Draft Eecb433 Note 7 - Sdh

8/3/2019 Draft Eecb433 Note 7 - Sdh

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Applied Telecommunication Systems

(EECB433)

Draft Note 7 Synchronous Digital

Hierarchy (SDH)

By

Cheah Cheng Lai


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Table of Content

1. Introduction

2. SDH Frame

3. Multiplexing Structure

4. Network Elements and Topology

5. Network Resiliency

6. Next Generation SDH

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1. Introduction

Why SDH?


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SDH

Synchronous digital hierarchy (SDH) is a newer

multiplexing system for fiber optic transmissions that

provides increases throughput and bandwidth.

Operate in Synchronous timing by using a master clock

The SDH used in North America is called SynchronousOptical Network (SONET).

Developed out of a need for standardization within fiber

based systems ITU-T G.707, 708 and 709.

Note: All explanation in this lecture note are basedon SDH, however, it is applicable for SONET unless

otherwise specify.

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Problems with PDH

Max Line Capacity: 565

Mbit/s

Multiplexer Mountain

No direct access to

individual 2Mbit/s

streams (add/drop)

Manual wiring and re-

wiring needed to make

any change to the

network configuration Limited supervision

capabilities.

SDH

a much simpler structure

PDH North America

PDH International

5Source: Lee 1996


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Multiplexing Mountain

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Multiplexing Hierarchies

PDH

Plesiochronous Digital Hierarchy

Multiplexes lower bit rate PDH signals together into higher bit rate

signals.

The transmission can be over optical, microwave and copper.

64 kbit/s, 2 Mbit/s, 8 Mbit/s, 34 Mbit/s, 140 Mbit/s, (565 Mbit/s)

SDH

Synchronous Digital Hierarchy

Multiplexes PDH and lower level SDH signals.

The transmission are mainly over optical fiber. 155 Mbit/s, 622 Mbit/s, 2500 Mbit/s, 10 Gbit/s

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2. SDH Frame


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Synchronous Transport Module (STM)

STM-1 is the

basic frame of

SDH

Each STM-1

frame consists of2430 bytes

Arranged in a

two-dimensional

frame

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STM-1 Frame

As with PCM, SDH sends 8,000 frame in one second.

The data rate for STM-1 = 9 rows x 270 Bytes x 8000

= 155,520,000 b/s (155 Mb/s)

10

bytes


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Overhead

Overhead functionality two types.

operation and maintenance of the SDH signal itself

Provides framing, identification and alarm indication.

error performance indication and data communications

channels,

Provide error performance monitoring and an embedded

management communication channel.


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Section overhead (Only for reference)

regenerator section overhead(RSOH)

multiplex section overhead(MSOH).

A1 and A2 bytes togethercontain a frame alignmentword.

The frame alignment word isrepeated with each frame tomaintain alignment and re-alignement.

When STM-1 signals aremultiplexed into an STM-4,then the C1 byteallows eachSTM-1 to be uniquelyidentified.

The B2 bytes provide an errormonitoring capability

(D1 to D12) is to provide anembedded datacommunications link


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SDH Protocol Stack

Multiplex Section Layer

Regenerator Section Layer

SDH SONET


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Layering Concept


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Building transport (interleaving)

The transmission of digital signals over optical fibre allows fortransmission rates far in excess of the 155.52 Mbit/s defined as the

aggregate rate for STM-1. STM- 4 622.080 Mbit/s

STM-16 2488.32 Mbit/s

STM-64 9953.28 Mbit/s

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SDH Hierarchy

STM-N Synchronous Transport Module level N.

16

STM-051.84

Mb/s

STM-1155.52

Mb/s

STM-4622.08

Mb/s

STM-162.488

Gb/s

STM-649.953

Gb/s

x3 x4 x4 x4


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SDH and SONET Rate

STS-N Synchronous Transport Signal level N.

