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Internet Protocols for Multimedia

Internet Protocols for Multimedia. DS VT-00 Jerry Eriksson. Multimedia Networking. Animation, voice and video - not only text distance learning, distributed simulation, distribute work groups Multimedia networks may replace telephone, television, etc

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Internet Protocols for Multimedia

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  1. Internet Protocols for Multimedia DS VT-00 Jerry Eriksson

  2. Multimedia Networking • Animation, voice and video - not only text • distance learning, distributed simulation, distribute work groups • Multimedia networks may replace telephone, television, etc • Challenges - Build hardware and software infrastructure and applications to support multimedia

  3. Real-time challenges Real-time protocols RTP, RTCP, RTSP QoS Definitions Goals Traffic management architectures IntServ, Diffserv, RSVP VoIP H.323, SIP Outline

  4. Real-time Challenges • High bandwidth • Audio and video must be played back at the rate they were sampled (voice may be even more difficult) • Multimedia data streams are bursty

  5. Internet • Primary reason: Platform for most networking activities • Integrated data and multimedia service over a single network (investments) • Not suitable for real-time traffic • Offers only best-effort quality

  6. Provide enough bandwidth Provide multicast to reduce traffic Provide protocols that handle that that care of timing issues Delay, Jitter QoS- guarantee quality Reserve resource on the internet Transport protocols Presentation of the multimedia data (WAP, Voice) Charging and policing mechaninsm Problems to solve

  7. QoS Definitions • Qos is a set of technologies that enables network administrators to manage the effects of congestion on application traffic by using network resources optimally • or, allocate different resourses for different data flows

  8. QoS classes • Best-effort - No gurantees at all • Soft QoS - differentiated guarantess • Hard QoS - full guarantees

  9. RTP- Real-time transport protocols • Ip-based protocol providing • time-reconstruction • loss detection • security • content identification • Designed primarily for multicast of real-time data (also unicast, simplex, duplex)

  10. RTP - development • December 1992, Henning Schulzrinne, GMD Berlin, published RPT version 1 • Proposed (version 2) as standard November,1995 • Netscape and Microsoft uses RTP

  11. How does RTP works • Timestamping - most important information for real-time applications. • The sender timestamp according to the instant the first octet in the packet was sampled. • The receiver uses timestamp to reconstruct the original timing • Also used for synchronize different streams; audio an video in MPEG. ( Application level responsible for the actual synchronization)

  12. How does RTP work • Payload type identifier • specifies the payload format as well as encoding/compression schemes • The application then knows how to interpret the payload • Source identification • Audio conference

  13. Where is RPT reside • RPT is typically run on top of UDP • Uses UDP’s multiplexing and checksum functions • RPT is usually implemented within the application (Lost packets and congestion control have to be implemented in the application level

  14. RTCP - Real Time Control Protocol • Designed to work together with RTP • In an RTP session the participants periodically send RTCP packet to give feedback on the quailty of the data. • Comparable to flow and congestion control of other transport protocols. • RTP produces sender and receivers reports; statistics and packet counts

  15. RTCT packet types • Recevier reports: feedback of data delivery • Packet lost, jitter, timestamps • Sender report: • Intermedia synchronization, number of bytes sent, packet counters • SDES, BYE, APP

  16. RTCP provides the following services • QoS monitoring and congestion control • Primary function: QoS feedback to the application • The sender can adjust its transmission • The receiver can determine if the congestion is local, regional, or global • Network managers can evaluate the network performance for multicast distribution

  17. RTCP provides the following services (Cont) • Source identification • inter-media synchronization • control information scaling • Limit control traffic (most 5 % of the overall session traffic)

  18. Provides end-to-end real-time data delivery (functionality and control mechanisms) timestamps sequences numbering (up to the application to use it) Uses UDP Provides not timely delivery (needs lower layer reservations) any form of reliability or flow/congestion control (RTCP) Not complete - new payload format RTP/RTCP features

  19. What is Streaming? • Streaming breaks data into packets; real-time data through the transmission, decompressing just like a water stream. • A client can play the first packet, decompress the second, while receiving the third. • The user can start enjoying the multimedia without waiting to the end of the transmission

  20. RTSP - real time streaming protocol • Client-server multimedia presentation protocol to enable controlled delivery • provides ”vcr”-style remote control functionality of streamings over IP. • RTSP is an application-level protocol designed to work with RTP (and RSVP) to provide a complete streaming service over internet • It provides means for choosing channels (UDP etc) and delivery mechanisms (RTP) • Developed by RealNetworks, netscape, and columbia university (still an internet draft)

  21. RTSP operations and methods • RTSP establish and controls streams • A media server provides playback or recording services • A client requests continues media data from the media server • RTSP is the network is the ”network remote control” between the server and the client

  22. RTSP provides • Retrieval of media from media server • Invitation of a media server to a conference • Adding media to an existing presentation • Similar services on streamed audio and video, just as HTTP does for text and graphics

  23. HTTP/RTSP differences • HTTP stateless protocol; an RTSP server has to maintain ”session states” • HTTP is asymmetric; in RTSP both client and server can issue requests • It uses URL, like HTTP

  24. Resources reservation and prioriations • Any QoS better than best-effort. • Routing delays and congestion losses • Real-time traffic

  25. Now IP QoS Networking -Integrated services • Defined by an IETF working group to be a key-stone • IS was developed to optimize network and resource utilization which require QoS. • Divided traffic between into different QoS classes. • An internet router must be able to provide an appriopriate QoS for each flow. (according to a service model)

  26. Router function: Traffic control • Packet scheduler manages forwarding of different packet streams. • Service class, queue management, algorithms • Police and shape traffic • must be implemented at the point where the packets are queued.

