Internet Protocols for Multimedia DS VT-01 Jerry Eriksson - PDF document

Internet Protocols for Multimedia DS VT-01 Jerry Eriksson Multimedia Netw orking T Animation, voice and video - not only text T Video, Distributed simulation, distribute work groups T Multimedia networks may replace telephone, television, etc T Challenges - build hardware and software infrastructure and applications to support multimedia Outline T Real-time challenges T Traffic management T Real-time protocols architectures S IntServ , Diffserv , S RTP, RTCP, RTSP RSVP T QoS T VoIP S Definitions S H.323 S Goals S SIP, some 1

Real-time Challenges T Bandwidth T Latency, jitter T Audio and video must be played back at the rate they were sampled (voice may be even more difficult) T Multimedia data streams are bursty Internet T Primary reason: Platform for most networking activities T Integrated data and multimedia service over a single network (investments) T Not suitable for real-time traffic S Offers only best-effort quality Problems to solve T Provide T QoS S enough bandwidth S ’guarantee’ quality S multicast to reduce S Reserve resource on traffic the internet S protocols that handle S Transport protocols care of timing issues T Presentation of the R Delay, Jitter multimedia data T Charging and policing mechaninsm 2

RTP - development T December 1992, Henning Schulzrinne, GMD Berlin, published RPT version 1 S see www.cs.columbia.edu/~ hgs/rtp T Proposed (version 2) as standard November,1995 Some RTP Implementations Tool Who Media NeVoT GMD Fokus Audio vic LBNL Video vat LBNL Audio Rat UCL Audio Rendezvous INRIA A/V NetMeeting Microsoft A/V IP/TV Cisco A/V RM G2 Real A/V RTP- Real time transport protocols T IP-based protocol providing S time-reconstruction S loss detection S security S content identification T Designed primarily for multicast of real- time data (also unicast, simplex, duplex) T Separate Control/Data 3

Where is RTP reside T RTP is typically run on top of UDP S Uses UDP’s multiplexing and checksum functions. May be viewed as a sublayer of the transport layer T RTP is usually implemented within the application S Lost packets and congestion control have to be implemented in the application level Header fields Sequence Time- Synch Miscellaneous Type fields number stamp source ID 7 bits 16 bits 32 bits 32 bits How does RTP works T Timestamping - most important information for real- time applications. S The sender timestamp according to the instant t he first octet in the packet was sampled. S The receiver uses timestamp to reconstruct the original timing S Also used for synchronize different streams; audio an video in MPEG. ( Application level responsible for the actual synchronization) 4

How does RTP w ork T Payload type identifier S specifies the payload format as well as encoding/compression schemes S The application then knows how to interpret the payload T Source identification S Identifies the source, not IP adress RTCP - Real Time Control Protocol (RFC 1889) T Designed to work together with RTP T In an RTP session the participants periodically send RTCP packet to give feedback on the quailty of the data. T Comparable to flow and congestion control of other transport protocols. T RTP produces sender and receivers reports; statistics and packet counts RTCP packet types; reports T Recevier (RR) S SSRC, Packet lost, jitter, timestamps T Sender (SR) S SSRC, S NTP Timestamp, wall clock of RTP packet S RTP Timestamp S Intermedia synchronization, number of bytes sent, packet counters 5

RTCP provides the follow ing services T QoS monitoring and congestion control S Primary function: QoS feedback to the application S The sender can adjust its transmission S The receiver can determine if the congestion is local, regional, or global S Network managers can evaluate the network performance for multicast distribution RTCP provides the follow ing services (Cont) T Source identification T inter-media synchronization T control information scaling S Limit control traffic (most 5 % of the overall session traffic) RTP/RTCP features T Provides T Provides not S end-to-end real- time S timely delivery (needs data delivery lower layer (functionality and reservations) control mechanisms) S any form of reliability S timestamps sequences or flow/congestion numbering (up to the control (RTCP) application to use it) T Not complete - new T Uses UDP payload format 6

