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RTP - Real Time Protocol

RTP - Real Time Protocol. Presented by Satish Lakkoju Date : 04/24/2007. Introduction. Developed by the Audio-Video Transport Working Group of the IETF Transport protocol for real time data. Primarily used for audio and video. Why not TCP? Not suitable for real-time

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RTP - Real Time Protocol

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  1. RTP - Real Time Protocol Presented by SatishLakkoju Date : 04/24/2007

  2. Introduction • Developed by the Audio-Video Transport Working Group of the IETF • Transport protocol for real time data. • Primarily used for audio and video. • Why not TCP? • Not suitable for real-time • Retransmissions can lead to high delay • Does not support multicast • Congestion control mechanism (slow start) not suitable for AV media • Why not UDP? • UDP offers datagram-like service

  3. RTP contd.. • RTP itself gives no guarantee for timely delivery. • It relies on lower-layer services (e.g. UDP, TCP) to do so. • Structure of a RTP packet .

  4. Components of RTP • RTP Data Transfer Protocol: It carries real-time data. • RTP Control Protocol (RTCP): It monitors the quality of service and conveys information about the participants.

  5. RTP Header V - Version. 2 bits.RTP version number. Always set to 2. Sequence Number. 16 bits. used by the receiver to detect packet loss and to restore packet sequence. X - Extension. 1 bit.If set, the fixed header is followed by exactly one header extension. Timestamp. 32 bits.used to place the incoming audio and video packets in the correct timing order CC - CSRC count. 4 bits.The number of CSRC identifiers that follow the fixed header. M - Marker.1 bit.The interpretation of the marker is defined by a profile. SSRC, Synchronization source. 32 bits.Uniquely Identifies the source. CSRC, Contributing source. 32 bits.An array of 0 to 15 CSRC elements identifying the contributing sources for the payload contained in this packet. PT - Payload Type. 7 bits.Identifies the format of the RTP payload and determines its interpretation by the application.

  6. Mixer : • An RTP mixer is an intermediate system that receives & combines packets of one or more RTP sessions into a new packet. • Mixer is used when all participants do not have same connection bandwidth . • Placed near lower bandwidth area. Translator : • an intermediate system that modifies the stream without changing the stream’s timing. • Used when one or more participants of a conference are behind a firewall which won't allow an IP packet containing the RTP message to pass.

  7. References www.cs.columbia.edu/~hgs/rtp/papers.html http://www.networksorcery.com/enp/protocol/rtp.htm http://www.geocities.com/intro_to_multimedia/RTP/index.html

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