CS 414 – Multimedia Systems Design Lecture 18 – Multimedia Session ProtocolsAdministrativeOutlineInternet Multimedia Protocol StackService Requirements for Real-time Flows (Voice/Video)Real-time Transmission Protocol (RTP)Relation between RTP and RTCPRTCP: Control and ManagementRTCP FunctionsRTP ServicesRTP MessageRTP Services – Support of HeterogeneityDifference between Mixers and TranslatorsPayload FormatsSession Management (Layer 5)Session ManagerSession ControlSlide 18Real-Time Streaming Protocol (RTSP)RTSPRTSP MethodsRTSP ExtensionsConclusionCS 414 - Spring 2011CS 414 – Multimedia Systems Design Lecture 18 – Multimedia Session Protocols Klara NahrstedtSpring 2011AdministrativeHW1 deadline March 2, midnight 11:59pmIndividual effort!!! (take it as a midterm preparation)Midterm, March 7 11-11:50am in classAll topics/lectures until February 28, i.e., the material covered this week March 2 and 4 will not be on the midtermYou can bring calculator and 1 page of cheat-sheet (otherwise, exam is closed book, closed notes)Class on Friday, March 4 - discussion of midterm topicsCS 414 - Spring 2011Outline Multimedia Protocols – StandardsRTP/UDP/IP – Transmission Protocol RTCP Control/Negotiation Protocol to RTPRTSP – Control VOD Negotiation ProtocolCS 414 - Spring 2011Internet Multimedia Protocol StackCS 414 - Spring 2011AAL3/4 IP Version 4, IP Version 6 UDPMedia encaps(H.264, MPEG-4)RTPATM/Fiber OpticsEthernet/WiFiTCPSIPRTSP RSVP RTCPAAL5KERNELAPPLICATIONLayer 4(Transport)Layer 3(Network)Layer 2(Link/MAC)Layer 5(Session)MPLSDCCPService Requirements for Real-time Flows (Voice/Video)SequencingIntra-media synchronizationInter-media synchronizationPayload identificationFrame indication CS 414 - Spring 2011Real-time Transmission Protocol (RTP)RTP provides end-to-end transport functions suitable for real-time audio/video applications over multicast and unicast network servicesRTP companion protocol – Real-time Transport Control Protocol (RTCP)CS 414 - Spring 2011RTP RTCPUser Datagram ProtocolInternet ProtocolEthernet 802.13 or Wi-Fi 802.11PHY (Wired or Wireless)Layer 4Relation between RTP and RTCPCS 414 - Spring 2011Decoding CodingRTP RTCPUDP/IPApplicationCoding DecodingRTCP RTPUDP/IPApplicationRTCP: Control and ManagementOut-of-band control information for RTP flow. Monitors QoS for RTP in the delivery and packaging of multimedia dataUsed periodically to transmit control packets to participants in a streaming multimedia session.Provides feedback on the quality of service being provided by RTP.Gathers statistics on media connection Bytes sent, packets sent, lost packets, jitter, feedback and round trip delay. Application may use this information to increase the quality of service, perhaps by limiting flow or using a different codec.CS 414 - Spring 2011RTCP FunctionsThere are several type of RTCP packets:Sender report packet, Receiver report packet, Source Description RTCP Packet, Goodbye RTCP Packet and Application Specific RTCP packets.RTCP itself does not provide any flow encryption or authentication means. SRTCP protocol can be used for that purpose.CS 414 - Spring 2011RTP ServicesPayload Type IdentificationDetermination of media codingSource identificationRTP works with Profiles Profile defines a set of payload type codes and their mappings to payload formatsSequence numberingError detectionTime-stampingTime monitoring, synchronization, jitter calculationDelivery monitoringCS 414 - Spring 2011RTP MessageMAC header IP header UDP header RTP messageCS 414 - Spring 20110001020304050607080910111213141516171819202122232425262728293031Ver P X CC M PT Sequence NumberTimestampSSRCCSRC [0..15] :::Ver – Version 2P – PaddingX – Extension, if set, the fixed head is followed by exactly one header extensionCC – CSRC countM – Marker – intended to allow significant events such as frame boundaries to be marked (defined by profile)PT – Payload type SSRS – synchronization source, CSRC – contribution sourceRTP Services – Support of HeterogeneityMixer serviceAllows for resynchronization of incoming audio packetsReconstructs constant 20 ms spacing generated by senderMixes reconstructed audio streams into single streamTranslates audio encoding to lower bandwidthForwards lower bandwidth packet streamsTranslator serviceAllows for translation between IP and other high speed protocols May change encoding data CS 414 - Spring 2011Difference between Mixers and TranslatorsCS 414 - Spring 2011S1S2 S4S3R1M1TM2Payload FormatsStatic Payload formatsEstablished in RTP Profile Payload type 0 := µ-law audio codecDynamic Payload formatsApplications agree per session on payload formatH.263, JPEG, MPEGCS 414 - Spring 2011Session Management (Layer 5)Important part of multimedia communication Separates control aspects from transport aspectsCS 414 - Spring 2011ParticipantManagementMedia controlSessionControlConferencecontrolConfigurationcontrolSession Control Protocol (e.g., RTSP)videoaudiowhiteboardPresentation data communication Continuous data communicationContinuous data communicationSESSION MANAGERSession ManagerTasks: Membership controlMonitoring of shared workspaceCoordination of Media control managementExchange of QoS parametersConference control management – establishment, modification, termination CS 414 - Spring 2011Session Control Session Described bySession state Name of session, start, valid policiesSession management – two steps for state processingEstablishment of session Modification of sessionCS 414 - Spring 2011Session Control Conference Control Centralized or distributed approachMedia Control Synchronization Configuration ControlNegotiation of QoS parameters, admission control and reservation/allocation of resourcesMembership ControlInvitation of users; registration of users, change of membershipCS 414 - Spring 2011Real-Time Streaming Protocol (RTSP)Application Protocol for Control of multimedia streamsThis is not an application data transmission protocol, just remote control protocol between client and serverCS 414 - Spring 2011SERVERCLIENTRTPRTPRTSP RTSPSession ControlAudiovideoCoderAudioVideoDecoderRTSP Approved as Internet Draft, February 2, 1998, authors H. Schulzrinne, A. Rao, R. LanphierEnables
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