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
Application daemon
MGCP/Megaco
Reservation
Measurement
H.261, MPEG
H.323
SDP
RTSP
RSVP
RTCP
SIP
RTP
TCP
UDP
network
IPv4, IPv6
kernel
link
PPP
AAL3/4
AAL5
PPP
physical
Sonet
ATM
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 SIP SDP SIP SDP DNS RSVP
Address lookup
SIP
SDP
SIP
SDP
May
trigger
Next-Hop
Sets up
DNS
RSVP
RSVP
RTP
UDP
RTP
UDP

9. SIP components User Agent Client (UAC) User Agent Server (UAS)
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 Proxy Server Registrar
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 Media SIP Redirect Server1 2 3 4 5 6 7 8 9 10 11 12
SIP Client
SIP Redirect
Server
SIP Proxy
(User Agent Server)
Location Service 13 14
columbia.edu
berkeley.edu
sip.com
sales.sip.com

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.)
SQL/LDAP/?
Proxy Farm
INVITE DB
Registrar
REGISTER
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

14. SIP architecture (cont.)
SIP INVITE Can Contain Phone Numbers
tel:
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
longdistance.com
tel:

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
INVITE
100 Trying
INVITE
100 Trying
180 Ringing
180 Ringing
180 Ringing
200 OK
200 OK
200 OK
ACK
ACK
ACK
BOTH WAY RTP
BYE
BYE
BYE
200 OK
200 OK
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 Admission control
H.323 Alias to transport (IP) address based on terminal registration
“ -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 Call Signaling
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 Manage Ad Hoc multipoint calls
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 Gate-
keeper
Reg,
Adm,
Status
(RAS)
G.7xx
H.26x
RTCP
H H.245
T.120
RTP
TCP
UDP IP

27. H.323 protocol stack (cont.)
H System Document
H Call Signaling, Packetization
Gatekeeper Registration, Admission, and Status
H Control (also used in H.324, H.310)
T 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 (2a) GK resolves “Bob”
to IP address through H.323
registration or external
name service
(e.g. DNS, ULS, etc..)
(2b) Admission Policy
Applied
(1) ARQ
Can I call
“Bob”?
(3) ACF
Yes, use this
IP Address
PictureTel
Bob
Bill

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

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