Internet Multimedia Architecture. Outline Overview Multimedia Applications Signaling Protocols (SIP/SDP, SAP, H.323, MGCP) Streaming Protocols (RTP, RTSP,

Internet Multimedia Architecture

Outline

Overview Multimedia Applications Signaling Protocols (SIP/SDP, SAP, H.323, MGCP) Streaming Protocols (RTP, RTSP, HTTP, etc.) QoS (RSVP, Diff-Serv, IntServ) Conclusions

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

netwo

rklink

physical

Application daem

onkernel

Multimedia applications

Audio– Speech (CELP – type codecs)– Music (MP3, WAV, WMA, Real)

Video (MPEG –1, 2, 4)Conferencing Streaming using HTTP/TCP (MP3), or RTP/UDP (Video).

RTP

Communicate choice of codingTiming for dataSynchronize different streamsCommunicate loss information (UDP)Congestion avoidance (UDP)Frame BoundariesUser identification ([email protected])Efficient for small audio packets

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

RTSP

Real Time Streaming ProtocolText based like httpBidirectional requests from client to server and server to client

RTCP

Real Time Transport Control ProtocolDefines profile– Information for interpreting RTP header

Defines format– How data following RTP header is interpreted

Can adapt to new applications

Signaling protocols

VoIP predominantly uses two:– SIP/SDP– H.323

Session initiation protocol (SIP)

Developed in mmusic Group in IETF– Proposed standard RFC2543, February 1999– Work began 1995– Part of Internet Multimedia Conferencing Suite (MBONE)

Main Functions– Invite users to sessions

• Find the user’s current location, match with their capabilities and preferences in order to deliver invitation

• Carry opaque session descriptions– Modification of sessions– Termination of sessions

SIP overview

SIPSDP

SIPSDP

RTPUDP

RTPUDP

LDAP

DNS RSVP RSVP

TRIP

PSTN gateway lookupAddress lookup

Next-Hop May trigger

Sets up

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

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

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]

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

SIP architecture (cont.)

On Startup, SIP UA Sends REGISTER to Registrar

Registration Data Provides Addresses to Reach User

Registration Database Forms a Dynamic Routing Database of Users

Centralized Store is Desired for Scalability

SQL/LDAP/?

Proxy Farm

INVITE

DB

Registrar

RE

GIS

TER

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 Arranged Through Peering

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

Route Table is Mapping From Prefixes to Next Hop IP address/port/transport Plus URL Rewrite Rules

1-732 regional.com

1 longdistance.com

international.com

tel:19735551212

sip:19735551212@ longdistance.com

SIP architecture (cont.)

Inter-domain Protocol for Gateway Route Exchange– Completed February 2000

TRIP (Telephone Routing over IP) Supports Various Models– Bilateral agreements– Centralized settlements provider End

Users

Gateways

LocationServer

ISP A

TRIP

FrontEnd

ISP B

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 OK200 OK

Session Description Protocol (SDP)

Used to specify client capabilities

Example (client can support MPEG-1 video codec, and MP3 codecs)

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.

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)

H.323 Components

TerminalsGatekeepersGateways (H.323 to H.320/H.324/POTS)MCUs – Multipoint Controller (MC)– Multipoint Processor (MP)

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

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 functionality

Call Management/Reporting/Logging

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

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

H.323 protocol stack (cont.)

H.323 - System DocumentH.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

H.323 example

A Call Setup Example

a point to point call

One Gatekeeper using the Direct Call Model

H.323 example (cont.)

PictureTel

PictureTel

PictureTel

(1) ARQCan I call“Bob”?

(2a) GK resolves “Bob”to IP address through H.323registration or externalname service (e.g. DNS, ULS, etc..)(2b) Admission PolicyApplied(3) ACF

Yes, use thisIP Address

Bill Bob

GK

H.323 example (cont.)

PictureTel

PictureTel

PictureTel

(4) SETUP (Create)

Bill Bob

GK

(5) ARQMay I answer?

(6) ACFYes

(7) ALERTING

(8) CONNECT (User answers)

H.323 example (cont.)

PictureTel

PictureTel

PictureTel

Bill Bob

(9) H.245 connection established

- Capability Exchange

- Open Logical Channels (audio, video)