Introduction RTP Issues: The protocol itself does not provide mechanisms to ensure timely delivery Relies on lower-layer protocols prevent out-of-order delivery of packets give any Quality of Service (QoS) Guarantee. RTP to transport real-time data RTCP: RTP control protocol QoS monitoring and feedback Session control Protocol architecture: usually works over UDP/IP RTP Outline 8 Media Application RTP IP RTCP UDP Introduction A session consists of an RTP/RTCP pair of channels, containing two closely linked parts: Data + Control. RTP RTP specifications RTP profiles RTP payload formats Optional elements 8 Standard elements of RTP Framework Intelligence is at the endpoints, not within the network (smart, network-aware endpoints and a dumb network) Achieving flexibility Provides a unifying framework for real-time audio/video transport, satisfying most application directly. RTP Application-Level Framing A transport protocol should accept data in application-meaningful units (ADUs) A transport protocol should expose the details of the data delivery as much as possible The end-to-end principle The system can pass responsibility for the correct delivery of data along that with data, meaning it relies on the lower protocols. Internet standard for real-time data Interactive and streamed audio and video Designed for multi-user multimedia conferencing Provides end-to-end transport functions for real-time applications Delay-oriented rather than loss-oriented (such as TCP) RTP Outline 8 Introduction RTP: Defines a standardized packet format for delivering audio and video over the internet. They are then grouped to form complete frames that are decoded to play out. Next, they are put into a playout-buffer, and any variation in interpacket timing caused by the network has been smoothed. Packets then are passed to a channel- coding routine for loss correct. Collect packets from network, and insert them into a per-sender input queue.
Introduction Real-time data transport at glance 8 Encoded frames are produced They are assigned a timestamp and a sequence number Then, they are load into RTP packet and ready for transmission The sender also generates periodic status reports in the form of RTCP packets to participants The participants also send quality feedback to the sender. Introduction The standard real-time transport protocol was developed by the Audio-Video Transport Working Group of the IETF and first published in 1996 as RFC 1889 – A solution to these described problems. But it is: No defined technique for synchronizing Streams from different servers may collide A feedback channel must be defined for quality control Motivation 8 Retransmissions can lead to high delay and cause delay jitter Does not support multicast Congestion control mechanism not suitable for audio-video (AV) media UDP/IP A UDP/IP-based should be suitable, provided that the variation in transit time of the network can be characterized and loss rates are acceptable. Introduction Requirements drive the choice of transport protocols TCP/IP It favors reliability over timeliness, but these applications require timely delivery. Introduction Requirements for delivery of media stream Examples of real-time applications: Videoconferencing VoIP, IP telephone system Game online… Real-time data: interactive audio and video Receivers: playing out immediately and synchronously, rather than playing back Requirements for transport protocols: Predictable variation in network transit time Reliable delivery of all packets Motivation 8 Real-Time Transport Protocol (RTP) Tung Dao Manh Future Internet Class, 2007.04.15 1Īgenda Introduction Motivation RTP outline Fundamental design philosophies of RTP Application-level framing The end-to-end principle Flexibility Standard elements of RTP RTP Specification RTP Profile RTP Payload Format RTP Packet Format Potential further development of RTP Related Protocol RTCP Conclusion 2