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SDH Rates SONET Rates Speed

STM-0 STS-1 51.84 Mb/s

STM-1 STS-3 155.52 Mb/s

STM-4 STS-12 622.08 Mb/s

STM-16 STS-48 2.488 Gb/s

STM-64 STS-192 9.953 Gb/s


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STM-n Frame

The SDH frame is called Synchronous Transport Module leveln (STM-n).

8000 STM-n is transmitter per second, i.e. 125 s / frame.

18Source: Lee 1996

bytes


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3. Multiplexing Structure


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SDH Multiplexing Structure

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Justification to cater for the slightly

different timing of PDH payload

21Source: Ericsson presentation slides

(E4)

(T3)(E3)

(T2)

(E1)

(T1)


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Mapping - Path Overhead (POH) is Added

Source: Ericsson presentation slides 22


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POINTER ADJUSTMENT

Pointers are used to indicate the beginning of the payload in the SDHframe

There are two types of pointer, AU and TU pointer

AU pointers for higher order VCs (VC4 &VC3)

TU pointers for lower order VCs (VC12)

Has two basic function :

- Minimisation of multiplexing delay.

- Justification of frequency difference between a

frame and a payload.


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Aligning

The process of loading a VC onto a TU, along with the frame

offset information.

The frame offset is due to the clock discrepancy between the

VC and the corresponding TU.

24

VC

TU TU

pointer


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Tributary Unit (TU)

Tributary Tributary Rate Justifi-cation

Mapping Aligning TU Rate TU Size

T1 1.544 Mbps C11 VC-11 TU-11 1.728Mbps

9 rows 3columns

E1 2.048 Mbps C12 VC-12 TU-12 2.304Mbps

9 rows 4columns

T2 6.312 Mbps C2 VC-2 TU-2 6.912Mbps

9 rows 12columns

E3/T3 34.368/44.736

Mbps

C3 VC-3 TU-3 48.96

Mbps

9 rows 85

columns

E4 139.264 Mbps C4 VC-4 AU-4 150.336Mbps

9 rows261

columns


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The STM-1 Frame

The VC-4 is floating inside the STM-1.

The AU pointer always points to the position where VC-4 starts.

26

Note:V5 is the starting position oflower order VCs.


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Multiplexing Structure (ITU-T G.707)

27Source: G.707 2003


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Multiplexing Structure

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4. Network Elements and Topology


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Network Elements (1/2)

Terminal multiplexer (TM)

(de-)multiplexes between

multiple low-speed signals

and a high-speed signal.

Regenerator

Terminates, regenerate and

transmits SDH signal.

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Network Elements (2/2)

Add-Drop Multiplexer (ADM)

De-multiplexes and terminates anynumber of PDH and SDH signals,

m > n

Multiplexes and adds new PDH and SDH

signals

Convert to SDH optical signal and

transmits out

Digital cross-connect (DCS)

accesses the STM-N signals, and

switches (cross-connect) at the

lower level.

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Bus Topology

ADM is needed for bus topology.

33

TM

E1

E1

E3

STM-1

STM-N

TM

E1

E1

E3

STM-1

ADM

E1E1

E3STM-1

STM-N

ADM

E1E1

E3STM-1

STM-N


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Mesh Topology

DCS are used for forming mesh topology.

Note: the tributaries are not shown in this diagram

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DCS ADMDCS

ADM ADMDCS


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5. SDH Resiliency

Automatic Protection Switching (APS)


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Span (Point-to-Point) Switching

Point-to-point protection between two nodes.

This can be either 1:1 or 1:N.

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A B

D C

Working route

Protection route

Fiber break

Optical fiber


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1:1 Protection Switching

The far end is receiving both signals from working and protection facilities.

Examples of the failure condition are lost of frame (LOF) or a signal degrade.

Switching can be either revertive or non-revertive.

38Source: Tektronix 2001


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1:N Protection Switching

In 1:N protection architecture, all communication from the Near End to the FarEnd is carried out over the APS channel, using the K1 and K2 bytes.

