to determine if the device will operate withother devices of a similar type or with devices that have been designed andtested to specifications (e.g. industry standards). Interoperability testing isvery important to IPTV systems because different products, models, andsoftware versions may not operate as expected when used with other prod-ucts, models, and software versions.

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Load Testing

Load testing is the setup of a system where the services are consumed orprovided at defined rates such as near or at maximum designed capacitylimits. Load testing is performed to help ensure that a system will meet orexceed its performance requirements during high-capacity operating condi-tions.

Stress Testing

Stress tests are observations and/or measurements of devices or servicesunder operational conditions that are near or above their design limitations.Stress tests are performed to determine how a network or system will oper-ate under loaded or failed conditions.

Service Capacity Testing

Service capacity is the maximum amount of resources that can be effective-ly used to provide for processing or transmission of functions within a sys-tem or network. Service capacity testing gathers information about theusage patterns that exist in the network.

A data network may be monitored for several days to determine the capaci-ty and transmission delays at concentration points (routers and switches)within the network. A data network that has several routers can transferdata between computers in the company and other computers connected tothe Internet. As part of the IPTV capability pre-test, each router can bemonitored for peak data transfer activity detection for several days. Thishelps to determine if the data network lines and switching points haveenough capacity to provide both the data network and IPTV system needs.

Content Flow

Content flow in an IPTV system is the transfer of media from one function-al area to another. Content flow includes capturing media, compression,packetization, transmission, packet reception, decompression, and decodingof the media signal back into its original form.

Media Capturing

Media capturing is the process of gathering and processing signals or infor-mation. For IPTV systems, media capturing can involve the conversion fromanalog video to digital video (A/D conversion). Because the digital video datarates are relatively high (270 Mbps for standard definition video and 1.5Gpbs for high definition video), the digital video signal is compressed.

Compression

Compression is the processing of digital information to a form that reducesthe space required for storage. There are several types of compression thatcan be used for video and audio. Some of the compression techniques replacecommonly occurring sequences of characters by tokens that take up lessspace and others convert media segments to other formats that approximatethe media to dramatically reduce the data rate (lossy compression). Thehigher the compression level (MPEG-3 video is approximately 200:1 com-pression), the more sensitive the media is to distortion (such as corrupted orlost data packets).

Packetization

Packetization is the process of dividing data files or blocks of data intosmaller blocks (packets) of data. For IPTV systems, packetization involvesconverting media into fixed size data packets (MPEG packets). Each MPEGpacket only contains a certain type of media such as a video segment, audiosegment, or clock reference message. These packets are relatively small so

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several MPEG packets fit into the data portion (the payload) of an IP datapacket. This means that if one IP packet is lost during transmission, sever-al MPEG packets may be lost (including timing reference information).

Packet Transmission

Packet transmission is the process of addressing, transferring, and control-ling packets as they pass through switching points in a packet data network.A destination address is added to the header part of each packet before it issent into the packet data network. Control information (such as the maxi-mum number of transfers or hops that may occur) is also added to the pack-et header.

Packet Reception

Packet reception is the process of identifying and gathering packets with thecorrect destination address and routing them to the appropriate function orservice within the receiving device (via the port number on the IP address).Packet reception may involve the requesting of retransmission of missingpackets and filtering (elimination) of duplicate packets that are received.

Decompression

Decompression is the processing of compressed digital information to con-vert it into its original uncompressed format. IPTV systems decompressmultiple types of media such as video and audio.

Decoding

Decoding is the process of converting encoded data into its original signalformat. For IPTV systems, the decoding process may involve converting dig-ital audio and video into forms that can be played or displayed to the user.

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Figure 1.5 shows how video can be sent via an IP transmission system. Thisdiagram shows that an IP video system digitizes (A/D) and reformats (codes)the original media (video and audio). The system analyzes and compressesthe media. The IP address and transmission control information is added toeach packet. The packets travel through a packet data network. The receiv-er gathers and assembles the packets. The media is decompressed back intoits original video and audio data form. The data is then converted into itsoriginal video and audio forms.

IPTV System

IPTV systems deliver multiple video and audio channels to viewing devices.IP Television networks are primarily constructed of computer servers, gate-ways, access connections and end user display devices. Servers control theoverall system access and processing of channel connection requests andgateways convert the IP television network data to signals that can be usedby television media viewers.

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Figure 1.5, IPTV System Content Flow

IPTV system operators link content providers to content consumers. To dothis, IPTV systems gather content via a content acquisition network andconvert the content to a format that it can use via a headend system. It thenmanages (e.g. playout) the content via an asset management system andtransfers the content via a distribution network. The media is then convert-ed to display on the desired viewing devices.

Content Aggregation

Content aggregation is the process of combining multiple content sources fordistribution through other communication channels. Content (such asmovies or television programs) may be gathered or provided via communi-cation lines (leased lines), radio systems (satellite), or via stored media(DVDs or VHS tapes).

Headend

A headend is part of a television system that selects and processes video sig-nals for distribution into a television distribution network. A variety ofequipment is used at the headend, including antennas and satellite dishesto receive signals, preamplifiers, frequency converters, demodulators andmodulators, processors, and scrambling and de-scrambling equipment. Asystem may interconnect headends in different geographic regions throughthe use of regional or super headends.

Core Network

The core network is the central network portion of a communication system.The core network primarily provides interconnection and transfer betweenedge networks. Core networks for IPTV systems can be fiber optic rings thatcan simultaneously distribute (simulcast) simultaneously transmitted tele-vision signals (live channels) throughout a large geographic area and pro-vide connections to other media sources (such as direct connection to a tele-

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vision studio). The core network may also be used to provide individual con-nection to stored media programs (on demand programming).

Access Network

An access network is a portion of a communication network (such as thepublic switched telephone network) that allows individual subscribers ordevices to connect to the core network. IPTV access networks can be DSL,cable modem, wireless broadband, optical lines, or powerline data lines.

Premises Network

A premises distribution network (PDN) consists of the equipment and soft-ware that are used to transfer data and other media in a customer’s facilityor home. A PDN is used to connect terminals (computers) and media devices(such as TV set top boxes) to each other and to wide area network connec-tions. PDN systems may use wired Ethernet, wireless LAN, powerline, coax-ial and phone lines to transfer data or media.

Viewing Devices

A viewing device is a combination of hardware and software that can con-vert media such as video, audio or images into a form that can be experi-enced by humans. Viewing devices may contain support for servicing differ-ent media formats and compression (codec) formats, as well as being able tocommunicate using multiple types of access networks and streaming proto-cols.

Figure 1.6 shows a sample IPTV system. This diagram shows how the IPTVsystem gathers content from a variety of sources including network feeds,stored media, communication links and live studio sources. The headendconverts the media sources into a form that can be managed and distrib-uted. The asset management system stores, moves and sends out (playout)the media at scheduled times. The distribution system simultaneously

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transfers multiple channels to users who are connected to the IPTV system.Users view IPTV programming on analog televisions that are converted byadapter boxes (IP set top boxes), on multimedia computers or on IP televi-sions (data only televisions).

Audio

IP audio is the transfer of audio (sound) information in IP packet data for-mat. Transmission of IP audio involves digitizing audio, coding, addressing,transferring, receiving, decoding and converting (rendering) IP audio datainto its original audio form.

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Figure 1.6, IPTV System

Figure 1.7 shows how audio can be sent via an IP transmission system. Thisdiagram shows that an IP audio system digitizes and reformats the originalaudio, codes and/or compresses the data, adds IP address information toeach packet, transfers the packets through a packet data network, recom-bines the packets and extracts the digitized audio, decodes the data and con-verts the digital audio back into its original video form.

Audio Compression

Audio compression is a technique for converting or encoding audio (sound)information so that a smaller amount of information elements or reducedbandwidth is required to represent, store or transfer audio signals. Audio

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Figure 1.7, IP Audio System

compression coders and decoders (codecs) analyze digital audio signals toremove signal redundancies and sounds that cannot be heard by humans.Some of the basic coding processes include waveform coding, perceptual cod-ing and voice coding.

Audio compression systems can be lossless or lossy. Lossless compression isa coding system that analyzes a data or media signal and produces a newfile format that can be converted back to its exact original form. Losslesscompression searches the data or file for redundant patterns and convertsthem to smaller codes or tokens. Lossy compression is the process of reduc-ing an amount of information (usually in digital form) by converting it intoanother format (such as MP3 or AAC) that represents the initial form ofinformation. However, lossy compression does not have the ability to guar-antee the exact recreation of the original signal when it is expanded backfrom its compressed form.

Digital audio data is random in nature unlike digital video, which has repet-itive information that occurs on adjacent image frames. This means thataudio signals do not have a high amount of redundancy, making traditionaldata compression and prediction processes ineffective at compressing digitalaudio. It is possible to highly compress digital audio by removing soundsthat can be heard or perceived by listeners through the process of perceptu-al (lossy) coding.

The characteristics and limitations of human hearing can be taken advan-tage of when selecting, designing and using audio signals. The human earcan hear sounds from very low frequencies (20 Hz) to approximately 20 kHz.However, the ear is most sensitive to sounds in the 1 kHz to 5 kHz.

Compression ratio is a comparison of data that has been compressed to thetotal amount of data before compression. For example, a file compressed to1/4th its original size can be expressed as 4:1. In telecommunications, com-pression ratio also refers to the amount of bandwidth-reduction achieved.For example, 4:1 compression of a 64 kbps channel is 16 kbps.

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The type of coder (type of analysis and compression) can dramatically varyand different types of coders may perform better for different types of audiosounds (e.g. speech audio as compared to music). Key types of audio codinginclude waveform coding, perceptual coding and voice coders.

Waveform Coding

Waveform coding consists of an analog to digital converter and a data com-pression circuit that converts analog waveform signals into digital signalsthat represent the waveform shapes. Waveform coders are capable of com-pressing and decompressing voice, audio, music and other complex signalssuch as fax or modem signals. Because waveform coding processes representmost of the information in an audio signal waveform, waveform coders donot offer much compression. This commonly results in larger media files orhigher data transmission rates for waveform coders as compared to percep-tual coders or voice coders.

Perceptual Coding

Perceptual coding is the process of converting information into a format thatmatches the human senses’ ability to perceive or capture the information.Perceptual coding can take advantage of the inability of human senses tocapture specific types of information. For example, the human ear cannotsimultaneously hear loud sounds at one tone (frequency) and soft sounds atanother tone (different frequency). Using perceptual coding, it would not benecessary to send signals that cannot be heard even if the original signalcontained multiple audio components. Perceptual coding may remove fre-quency components (frequency masking) or sequences of sounds (temporalmasking) that a listener cannot hear.

Because audio coders compress information or data into codes or data thatrepresent tones or other audio attributes, small errors that occur duringtransmission can produce dramatically different sounds. As a result, errorsthat occur on some of the audio data bits (e.g. high volume levels or key fre-quency tones) can be more sensitive to the listener than errors that occur onother data bits. In some cases, error protection bits may be added to themore significant bits of the compressed audio stream to maintain the audioquality when errors occur.

