B.Bharat Shetty

4th semester CS&E

SJCE

DEFNITION: Multimedia is often described as a holy grail by some people.Literally the term multimedia is just two or more media.To be precise “Multimedia” generally means the combination of two or more continuous media i.e. media that has to be played during some well defined interval usually with some user defined interaction.

Before Proceeding concept of a protocol must be clear to you

Multimedia Networking Applications

Streaming stored audio and videoRTSP

Protocols for Real-Time Interactive Applications

RTP

RTCP

SIP.

RSVP

H.323 standard

Summary

MM Networking Applications

Fundamental characteristics:

• Typically delay sensitive.• End-to-end delay.• Delay jitter.

• But loss tolerant: infrequent losses cause minor glitches.

• Antithesis of data, which are loss intolerant but delay tolerant.

Classes of MM applications:

1) streaming stored audio and video

2) streaming live audio and video

3) real-time interactive audio and video

Jitter -the variability of packet delays within the same packet stream

Multimedia, Quality of Service: What is it?

Multimedia applications: network audio and video(“continuous media”)

level of performance needed for application to function.

QoS

Streaming Stored Multimedia

• Streaming: • media stored at source• transmitted to client• streaming: client playout begins before

all data has arrived• timing constraint for still-to-be

transmitted data: in time for playout

SSM: What Is It?

1. videorecorded

2. videosent

3. video received,played out at client

Cum

ula

tive

data

streaming: at this time, client playing out early part of video, while server still sending laterpart of video

networkdelay

time

Streaming Stored Multimedia: Interactivity

functionality similar to a VCR: client can pause, rewind, FF, push slider

bar• 10 sec initial delay causes no problem• 1-2 sec until command effect OK• RTSP often used

• timing constraint for still-to-be transmitted data: in time for playout

Streaming Live Multimedia

Examples:• Talk shows over the web.• Events brought live to home.Streaming.• Playback buffer.• Playback can lag tens of seconds after

transmission.• Still have timing constraint.Interactivity.• Fast forward impossible.• Rewind, pause possible!

Video servers

ATM or SONET Backbone network

LDN*

Local spooling server

switchCustomer’s

House

LDN-local distribution network

User Control of Streaming Media: RTSP

RTSP: • Client-server application layer protocol.

• User can control display: rewind, fast forward, pause, resume, repositioning, etc…

Disadvantages:

• Does not define how audio/video is encapsulated for streaming over network.

• No restrictions on how sm is transported. It can be transported over UDP or TCP.

• No specifications on how the media player buffers audio/video.

Real-time Protocol (RTP)

RTP specifies a packet structure for packets carrying audio and video data.RFC 1889.RTP packet provides.

Payload type identification.Packet sequence numbering.Timestamping.

RTP runs in the end systems.RTP packets are encapsulated in UDP segments.Interoperability: if two internet phone applications run RTP, then they may be able to work together.

RTP Runs on Top of UDP

RTP libraries provide a transport-layer interface that extend UDP:

• port numbers, IP addresses

• payload type identification

• packet sequence numbering

• time-stamping

RTP Header

Payload Type (7 bits): Indicates type of encoding currently being used. If sender changes encoding in middle of conference, sender informs the receiver through this payload type field.

•Payload type 0: PCM mu-law, 64 kbps•Payload type 3, GSM, 13 kbps•Payload type 7, LPC, 2.4 kbps•Payload type 26, Motion JPEG•Payload type 31. H.261•Payload type 33, MPEG2 video

Sequence Number (16 bits): Increments by one for each RTP packet sent, and may be used to detect packet loss and to restore packet sequence.

Real-time Control Protocol (RTCP)

Works in conjunction with RTP. Each participant in RTP session

periodically transmits RTCP control packets to all other participants.

Each RTCP packet contains sender and/or receiver reports.

Key things:-Number of packets sent.

-Number of packets lost. -Inter arrival jitter.

RTCP - Continued

- RTP session typically has a single multicast address; all RTP and RTCP packets belonging to the session use the multicast address.

- RTP and RTCP packets are distinguished from each other through the use of distinct port numbers.

- To limit traffic, each participant reduces his RTCP traffic as the number of conference participants increases.

RTCP Packets

Receiver report packets: Fraction of packets lost, last sequence number, average interarrival jitter.

Sender report packets: SSRC of the RTP stream,the current

time,the number of packets sent and the number of bytes sent.Source description packets:

E-mail address of sender,sender's name, SSRC of associated RTP stream.

Enable mapping between the SSRC and the user/host name.

SIP

• Session initiation protocol.• Comes from IETF.

• Usually a single module suitable for internetworking.

• People are identified by names or e-mail addresses, rather than by phone numbers.

• You can reach the callee, no matter where the callee roams, no matter what IP device the callee is currently using.

