Internet Protocols Multimedia Netw orking for Multimedia T - PDF document

Internet Protocols Multimedia Netw orking for Multimedia T Animation, voice and video - not only text T Video, Distributed simulation, distribute work groups T Multimedia networks may replace DS VT-01 Jerry Eriksson telephone, television, etc T Challenges - build hardware and software infrastructure and applications to support multimedia Outline Real-time Challenges T Bandwidth T Real-time challenges T Traffic management architectures T Real-time protocols T Latency, jitter S IntServ , Diffserv , S RTP, RTCP, RTSP T Audio and video must be played back at RSVP T QoS the rate they were sampled (voice may be T VoIP S Definitions even more difficult) S H.323 S Goals S SIP, some T Multimedia data streams are bursty Internet Problems to solve T Primary reason: Platform for most T Provide T QoS S enough bandwidth S ’guarantee’ quality networking activities S multicast to reduce S Reserve resource on T Integrated data and multimedia service traffic the internet over a single network (investments) S protocols that handle S Transport protocols T Not suitable for real-time traffic care of timing issues T Presentation of the R Delay, Jitter multimedia data S Offers only best-effort quality T Charging and policing mechaninsm 1

RTP - development Some RTP Implementations T December 1992, Henning Schulzrinne, Tool Who Media GMD Berlin, published RPT version 1 NeVoT GMD Fokus Audio S see www.cs.columbia.edu/~ hgs/rtp vic LBNL Video vat LBNL Audio T Proposed (version 2) as standard Rat UCL Audio November,1995 Rendezvous INRIA A/V NetMeeting Microsoft A/V IP/TV Cisco A/V RM G2 Real A/V RTP- Real time transport protocols Where is RTP reside T IP-based protocol providing T RTP is typically run on top of UDP S time-reconstruction S Uses UDP’s multiplexing and checksum functions. May be viewed as a sublayer of the S loss detection transport layer S security T RTP is usually implemented within the S content identification application T Designed primarily for multicast of real- S Lost packets and congestion control have to time data (also unicast, simplex, duplex) be implemented in the application level T Separate Control/Data Header fields How does RTP works T Timestamping - most important information for real- time applications. S The sender timestamp according to the instant t he Sequence Time- Synch Miscellaneous Type fields first octet in the packet was sampled. number stamp source ID S The receiver uses timestamp to reconstruct the 7 bits 16 bits 32 bits 32 bits original timing S Also used for synchronize different streams; audio an video in MPEG. ( Application level responsible for the actual synchronization) 2

RTCP - Real Time Control How does RTP w ork Protocol (RFC 1889) T Payload type identifier T Designed to work together with RTP S specifies the payload format as well as T In an RTP session the participants encoding/compression schemes periodically send RTCP packet to give S The application then knows how to interpret feedback on the quailty of the data. the payload T Comparable to flow and congestion T Source identification control of other transport protocols. S Identifies the source, not IP adress T RTP produces sender and receivers reports; statistics and packet counts RTCP provides the follow ing RTCP packet types; reports services T Recevier (RR) T QoS monitoring and congestion control S SSRC, Packet lost, jitter, timestamps S Primary function: QoS feedback to the application T Sender (SR) S The sender can adjust its transmission S SSRC, S The receiver can determine if the congestion S NTP Timestamp, wall clock of RTP packet is local, regional, or global S RTP Timestamp S Network managers can evaluate the network S Intermedia synchronization, number of bytes performance for multicast distribution sent, packet counters RTCP provides the follow ing services (Cont) RTP/RTCP features T Source identification T Provides T Provides not S end-to-end real- time S timely delivery (needs T inter-media synchronization data delivery lower layer T control information scaling (functionality and reservations) control mechanisms) S any form of reliability S Limit control traffic (most 5 % of the overall S timestamps sequences or flow/congestion session traffic) numbering (up to the control (RTCP) application to use it) T Not complete - new T Uses UDP payload format 3