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Figure 1.8 shows the basic operation of an audio codec. This diagram showsthat the audio coding process begins with digitization of audio signals. Thenext step is to analyze the signal into key parts or segments and to repre-sent the digital audio signal with a compressed code or set of codes that rep-resent the characteristics of the audio signal. The compressed code is trans-mitted to the receiving device that converts the code back into its originalaudio form.

Video

Digital video is a sequence of picture signals (frames) that are representedby binary data (bits) that describe a finite set of color and luminance levels.Sending a digital video picture involves the conversion of an image into dig-ital information that is transferred to a digital video receiver. The digitalinformation contains characteristics of the video signal and the position ofthe image (bit location) that will be displayed.

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Figure 1.8, Audio Codec Operation

IP video is the transfer of video information in IP packet data format.Transmission of IP video involves digitizing video, coding, addressing, trans-ferring, receiving, decoding and converting (rendering) IP video data into itsoriginal video form.

Figure 1.9 shows how video can be sent via an IP transmission system. Thisdiagram shows that an IP video system digitizes and reformats the originalvideo, codes and/or compresses the data, adds IP address information toeach packet, transfers the packets through a packet data network, recom-bines the packets and extracts the digitized video, decodes the data and con-verts the digital video back into its original video form.

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Figure 1.9, IP Video System

Video Compression

Video compression is the process of reducing the amount of transmissionbandwidth or the data transmission rate by analog processing and/or digitalcoding techniques. Moving pictures can be compressed by removing redun-dancy within each image (spatial redundancy) or between successive imagesover a period of time (temporal redundancy). When compressed, a video sig-nal can be transmitted on circuits with relatively narrow channel band-width or using data rates 50 to 200 times lower than their original uncom-pressed form.

Spatial Compression (Image Compression)

Spatial compression is the analysis and compression of information or datawithin a single frame, image or section of information.

One of the common forms of spatial compression is specified by the joint pic-ture experts group (JPEG). JPEG is a working committee under the aus-pices of the International Standards Organization (ISO) with the goal ofdefining a standard for digital compression and decompression of stillimages for use in computer systems. The JPEG committee has produced animage compression standard format that is able to reduce the bit per pixelratio to approximately 0.25 bits per pixel for fair quality to 2.5 bits per pixelfor high quality.

JPEG uses lossy compression methods that result in some loss of the origi-nal data. When you decompress the original image, you don’t get exactly thesame image that you started with despite the fact JPEG was specificallydesigned to discard information not easily detected by the human eye.

The JPEG committee has defined a set of compression methods that areused to provide for high-quality images at varying levels of compression upto approximately 50:1. The JPEG compression system can use compressionthat is fully reversible (no loss of information) or that is lossy (reversiblewith some loss of quality). However, this has a much lower compressionratio.

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JPEG compression typically works better for photographs and referencevideo frames (key reference frames) rather than line art of cartoon graphics.This is because the compression methods tend to approximate portions ofthe image and the approximation of lines or sharp boundaries tends to getblurry with unwanted artifacts.

The JPEG compression process begins by dividing a digital image intogroups of blocks. These blocks are then converted from a pixel domain (bitmaps) into a frequency domain (a group of images with different detail lev-els) using a discrete cosine transform (DCT) process. These frequency com-ponents are then converted into specific levels. The compression system maychoose to remove frequency components that have a limited amount of infor-mation (low levels) through a threshold process. The data is then com-pressed using run length encoding to remove (to represent) long sequencesby shorter codes (run length encoding) and then by variable length coding toconvert repeated sequences over varying lengths into shorter codes (variablelength encoding).

DCT is a form of frequency analysis that is applied to discrete signals (e.g.binary data) to produce an output that is composed of the frequency compo-nents and the levels (coefficients) that represent the original digital signal.A DCT output is composed of a DC component (basic intensity) and a seriesof increasing frequency components that reflect the complexity of the under-lying data.

DCT uses thresholding to vary the amount of compression on an image.Thresholding is the process of modifying numbers or measurements that arewithin a range or meet some criteria to produce a lower or lesser number ofdata elements. Thresholding is used in lossy data compression processes(such as image compression) to reduce the amount of data through the lossof accuracy of information that has little impact on the user.

In addition to analyzing and compressing images into its frequency compo-nents, the resulting data is then also compressed using run length encoding(RLE) and variable length encoding (VLE) processes. RLE represents repet-itive data information by a notation that indicates the data that will berepeated and how many times the data will be repeated (run length). VLE

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represents repetitive groups of data information by codes that are used tolook up the data sequence along with how many times the data will berepeated (variable length).

Figure 1.10 shows the basic process that can be used for JPEG image com-pression. This diagram shows that JPEG compression takes a portion(block) of a digital image (lines and column sample points) and analyzes theblock of digital information into a new block sequence of frequency compo-nents (DCT). The sum of these DCT coefficient components can be processedand added together to reproduce the original block. Optionally, the coeffi-cient levels can be changed a small amount (lossy compression) without sig-nificant image differences (thresholding). The new block of coefficients isconverted to a sequence of data (serial format) by a zigzag process. The datais then further compressed, first using run length coding (RLC) to reducerepetitive bit patterns and then using variable length coding (VLC) to con-vert and reduce highly repetitive data sequences.

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Figure 1.10, JPEG Image Compression

Time Compression (Temporal Compression)

Temporal compression is the analysis and compression of information ordata over a sequence of frames, images or sections of information.

One of the more common forms of temporal compression used for digital isspecified by the Motion Picture Experts Group (MPEG). MPEG is a workingcommittee that defines and develops industry standards for digital videosystems. These standards specify the data compression and decompressionprocesses and how they are delivered on digital broadcast systems. MPEGis part of International Standards Organization (ISO).

Temporal video compression involves analyzing the changes that occurbetween successive images in a video sequence so that only the differencebetween the images is sent instead of all of the information in each image.To accomplish this, time compression can use key frames and motion esti-mation.

Figure 1.11 shows how key frames can be used to reduce the amount of datathat is transmitted for video signals. This example shows two scenes in a

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Figure 1.11, Using Key Frames in Digital Video

video clip. The first scene is of a sail boat that is slowly moving across thehorizon on the water and the second scene is of a house on the shoreline.This example shows that a key frame is sent at the beginning of a scene andonly the changes to the key frame are subsequently sent. When a new sceneoccurs, a new key frame is sent.

Motion estimation is the process of searching a fixed region of a previousframe of video to find a matching block of pixels of the same size under con-sideration in the current frame. The process involves an exhaustive searchof the many blocks surrounding the current block from the previous frame.Motion estimation is a computer-intensive process that is used to achievehigh compression ratios. Block matching is the process of matching theimages in a block (a portion of an image) to locations in other frames of adigital picture sequence (e.g. digital video).

Figure 1.12 shows how a digital video system can use motion estimation toidentify objects and how their positions change in a series of pictures. Thisdiagram shows that a bird in a picture is flying across the picture. In eachpicture frame, the motion estimation system looks for blocks that approxi-mate other blocks in previous pictures. Over time, the digital video motion

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Figure 1.12, Motion Estimation

estimation system finds matches and determines the paths (motion vectors)that these objects take.

Coding Redundancy (Data Compression)

Coding redundancy is the repetition of information or bits of data within asequence of data. Using data compression can help to reduce coding redun-dancy. Data compression is a technique for encoding information so thatfewer data bits of information are required to represent a given amount ofdata. Some of the common forms of data compression used in video com-pression include run length encoding (RLE) and variable length encoding(VLE).

Figure 1.13 shows how video compression may use spatial and temporalcompression to reduce the amount of data to represent a video sequence.This diagram shows that a frame in a video sequence may use spatial com-pression by representing the graphic elements within the frame by objectsor codes. The first frame of this example shows how a picture of a bird thatis flying in the sky can be compressed by separating the bird image from theblue background and making the bird an object and representing the bluebackground as a box (spatial compression). The next sequence of imagesonly needs to move the bird on the background (temporal compression).

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Video Elements

Video images are composed of pixels. Digital video systems group pixelswithin each image into small blocks and these blocks are grouped into mac-roblocks. Macroblocks can be combined into slices and each image may con-tain several slices. Slices make up frames, which come in several differenttypes. The different types of frames can be combined into a group of pic-tures.

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Figure 1.13, Video Compression

Pixels

A pixel is the smallest component in an image. Pixels can range in size andshape and are composed of color (possibly only black on white paper) andintensity. The number of pixels per unit of area is called the resolution.More pixels per unit area provide more detail in the image.

Blocks

Blocks are portions of an image within a frame of video usually defined by anumber of horizontal and vertical pixels. For the MPEG system, each blockis composed of 8 by 8 pixels and each block is processed separately.

Macroblocks

A macroblock is a region of a picture in a digital picture sequence (motionpicture) that may be used to determine the motion compensation from a ref-erence frame to other pictures in a sequence of images. Typically, a frame isdivided into 16 by 16 pixel sized macroblocks, which is four 8 by 8-pixelblocks.

Slice

A slice is a part of an image that is used in digital video and is composed ofa continuous group of macroblocks. Slices can vary in size and shape.

Frames

A frame is a single still image within the sequence of images that comprisethe video. In an interlaced scanning video system, a frame comprises twofields. Each field contains half of the video scan lines that make up the pic-ture, with the first field typically containing the odd numbered scan linesand the second field typically containing the even numbered scan lines.

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To compress video signals, the MPEG system categorizes video images(frames) into different formats. These formats vary from frame types thatonly use spatial compression (independently compressed) to frame typesthat use both spatial compression and temporal compression (predictedframes).

MPEG system frame types include independent reference frames (I-frames),predicted frames that are based on previous reference frames (P-frames), bi-directionally predicted frames using preceding frames and bidirectionalframes (B-Frames).

Intra Frames (I-Frames)

Intra frames (I-Frames) are complete images (pictures) within a sequence ofimages (such as in a video sequence). I-frames are used as a reference forother compressed image frames and I frames are completely independent ofother frames. The only redundancy that can be removed from I frames isspatial redundancy. This means that I-frames usually require more datathan other types of compressed frames.

Predicted Frames (P-Frames)

Predicted frames (P-Frames) are images (pictures) within a sequence ofimages (such as in a video sequence) that are created using informationfrom other images (such as from I-Frames).

Since image components are often repeated within a sequence of images(temporal redundancy), the use of P-Frames provides substantial reductionin the number of bits that are used to represent a digital video sequence(temporal data compression).

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Bi-Directional Frames (B-Frames)

Bi-directional frames (B-Frames) are images (pictures) within a sequence ofimages (such as in a video sequence) that are created using informationfrom preceding images, or images that follow (such as from intra frames (I-Frames) and predicted frames (P-Frames).

Because B-Frames are created using both preceding images and images thatfollow, B-frames offer more data compression capability than P-Frames. B-frames require the use of frames that both precede and follow the B-frames.Because B-frames must be compared to two other frames, the amount ofimage processing that is required for B-frames (e.g. motion estimation) istypically higher than P frames.

