internet multimedia architechture

7/28/2019 internet multimedia architechture

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Internet Multimedia Architecture


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Outline

Overview

Multimedia Applications

Signaling Protocols (SIP/SDP, SAP, H.323,

MGCP)

Streaming Protocols (RTP, RTSP, HTTP, etc.)

QoS (RSVP, Diff-Serv, IntServ)

Conclusions


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Multimedia protocol stack

MGCP/Megaco

TCP UDP

IPv4, IPv6

H.323 SDP

SIP

RTSP RSVP RTCP

RTP

H.261, MPEG

PPP AAL3/4 AAL5 PPP

Sonet ATM Ethernet V.34

Signaling Quality of Service

Reservation Measurement

Media Transport

network

link

physi

cal

Applicationdaemon

kernel


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Multimedia applications

Audio

Speech (CELP type codecs)

Music (MP3, WAV, WMA, Real)

Video (MPEG1, 2, 4)

Conferencing

Streaming using HTTP/TCP (MP3), or

RTP/UDP (Video).


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RTP

Communicate choice of coding

Timing for data

Synchronize different streams

Communicate loss information (UDP)

Congestion avoidance (UDP)

Frame BoundariesUser identification ([email protected])

Efficient for small audio packets
mailto:[email protected]:[email protected]


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RTP Header

QuickTime and aTIFF (LZW) decompressor

are needed to see this picture.

V=version, P=padding, X=extension,

CC=contributing sources, M=marker bit for frame,

PT=payload type, Timestamp for first byte,

SSRC=Synchronization source - independence from

Lower protocol, CSRC=Contributing Source -mixer


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RTSP

Real Time Streaming Protocol

Text based like http

Bidirectional requests from client to server and

server to client


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RTCP

Real Time Transport Control Protocol

Defines profile

Information for interpreting RTP header

Defines format

How data following RTP header is interpreted

Can adapt to new applications


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Signaling protocols

VoIP predominantly uses two:

SIP/SDP

H.323


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Session initiation protocol (SIP)

Developed in mmusic Group in IETF Proposed standard RFC2543, February 1999

Work began 1995 Part ofInternet Multimedia Conferencing Suite (MBONE)

Main Functions Invite users to sessions

Find the users current location, match with their capabilities andpreferences in order to deliver invitation

Carry opaque session descriptions

Modification of sessions

Termination of sessions


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SIP overview

SIP

SDP

SIP

SDP

RTPUDP

RTPUDP

LDAP

DNS RSVP RSVP

TRIP

PSTN gateway lookupAddress lookup

Next-HopMay

triggerSets up


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SIP components

User Agent Client (UAC) End systems

Send SIP requests

User Agent Server (UAS) Listens for call requests

Prompts user or executes program to determine response

User Agent UAC plus UAS


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SIP components (cont.)

Redirect Server Network server - redirects users to try other server

Proxy Server Network server - a proxy request to another server can fork

request to multiple servers, creating a search tree

Registrar Receives registrations regarding current user locations


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SIP architecture

1

2

3

45

67

8

9

1011

12

SIP Client

SIP Redirect

Server

SIP ProxySIP Proxy

SIP Client

(User Agent Server)

Location Service

13

14

Request

Response

Media

sip:[email protected]

berkeley.edu

columbia.edu

sip.com

sales.sip.com

[email protected]


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Sip architecture (cont.)

SIP state-less proxies (near core of network) used for re-direction

SIP state-ful proxies (near periphery of network) Keeps track of state of call

Useful for billing/logging, authentication

Routing Registration database, external database

TRIP


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SIP architecture (cont.)

On Startup, SIP UA Sends

REGISTER to Registrar

Registration Data ProvidesAddresses to Reach User

Registration Database Forms a

Dynamic Routing Database ofUsers

Centralized Store is Desired for

Scalability

SQL/LDAP/?