What is Streaming? T Streaming breaks data into packets; real- time data through the transmission, decompressing just like a water stream. S A client can play the first packet, decompress the second, while receiving the third. S The user can start enjoying the multimedia without waiting to the end of the transmission RTSP - real time streaming protocol T Client -server multimedia presentation protocol to enable controlled delivery S provides ”vcr”-style remote control functionality of streamings over IP. S RTSP is an application-level protocol designed to work with RTP (and RSVP) to provide a complete streaming service over internet S It provides means for choosing channels (UDP etc) and delivery mechanisms (RTP) T Developed by RealNetworks , netscape, and columbia university (still an internet draft) RTSP operations and methods T RTSP establish and controls streams T A media server provides playback or recording services T A client requests continues media data from the media server T RTSP is the network is the ”network remote control” between the server and the client 7

RTSP provides T Retrieval of media from media server T Invitation of a media server to a conference T Adding media to an existing presentation T Similar services on streamed audio and video, just as HTTP does for text and graphics HTTP/RTSP differences T HTTP stateless protocol; an RTSP server has to maintain ”session states” T HTTP is asymmetric; in RTSP both client and server can issue requests T It uses URL, like HTTP T visa bild QoS Definitions T Qos is a set of technologies S enables network administrators to manage the effects of congestion on application traffic by using network resources optimally, or S allocate different resourses for different data flows, or S …. 8

QoS classes T Best-effort - No gurantees at all T Soft QoS - differentiated guarantess T Hard QoS - full guarantees Resources reservation and prioriations T Any QoS better than best-effort. S Routing delays and congestion losses T Real-time traffic IP QoS Netw orking - Integrated services T Defined by an IETF working group to be a key- stone T IS was developed to optimize network and resource utilization which require QoS. T Divided traffic between into different QoS classes. T An internet router must be able to provide an appriopriate QoS for each flow. (according to a service model) 9

Router function: Traffic control T Packet scheduler manages forwarding of different packet streams. S Service class, queue management, algorithms S Police and shape traffic S implemented where the packets are queued . Router function: Traffic control T Packet classifier indentifies packets of an IP flow in hosts and routers that will receive a certian level of service. S Each packet is mapped by the classifier into a specific class. (same class, same treatment) S The choice of class is based upon the source and destination, and port number in packet header Admission control T Decision algorithms that a router uses to determine if there are routing resources to accept the requested QoS for a flow S If the flow is accepted; the packet classifier and packet scheduler reservs the requested Qos for this flow . T Checks user authentification T Will play an important role for charging 10

IntServ (cont) T Communicates with RSVP to create and maintain flow-specific states in the endpoint hosts and in routers along the path of a flow T RSVP/Intserv are complementary T Not suitable for high volume traffic (speech) Differentiated services T IETF working group (draft, no RFC) T Simplify scheduling and classification using the priority bits in the IP header. T Packet flow must be marked according to SLA; Servive Level Agreements at the edge of the network T The ISP must assures that a user gets his requsted QoS. T Improves scalability greatly. Mechanisms needed T Setting bits in DS at the network edges and administrative boundaries T Using those bits to determine how packets are treated by routers inside the network T DS architecture is currently asymmetric; S on-going research for symmetric architecture 11

Diffserv architecture T Static and long-term S Not need to set up QoS reservation for specific data packets S DS routing example (it is not that easy) T Handle aggregate traffic (not per- conversation) S require significantly less sates and processing power than per-conversation. RSVP - reservation protocol T Internet control protocol - not routing protocol T Runs on top of IP and UDP T Key concepts: flows and reservations T Applies for a specific flow of data packets on a specific path. Each flow has a flow descritpor. T Both unicast and multicast . T Doesn’t understand the content of the flow descriptor RSVP - reservation protocol T Simplex protocol; reservation is done in one direction; T Receiver-initiated. The sender sends QoS wanted to the receiver which sends an RSVP message back to the sender. T The sender does not need to know the capabilities along the path or at the receiver 12