Frame Rate

Frame rate is the number of images (frames or fields) that are displayed toa movie viewer over a period of time. Frame rate is typically indicated inframes per second (fps). The common frame rates for television signalsrange from 25 to 30 frames per second (fps) and 50 to 60 fields per second(fps).

To reduce the bandwidth of video streams, some frames can be dropped.Frame dropping is the process of discarding or not using all the video framesin a sequence of frames. The process of dropping frames can be prioritizedby dropping B frames first (lowest impact on video quality), P frames, and Iframes (very high impact on video quality). When a frame is dropped, it maybe replaced by an adjacent frame.

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When frames are dropped, the viewer may perceive motion judder distortionin the video. Motion judder is the perceived variations in a sequence ofimages. Viewers are more sensitive to motion judder during motion or highactivity scenes.

Groups of Pictures (GOP)

Frames can be grouped into sequences called a group of pictures (GOP). AGOP is an encoding of a sequence of frames (I-frame, P-frame, and B-frames) that contain all the information that can be completely decodedwithin that GOP. For all frames within a GOP that reference other frames(such as B-frames and P-frames), the frames so referenced (I-frames and P-frames) are also included within that same GOP.

The types of frames and their location within a GOP can be defined in time(temporal) sequence. The temporal distance of images is the time or numberof images between specific types of images in a digital video. M is the dis-tance between successive P-Frames and N is the distance between succes-sive I-Frames. Typical values for MPEG GOP are M equals 3 and N equals12.

The longer the GOP length, the lower the bandwidth that is used (highervideo compression). However, the longer the GOP length, the longer it takesfor a video error to be corrected as errors are propagated over the P and Bframes until the next I frame occurs.

Figure 1.14 shows how different types of frames can compose a group of pic-tures (GOP). A GOP can be characterized as the depth of compressed pre-dicted frames (m) as compared to the total number of frames (n). This exam-ple shows that a GOP starts within an intra-frame (I-frame) and that intra-frames typically require the largest number of bytes to represent the image(200 kB in this example). The depth m represents the number of frames thatexist between the I-frames and P-frames.

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Groups of pictures can be independent (closed) GOPs or they can be relative(open) to other GOPs. An open group of pictures is a sequence of imageframes that requires information from other GOPs to successfully decode allthe frames within its sequence. A closed group of pictures is a sequence ofimage frames that can successfully decode all the frames within its sequencewithout using information from other GOPs.

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Figure 1.14, MPEG Group of Pictures (GOP)

Because P and B frames are created using other frames, when errors occuron previous frames, the error may propagate through additional frames(error retention). To overcome the challenge of error propagation, I framesare sent periodically to refresh the images and remove and existing errorblocks.

Figure 1.15 shows how errors that occur in an MPEG image may be retainedin frames that follow. This example shows how errors in a B-Frame aretransferred to frames that follow as the B-Frame images are created frompreceding images.

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Figure 1.15, MPEG Error Retention

Quantizer Scaling

Quantizer scaling is the process of changing the quantizer threshold levelsto adjust the data transmission rates from a media encoder. The use ofquantizer scaling allows an MPEG system to provide a fixed data transmis-sion rate by adjusting the amount of media compression.

To perform quantizer scaling, image blocks (macroblocks) are converted intotheir frequency components through the use of discrete cosine transform(DCT). The DCT converts an image map into its frequency components(from low detail to high detail). Each frequency component is converted(quantized) into a specific value (coefficient). The accuracy of each of thesequantized values determines how closely the image block represents theoriginal image.

Because many of the frequency components hold small values (smallamounts of detail), it is possible to reduce the amount of data that repre-sents a block of an image by eliminating the fine details through the use ofthresholding. Thresholds are values that must be exceeded for an event tooccur or for data to be recorded. Quantizer scaling uses an adjustablethreshold level that determines if the level of frequency component shouldbe included in the data or if a 0 level (no information) should be transmittedin its place.

The higher the quantizer level, the higher the amount of compression.However, as the quantizer level increases, so do the image distortion levels.

Figure 1.16 shows how MPEG systems can use quantizer scaling to controlthe data rate by varying the amount of detail in an image. This exampleshows that an image is converted into frequency component levels and thateach component has a specific level. This example shows that setting thequantizer level determines if the coefficient data will be sent or if a 0 (nodata) will be used in its place.

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MPEG

Motion picture experts group (MPEG) standards are digital video transmis-sion and control processes that coordinate the transmission of multipleforms of media (multimedia). MPEG is a working committee that definesand develops industry standards for digital video systems. These standardsspecify the data compression and decompression processes and how they aredelivered on digital broadcast systems. MPEG is part of InternationalStandards Organization (ISO).

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Figure 1.16., MPEG Quantizer Scaling

The MPEG system defines the components (such as a media stream or chan-nel) of a multimedia signal (such as a digital television channel) and howthese channels are combined, transmitted, received, separated, synchro-nized and converted (rendered) back into a multimedia format.

The basic components of an MPEG system include elementary streams (theraw audio, data or video media), program streams (a group of elementarystreams that make up a program) and transport streams that carry multi-ple programs.

Figure 1.17 shows the basic operation of an MPEG system. This diagramshows that the MPEG system allows multiple media types to be used (voice,

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Figure 1.17, MPEG System

audio and data), codes and compresses each media type, adds timing infor-mation and combines (multiplexes) the media channels into an MPEG pro-gram stream. This example shows that multiple program streams (e.g. tele-vision programs) can be combined into a transport channel. When theMPEG signal is received, the program channels are separated (demulti-plexed), individual media channels are decoded and decompressed and theyare converted back into their original media form.

Media Stream (MS)

A media stream is a flow of information that represents a media signal (suchas digital audio or digital video). A media stream may be continuous (circuitbased) or bursty (packetized). MPEG systems are composed of various typesof streams ranging from the basic raw data stream (elementary streams) tostreams that contain a single television video (a program stream) or streamsthat combine multiple programs (transport streams).

The key elements to streaming in the MPEG system include combining mul-tiple packet streams into a single program or transport stream, adding thetime reference information into the streams, and managing the data buffersthat are required to receive and process the elementary streams regardlessof the varying packet transmission delays.

Figure 1.18 shows the basic process of streaming video programs through apacket data network. This diagram shows that media streaming involvesconverting media into a stream of packets, periodically inserting time refer-ences and controlling temporary buffer sizes. .

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Elementary Stream (ES)

Elementary streams are the raw information component streams (such asaudio and video) that are part of a program stream. MPEG system dividesa multimedia source component into an elementary stream (ES).Elementary streams may be video, audio or data and there may be severalelementary streams for each type of media (such as multiple audio channelsfor surround sound).

Packet Elementary Stream (PES)

A packet elementary stream is a raw information component stream (suchas audio or video) that has been converted to packet form (a sequence ofpackets). This packetization process involves dividing (segmenting) a groupof bits in an elementary stream and adding packet header information to the

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Figure 1.18, Media Streaming

data. This packet header includes a packet identification code (PID) thatuniquely identifies the packetized elementary stream from all other packe-tized elementary streams that are transmitted. PES packets are variablelength packets which have a length limit determined by 16 bits length fieldin the header of each packet.

PES streams may include time decoding and presentation time stamps thathelp the receiver to decode and present the media. Decoding time stampsare the insertion of reference timing information that indicates when thedecoding of a packet or stream of data should occur. A presentation timestamp is reference timing values that are included in MPEG packet mediastreams (digital audio, video or data) that are used to control the presenta-tion time alignment of media.

Program Stream (PS)

A program stream is a combination of elementary streams (such as videoand audio) that compose a media program (such as a television program). Aprogram stream is called a single program transport stream (SPTS). All thepackets in a program stream must share the same time reference systemtime clock (STC).

The packet sizes for program streams can have different lengths. For mediadistribution systems that have a low error rate, longer packets may be used.For media distribution systems that have medium to high error rates (suchas radio transmission or Internet systems), shorter packet lengths are typi-cally used.

Transport Stream (TS)

Transport Streams are the combining (multiplexing) of multiple programchannels (typically digital video channels) onto a signal communicationchannel (such as a satellite transponder channel). A MPEG transportstream (MPEG-TS) is also called a multi-program transport stream (MPTS).

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MPEG transport streams (MPEG-TS) use a fixed length packet size andeach transport packet within the transport stream is identified by a packetidentifier. A packet identifier in an MPEG system identifies the packetizedelementary streams (PES) of a program channel. A program (such as a tele-vision show) is usually composed of multiple PES channels (e.g. video andaudio).

Because MPEG-TSs can carry multiple programs, to identify the programscarried on a MPEG-TS, a program allocation table and program mappingtable are periodically transmitted, which provide a list of the programs con-tained within the MPEG-TS. These program tables provide a list of pro-grams and the associated PIDs for specific programs which allows theMPEG receiver/decoder to select and decode the correct packets for that spe-cific program.

MPEG transport packets are a fixed size of 188 bytes with a 4 byte header.The payload portion of the MPEG-TS packet is 184 bytes. The beginning ofa transport packet includes a synchronization byte that allows the receiverto determine the exact start time of the packet. This is followed by an errorindication (EI) bit that determines if there was an error in a previous trans-mission process. A payload unit start indicator (PUSI) flag alerts the receiv-er if the packet contains the beginning (start) of a new PES. The transportpriority indicator identifies if the packet has low or high priority. The 13 bitpacket identifier (PID) is used to define which PES is contained in the pack-et. The scrambling control flag identifies if the data is encrypted. An adap-tation field control defines if an adaptation field is used in the payload of thetransport packet and a continuity counter maintains a count index betweensequential packets.

Figure 1.19 shows an MPEG transport stream and a transport packet struc-ture. This diagram shows that the MPEG-TS packet has a fixed size of 188bytes including a 4 byte header. The header contains various fields includ-ing an initial synchronization (time alignment) field, flow control bits, pack-et identifier (tells which PES stream is contained in the payload) and addi-tional format and flow control bits.

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PES packets tend to be much longer than transport packets. This requiresthat the PES packets be divided into segments so they can fit into the 184byte payload of a transport packet. Each packet in the transport stream onlycontains data from a single PES. Since the division of PES packets into 184byte segments will likely result in a remainder portion (segment) that is notexactly 184 bytes, an adaptation field is used to fill the transport packet. Anadaptation field is a portion of a data packet or block of data that is used toadjust (define) the length or format of data that is located in the packet orblock of data.

Figure 1.20 shows how PES packets are inserted into an MPEG transportstream. This example shows how a video and an audio packet elementarystream may be combined on an MPEG-TS. This example shows that each ofthe PES packets is larger than each MPEG transport stream packet. EachPES packet is divided into segments that fit into the transport stream pack-ets.

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Figure 1.19, MPEG Transport Stream (MPEG-TS) Packet

Quality Metrics

Quality metrics are the gathering and/or use of values that indicate howaccurately a system or service can reproduce media or perform actions with-in desired levels.