Proxy Farm

INVITE

DB

Registrar


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SIP architecture (cont.)SIP INVITE Can Contain Phone Numbers sip:[email protected]

tel:17325551212

Do Not Correspond to Users on IP Network, but PSTN

Terminals

Call Must Be Routed to Gateway

Gateways Often ArrangedThrough Peering

Which One to Use Based on Prefixes(Domestic = gw1, Europe = gw2)

Route Table is Mapping From Prefixes to Next Hop IPaddress/port/transportPlus URL Rewrite Rules

1-732 regional.com

1 longdistance.com

international.com

tel:19735551212

sip:19735551212@

longdistance.com


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SIP architecture (cont.)

Inter-domain Protocol forGateway Route Exchange Completed February 2000

TRIP (Telephone Routing overIP) Supports Various Models Bilateral agreements

Centralized settlements providerEndUsers

Gateways

LocationServer

ISP A

TRIP

Front

End

ISP B


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SIP call flow example

USER A USER BPROXY PROXY

INVITE

407 Proxy Authenticate

ACK

INVITE

INVITEINVITE

180 Ringing100 Trying

100 Trying

180 Ringing180 Ringing 200 OK

200 OK200 OK

ACKACK

ACK

BOTH WAY RTP

BYEBYE

BYE

200 OK 200 OK

200 OK


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Session Description Protocol (SDP)

Used to specify client capabilities

Example (client can support MPEG-1 video

codec, and MP3 codecs)


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Session Anouncement Protocol

(SAP)Originated around same time as SIP

Used to announce multimedia sessions

Announcement goes to users in a multicast group

Announcements can contain start time of session,

duration of session, etc.


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H.323

May 1995 - H.323 work started

June 1996 - Decided by ITU-T

Designed for exchanging multimedia over IP

networks (4 versions of H.323)


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H.323 Components

Terminals

Gatekeepers

Gateways (H.323 to H.320/H.324/POTS)

MCUs

Multipoint Controller (MC)

Multipoint Processor (MP)


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H.323 Gatekeeper

Address Translation

H.323 Alias to transport (IP) address based on terminal

registration

email-like names possible

phone number like names possible

Admission control

Permission to complete call

Can apply bandwidth limits

Method to control LAN traffic


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H.323 Gatekeeper (cont.)

Management of gateway

H.320, H.324, POTS, etc.

Call Signaling

May route calls in order to provide supplementary

services or to provide Multipoint Controller

functionalityCall Management/Reporting/Logging


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H.323 MCU

Media Distribution

Unicast - send media to one terminal (centralized in

MP; traditional model) Multicast - send to each receiver directly

Hybrid - some of each

Manage Ad Hoc multipoint calls

Join, invite, control of conference modes

Multiprotocol via Gateways


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H.323 protocol stack

H.225.0 H.245

G.7xx H.26x

RTP

RTCP

Gate-

keeper

Reg,

Adm,

Status

(RAS)

Control Data Audio Video A/V Cntl Control

TCP UDP

IP

T.120


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H.323 protocol stack (cont.)

H.323 - System Document

H.225.0 - Call Signaling, Packetization

Gatekeeper Registration, Admission, and Status

H.245 - Control (also used in H.324, H.310)

T.120 - Data and Conference Control


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H.323 example

A Call Setup Example

a point to point call

One Gatekeeper using the Direct Call Model


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H.323 example (cont.)

PictureTel

(1) ARQ

Can I call

Bob?

(2a) GK resolves Bob

to IP address through H.323registration or external

name service

(e.g. DNS, ULS, etc..)

(2b) Admission Policy

Applied(3) ACF

Yes, use this

IP Address

BillBob

GK


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PictureTel

(4) SETUP (Create)

BillBob

GK

(5) ARQ

May I answer?(6) ACF

Yes

(7) ALERTING

(8) CONNECT (User answers)


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PictureTel

Bill Bob

(9) H.245 connection established

- Capability Exchange

- Open Logical

Channels (audio, video)

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