ITTC © James P.G. Sterbenz Communication Networksjpgs/courses/nets/lecture-mm... · 2017-12-11 ·...

Communication NetworksThe University of Kansas EECS 780

Multimedia and Session Control

James P.G. Sterbenz

Department of Electrical Engineering & Computer Science

Information Technology & Telecommunications Research Center

The University of Kansas

jpgs@eecs.ku.edu

http://www.ittc.ku.edu/~jpgs/courses/nets

04 December 2017 KU EECS 780 – Comm Nets – Multimedia & Session Control NET-MS-2

Multimedia and Session ControlMS.1 Multimedia Applications

MS.1 Multimedia applications

MS.2 Multimedia streaming and transport

MS.3 Session Control

Multimedia ApplicationsOverview

• Multimedia applications

– involve audio and/or video

– perhaps in addition to conventional data

• Modes of operation

– streaming

– interactive

Multimedia ApplicationsStreaming

• Streaming multimedia

– media is streamed from server to client

• not download and then play

– user may have back-channel to server to control playback

• Examples

– Youtube, Dailymotion, Netflix, Hulu Lecture AL

– IPTV: television broadcast over IP

– Internet VOD (video on demand)

Multimedia ApplicationsInteractive

• Interactive multimedia

– users communicate with using audio and/or video

– peer-to-peer interaction

• E2E or shared multicast with reflector Lecture AL

– may combine with collaborative data sharing

• document sharing or shared whiteboard

• distance learning with information access

Multimedia ApplicationsInteractive Examples

• Examples

– VoIP (voice over IP) telephony and video conferencing

• e.g. skype

– shared collaboration environments

– virtual reality interactions, e.g Second Life

– multiuser games

Multimedia and Session ControlMS.2 Multimedia Streaming and Transport

MS.2 Multimedia streaming and transportMS.2.1 Multimedia streaming and RTSP

MS.2.2 Multimedia transport: RTP and RTCP

Multimedia Streaming and TransportMS.2.1 Multimedia Streaming and Transport

Multimedia Streaming Stream Transfer Mode

• Various mechanisms to start stream– explicit client request

– server push

– may or may not establish connection state

• Data flow – synchronisation and control

• embedded or

• out-of-band

REQUEST

RELEASE

CONNECT

Multimedia StreamingInternet-Based Techniques

• Server

– source of media stream

• Client

– media player

• Transport

– end-to-end data transfer and control protocols

is TCP appropriate?

Multimedia StreamingDelay and Jitter

• Assume CBR source

– note that some codecs are VBR

constant bit

rate video

transmission

• Network imposes jitter

constant bit

rate video

transmission

– variable network delay

Consequences?

constant bit

rate video

transmission

variable

network

• Received flow no longer CBR

– implication?

constant bit

rate video

transmission

variable

network

client video

reception

constant bit

rate video

transmission

variable

network

client video

reception constant bit

rate video

playout at client

client playout delay

• Received flow no longer CBR

– receiver must buffer to compensate and playback CBR

Multimedia Streaming Client Playback Buffer

• Playback buffer absorb jitter– adds delay proportional to jitter

– may also be used to reorder if misordering permitted by TP

maximum playout point

application

2 3 4 6

playout buffer

receiving end system

Multimedia StreamingServer Operation

• Server

– match stream rate to path bandwidth

what is this?

– match stream rate to client capabilities

what is this?

Multimedia StreamingServer Operation

• Server

– match stream rate to path bandwidth

• congestion avoidance

– match stream rate to client capabilities

• flow control

Multimedia StreamingClient Operation

• Client: media player

– adaptive playout to compensate for jitter

– decompression

– error concealment

– GUI (graphical user interface)

• controls for interactivity

Multimedia StreamingInternet Transport

Is TCP appropriate for media streaming?

Multimedia StreamingInternet Transport

• Transport: RTP over UDP

– avoid TCP control loop delays

– avoid TCP congestion control throttling

– UDP: datagram-based transport with loss tolerance

– RTP: synchronisation added

Multimedia StreamingTypical Web-Based Architecture

• Web browser– GETs metafile

– launches or embeds player, passing metafile

• HTML5 replacing Flash for embedded streaming

• Media player contacts server

• Server streams audio/video to player

[Kurose]

Multimedia Streaming ControlRTSP Overview

• RTSP: real time streaming protocol [RFC 2326]

– client-server application layer protocol

• User to control of streaming

– rewind

– fast forward

– pause

– resume

– repositioning …

• Out-of-band control

– port 554

Multimedia Streaming ControlRTSP Operation

• Metafile communicatedto web browser

• Web browserlaunches player

• Player sets up

– RTSP control connection

– data flow withstreaming server

[Kurose]

