Internet multimedia
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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.
Internet multimedia
- 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