Objective Quality

Objective quality is the determination of accuracy or the ability of a systemto provide desired results using evaluation criteria and sources that arerepeatable. Objective quality of video signals can be calculated by compar-ing the pixel locations or signal levels in a source (reference) image to thepixel location or signal levels in a received image. These calculations can bein the form of average or peak error between the images or signals.

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Figure 1.20, Transferring MPEG PES packets into TS Packets

Mean Square Error (MSE)

Mean square error is the sum of the average error amount squared adjust-ed for by offset bias squared. MSE indicates the expected amount of error fora sample set of values.

Peak Signal to Noise Ratio (PSNR)

Peak signal to noise ratio is a measure of the difference between the maxi-mum received signal level and the level of interfering signals (noise). Thelarger the PSNR level, the better the quality. For video signals, a PSNR thathas less than 20 dB (100x) is considered unwatchable.

Subjective Quality

Subjective quality is determination of accuracy or the ability of a system toprovide desired results using evaluation sources that can vary (such as theopinions of people) for determining the amount of a quantity or quality ofdata or media.

Audio Quality

Audio quality is the ability of a speaker or audio transfer system to recreatethe key characteristics of an original digital audio signal. Some of the mea-sures of audio quality include fidelity, frequency response, total harmonicdistortion, noise level and signal to noise ratio.

The type of audio coder that is used along with its compression parametersinfluences digital audio quality. Audio compression devices reduce the datatransmission rate by approximating the audio signal and this may add dis-tortion.

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Packet loss and packet corruption errors will result in the distortion or mut-ing of the audio signal. The compression type influences the amount of dis-tortion that occurs with packet loss or bit errors. Audio coders that havehigh compression ratios (high efficiency) tend to be more sensitive to packetloss and errors. Even when small amounts of error occur in a speech coder,the result may be very different sounds (a “warble”) due to the use of code-books. Warbles are sounds that are produced during the decoding of a com-pressed digital audio signal that has been corrupted (has errors) duringtransmission. The warble sound results from the creation of differentsounds than those originally sent. Muting is the process of inhibiting audio(squelching). Muting can be automatically performed when packet loss isdetected.

Figure 1.21 shows some of the causes and effects of audio distortion in IPTelevision systems. This example shows that audio signals are digitized,compressed and error protection coded prior to transmission. During thetransmission process, some packets are lost or corrupted. The loss of pack-ets can result in the temporary muting of the audio signal. Because the data

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Figure 1.21, IP Audio Distortion

compression process represents sounds by different codes that represent theoriginal audio signal, packet corruption results in the creation of a differentaltered sound than the sound that was previously transmitted. When thereis significant data corruption, unusual artifact sounds (“Warble” sounds)can be created.

Audio Fidelity

Audio fidelity is the degree to which a system or a portion of a system accu-rately reproduces upon its output, the essential characteristics of the signalimpressed upon its input. Audio fidelity can be determined by comparing anoriginal (reference) audio signal with a received audio signal to determinethe difference levels. The difference in signal levels represents the distortionthat occurs between the source and receiver of the audio signal.

Figure 1.22 shows how to measure audio fidelity. This diagram shows thatfidelity testing can identify the distortion that is added at various places inthe recording, transmission and recreation of an audio signal. This example

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Figure 1.22, Audio Fidelity Testing

explains that the same reference test signal is applied to the input of thesystem and to a comparator. The comparator removes the original referencesignal to show the amount of distortion that is added in the transmissionand processing of the signal.

Frequency Response (FR)

Frequency response is a measure of system linearity or performance inreproducing signals across a specified bandwidth. Frequency response isexpressed as a frequency range with a specified amplitude tolerance in deci-bels. Frequency response in digital audio systems is typically limited to onehalf the sampling frequency (Nyquist limit).

Total Harmonic Distortion (THD)

Total harmonic distortion is a ratio of the combined amplitudes of all signalsrelated harmonically to the amplitude of a fundamental signal. THD is typ-ically expressed as a percentage of signal level.

Noise Level

Noise level is a measure of the combined energy of unwanted signals. Noiselevel is commonly specified as a ratio (in decibels) of noise level on a givencircuit as compared to decibels above reference noise level for an electricalsystem or decibels sound pressure level for an acoustical system.

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Signal to Noise Ratio (SNR)

Signal to noise ratio is a comparison of the information-carrying signalpower to the noise power in a system. For SNR testing, a connection is setupand a test audio signal is applied to the transmitter. The energy level at thereceiving end is measured and recorded. The audio test signal is thenremoved and the energy level at the receiving end (the noise) is measuredand recorded. The difference between these two levels (commonly convertedto dB) is the signal to noise ratio.

Video Quality

Digital video quality is the ability of a display or video transfer system torecreate the key characteristics of an original digital video signal. Digitalvideo and transmission system impairments include tiling, error blocks,jerkiness, artifacts (edge busyness) and object retention.

Distortion indicators are characteristics values of media (such as errorblocks on a video display) that can be used to qualify and quantify distortioncharacteristics. Distortion indicators for video signals can include differ-ences in brightness (luminance), differences in color components (Cr, Cb),and time shifts in object or frame display.

Figure 1.23 shows some of the causes and effects of video distortion thatmay occur in IP Television systems. This example shows that video digiti-zation and compression convert video into packets that can be sent throughdata networks (such as the Internet). Packet loss and packet corruptionresult in distorted video signals. This example shows that some types of dis-tortion include tiling, error blocks and retained images.

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Tiling

Tiling is the changing of a digital video image into square tiles that arelocated in positions other than their original positions on the screen. Tilingcan occur during a burst of data errors where multiple blocks are incorrect-ly displayed.

Error Blocks

Block distortion (blockiness) is a variation in graphics display where squareor rectangular areas of the display have been changed. Block distortion canoccur in compressed image or video signals that use media blocking for com-pression (areas of the graphics are compressed separately) when some of theblocks or lost or distorted.

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Figure 1.23, IP Video Distortion

Error blocks are groups of image bits (a block of pixels) in a digital video sig-nal that do not represent error signals other than the original image bitsthat were supposed to be in that image block.

Figure 1.24 shows an example of how error blocks are displayed on a digitalvideo signal. This diagram shows that transmission errors result in the lossof picture blocks. In this example, the error blocks continue to display untila new image that is received does not contain the errors.

Jerkiness

Jerkiness is the holding or skipping of video image frames or fields in a dig-ital video. Jerkiness may occur when a significant number of burst errorsoccur during transmission resulting in the inability of a receiver to displaya new image frame. Instead, the digital video receiver may display the pre-vious frame to minimize the perceived distortion (a jittery image is betterthan no image).

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Figure 1.24, Digital Video Error Blocks

Ringing

Ringing is the process of the inclusion of repetitive variations (such as rip-ples in a video) that results from the conversion (quantization) of a mediasignal. Ringing can be reduced or eliminated through the use of a capturesystem that can detect and compensate for ringing variations.

Quantization Noise

Quantization noise (or distortion) is the error that results from the conver-sion of a continuous analog signal into a finite number of digital samplesthat can not accurately reflect every possible analog signal level.Quantization noise is reduced by increasing the number of samples or thenumber of bits that represent each sample. This term also is known as quan-tization distortion.

Quantization noise in video signals appears as a display of distortions(snow) across an entire image. Quantization noise can be caused by theprocesses or settings in the capture card or A/D converter assembly.

Aliasing Effects

Aliasing effects are unwanted distortions that result from the conversion ofan image where the sampling of the image is at a speed less than half of themost rapid changes in the image. Aliasing effects commonly appear as linesor ripples in the scanned or converted image.

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Artifacts

Artifacts are unintended, unwanted aberrations in media or information(such as blocks on a video image or speckles on a picture image aroundsharp edges). Artifacts may be created during the media compressionprocess. A common artifact that is produced in digital video systems is mos-quito noise.

Mosquito noise is a blurring effect that occurs around the edges of imageshapes that have a high contrast ratio. Mosquito noise can be createdthrough the use of lossy compression when it is applied to objects that havesharp edges (such as text).

Figure 1.25 shows an example of mosquito noise artifacts. This diagramshows that the use of lossy compression on images that have sharp edges(such as text) can generate blurry images.

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Figure 1.25, Mosquito Noise Artifacts

Object Retention

Object retention is the keeping of a portion of a frame or field on a digitalvideo display when the image has changed. Object retention occurs whenthe data stream that represents the object becomes unusable to the digitalvideo receiver. The digital video receiver decides to keep displaying theexisting object in successive frames until an error free frame can bereceived.

Advanced compression systems (such as MPEG-4) can represent compo-nents of media as objects rather than video. This means that object reten-tion may occur only in parts of IPTV systems that use MPEG-4 compression.

Figure 1.26 shows a how a compressed digital video signal may have objectsretained when errors occur. This example shows an original sequence where

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Figure 1.26, Digital Video Object Retention

the images have been converted into objects. When the scene change occurs,some of the bits from image objects are received in error, which results inthe objects remaining (a bird and the sail of a boat) in the next few imagesuntil an error free portion of the image is received.

Brightness

Brightness is an attribute of a video display which is the amount of lightthat a display appears to emit. The eye is more sensitive to the intensity(brightness) of some colors than others.

Contrast

Contrast is the range of light-to-dark values of an image. For video signals,contrast is proportional to the difference between black and white voltagelevels of the video signal. The contrast control adjusts video gain (white bar,white reference).

Slice Losses

Slice losses are sequential blocks of display information that are lost orunable to be displayed.

Blurring

Blurring is the reduction of detail images or sequences of images near theboundaries of graphics areas on the display. Because the amount of blurringthat can occur increases as the amount of compression increases, blurringcan become more pronounced during video sequences that have high motionor activity.

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Color Pixelation

Color pixelation is the changing of small image elements (pixels) on a graph-ics image or display. Color pixelation can occur when the format of media ischanged or sent through a transcoder process.

Testing Models

Testing models are a set of equipment configurations and tests that can beused to identify and quantify the operation or performance of devices, sys-tems, or services. IPTV testing models can use full reference, partial refer-ence, or zero reference testing models.

Full Reference

Full reference testing is the process of verifying the operation or perfor-mance of a system using a comparison between the received signal and thecomplete original signal.

Video quality measurement full reference is a subjective testing process forvideo that is defined in ITU-T J.144. The full reference video quality systemranks the quality using a variety of metrics including MOS, blockiness, blurand PSNR. Because full reference testing requires both the original signaland the signal under test, it is commonly used for laboratory testing whereboth are available at the same location.

Figure 1.27 shows how full reference testing compares an original signal(full reference) with a received or test signal to determine the quality oraccuracy of the signal. The first step for full reference testing is to time alignthe signals (image frames) so they can be compared. The components (pixellocation and levels) are then compared to determine the error between thereference signal and the signal (PSNR) under test.

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Reduced Rate Reference

Reduced rate reference testing is the process of verifying the operation orperformance of a system using a comparison between the received signaland a portion of the original signal. Reduced rate reference testing can beused to provide an end to end reliable test while using a small amount ofbandwidth for the reduced rate signal.