All switching is revertive; that is, the traffic reverts to the working facility assoon as the failure has been corrected.

39Source: Tektronix 2001


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Ring Switching

Point-to-point protection between two nodes.

This can be either 1:1 or 1:N.

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A B

D C

Working route

Protection route

Fiber break

Optical fiber

Bidirectional Line Switching Ring (BLSR)


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Bidirectional Line Switching Ring (BLSR) -

Normal Operation

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A B

D C

Working route

Protection route

Fiber break

Optical fiber


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BLSR Fiber Break

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A B

D C

Working route

Protection route

Fiber break

Optical fiber


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BLSR Node Failure

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A B

D C

Working route

Protection route

Node failure

Optical fiber


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Path Switching

Diverse route over multiple sections.

Implemented by a network management system (NMS).

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DCS ADMDCS

ADM ADMDCS

Working path

Protection path

Fiber break

Optical fiber


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A Fiber Network

in Malaysia

45

Kota Bharu

K. Terengganu

Tg. Seginting

Melaka

Singapore

Lumut

Kuala Dungun

Kuala Muda

T. Karang

Rompin

Pontian Kechil

K. Perlis

Port Klang

Muar

Port Dickson

Pasir Puteh

Mersing

Tg. Sekakap

Desaru

Langkawi

Pulau P inang

67.332km

141.896km

87.316km

130.550km

94.391km

125.536km

34.460km

101.951km

24.450km

31.570km

135.982km

116.790km

124.011km

101.484km

75.116km

47.593km

57.579km

72.163km

13.316km

33.431km

25km

K. Kurau

KUANTAN

Jitra

IPOH

GLENMARIE

UPM

J.BHARU

199.152km

20.890km

182.359km

46.219km

229.107km

162.945km

118.645km

Kangar

165.022km

170km

30.382km

HONG KONGJAPANUSA

AUSTRALIA

INDONESIA

FLAGSEA-ME-WE

TRUNK LOCAL SWITH

INTERNATIONAL SWITCH

LAND BASED

LAND BASED

SUBMA RINE BASED NETWORK

INTERNATIONAL SUBMARINE NETWORK

EARTH STATION

LEGEND:

SEBERANG PRAI

Tak Bai

Satun

APCN 2


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6. Next Generation SDH (NG SDH)

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Packet Over SDH Legacy Approach

IP packets

framed using packet over SDH (POS) and placed into the SDH payload area.

Multimedia traffic with stringent quality of service (QoS) requirements

ATM cells are placed into the SDH interface according to standardized optical

interfaces

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Driving Force

New services and applications based on internet, mobile, multimedia, DVB,SAN, Ethernet or VPN, are demanding long haul transport. State of the art:

1. Ethernet, are in an early stage of development for efficient opticaltransport.

2. Most have their transport infrastructure entirely based on SDH/SONET.

3. There is a lot of experience in managing SDH/SONET.

No other technology than SDH/SONET has this maturity grade at the opticalphysical layer.

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Ethernet vs SONET/SDH

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Next Generation SDH: Packet Friendly

SDH has also evolved to more efficiently adapt statisticalmultiplexing traffic based on data packets.

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Key Techniques for NG SDH

GFP (Generic Framing Protocol)

is robust and standardized encapsulation procedure for thetransport of packetised data on SDH.

VCAT (Virtual Concatenation)

is a mechanism which assigns granular bandwidth sizes ratherthan the exponential provision of the ContiguousConcatenation. Therefore VCAT is more flexible and efficient.

LCAS (Link Capacity Adjustment Scheme)

LCAS can modify dynamically the allocated VCAT bandwidthby adding/removing members of a pipe in use. LCAS is beingused also to implement diversity for traffic resilience.

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SDH Payload Sizes for transporting data

Beside PDH payload, the SDH can be used for

transporting data payload.

