Rtp

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Rtp

  1. 1. Real-time Transport Protocol(RTP) Emil Diaz VoIP Security COMS 4995 – 03 Dept. of Computer Science Henning Schulzrinne Columbia University Fall 2008
  2. 2. Overview  Protocol goals & background  Real-time Transport Protocol (RTP)  RTP Control Protocol (RTCP)  Use Scenarios12/04/12 Real-time Transport Protocol 2
  3. 3. Real-Time Transport Protocol  End-to-end delivery services for applications transmitting real-time data, such as audio and video  Payload type identification  Sequence numbering  Time stamping  Delivery monitoring  Goals  lightweight  flexible  scalable12/04/12 Real-time Transport Protocol 3
  4. 4. Origin of Protocol  Developed by the Audio-Video Transport Working Group of the IETF:  H. Schulzrinne (Columbia University)  S. Casner (Packet Design)  R. Frederick (Blue Coat Systems Inc.)  V. Jacobson (Packet Design)  First published as RFC 1889 in the year 1996  Superseded by RFC 3550 in the year 200312/04/12 Real-time Transport Protocol 4
  5. 5. Protocol Structure  Application layer protocol  Typically used on top of IP and UDP  Applications that use RTP are:  Less sensitive to packet loss  Very sensitive to packet delays  UDP provides key services:  Multiplexing  Checksum12/04/12 Real-time Transport Protocol 5
  6. 6. RTP Does NOT  Define media data formats or encodings  Need media specific profiles  Handle connection setups or tear-downs  Need other protocols like SIP or H.323  Handle resource reservation  Need other protocols like RSVP  Guarantee timely delivery or Quality of Service  However, it does provide necessary data to application to order packets and adjust signal quality12/04/12 Real-time Transport Protocol 6
  7. 7. RTP Sample Packet http://www.codeproject.com/KB/IP/Video_Voice_Conferencing.aspx12/04/12 Real-time Transport Protocol 7
  8. 8. RTCP Sample Packet 5 main types:  Sender Report (SR)  Receiver Report (RR)  Source Description (SDES)  Bye Message (BYE)  Application-defined (APP) http://developer.apple.com/documentation/QuickTime/QTSS/Concepts/chapter_2_section_13.html12/04/12 Real-time Transport Protocol 8
  9. 9. Use Scenarios12/04/12 Real-time Transport Protocol 9
  10. 10. Simple Multicast Audio Conference 1. Call connection established 2. Audio sampled at 20ms durations 3. Each data chunk is packaged with an RTP header 4. RTP packet is wrapped around UDP packet 5. Sent through network 6. Receiver receives and parses RTP header 7. Based on payload type, application reconstructs audio stream in 20ms chunks12/04/12 Real-time Transport Protocol 10
  11. 11. Audio and Video Conference  Audio and Video has separate RTP/RTCP sessions  Receiver can choose media type to use  Encodings can change independently  Network resource allocations per media basis12/04/12 Real-time Transport Protocol 11
  12. 12. Mixers and Translators  Accommodate participant network resources  Mixer – Low Bandwidth  Mixer – Combining media streams  Translator – Forward RTP packets to private networks12/04/12 Real-time Transport Protocol 12
  13. 13. Quality & Data Distribution Feedback  Packet loss, congestion, jitter, delivery times  Directly useful for control of adaptive encodings  Identify if problems are local or global  Short-term and long-term statistical analysis  Self-adjusting network  Each participant eventually knows about the other members  Source description dynamically identifies who is sending  Active senders get more bandwidth  Session bandwidth kept constant by adjusting transmission rate based on the number of participants12/04/12 Real-time Transport Protocol 13
  14. 14. Source Description Information  CNAME – Conical name (joe@example.com)  NAME – Display Name (Joe Smith)  EMAIL – Email (different than CNAME)  PHONE – International phone number  LOC – Location information (City, Building, Room?)  TOOL – Application (VideoView 2.0)12/04/12 Real-time Transport Protocol 14
  15. 15. References  RFC 3550 - http://tools.ietf.org/html/rfc1889  RFC 3551 - http://tools.ietf.org/html/rfc3551  RTP News - http://www.cs.columbia.edu/~hgs/rtp/  Wikepedia:  RTP - http://en.wikipedia.org/wiki/Real-time_Transport_Protocol  RTCP - http://en.wikipedia.org/wiki/RTCP12/04/12 Real-time Transport Protocol 15
  16. 16. Summary  Services:  payload type identification  sequence numbering  time stamping  delivery monitoring  mixers & translators  Goals :  lightweight  flexible  protocol-neutral  scalable  separate control/data  secure12/04/12 Real-time Transport Protocol 16

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