Figure 1.28 shows how reduced rate reference testing compares a portion ofan original signal (partial reference) with a received or test signal to deter-mine the quality or accuracy of the signal. The reduced rate reference is cre-ated from portions or components of the original reference signal. After thereduced rate testing is time aligned, the portion of the signal to be comparedis spatial aligned. The components (pixel location and levels) within thereduced area are then compared to determine the error between the refer-ence signal and the signal (PSNR) under test.

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Figure 1.27, Full Reference Testing

Zero Reference (Non Reference)

Zero reference testing is the process of verifying the operation or perfor-mance of a system using characteristics of the received signal without usingany of the original signals.

IPTV zero reference testing can determine the quality of a system using lossof signal information, error rate, data format, and by determining how thedata is processed (compression levels).

Figure 1.29 shows how zero rate reference testing evaluates the quality oraccuracy of a received or test signal using information contained within thesignal (no reference signal required). This example shows that zero refer-ence testing for video signals can detect missing packets, packet jitter, andmedia display errors (missing I, P, and B frames). This example shows thatthe loss of a B-frame has relatively low impact on the viewer as only a sin-gle frame is lost.

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Figure 1.28, Reduced Rate Reference Testing

Network Measurements

Network measurements are the identification and quantity determinationof data related to the operation and performance of a network. Some of thekey network measurements for IPTV systems include packet loss rate, errorrate, latency, delay, and jitter.

Packet Loss Rate (PLR)

Packet loss rate is a ratio of the number of data packets that have been lostin transmission compared to the total number of packets that have beentransmitted. Packet loss rate can be a significant challenge for IPTV sys-tems as each IP packet can hold up to 7 MPEG media packets.

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Figure 1.29, Zero Reference Testing

IP systems are designed to lose packets during temporary increases in datatraffic. If packets are not discarded in IP data networks, the capacity of thesystem is overbuilt. The key to a successful IP data network is to design thesystem to discard packets that have low priority or low impact on the ser-vice they are providing.

Figure 1.30 shows how some packets may be lost during transmissionthrough a communications system. This example shows that several pack-ets enter into the Internet. The packets are forwarded toward their desti-nation as usual. Unfortunately, a lighting strike corrupts (distorts) packet 8and it cannot be forwarded. Packet 6 is lost (discarded) when a router hasexceeded its capacity to forward packets because too many were arriving atthe same time. This diagram shows that the packets are serialized to allowthem to be placed in correct order at the receiving end. When the receivingend determines a packet is missing in the sequence, it can request thatanother packet be retransmitted. If the time delivery of packets is critical(such as for packetized voice), it is common that packet retransmissionrequests are not performed and the lost packets simply result in distortionof the received information (such as poor audio quality).

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Figure 1.30, Packet Loss Rate

Packet Discard Rate (PDR)

Packet discard rate is a ratio of the number of data packets that have beeneliminated during reception compared to the total number of packets thathad to be eliminated.

Packet Latency

Packet latency is the amount of time delay between the sending of a packetto the time when the packet is received or decoded. Packet latency is causedby a combination of delays that include transmitter queuing time (waitingfor a transmit slot), transmission propagation time (packet travel time) andpacket processing time (switching).

Packet Jitter

Packet jitter is the undesirable random change in the arrival rate of pack-ets. Packet jitter can be caused by changes in packet travel paths (routeflapping) and changes in how packets are received, processed, and forwardby routers in the connection path.

To overcome packet jitter, packet buffering can be used. Packet buffering isthe process of temporarily storing (buffering) packets during the transmis-sion of information to create a reserve of packets that can be used duringpacket transmission delays or retransmission requests. While a packetbuffer is commonly located in the receiving device, a packet buffer may alsobe used in the sending device to allow the rapid selection and retransmis-sion of packets when they are requested by the receiving device.

Packet Delay Variation (PDV)

Packet delay variation is the difference between the maximum and mini-mum possible delay that a packet will experience as it goes out over a com-munication channel. PDV is used by applications to determine the amount

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of buffer space needed at the receiving side in order to restore the originaldata transmission pattern.

Figure 1.31 shows how packet buffering can be used to reduce the effects ofpacket delays and packet loss for streaming media systems. This diagramshows that during the transmission of packets from the media server to theviewer, some of the packet transmission times vary (jitter) and some of thepackets are lost during transmission. The packet buffer temporarily storesdata before providing it to the media player. This provides the time neces-sary to synchronize the packets and to request and replace packets thathave been lost during transmission.

Out of Order Packets

Out of order packets are the receipt of packets in an order than was origi-nally processed or scheduled. Out of order packets can occur due to variabletransmission delays. Packets may take different routes to reach their desti-nation or routers in the connection path resulting in varying transmissiontimes.

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Figure 1.31, Packet Buffer

Out of order packets may cause additional distortion because MPEG packetsequencing from the encoder is not necessarily the same sequence that isrequired by the decoder. The decoding and presentation times for framesmay not be the same because some of the frames may be created from futureframes.

Out of order packets may be measured by an out of sequence packet rate.Out of sequence packet rate is the ratio of the number of packets that havebeen received out of sequence to the total number of packets that have beenreceived.

The quality of packet delivery can also be indicated by measuring the num-ber of duplicated packets. Duplicate packet rate is the ratio of the numberof packets that have been received more than one to the total number ofpackets that have been received.

Figure 1.32 shows how packets may arrive out of order when transmittedthrough a packet network. Packets may travel through the network over dif-ferent paths which can result in variable transmission delays. Some proto-

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Figure 1.32, Out of Order Packets

cols add a packet sequence number that allows the received packets to bereassembled in the correct order.

Gap Loss

Gap loss is the number of packets or data that are not able to be received orprocessed due to a transmission delay that exceeds the amount of jitterbuffer time. Gap length is the amount of time between the beginning andend of gap losses (when packets arrive after the buffer can accept them).

Gap loss rate is the ratio of the number of packets that have not beenreceived during a gap interval (when packets arrive after the buffer canaccept them) to the total number of packets that should have been received.

Packet Gap

Packet gap is the time duration between successive packets. If the packetgap is excessive, the packet may be discarded if the time delay is higherthan the jitter buffer time.

Figure 1.33 shows how inter-packet gap loss can occur in IPTV systems.This diagram shows 3 media sources (channels). Each of these channels areproviding an MPEG transport stream (MPEG-TS) that contains a mix ofvideo (V), audio (A), and program clock reference - PCR (C) packets. SevenMPEG-TS packets are put into the payload of an IP data datagram (packet).These packets are combined onto a single transmission channel through arouter. The time duration between these packets is the inter-packet gaptime. This example shows that when other packets are mixed in with thepackets (from other parts of the network), the inter-packet gap time canincrease.

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Route Flapping

Route flapping is the continual changing of a network connection path thatresults from an intermittent congestion period or loss of circuit connectionthat indicates to the current router connection path that there is a loss inconnection or that a better connection path exists. This causes the packetrouting path to continually change. These different paths can result in sig-nificant variance in transmission delay times (excessive jitter). Router flap-ping is overcome by newer IPV6 protocols and reservation protocols.

Loss of Signal

Loss of signal is the inability of a receiver or device to successfully receive orprocess a signal.

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Figure 1.33, Inter-Packet Gap

Error Free Seconds (EFS)

Error free seconds are the amount of time that a signal or operation hasbeen performed without any errors.

Bit Error Rate (BER)

BER is calculated by dividing the number of bits received in error by thetotal number of bits transmitted. It is generally used to denote the qualityof a digital transmission channel.

Connection Success Rate (CSR)

Connection success rate is a measure of how many connection requestattempts have achieved their desired or allowable connection results.Connection success rates can be influenced by network activity or packetcongestion resulting in the inability for devices or services to request and toreceive an assigned a service connection.

Line Rate

Line rate is the total amount of information that is transferred over atransmission line during a specific period of time.

Stream Rate

Stream rate is the amount of media information (the stream) that is trans-ferred through a system or to a device over a specific period of time.

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Content Quality Measurements

Content quality measurements are the identification and quantity determi-nation of how accurately media can be rendered (displayed) to a user. Someof the key measurements for IPTV for content include delay factor, frameloss rate, media loss rate, rebuffering events, stream integrity, and syn-chronization offset.

Delay Factor (DF)

The media delay factor can be used to determine how long a media streammust be buffered to prevent packet loss and it can provide information thatdetermines the amount of jitter that occurs within a network. Packet delayis the amount of time packets take to travel from their source to their des-tination. Packet delay occurs due to the processing time of routers, trafficcongestion and the ability of packets to take alternative routes to reach theirdestination.

Frame Count

Frame count is the number of frames that have been transferred or receivedover a period of time. Frame count may be divided into categories of framessuch as independent frames (I-frames), predictive frames (P-frames), orbidirectional frames (B-frames).

Frame Loss Rate (FLR)

Frame loss rate is a ratio of the number of frames (data or image frames)that have been lost in transmission compared to the total number of framesthat have been transmitted.

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Media Loss Rate (MLR)

Media loss rate is a ratio of the number of data packets that have been lostin transmission compared to the total number of packets that have beentransmitted over a period of time (such as over 1 second).

Buffer Time

Buffer time is the duration that occurs between the request to setup a bufferstorage area to when a buffer begins to provide data to an application or ser-vice. Buffer time should be long enough to ensure enough packets are avail-able to continuously supply the application when packet transmissiondelays occur. For IP media streaming services, buffer time can be severalseconds.

Rebuffer Events

Rebuffer events are processes that initiate the setup of a new buffer.Rebuffer events may be triggered when a buffer runs out of data due to longpacket transmission delays or a high number of packet retransmissionrequests. Rebuffer events usually cause video or audio to stop playing on thelast available media frame. Like buffer delays, rebuffer events can last forseveral seconds. Rebuffer events may be measured over a time period (suchas 15 rebuffer events per hour).

Rebuffer Time

Rebuffer time is the time period that occurs from when a request forrebuffering is initiated to when media playing starts again. Rebuffer timecan be used to calculate the rebuffer ratio, which is the amount of rebuffertime as compared to the amount of play time.

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Stream Integrity

Stream integrity is the accuracy of a sequence of data or information as com-pared to its original information source. Stream integrity may be verifiablethrough the use of protocol analysis and error detection codes that are sentalong with the original data information.

Audio Visual Synchronization Offset

Audio visual synchronization offset is the time duration between the play-ing of audio information as compared to the associated video components(such as facial characteristics) of a presentation. Synchronization offset canvary due to transmission and processing delays that vary between eachmedia stream.

Transport Stream Rate

Transport stream rate is the amount of data or media information for a com-bination of control and data transport (the transport channel) that is trans-ferred through a system or to a device over a specific period of time. A trans-port stream may contain multiple program or communication channels.

Transport Streams are the combining (multiplexing) of multiple programchannels (typically digital video channels) onto a signal communicationchannel (such as a satellite transponder channel). These channels may bestatistically combined in such a way that the bursty transmission (highvideo activity) of one channel is merged with the low-speed data transmis-sion (low video activity) of other channels so that more program channelscan share the same limited bandwidth communication channel.