Calling a Known IP Address• Alice’s SIP invite message indicates her port number & IP address. Indicates encoding that Alice prefers to receive

• Bob’s 200 OK message indicates his port number, IP address & preferred encoding (GSM)

• SIP messages can be sent over TCP or UDP; here sent over RTP/UDP. •Default SIP port number is 5060.

time time

Bob'stermina l rings

A lice

167.180.112.24

Bob

193.64.210.89

port 38060

Law audio

G SMport 48753

Example of SI P message

INVITE sip:bob@domain.com SIP/2.0 Via: SIP/2.0/UDP 167.180.112.24 From: sip:alice@hereway.com To: sip:bob@domain.com Call-ID: a2e3a@pigeon.hereway.com Content-Type: application/sdp Content-Length: 885 c=IN IP4 167.180.112.24 m=audio 38060 RTP/AVP 0 Notes:

r HTTP message syntax

r sdp = session description protocol

r Call-I D is unique f or every call.

• Here we don’t know Bob’s I P address. I ntermediate SI P servers will be necessary.

• Alice sends and receives SI P messages using the SI P def ault port number 506. • Alice specifies in Via: header that SI P client sends and receives SI P messages over UDP More details

Definition of H.323 standard

H.323 is a standard that specifies the components, protocols and procedures that provide multimedia communication services—real-time audio, video, and data communications—over packet networks, including Internet protocol (IP)–based networks. H.323 is part of a family of ITU—T recommendations called H.32x that provides multimedia communication services over a variety of networks

-Emergence of voice-over–IP (VoIP) applications and IP telephony

-The absence of a standard for voice over IP meant products that were incompatible.

- Such requirements forced the need for a standard for IP telephony.

E.g.:Version 2 of H.323—packet-based multimedia communications systems

H.323 - lications

H.323 is applied in a variety of mechanisms

Audio only (I P telephony) Audio and video (video telephony) Audio and data and audio Video and data.

H.323 can also be applied to multipoint- multimedia communications. H.323 provides myriad services and, therefore, can be applied in a wide variety of areas— consumer, business, and entertainment application The features being added currently include fax- over- packet networks, gatekeeper- gatekeeper.

Data Link Protocol

IP

TCPUDP

H.225(RAS)H.225(RAS)

RTCPRTCP

Physical Layer Protocol

H.245(call control)Q.931

RTP

ControlSpeech

H.323 Packet NetworkH.323 Packet Network

INTERNET

GATEWAY

TELEPHONENETWORK

The H.323 architectural Model for Internet Telephony

Terminal

Gatekeeper

ZONE

Allow two Party and multiparty calls

Support parameter negotiation

Support Encryption

Support Media transport on RTP/RTCP protocols

Feature sets are almost similar

Similarities b/w H.323 and SIPSimilarities b/w H.323 and SIP

H.323 SIP

ITU ITEF

Yes Largely

No Yes

Monolithic Modular

Full Protocol Stack Handles only setup

Binary ASCII

Yes No

Host or Telephone no URL

No Yes

Large and complex Moderate

1400 pages 250 pages

ITEM

Designed By

Compatibility with PSTN

Compatibility with net

Architecture

Completeness

Message Format

Multimedia conferences

Addressing

Instant Messaging

Implementation

Standards size

RSVP designed at

-MIT

-PARC

-California University.

RSVP Features:

RSVP is a novel signaling protocol in at least 4 ways:

1. It accommodates multicast, not just point-to-multipoint (one-to-many) reservations.

2. QoS routing can be deployed separately (in more operations, and so is

3. relatively low cost

4. Scalability.

RESERVATION IMPLEMENTATIONS

Reservations are implemented through two types of RSVP messages:

PATH and RESV.

The PATH messages are sent periodically from the sender to the multicast address. A PATH message contains flow spec to describe sender template (data format, source address, source port) and traffic characteristics.

RESV messages are generated by the receivers and contains reservation parameters including flow spec and filter spec.

R1

R3R2

R4 S1

S2

H4

H5

H3

R1

R3R2

R4 S1

S2

H4

H5

H3

Multimedia Networking: Summary

Video conferencing,distance learning.Distributed networking and sharing of data and info resources.Future holds so much promise.Virtual reality,digital animation,net telephony.Interactivity enabled in all sectors.Next generation internet: Intserv, RSVP, Diffserv.

Graphical Analysis Ahead

Multimedia market A graphical analysis

0 20 40 60 80 100 120 140 160

Market Value in Billions

Telecom

Computers

Publishing

Catalog

TV/Radio

Cable networks

Home video

Info servers

CDs/Tapes

Video

Arcades

Movies

Worldwide Statistics of multimedia market compiled by NASDAQ

Values in Billions

Growth of Multimedia Networks

2003

N

E

T

W

O

R

K

s

Years

Source: NASDAQ and NASSCOM survey

The real-time challenges

However, multimedia networking is not a trivial task. We can expect at least three difficulties.

1. When compared with traditional textual applications, multimedia applications usually require much higher bandwidth.

2. Most multimedia applications require the real-time traffic

3. In addition to the delay, network congestion also has more serious effects on real-time traffic

4. Multimedia data stream is usually bursty

Books:

1.Multimedia Handbook- Jessica Keyes-TMH

2.Computer networks – Andrew Tanenbaum

3.Multimedia systems- a perspective (IEEE)

Internet:

1.www.cis.ohio-state.edu/~jain/

2.www.google.com

3.University of colombia website.

4.IEEE papers on net

B.Bharat Shetty 4th sem CS&E SJCE