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Internet Multimedia Architecture
Jim Chou and Thinh Nguyen
February 12, 2002
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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 (CELPtype codecs)
Music (MP3, WAV, WMA, Real)
Video (MPEG1, 2, 4)
Streaming done using HTTP/TCP (MP3), orRTP/UDP (Video).
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Multimedia applications (cont.)
Gateway
Media server
Wireless network
PSTN
9.6 kbps
28 kbps
1 Mbps
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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 of Internet 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
berkeley.edu
columbia.edu
sip.com
sales.sip.com
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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 Supports Various Models Bilateral agreements
Centralized settlements provider
EndUsers
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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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
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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 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)
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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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H.323 example (cont.)
PictureTel
(4) SETUP (Create)
BillBob
GK
(5) ARQ
May I answer?(6) ACF
Yes
(7) ALERTING
(8) CONNECT (User answers)
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H.323 example (cont.)
PictureTel
Bill Bob
(9) H.245 connection established
- Capability Exchange
- Open Logical
Channels (audio, video)