Multimedia Streaming ControlRTSP Metafile Example

<title>Twister</title>

<track type=audio

e="PCMU/8000/1"

src="rtsp://audio.example.com/twister/audio.en/lofi">

<track type=audio

e="DVI4/16000/2" pt="90 DVI4/8000/1“

src="rtsp://audio.example.com/twister/audio.en/hifi">

</switch>

<track type="video/jpeg"

src="rtsp://video.example.com/twister/video">

</group>

</session>

Multimedia Streaming ControlRTSP Example

C: SETUP rtsp://audio.example.com/twister/audio RTSP/1.0

Transport: rtp/udp; compression; port=3056; mode=PLAY

S: RTSP/1.0 200 1 OK

Session 4231

C: PLAY rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0

Session: 4231

Range: npt=0-

C: PAUSE rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0

Session: 4231

Range: npt=37

C: TEARDOWN rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0

Session: 4231

S: 200 3 OK

Multimedia Streaming and TransportMS.2.1 Multimedia Transport: RTP and RTCP

Real-Time ProtocolOverview and Transfer Mode

• RTP: real-time protocol [RFC 3550 / STD 0064]

• Streaming of data with real-time properties

– uses UDP for basic transport

• no connection establishment

• basic end-to-end multiplexing

• no reliability

• no flow or congestion control

– adds real-time support fields

• sequence number

• timestamp

• source identifiers

Real-Time ProtocolSegment Format

• Encapsulated in UDP• RTP header

– version = 02– P: padding bytes at end– X: extension header– CC: CSRC count [4b]– PT: payload type [7b]– sequence # [16b]– timestamp [32b]

• resolution app dependent

– source identifiers• SSRC• CSRC (mixed in)

destination port #source port#

length checksum

CSRC list: contributing source ids

optional padding

application payload

SSRC: synchronisation source id

timestamp

sequence #02 P X CC PT

#B pad

Real-Time ProtocolRTP Payloads

• PT: payload type– [www.iana.org/assignments/rtp-parameters]

• Payload formats and encodings

– specified in various RFCs

– audio: RFC 3551, etc.

– video: RFC 2250, etc.

Real-Time ProtocolControl Protocol Overview

• RTCP: real-time control protocol [RFC 3550 / STD 0064]

• Protocol to control RTP streams

– monitoring quality of service

– convey participant status information

• periodically transmits RTCP control packets to others

• RTCP packet

– contains sender and/or receiver reports

– report statistics useful to application

• # packets sent, # packets lost, interarrival jitter, …

• Feedback can be used to control performance

– sender may modify transmission based on feedback

Real-Time ProtocolRTCP Functions

• Stream synchronisation

• Bandwidth scaling

todo: expand from Kurose foils

Multimedia Streaming and TransportMS.3 Session Control

MS.3 Session ControlMS.3.1 Session layer functions and services

MS.3.2 Session control protocols: SIP

MS.3.3 Session control protocols: H.323

SessionDefinition

• Session is association among usersor application entities

– e.g. teleconference, distance learning session, game

• Participants

– end-system users or application programs

– network-embedded resources

• e.g., transcoders, audio mixers

• Topology

– set of end-to-end transport flows

– multipoint (or point-to-point if only 2 participants)

Session ControlHybrid Layer/Plane Cube

physical

network

transport

session

application

data plane control plane

management plane

socialL8

virtual linkL2.5

Session layer (layer 5):

control plane

Session LayerSession Control Protocol

• Session protocol

– is responsible for coordination/control of application sessions

network

application

session

transport

network

end system

network

intermediate

system

network

intermediate

systemnetwork

intermediate

system

application

session

transport

network

end system

Multimedia Streaming and TransportMS.3.1 Session Layer Functions and Services

Session LayerService and Interfaces

• Session layer (L5) service to application layer (L7)

– establishes and maintains sessions among users/applications

– naming and addressing : to identify and locate participants

– signalling : messages to control application sessions

– may perform routing functions among session resources

• e.g. to transcoders or reflectors

– higher layer analogue of network layer services

• Session layer uses transport layer (L4) services

– a session consists of a coördinated set of end-to-end flows*

* this is not the OSI definition,

but the layer happens to be in the right place (L5)

Session Control ProtocolSession Establishment

• Establish session: signalling

– assist in location and invitation of participants

– establish one or more transport-layer associations

• flows or connections

– discovery of needed resources

• e.g. transcoders

– routing among participants and resources

– establish session state

• distributed among participants (good scalability)

• centralised in a session controller (efficient coördination)

• combination

Session Control ProtocolSession Maintenance

• Maintain session

– adjust to dynamic session group membership

• add and removal of participants

• merge and split of sessions

– initiate and terminate transport associations as needed

– add and remove resources as needed

– update session state

Session Control ProtocolSession Termination

• Terminate session

– signal termination to all participants

– teardown all transport layer flows and connections

– release resources

– remove session state

Session Control ProtocolSignalling Flow

1. Session signalling

2. Flow setup

3. Data transfer

4. Termination

CONNECT

SESS-REQUEST

SESS-ESTABLISH

user negotiation

user initiation

end system end system user user

session establishment

connection establishment

data transfer

network

Multimedia Streaming and TransportMS.3.2 Session Control Protocols: SIP

Session Control ProtocolsExample: SIP

• SIP (session initiation protocol)

– IETF session protocol

– Internet style signalling based on HTTP messages

– single component

• H.323

– ITU session protocol

– telephony style signalling

– integrated protocol suite for multimedia conferencing:

