internet multimedia architecture jim chou and thinh nguyen february 12, 2002
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Internet Multimedia Architecture
Jim Chou and Thinh Nguyen
February 12, 2002
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)
Streaming done using HTTP/TCP (MP3), or RTP/UDP (Video).
Multimedia applications (cont.)
Gateway
Media server
Wireless network
PSTN
9.6 kbps
28 kbps
1 Mbps
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
berkeley.edu
columbia.edu
sip.com
sales.sip.com
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 Supports Various Models– Bilateral agreements– Centralized settlements provider
EndUsers
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.
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
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 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)
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)