The document provides an overview of Internet multimedia architecture and protocols. It describes key signaling protocols like SIP, SDP, and H.323 for setting up multimedia sessions over IP networks. Streaming protocols like RTP, RTSP, and HTTP are covered for transporting media. Quality of service mechanisms like RSVP and DiffServ are also summarized. Common multimedia applications including voice, video, and wireless are briefly outlined. The multimedia protocol stack and functions of components in signaling architectures for SIP and H.323 are defined at a high level. An example call flow is given to illustrate how H.323 signaling works through a gatekeeper to set up a call between two terminals.

1. Internet Multimedia Architecture
Jim Chou and Thinh Nguyen
February 12, 2002

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

3. Multimedia protocol stack
Signaling
Quality of Service
Media Transport
Reservation
H.323
SDP
RSVP
RTSP
Measurement
RTCP
SIP
H.261, MPEG
RTP
TCP
Application daemon
MGCP/Megaco
UDP
network
IPv4, IPv6
kernel
link
PPP
physical
Sonet
AAL3/4
AAL5
ATM
PPP
Ethernet
V.34

4. Multimedia applications
Audio
– Speech (CELP – type codecs)
– Music (MP3, WAV, WMA, Real)
Video (MPEG –1, 2, 4)
Streaming done using HTTP/TCP (MP3), or
RTP/UDP (Video).

5. Multimedia applications (cont.)
Wireless network
Gateway
9.6 kbps
Media server
1 Mbps
PSTN
28 kbps

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

7. 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

8. SIP overview
TRIP
LDAP
PSTN gateway lookup
Address lookup
SIP
SDP
Next-Hop
DNS
SIP
SDP
RSVP
RTP
UDP
RSVP
RTP
UDP
May
trigger
Sets up

9. 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

10. 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

11. SIP architecture
Request
Response
columbia.edu
Media
SIP Redirect
Server
Location Service
2
3
berkeley.edu
sip.com
5
4
sip:alice@eecs.berkeley.edu
1
7
11
12
13
SIP Client
6
SIP Proxy
sales.sip.com
10
SIP Proxy
8
14
9
bob@mypc.sales.sip.com
SIP Client
(User Agent Server)

12. 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

13. SIP architecture (cont.)
DB
On Startup, SIP UA Sends
REGISTER to Registrar
Registration Database Forms a
Dynamic Routing Database of
Users
Centralized Store is Desired for
Scalability
SQL/LDAP/?
RE
GI
ST
ER
Registration Data Provides
Addresses to Reach User
Registrar
Proxy Farm
INVITE

14. SIP architecture (cont.)
SIP INVITE Can Contain Phone Numbers
– sip:17325551212@domain.com
– 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
tel:19735551212
sip:19735551212@
longdistance.com
1-732
regional.com
1
longdistance.com
international.com

15. SIP architecture (cont.)
Gateways
Inter-domain Protocol for
Gateway Route Exchange
– Completed February 2000
TRIP Supports Various Models
– Bilateral agreements
– Centralized settlements provider
Location
Server
ISP B
TRIP
End
Users
ISP A
Front
End

16. SIP call flow example
USER A
PROXY
PROXY
USER B
INVITE
407 Proxy Authenticate
ACK
INVITE
100 Trying
180 Ringing
200 OK
ACK
INVITE
100 Trying
180 Ringing
200 OK
ACK
INVITE
180 Ringing
200 OK
ACK
BOTH WAY RTP
BYE
200 OK
BYE
200 OK
BYE
200 OK

17. Session Description Protocol (SDP)
Used to specify client capabilities
Example (client can support MPEG-1 video
codec, and MP3 codecs)

18. 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.

19. Multimedia Gateway Control Protocol
(MGCP)
Decompose gateway into a controlling signalling
component and a controlled media component.
Can be used in phones or gateways in
conjunction with SIP

20. 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)

21. H.323 Components
Terminals
Gatekeepers
Gateways (H.323 to H.320/H.324/POTS)
MCUs
– Multipoint Controller (MC)
– Multipoint Processor (MP)

22. 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

23. 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

24. H.323 Gateway
Provide world wide connectivity and
interoperability from LAN
– H.320, H.324, regular POTS telephones
Map Call Signaling (Q.931 to H.225.0)
Map Control (H.242/H.243 to H.245)
Media Mapping (FEC, multiplex, rate matching,
audio transcoding)

25. 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

26. H.323 protocol stack
Control
Data
Audio
Video
A/V Cntl Control
Gatekeeper
G.7xx H.26x
RTCP
H.225.0 H.245 T.120
RTP
TCP
UDP
IP
Reg,
Adm,
Status
(RAS)

27. 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

28. H.323 example
A Call Setup Example
a point to point call
One Gatekeeper using the Direct Call Model

29. H.323 example (cont.)
GK
(1) ARQ
Can I call
“Bob”?
PictureTel
PictureTel
Bill
(3) ACF
Yes, use this
IP Address
(2a) GK resolves “Bob”
to IP address through H.323
registration or external
name service
(e.g. DNS, ULS, etc..)
(2b) Admission Policy
Applied
PictureTel
Bob

30. H.323 example (cont.)
GK
(6) ACF
Yes
(5) ARQ
May I answer?
(4) SETUP (Create)
P
ictureTel
PictureTel
(7) ALERTING
(8) CONNECT (User answers)
Bill
PictureTel
Bob

31. H.323 example (cont.)
PictureTel
P
ictureTel
PictureTel
(9) H.245 connection established
Bill
- Capability Exchange
- Open Logical Channels
(audio, video)
Bob