The justification bits are not required, the whole container

can be used transporting data payload.

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Contiguous and Virtual Concatenation

Contiguous concatenation, which creates big containers that cannot split into smaller pieces duringtransmission. For this, each NE must have a concatenation functionality.

Virtual concatenation, which transports the individual VCs and aggregates them at the end point ofthe transmission path. For this, concatenation functionality is only needed at the path terminationequipment.

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Notations

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57

ff


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VCAT Efficiency

Comparison between contiguous and virtual

concatenation efficiency.

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d d h d


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Bandwidth Provisioning - Today

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C S dd d id h i l


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LCAS Add Bandwidth Hitless

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However about Future?

M i Hi h C i R i


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Meeting Higher Capacity Requirement

To meet the ever growing demand for network

capacity

Increase Data Rate

Limited range up to 10 Gb/s or 40 Gb/s are commercially

available.

Higher bit rates require more frequent signal regeneration.

Lay more fibers

Expensive, time delay, more regenerators needed per fiber pair.

Wavelength Division Multiplexing (WDM)

A technology which allows network operators to carry moreinformation over existing optical fiber networks by combining

multiple optical signals for transmission over the same optical

fiber.

WDM


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WDM

Transmission of Multiple Optical Signals (i.e.

wavelengths) in the same optical fibre

A single core of optical fiber

O ti l T t N t k (OTN)


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Optical Transport Network (OTN)

Standardized by ITU-T G.709.

Created with the intention of combining the benefits of SONET/SDH technologywith the bandwidth expansion capabilities offered by dense wavelength-division

multiplexing (DWDM) technology.

Source: Gorshe 2009 64

Q ti ?


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Question?

Q1. Referring to the SDH multiplexing structure below (slide 15).

A STM-1 can transport how many T1

Answer: 84

E1

Answer: 63 E3

Answer: 3

65

Q2 & Q3


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Q2 & Q3

Q2) Show two paths that an E3 can be multiplexed to

become a STM-1.

Answer: Path 1: E3 -> C-3 -> VC-3 -> AU-3 -> AUG-1 ->

STM-1. Path 2: E3 -> C-3 -> VC-3 -> TU-3 -> TUG-3 ->

VC-4 -> AU-4 -> AUG-1 -> STM-1

Q3) Which path is more efficient?

Answer: Path 1

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Q4


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Q4

Q4) Exchange A and B are connected by 100 E1 of the interoffice trunks.

Propose a suitable SDH system to overcome the wiring nightmare anddraw the proposed system architecture.

Answer: STM-4

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Exchange

A

Exchange

B

100 x E1

ExchangeA

ExchangeB

100E1

100E1

TerminalMultiplexer

TerminalMultiplexer

STM-4


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Reference


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Reference

[Cavendish 2002] New Transport Services for Next-Generation

SONET/SDH Systems, Dirceu Cavendish, Kurenai Murakami, Su-HunYun, Osamu Matsuda, Motoo Nishihara, IEEE CommunicationsMagazine, May 2002, pp. 80-87.

[Lee 1996] Broadband Telecommunications Technology, SecondEdition, Byeong Gi Lee, Minho Kang and Johnhee Lee, Artech House1996.

[G.707 2003] ITU-T Recommendation G.707/Y.1322, Network NodeInterface for Synchronous Digital Hierarchy (SDH), 12/2003.Available:http://www.itu.int/publications/sector.aspx?lang=en&sector=2

[Tektronix 2001] SDH Telecommunications Standard Primer, TektronixApplication Note, 2001. Available:http://www.tek.com/Measurement/App_Notes/sdhprimer/

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http://www.itu.int/publications/sector.aspx?lang=en&sector=2http://www.tek.com/Measurement/App_Notes/sdhprimer/http://www.tek.com/Measurement/App_Notes/sdhprimer/http://www.itu.int/publications/sector.aspx?lang=en&sector=2


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Thank you

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