RTSP - real time streaming What is Streaming? protocol T T Streaming breaks data into packets; real- Client -server multimedia presentation protocol to enable controlled delivery time data through the transmission, S provides ”vcr”-style remote control functionality of decompressing just like a water stream. streamings over IP. S RTSP is an application-level protocol designed to work S A client can play the first packet, decompress with RTP (and RSVP) to provide a complete streaming the second, while receiving the third. service over internet S The user can start enjoying the multimedia S It provides means for choosing channels (UDP etc) and delivery mechanisms (RTP) without waiting to the end of the transmission T Developed by RealNetworks , netscape, and columbia university (still an internet draft) RTSP operations and methods RTSP provides T Retrieval of media from media server T RTSP establish and controls streams T Invitation of a media server to a T A media server provides playback or conference recording services T Adding media to an existing presentation T A client requests continues media data T Similar services on streamed audio and from the media server video, just as HTTP does for text and T RTSP is the network is the ”network graphics remote control” between the server and the client HTTP/RTSP differences QoS Definitions T HTTP stateless protocol; an RTSP server T Qos is a set of technologies has to maintain ”session states” S enables network administrators to manage the effects of congestion on application traffic T HTTP is asymmetric; in RTSP both client by using network resources optimally, or and server can issue requests S allocate different resourses for different data T It uses URL, like HTTP flows, or T visa bild S …. 4

Resources reservation and QoS classes prioriations T Best-effort - No gurantees at all T Any QoS better than best-effort. T Soft QoS - differentiated guarantess S Routing delays and congestion losses T Real-time traffic T Hard QoS - full guarantees IP QoS Netw orking - Router function: Integrated services Traffic control T Packet scheduler manages forwarding of T Defined by an IETF working group to be a key- stone different packet streams. T IS was developed to optimize network and S Service class, queue management, algorithms resource utilization which require QoS. S Police and shape traffic T Divided traffic between into different QoS S implemented where the packets are queued . classes. T An internet router must be able to provide an appriopriate QoS for each flow. (according to a service model) Router function: Traffic control Admission control T Packet classifier indentifies packets of an T Decision algorithms that a router uses to IP flow in hosts and routers that will determine if there are routing resources receive a certian level of service. to accept the requested QoS for a flow S Each packet is mapped by the classifier into a S If the flow is accepted; the packet classifier specific class. (same class, same treatment) and packet scheduler reservs the requested Qos for this flow . S The choice of class is based upon the source T Checks user authentification and destination, and port number in packet header T Will play an important role for charging 5

IntServ (cont) Differentiated services T Communicates with RSVP to create and T IETF working group (draft, no RFC) maintain flow-specific states in the T Simplify scheduling and classification using the endpoint hosts and in routers along the priority bits in the IP header. T Packet flow must be marked according to SLA; path of a flow Servive Level Agreements at the edge of the T RSVP/Intserv are complementary network T Not suitable for high volume traffic T The ISP must assures that a user gets his (speech) requsted QoS. T Improves scalability greatly. Mechanisms needed Diffserv architecture T Setting bits in DS at the network edges T Static and long-term and administrative boundaries S Not need to set up QoS reservation for specific data packets T Using those bits to determine how packets S DS routing example (it is not that easy) are treated by routers inside the network T Handle aggregate traffic (not per- T DS architecture is currently asymmetric; conversation) S on-going research for symmetric architecture S require significantly less sates and processing power than per-conversation. RSVP - reservation protocol RSVP - reservation protocol T Simplex protocol; reservation is done in T Internet control protocol - not routing protocol T Runs on top of IP and UDP one direction; T Key concepts: flows and reservations T Receiver-initiated. The sender sends QoS T Applies for a specific flow of data packets on a wanted to the receiver which sends an specific path. Each flow has a flow descritpor. RSVP message back to the sender. T Both unicast and multicast . T The sender does not need to know the T Doesn’t understand the content of the flow capabilities along the path or at the descriptor receiver 6