  27. Router function: Traffic control • Packet classifier indentifies packets of an IP flow in hosts and routers that will receive a certian level of service. • Each packet is mapped by the classifier into a specific class. (same class, same treatment) • The choice of class is based upon the source and destination, and port number in packet header

  28. Admission control • Decision algorithms that a router uses to determine if there are routing resources to accept the requested QoS for a flow • If the flow is accepted; the packet classifier and packet scheduler reservs the requested Qos for this flow. • Checks user authentification • Will play an important role for charging

  29. IntServ (cont) • Communicates with RSVP to create and maintain flow-specific states in the endpoint hosts and in routers along the path of a flow • RSVP/Intserv are complementary • Not suitable for high volume traffic (speech)

  30. Differentiated services • IETF working group (draft, no RFC) • Simplify scheduling and classification using the priority bits in the IP header. • Packet flow must be marked according to SLA; Servive Level Agreements at the edge of the network • The ISP must assures that a user gets his requsted QoS. • Improves scalability greatly.

  31. Mechanisms needed • Setting bits in DS at the network edges and administrative boundaries • Using those bits to determine how packets are treated by routers inside the network • DS architecture is currently asymmetric; • on-going research for symmetric architecture

  32. Diffserv architecture • Static and long-term • Not need to set up QoS reservation for specific data packets • DS routing example (it is not that easy) • Handle aggregate traffic (not per-conversation) • require significantly less sates and processing power than per-conversation.

  33. RSVP - reservation protocol • Internet control protocol - not routing protocol • Runs on top of IP and UDP • Key concepts: flows and reservations • Applies for a specific flow of data packets on a specific path. Each flow has a flow descritpor. • Both unicast and multicast. • Doesn’t understand the content of the flow descriptor

  34. RSVP - reservation protocol • Simplex protocol; reservation is done in one direction; • Receiver-initiated. The sender sends QoS wanted to the receiver which sends an RSVP message back to the sender. • The sender does not need to know the capabilities along the path or at the receiver

  35. RSVP - reservation protocol • The RVSP daemon • checks admission and policy control. If either fails the RSVP returns error • sets parameters in the packet classifier and packet scheduler • communicates with the routing process to determine path

  36. Reservation messages PATH and RESV; • PATH messages are periodically from the sender to the receiver and contains a flow spec • data format, source address, source port • traffic characteristics • RECV is generated by the receiver and contains flow spec and filter spec • follows the exact reverse path setting up reservations for one or or more senders at each node

  37. Intserv drawbacks • Only implemented for UNIX platforms • Must be implemented on each node from ’end’-end’ - not scalable • No secure policy mechanisms • Protecting multimedia - most traffic still are non-multimedia • Close to death, September 1997

  38. RSVP renaissance today • Availability of RSVP signaling on a large number of hosts (Windows 2000) • Use Diffserv as well. • Availability of policy components and products from many vendors. • Recent work on RSVP signalling handle non-multimedia much better

  39. Top-down provisioning • Low overhead and aggregate traffic handling. Bilateral agreements • Difficulty learning the classification criteria that should be configured to specify specific traffic • Cannot offer high-quality guarantees required for multimedia applications, unless the network is overdimensioned • Top-down provisioning to coordinate traffic handling along a specific path

  40. Youram Bernet The combination of RSVP signaling with aggregate traffic handling mechanisms is able to address the deficiencies of the exclusively top-down provisioned approach without incurring the scalability problems of classical RSVP/intserv usage

  41. Enhancing efficiency within diffserv Network • Diffserv provider may dedicate resources support SLA • Statistical multiplexing • Dynamic signalling at certain key points; • dynamic admission control

  42. Yoram Bernet When managing a network to offer QoS, the manager is faced with certain trade-offs. A given network and its QoS mechanisms can offer a certain quality of guarantees at a certain level of efficiency.

  43. Quality/efficiency • Trade-off; An on-going debate • Over-provision the network;Efficiency decreases • Lower the resourses;Decrease QoS. • It is impossible to aviod the overhead of more sophisticated QoS mechanisms unless on is willing to compromise in the trade-off just mentioned

  44. Yoram Bernet, QoS expert Microsoft Despite the astounding rate at which netork capacity is increasing, we find ourselves contending with congested networks today and can expect ot do be doing so for the foreseeable future

  45. Why IP telephony (VoIP) • Regarded far too unreliable for mass market, but now reliability and quality have quickly improved • Advantages: Cheaper • No inter-connect charges; 6-8 kb/s (packet) vs 64kb/s • Regulation costs • New value-added features; conferencing • Single network

  46. Internet telephony standards • Still immature; latency major issue • ITU-T: H.323 (set of protocols) • SIP used to initate a session between users. Simple, cheap. Limited, but popular

  47. H.323 Standard architectures • Protocol stack (fig. 9-4) • Audio, video over RTP/RTCP/UDP • Data over TCP • System Control over TCP

  48. H.323 Architecture • Components • Gateway • Gatekeeper • MCU • Interwork with SS7

  49. Signalling within H.323 • H.323 uses a logicla channel on the LAN • RAS (Registration, admission and status) • Gatekeeper Discovery • Endpoint registration • Call management • Admission procedures • and several more

  50. VoIPoW (over wireless (wcdma)) • Rather important reserach in Ericsson • Challenge cube

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