• signaling, registration, admission control, transport, codecs

Session Initiation ProtocolOverview

– IETF session protocol [RFC 3261]

• Internet style signalling

– based on HTTP-like messages

– SDP typically used to describe media characteristics(session description protocol) [RFC 2327]

• Single component

– works with RTP but does not mandate it

Session Initiation ProtocolAssumptions and Design Goals

• Internet-based telephone video conference calls

• Addressing

– people identified by names or e-mail addresses

• Support for:

– roaming

– heterogeneous IP-based devices

• Simplicity

Session Initiation ProtocolCall Services

• Call setup

– mapping of user identifier to IP address

– caller invitation of callee

– negotiation of media type and encoding

– unique call identifier

– mechanisms to end call

• Call management

– add new media streams during call

– change encoding during call

– invite others to join call

– transfer and hold calls

Session Initiation ProtocolSIP Message

INVITE sip:bob@example.com SIP/2.0

Via: SIP/2.0/UDP 167.180.112.24

From: sip:alice@hereway.com

To: sip:bob@example.com

Call-ID: a2e3a@pigeon.example.com

Content-Type: application/sdp

Content-Length: 885

c=IN IP4 167.180.112.24

m=audio 38060 RTP/AVP 0

• Bob’s IP address unknown

– SIP servers will resolve

• Alice specifies in Via:SIP over UDP

• SDP used for sessiondescription

Session Initiation ProtocolCall Example

• Alice’s SIP INVITE message:

– port number & IP address

– PCM preferred audio encoding

• Bob’s reply message 200 OK

– his port number & IP address

– GSM preferred audio encoding

• SIP messages

– HTTP message syntax

– sent over TCP or UDP

• here sent over RTP/UDP

– default SIP port is 5060 time time

terminal rings

167.180.112.24

193.64.210.89

port 5060

port 38060

m Law audio

GSMport 48753

INVITE bob@193.64.210.89c=IN IP4 167.180.112.24m=audio 38060 RTP/AVP 0port 5060

200 OK

c=IN IP4 193.64.210.89

m=audio 48753 RTP/AVP 3

ACKport 5060

[Kurose]

Session Initiation ProtocolCall Negotiation

• Media can be sent over RTP or some other protocol

• Codec negotiation:

– suppose Bob doesn’t have PCM μlaw encoder

– Bob will instead reply with 606 Not Acceptable Reply

• and list encoders he can use

– Alice can then send a new INVITE message

• advertising an appropriate encoder

• Call be rejected with replies:

– busy, gone, payment required, forbidden

Session Initiation ProtocolName Translation and User Location

• Caller has callee’s “e-mail” address, not IP address

• Need to get IP address of callee’s current host:

– user moves around

– DHCP protocol

– user has different IP devices (PC, PDA, car device)

• Result can be based on:

– time of day (work, home)

– caller (don’t want boss to call you at home)

– status of callee

• e.g. sent to voicemail when callee is already talking

Session Initiation ProtocolSIP Proxy

• SIP Proxy used to resolve to IP address

• Alice sends invite message to her proxy server– contains address sip:bob@domain.com

• Proxy responsible for routing SIP messages to callee

– possibly through multiple proxies

• Callee sends response back

– through the same set of proxies.

• Proxy returns SIP response message to Alice

– contains Bob’s IP address

Note: proxy is analogous to local DNS server

Session Initiation ProtocolSIP Registrar

• SIP Registrar keeps track of users

– queried by SIP proxy

• When SIP client started

– REGISTER message sent to registrar server

• Register message exampleREGISTER sip:domain.com SIP/2.0

Via: SIP/2.0/UDP 193.64.210.89

From: sip:bob@domain.com

To: sip:bob@domain.com

Expires: 3600

Session Initiation ProtocolExample of Location and Name Resolution

• Example: jim@umass.edu calls keith@upenn.edu1. Jim sends INVITE mssage to umass SIP proxy

2. Proxy forwards request to upenn registrar server

3. upenn server returns redirect response to keith@eurecom.fr

4. umass proxy sends INVITE

to eurecom registrar

5. eurecom registrar forwardsINVITE to 197.87.54.21,

which runs Keith’s SIP client

6–8. SIP response sent back

9. media sent between clients

Note: ACK message not shownSIP client

217.123.56.89

SIP client

197.87.54.21

SIP proxy

umass.edu

SIP registrar

upenn.edu

registrar

eurecom.fr

[Kurose]

Multimedia Streaming and TransportMS.3.3 Session Control Protocols: H.323

Session Control ProtocolsExample: H.323

– IETF session protocol

– Internet style signalling based on HTTP messages

– single component

• H.323

– ITU standard session protocol

– telephony style signalling

– integrated protocol suite for multimedia conferencing:

• signaling, registration, admission control, transport, codecs

Multimedia and Session ControlAdditional References

Multimedia and Session ControlAcknowledgements

Some material in these foils comes from the textbook supplementary materials:

• Kurose & Ross,Computer Networking:

A Top-Down Approach Featuring the Internet

• Sterbenz & Touch,High-Speed Networking:

A Systematic Approach to

High-Bandwidth Low-Latency Communication

http://hsn-book.sterbenz.org

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