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Program Stream Rate

Program stream rate is the amount of data or media information in a com-bination of control and media for a program (such as the audio and videomedia sources in a television program) that is transferred through a systemor to a device over a specific period of time.

Clock Rate Jitter

Clock rate jitter is the undesirable random changes that occur in a clock tim-ing reference signal (such as a program clock rate - PCR)

Jitter Discards

Jitter discard are the number of packets that are eliminated due to exces-sive fluctuating (jitter) delay time.

Compression Ratio

Compression ratio is a comparison of data that has been compressed to thetotal amount of data before compression. The higher the compression ratio,the more sensitive the media is to bit errors, delays, and packet loss.Content quality measurement systems such as V Factor may use compres-sion ratio as a factor for the determination or rating of quality level.

Protocol Conformance

Protocol conformance is the ability of a device or system to communicate andprocess commands according to the syntax (structure) of a protocol specifi-cation or its rules.

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Program Transport Stream

A program transport stream is the combination (multiplexing) of multiplemedia streams (typically audio and video streams) on a signal transportchannel. IPTV systems may measure various components of a transportstream including table (program data) errors, continuity count, and syn-chronization loss.

Program Association Table Error (PAT Error)

A program association table contains the identification codes and systeminformation associated with MPEG programs that are contained in a trans-port stream. The PAT is usually sent every 20 msec to 100 msec to allow thereceiver to quickly acquire a list of available programs.

Continuity Count Error

A continuity count is a measure of how many packets in a sequence of pack-ets are lost, duplicated, or repeated.

Program Map Table Error (PMT Error)

Program map table error contains information that identifies and describesthe components (such as the video and audio elementary streams) that arepart of a program (such as a television show).

Packet Identifier Error (PID Error)

A packet identifier is information that is contained within a packet thatidentifies the contents and format of the packet. A packet identifier in anMPEG system identifies the elementary stream (ES) of a program channel.

Transport Stream Synchronization Loss (TS-Sync Loss)

Transport stream synchronization loss is the inability of a signal or processto time align itself or relate its information with data and media that is

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included in a transport stream. Synchronization loss can occur due to theloss or excessive delay of a packet containing MPEG PCR.

Transport Error

Transport error is a variation in the command structure, processing, oralteration of data that occurs on a transmission channel. Transport errorcan be detected by reviewing the header information of the transport pack-ets.

Program Clock Rate Error (PCR Error)

Program clock rate error is the reception of program clock rate values ormessages at times that are outside the expected receipt time limits (typical-ly 100 msec for PCR).

Presentation Time Stamp Error (PTS Error)

Presentation time stamp error is the reception of a time reference value forpresentation of media that is beyond a time limit (typically over 700 msecfor MPEG).

Cyclic Redundancy Check Error (CRC Error)

Cyclic redundancy check error is receipt of data which does not match thecyclic redundancy check validation process.

Channel Map

A channel map is a listing of media components within a transport channel(such a programs within an MPEG transport stream).

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Image Entropy

Image entropy is a measure of the amount of information that is containedwithin an image or display sequence. A high image entropy level usuallyindicates a higher level of image complexity or image objects. Image entropymay be used as a factor in determining the amount of compression that canbe used (less entropy, more compression).

Missing Channels

Missing channels are programs or data streams that are not available orcannot be received by recipients. A test set or network probe may monitorfor missing channels to determine where a stream or group of streams arelost (ended) within a network.

Command and Control Measurements

Control protocols are commands, processes and procedures that are used fordelivering and controlling the real-time delivery of media (such as audio andor video streaming). Control protocols control the setup, playing, pausing,recording and tear down of streaming sessions. Control protocols that areused for IPTV systems include real time streaming protocol (RTSP) and dig-ital storage media command and control (DSM-CC).

Channel Change Time (Zap Time)

Channel change time (CCT) is the period of time that occurs from when auser presses the channel change button on the remote until a stable pictureappears for the requested channel. Channel changing time is the sum of theindividual delays associated with processing in the set top box, communica-tion with the network, IGMP join & leave, channel rights validation, andfinally, acquisition and synchronization with the video stream itself.

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Channel change delay can be a significant amount of time associated withchanges in media stream signals (such as IPTV).

Identifying the causes of delays in channel change time can be difficult assome systems can use a fast channel change process that increases (bursts)the data transmission rate during a channel change request. This fills upthe buffer quickly which reduces the channel change time.

Figure 1.34 shows some of the contributors to channel change time in IPTVsystems. Channel change time is the sum of the individual delays associat-ed with processing the channel change request in the set top box, sending aIGMP join message to the nearest multicast router that is carrying thechannel, channel rights validation, adding the device to the multicast rout-ing table, filling up the channel buffer for the new channel, and presentingthe media to the viewer.

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Figure 1.34, Channel Change Time

Multicast Join Time

Multicast join time is the duration between the start of a multicast joinrequest process and when the media is received by the group participant.

Set Top Box Initialization Time

Set top box initialization time is the duration between when a set top box ispowered on (power button pressed) to when it begins to play media on a dis-play.

Encoder Initialization Time

Encoder initialization time is the duration between when an encoder (suchas a video encoder that is installed in a news broadcast vehicle) to xxx

Connect Time

Connect time is the time interval that occurs between the initiation of a ser-vice request (such as selecting an audio file to play) and when the servicebegins (when the audio starts playing).

Content Quality Rating Systems

Content quality rating systems analyze and process multiple measurementsto provide an indication of the relative quality level content. Some of the keyrating systems include moving picture quality metrics, media deliveryindex, and V Factor.

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Moving Picture Quality Metrics (MPQM)

Moving picture quality metrics is a video quality rating score that is calcu-lated using a mix of content dependent factors along with a combination ofnetwork impairments such as delay and packet loss rate. MPQM is a realtime quality monitoring system that is based on a model of the human visionsystem. MPQM is a single ended test system so it does not require compar-ative reference signals. The MPQM factor score ranges from 1 to 5.

MPQM uses entropy analysis to determine the amount of information in anobject or media (which can be expressed in units) and the program clock ref-erence in its signal quality analysis. Entropy analysis is used to determinethe complexity and value of the content. MPQM uses network impairmentssuch as packet delay, error rate, and packet loss as factors to the qualityscore.

Figure 1.35 shows that the MPQM quality metrics system uses measure-ments from timing jitter, image entropy, and network impairments to deter-

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Figure 1.35, MPQM Testing Model

mine the quality score The program clock reference is verified to determinetiming jitter and network measurements are used to determine qualitypacket loss. The MPQM system also evaluates the type of content to deter-mine the entropy that can influence how the video is displayed.

Media Delivery Index (MDI)

Media delivery index is a measure of the transmission of digital video sig-nals. Key MDI measurement parameters include media delay factor (MDI-DF) and media loss rate (MDI-MLR). MDI is displayed as delay factor:medialoss rate (DF:MLR). MDI is defined by RFC 4445.

Because MDI involves simple network measurements (lightweight calcula-tions), MDI is a highly scalable monitoring solution.

Figure 1.36 shows how media delivery index (MDI) video quality measure-ment uses delay factor (DF) and media loss rate to estimate the quality ofthe video signal as it progresses through a network. This example showsthat a headend and other sources are distributing media (packets) throughan IPTV system. As the packets progress through the network, some of themedia is lost (packet loss) due to congestion and other factors. Packets arealso delayed due to queuing and other factors. MDI quality is measured inthis network which displays how the quality changes as signals travel fromtheir content source, through the core network, through an optical networkunit (ONU), into a home access modem, and to an IPTV receiver (STB). Thekid’s central channel has had media loss at a core ONU and it has also expe-rienced delay at the customer’s access modem/router.

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V Factor

V factor is a video quality rating score that is based on MPQM and it addsmeasurements that help to evaluate quality based on the content formatand processing types. V-factor takes into account the underlying video con-tent processing differences (such as group of pictures and compressionamount) to adjust the quality score. The V-factor score ranges from 1 to 5.V-factor uses additional content related information such as compressiontype, group of pictures (GOP), and quantizer levels to determine the V fac-tor quality score.

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Figure 1.36, Video Quality Measurement using Media Delivery Index

Figure 1.37 shows that V-Factor uses and enhanced version of the MPQMquality metrics system to determine the quality of a video signal. V-Factoruses measurements from timing jitter, enhanced image entropy, and net-work impairments to determine the quality score. The program clock refer-ence is verified to determine timing jitter and network measurements areused to qualify packet loss. The MPQM system also evaluates the type ofcontent using the type of coder, the mix of image frames (I, P, and B), andthe quantizer level to determine the entropy that can influence how thevideo is displayed.

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Figure 1.37, V-Factor Testing Model

Video Service Transmission Quality (VSTQ)

Video service transmission quality is a value that indicates the ability of anInternet protocol data network to transport IP video signals. The VSTQvalue is codec independent and ranges from 0 to 50.

Video Service Picture Quality (VSPQ)

Video service picture quality is a value that indicates the ability of a mediadelivery system to display media to the viewer. VSPQ uses compressiontype, frame rate, packet loss, and GOP structure to determine a value thatranges from 0 to 50.

Video Service Audio Quality (VSAQ)

Video service audio quality is a value that indicates the ability of a mediadelivery system to play audio media to the listener. VSAQ uses compressiontype, bit rate, and packet loss to determine a value that ranges from 0 to 50.

Perceptual Evaluation of Video Quality (PEVQ)

Perceptual evaluation of video quality is a full reference objective test mea-surement system that can be used to assess the quality of video signals.PEVQ contains four key functions; media alignment (time and spatial), per-ceptual difference evaluation, distortion classification, and distortion indi-cator integration. The temporal and spatial alignment ensures that thesame components of the reference media and received media are correctlycompared. The perceptual difference function calculates the differences inluminance and chrominance. The distortion classification determines andgives values to the types of distortion. The distortion integration functionevaluates the types of distortion to determine a PEVQ score. The PEVQscore is determine by a combination of packet delay, brightness, contrast,PSNR, and other distortion indicators.

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Figure 1.38 shows how a PEVQ score is calculated. This example shows thata reference video source and test video source (received video) are aligned intime and space. The PEVQ system then determines the differences betweenthe video signals (Y, Cr, Cb). These differences are characterized and ratedto determine a PEVQ score.

Mean Opinion Score (MOS)

Mean opinion score (MOS) is a measurement of the level of quality as per-ceived by a person. The MOS is a number that is determined by a panel ofviewers or listeners who subjectively rate the quality of audio on varioussamples. The rating level varies from 1 (bad) to 5 (excellent). Good qualitytelephone service (called “toll quality”) has a MOS level of 4.0. There are

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Figure 1.38, PEVQ Analysis

variations of MOS that are used to rate video, audio, and audiovisual qual-ity during regular or burst error conditions.

