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Internet Multimedia Architecture

Internet Multimedia Architecture. 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. Signaling. Quality of Service.

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Internet Multimedia Architecture

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  1. Internet Multimedia Architecture

  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) • Conferencing • Streaming using HTTP/TCP (MP3), or RTP/UDP (Video).

  5. RTP • Communicate choice of coding • Timing for data • Synchronize different streams • Communicate loss information (UDP) • Congestion avoidance (UDP) • Frame Boundaries • User identification (user@domain.com) • Efficient for small audio packets

  6. RTP Header V=version, P=padding, X=extension, CC=contributing sources, M=marker bit for frame, PT=payload type, Timestamp for first byte, SSRC=Synchronization source - independence from Lower protocol, CSRC=Contributing Source -mixer

  7. RTSP • Real Time Streaming Protocol • Text based like http • Bidirectional requests from client to server and server to client

  8. RTCP • Real Time Transport Control Protocol • Defines profile • Information for interpreting RTP header • Defines format • How data following RTP header is interpreted • Can adapt to new applications

  9. Signaling protocols • VoIP predominantly uses two: • SIP/SDP • H.323

  10. 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

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

  12. 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

  13. 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

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

  15. 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

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

  17. 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 sip:19735551212@ longdistance.com tel:19735551212

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

  19. 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

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

  21. 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.

  22. 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)

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

  24. 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

  25. 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

  26. 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

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

  28. 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

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

  30. PictureTel 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 Bob Bill

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

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

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