RTP Real Time Protocol

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RTP - Real Time Protocol

• Presented by
• Satish Lakkoju
• Date 04/24/2007

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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

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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 .

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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.

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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.
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• 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 streams 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.

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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/i
  ndex.html