Video Mean Opinion Score (MOS-V)

Video mean opinion score is a measurement of the level of video quality asperceived by a person. The MOS-V is a number that is determined by apanel of viewers who subjectively rate the quality of video on various sam-ples. The rating level varies from 1 (bad) to 5 (excellent).

Audio Mean Opinion Score (MOS-A)

Audio mean opinion score is a measurement of the level of audio quality asperceived by a person. The MOS-A is a number that is determined by apanel of listeners who subjectively rate the quality of audio on various sam-ples. The rating level varies from 1 (bad) to 5 (excellent).

Audiovisual Mean Opinion Score (MOS-AV)

Audiovisual mean opinion score is a measurement of the level of audio andvideo quality as perceived by a person. The MOS-AV is a number that isdetermined by a panel of people who subjectively rate the quality of the com-bination of audio and video on various samples. The rating level varies from1 (bad) to 5 (excellent).

Gap Video Mean Opinion Score (Gap MOS-V)

Gap video mean opinion sore is a measure of the perceived video quality dur-ing normal or acceptable periods of operation.

Burst Video Mean Opinion Score (Burst MOS-V)

Burst video mean opinion sore is a measure of the perceived video qualityduring burst outage or poor transmission periods of operation.

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Single Stimulus Continuous Quality Evaluation (SSCQE)

Single stimulus continuous quality evaluation is a subjective testing processfor video that is defined in ITU-R B.T500. The SSCQE system ranks thequality on a scale of 0 to 100 where 100 is the best quality and 0 is the worstquality. The quality ranking criteria for SSCQE includes imperceptible, per-ceptible but not annoying, slightly annoying, annoying, and very annoying.

Test Equipment

Test equipment can consist of a device or assembly that can measure or ver-ify that a particular product or system meets specific requirements or if it iscapable of performing specific functions or actions. Some of the commontypes of test equipment that are used by IPTV service providers includevideo analyzers, MPEG generators, protocol analyzers, built in test equip-ment, and impairment emulators.

Video Analyzer

A video analyzer is a test instrument that is designed to receive and evalu-ate video or media signals. Most modern day media analyzers have the capa-bility of evaluating multiple types of media in various formats such asMPEG-1, MPEG-2 (broadcast TV), MPEG-4 (H.264 packet video), VC-1(windows media), VP6 (Flash video).

Video analyzers can usually identify the stream rates, bit rates, displaymotion vectors, quantizer values, frame rates, frame count, and can alsomeasure various types of errors such as bit error rate, frame loss rate. Videoanalyzers may include small video displays that allow the technicians to seethe channel content.

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MPEG Generator

MPEG generator is an instrument that can create signals which simulatethe source (headend) of a broadcast or IPTV system. MPEG generators areusually able to create both single program transport stream (SPTS) or mul-tiple program transport stream (MPTS). MPEG generators may have thecapability to insert or adjust the error rate to simulate common networkimpairments.

Protocol Analyzer

A protocol analyzer is a test instrument that is designed to monitor a net-work and provide analysis of the communication taking place on the net-work. This allows a technician to monitor a network and provides informa-tion for problem determination and resolution.

Most modern day protocol analyzers are aware of all commonly used, indus-try standard protocols. More advanced protocol analyzers sit “in-line”between two devices, without the devices being aware that the analyzer ispresent. Other less sophisticated protocol analyzers can be created usingstandard PCs with network interface cards in “promiscuous mode”, where-by they copy all packets that appear on the network, regardless of destina-tion address.

Built-in Test Equipment (BITE)

Built-in test equipment consists of capabilities and features that aredesigned or used within a device to support testing functions.

Impairment Emulator

An impairment emulator is a system that creates or simulates impairmentsto the operation or communication with a software program or hardware

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device. The purpose of an impairment emulator is to allow developers tosimulate the operation of programs or devices under conditions that mayhappen to their products or services and to determine the changes in per-formance or operation that may result from these impairments.

Some of the impairments the emulator may produce include jitter, latency,burst loss, gap loss, packet loss, out of order packets, route flapping, andlink failure. Impairment emulators may be used to evaluate the perfor-mance of systems under various conditions such as loaded and in failed con-ditions.

Network Monitoring

A network monitoring system is a combination of software and hardwarethat collects and analyzes information on network alarms and performancedata and alerts a center if it detects trouble in loop, interoffice, or switchingsystems. Network monitoring may be passive (doesn’t interfere with the net-work operation) or active (processes or interacts with media or data).Network monitoring may be setup in devices such as routers by copying orredirecting data to other ports (test ports) or through network probes thatare installed at various points in the network.

Mirror Port

A mirror port is a connection point (a port) on a switch that is configured toduplicate the traffic appearing on another one of the switch’s ports.

Active Port

An active port is a connection point (a port) on a router or switch that is con-figured to process traffic appearing on another one of the switch’s ports.

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In Line Monitoring

In line monitoring is the use of a device or process that receives from a lineinput, performs measurements, and produces or provides a signal on theline output.

Hierarchical Monitoring

Hierarchical monitoring is a structured measurement and reporting systemthat provides information on lower layer functions to areas combined withupper monitoring functions.

Alarm Views

Alarm views are the presentation of monitoring conditions or events. Alarmviews may be grouped into functional processes such as media acquisition,distribution, or reception.

Network Probes

A network probe is a device or process that is inserted into a network tomonitor for specific characteristics or conditions. Probes can be passive oractive. Passive probes monitor signals or operations without changing orimpacting the underlying functions or signals. Active probes process or alterprocesses to perform their measurement functions.

Measurement Probe

A measurement probe is a device or process that is inserted into a system ornetwork to monitor and measure specific characteristics or conditions.Measurement probes are can be non-intrusive and simply monitor andreport on information that passes through or by the probe.

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Reference Probe

A reference probe is a monitoring device that is used to gather values thatcan be used as a basis for comparison level that is used to compute othermeasurements or values.

Test Client

A test client is a software program and/or associated hardware that is con-figured to monitor and report information about the operation and serviceperformance within a device or network. Test clients may be installed innetwork equipment or end user devices (such as set top boxes).

Test clients operate under the control of the operating system of the devicefor which it is installed. These devices (such as set top boxes) may have lim-ited processing power of the device that will perform the test measurements(such as a set top box). As a result, the type of monitoring that a test clientcan use may be restricted by the device operating system and available per-formance capability.

The test client typically is controlled by and communicates with the systemwhich it is connected to. It can communicate using standard commands suchas simple network management protocol (SNMP) or via proprietary mes-sages.

Figure 1.39 shows how a software client may be installed in a set top box sothat it can monitor and report performance conditions. This example showsa test software module that has been downloaded and installed into thememory of the STB. This test software module can determine packet losses,monitor packet jitter, and analyze their impact on the display of the video.

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Heartbeat Generator

A heartbeat generator is a communication test function that uses a repeat-ed transmitted signal that travels through a system or network which iseventually returned back to the sender. If the heartbeat is received by thesender, it confirms that the network is still operating (it is alive).

Fault Management

Fault management identifies the network problems, failures and events,and corrects them. Fault management is the reactive form of network man-agement. SNMP traps, syslog, and RMON are typically used in fault man-agement. Fault management is one of the five functions defined in the

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Figure 1.39, STB Test Client

FCAPS model for network management. Fault management systems can beused to predict future failures, find faults, and analyze their causes.

Fault Predictions

Fault predictions are estimated unwanted conditions that are likely to occuras a result of measured or observed conditions.

Fault Finder

A fault finder is a test set or other type of device that enables faults to beidentified and localized.

Fault Analysis

Fault analysis is the evaluation of the failed components or processes in adevice or service to determine what caused the fault.

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95

Appendix 1 - Acronyms

AN-Access Network BER-Bit Error Rate BITE-Built-In Test Equipment Blockiness-Block Distortion CBR-Constant Bit Rate CCP-Channel Change Performance CCT-Channel Change Time CDE-Content Delivery Engine CDS-Content Delivery System CN-Core Network COS-Class of Service CP-Content Protection CRC Error-Cyclic Redundancy CheckError Demarc-Demarcation Point DEU-Data Extraction Unit DF-Delay Factor DPI-Deep Packet Inspection DPI-Digital Program Insertion DPU-Data Polling Unit DUT-Device Under Test DVQ-Digital Video Quality EFS-Error Free Seconds EPSNR-Estimated Peak Signal toNoise Ratio FEC Effectiveness-Forward ErrorCorrection Effectiveness FOA-First Office Application Gap MOS-V-Gap Video Mean OpinionScore HSS-Home Subscriber Subsystem HVS-Human Vision System IPLR-Internet Packet Loss Rate KQI-Key Quality Indicators

Lab Tests-Laboratory Testing LOS-Loss of Signal Luma-Luminance MAC Address-Medium Access ControlAddress MAPDV-Mean Absolute Packet DelayVariation MDI-Media Delivery Index MIB-Management Information Base MLR-Media Loss Rate MOS-Mean Opinion Score MOS-A-Mean Opinion Score Audio MOS-AV-Mean Opinion ScoreAudiovisual MOS-V-Mean Opinion Score Video MPEG TS Analysis-MPEG TransportStream Analysis MPLS-Multi-Protocol Label Switching MPQM-Moving Picture Quality Metrics MR-DVR-Multi-Room Digital VideoRecorder MSE-Mean Square Error nDVR-Network Digital Video Recorder NMS-Network Management Station NMS-Network Management System OID-Object Identifier OS-Operating System PAQ-Perceived Audio Quality PCR-Program Clock Reference PCR Error-Program Clock ReferenceError PDN-Premises Distribution Network PDR-Packet Discard Rate

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PEVQ-Perceptual Evaluation of VideoQuality PID-Packet Identifier PIP-Picture in Picture PLR-Packet Loss Rate PMT-Program Map Table POC-Proof of Concept POE-Point of Entry PQA-Picture Quality Analysis PS-Program Stream PSNR-Peak Signal to Noise Ratio PTS Error-Presentation Time StampError QoE-Quality of Experience QoS-Quality Of Service QoS Awareness-Quality of ServiceAwareness RMON-Remote network MONitoring RMON Probe-Remote MonitoringProbe SDI-Serial Digital Interface SHE-Super Headend SI-System Integration SLA-Service Level Agreement SLA Violations-Service LevelAgreement Violations SNMP-Simple Network ManagementProtocol SNMPv1-Simple Network ManagementProtocol version 1 SNMPv2-Simple Network ManagementProtocol version 2 SNMPv3-Simple Network ManagementProtocol Version 3 SOC-System On Chip SOM-Server Operations andManagement SRD-System Requirements Document SSCQE-Single Stimulus ContinuousQuality Evaluation SUT-System Under Test

SVS-Switched Video Service SVT-System Verification Test Sync Impairment-SynchronizationImpairments TAR-Test Accuracy Ratio Test Model-Testing Models TIMS-Transmission ImpairmentMeasurement System TPU-Threshold Processing Unit TS Analysis-Transport StreamAnalysis TS-Sync-Transport StreamSynchronization TS-Sync Loss-Transport StreamSynchronization Loss TV Server-Television Server TVQM-Television Video Quality Metrics VAC-Video Admission Control VBR-Variable Bit Rate V-Factor-Video Factor VPN-Virtual Private Network VQEG-Video Quality Experts Group VQS-Video Quality Score VSAQ-Video Service Audio Quality VSMQ-Video Service MultimediaQuality VSPQ-Video service picture quality VSTQ-Video Service TransmissionQuality VTS-Video Test System

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Agilent - IPTV Testinghttp://www.agilent.com

Anacise Testnology - Triple Playhttp://www.anacise.com/IPTV.htm

Empirix - IMShttp://www.empirix.com/

Azimuth - WiMAXhttp://www.Azimuth.com

Berkeley Varitronics - WiMAXhttp://www.bvsystems.com

EXFO - Transport Testinghttp://www.exfo.com

Hewlet Packard - IPTV and Communication Testinghttp://www.HP.com

Inneoquest - IPTV and Network Testinghttp://www.inneoquest.com

Ixia - IPTV and IP Testinghttp://www.Ixiacom.com

JDSU - IPTV and Communications Testinghttp://www.JDSU.com

MiraVid - Video Analyzershttp://www.miravid.com

Appendix 2 - IPTV Test EquipmentManufacturers

Omnicor - IP Network Testinghttp://www.omnicor.com

Opticom - Video Testinghttp://www.opticom.de

Pixelmetrix - IPTV and Broadcast Testinghttp://www.Pixelmetrix.com

Semaca - Video Quality Testinghttp://www.semaca.co.uk

Shenick - IPTV and Network Testinghttp://www.shenick.com

Spirent - IPTV and VoIP Testinghttp://www.spirent.com

Sunrise Telecom - IPTV and Optical Testinghttp://www.sunrisetelecom.com

Symmetricomhttp://www.symmetricom.com

Telchemy - Digital Videohttp://www.telchemy.com

Tektronix - IPTV and Other Test Equipmenthttp://Tektronix.com

Video Clarity - Video Quality Testinghttp://www.videoclarity.com

Witbe, Inc. - Website Load Testinghttp://www.witbe.net

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Acceptance Testing, 11Access Network (AN), 12, 20Active Port, 89Alarm Views, 90Alpha Testing, 13-14Audio Distortion, 50Audio Quality, 24, 49, 64, 84, 86Audio Visual Synchronization Offset, 73Audiovisual Quality, 86Beta Testing, 14Bit Error Rate (BER), 5, 70, 87Block Distortion (Blockiness), 54, 60Blurring, 57, 59Brightness, 53, 59, 84Built-In Test Equipment (BITE), 88Burst Errors, 1, 55Capture, 24, 56Certification, 13Channel Change Delay, 78Channel Change Time (CCT), 77-78Channel Map, 76Chrominance, 84Clock Rate Jitter, 74Color Pixelation, 60Compression Ratio, 23, 27, 74Constant Bit Rate (CBR), 5, 8Content Acquisition, 19Content Dependency Factors, 7Content Protection (CP), 9Continuity Count Error, 75Contrast, 57, 59, 84Conversion, 7-8, 16, 25, 56Core Network (CN), 12, 19-20, 81Customer Satisfaction, 5-6Cyclic Redundancy Check Error (CRCError), 76Decoding, 16-17, 21, 26, 45, 50, 67Decompression, 16-17, 27, 30, 41Delay Factor (DF), 71, 81

Device Operating System, 91Diagnostic Testing, 12Digital Video Quality (DVQ), 53Distortion Indicators, 53, 84Dropped Frame, 36Duplicate Packet Rate, 67Encoder Initialization Time, 79Encoding, 7, 22, 28, 32, 37End To End Testing, 11Entropy Analysis, 80Error Concealment, 7, 10Error Free Seconds (EFS), 70Error Protection, 24, 50Fault Analysis, 93Fault Finder, 93Fault Management, 92-93 Fault Predictions, 6, 93Feature Function Testing, 11Field Testing, 11, 13-14Frame Count, 71, 87Frame Dropping, 36Full Reference Testing, 60-61Functional Tests, 10Gap Length, 68Gap Loss, 68, 89Gap Loss Rate, 68Gap Video Mean Opinion Score (GapMOS-V), 86Headend, 12, 19-20, 81, 88Heartbeat, 92Hierarchical Monitoring, 90Human Vision System (HVS), 80Image Entropy, 77, 83Impairment Emulator, 88In Line Monitoring, 90Inter-Packet Gap, 68-69Interoperability Testing, 14J.144, 60Jerkiness, 53, 55

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Index

Jitter Discards, 74Laboratory Testing (Lab Tests), 13, 60Lightweight Calculations, 81Line Rate, 70Load Testing, 15Loopback Testing, 12-13Loss of Signal (LOS), 62, 69Lossy Compression, 8, 16, 23, 27, 29, 57Luminance (Luma), 25, 53, 84Mean Opinion Score (MOS), 60, 85-86Mean Opinion Score Audio (MOS-A), 86Mean Opinion Score Audiovisual (MOS-AV), 86Mean Opinion Score Video (MOS-V), 86Mean Square Error (MSE), 49Measurement Probe, 90Media Compression, 8, 16, 40, 57Media Delivery Index (MDI), 79, 81-82Media Loss Rate (MLR), 71-72, 81Media Player, 66Metrics, 48, 60, 79-80, 83Mirror Port, 89Missing Channels, 77Motion Judder, 37Moving Picture Quality Metrics (MPQM),79-83MPEG Generator, 88Multicast Join Time, 79Multilayer Testing, 10-11Network Impairments, 80, 83, 88Network Measurements, 63, 81, 83Network Monitoring System, 89Network Probe, 77, 90Network Utilization, 5-6Objective Quality, 4, 48Operating System (OS), 91Operational Testing, 10Out of Order Packets, 66-67, 89Out of Sequence Packet Rate, 67Packet Buffering, 65-66Packet Corruption, 50-51, 53

Packet Delay, 65, 71, 80, 84Packet Discard Rate (PDR), 65Packet Gap, 68Packet Identifier (PID), 45-46, 75Packet Jitter, 62, 65, 91Packet Loss Rate (PLR), 12, 63-64, 80Packet Reception, 16-17Packet Transmission, 1, 17, 43, 65-66,72Packetization, 16, 44Peak Signal to Noise Ratio (PSNR), 49,60-61, 84Perceived Quality, 7Perceptual Difference, 84Perceptual Evaluation of Video Quality(PEVQ), 84-85Performance Tests, 14Premises Distribution Network (PDN), 20Presentation, 45, 67, 73, 76, 90Presentation Time Stamp Error (PTSError), 76Program Clock Reference (PCR), 68, 74,76, 80-81, 83Program Clock Reference Error (PCRError), 76Program Map Table (PMT), 75Program Stream (PS), 43-45, 74Program Stream Rate, 74Program Transport Stream, 3, 45, 75, 88Protocol Analyzer, 88Protocol Conformance, 74Quality Metrics, 48, 79-80, 83Quality of Experience (QoE), 4-5Quality Of Service (QoS), 4-5Quality Score, 80-83Quantization Noise, 56Quantizer Scaling, 40-41Rebuffer Events, 72Rebuffering, 71-72Reference Probe, 91Reliability, 14


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Remote network MONitoring (RMON), 92Route Flapping, 65, 69, 89Service Capacity, 15Service Level Agreement (SLA), 5-6Set Top Box Initialization Time, 79Simple Network Management Protocol(SNMP), 91-92Single Stimulus Continuous QualityEvaluation (SSCQE), 87Slice Losses, 59Stream Integrity, 71, 73Stream Rate, 70, 73-74Stress Tests, 15Subjective Quality, 49Switched Video Service (SVS), 1-2Synchronization Loss, 75-76Test Client, 91-92Test Equipment, 11, 87-88Test System, 80Testing, 1-94Testing Models (Test Model), 60Transmission Rate, 27, 40, 49, 78Transport Error, 76Transport Stream Rate, 73Transport Stream Synchronization (TS-Sync), 75-76Transport Stream Synchronization Loss(TS-Sync Loss), 75-76Variable Bit Rate (VBR), 8Video Analyzer, 87Video Compression, 27, 30, 32-33, 37Video Distortion, 53-54Video Encoder, 79Video Factor (V-Factor), 74, 79, 82-83Video Quality, 36, 53, 60, 80-82, 84, 86Video Quality Measurement FullReference, 60Video Service Audio Quality (VSAQ), 84Video service picture quality (VSPQ), 84Video Service Transmission Quality(VSTQ), 84Viewing Device, 8, 12, 20

Zero Reference Testing, 60, 62-63

Index

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Althos Publishing404 Wake Chapel RoadFuquay-Varina, NC 27526 USA

IPTV Service Quality explains how to identify, measure, and analyze the operation,performance and quality of IPTV systems and services.

This book explains how to monitor, test, and diagnose IPTVsystems and services. Covered are the quantitative (packetloss, error rate) and qualitative (perceptual) quality measure-ment and control processes. Discover how quality of experi-

ence (QoE) can be very different than traditional quality of service (QoS)measurements.

IPTV systems are complex multimedia communication systems andcommunicating through them involves the use of multiple layers, whichcan make testing and diagnostics more difficult. Discover how differentlayers in an IPTV system can interact and why multilayer testing may beused to evaluate and diagnose operation and performance issues.

Learn about audio, video, and MPEG formats and what parts of themcan be measured in IPTV systems. Audio quality characteristics includ-ing fidelity, frequency response, and signal to noise ratio are described.Key video quality characteristics such as error blocks, aliasing effects,object retention, and artifacts are explained.

Discover the different types of network measurements such as packetloss, gap loss, and jitter and how they influence quality of service (QoS).The types of content measurements such as frame loss rate (FLR), syn-chronization loss, and audiovisual synchronization offset are explained.Command and control measurements such as channel change time,encoder initialization time, and connect time are described.

The fundamentals of full reference, partial reference, and zero referencequality processes such as MDI, MPQM, and V-Factor are explained.Other types of quality measures including video, audio, synchronization,interaction (control), and other measurable values are explained.

The different types of testing including laboratory, acceptance, confor-mance, field, and diagnostic testing are described along with some ofthe common types of IPTV test equipment that are used. You will learnabout the different types of network monitoring devices and probes thatare used in IPTV systems, what they can do, and how to understand andanalyze the information they provide.

This Book Covers:

• IPTV Testing Challenges

• Testing Methods

• Audio, Video, andMPEG Formats

• Audio Quality

• Video Quality

• Network Measurements

• Content QualityMeasurements

• Command andControl Metrics

• MDI, MPQM, V-Factor QualityRating

• IPTV Test Equipment

For Updates and Resources Visitwww.AlthosBooks.com

T

If you need to understand how to moni-tor, test, and diagnose IPTV systems andservices, this book is for you.

Lawrence Harte

IPTV TestingIPTV TestingService Quality Monitoring, Analysis,

and Diagnostics for IP Television Systemsand Services

Iptv Testing Book

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