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Real-time Transport Protocol (RTP)

Real-time Transport Protocol (RTP). Emil Diaz VoIP Security COMS 4995 – 03 Dept. of Computer Science Henning Schulzrinne Columbia University Fall 2008. Overview. Protocol goals & background Real-time Transport Protocol (RTP) RTP Control Protocol (RTCP) Use Scenarios.

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Real-time Transport Protocol (RTP)

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  1. Real-time Transport Protocol (RTP) Emil Diaz VoIP Security COMS 4995 – 03 Dept. of Computer Science Henning Schulzrinne Columbia University Fall 2008

  2. Real-time Transport Protocol Overview • Protocol goals & background • Real-time Transport Protocol (RTP) • RTP Control Protocol (RTCP) • Use Scenarios

  3. Real-time Transport Protocol 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 • scalable

  4. Real-time Transport Protocol 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• R. Frederick (Blue Coat Systems Inc.) • V. Jacobson (Packet Design) • First published as RFC 1889 in the year 1996 • Superseded by RFC 3550 in the year 2003

  5. Real-time Transport Protocol 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 • Checksum

  6. Real-time Transport Protocol 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 quality

  7. Real-time Transport Protocol RTP Sample Packet http://www.codeproject.com/KB/IP/Video_Voice_Conferencing.aspx

  8. Real-time Transport Protocol 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.html

  9. Real-time Transport Protocol Use Scenarios

  10. Real-time Transport Protocol Simple Multicast Audio Conference • Call connection established • Audio sampled at 20ms durations • Each data chunk is packaged with an RTP header • RTP packet is wrapped around UDP packet • Sent through network • Receiver receives and parses RTP header • Based on payload type, application reconstructs audio stream in 20ms chunks

  11. Real-time Transport Protocol 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 basis

  12. Real-time Transport Protocol Mixers and Translators • Accommodate participant network resources • Mixer – Low Bandwidth • Mixer – Combining media streams • Translator – Forward RTP packets to private networks

  13. Real-time Transport Protocol 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 participants

  14. Real-time Transport Protocol 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)

  15. Real-time Transport Protocol 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/RTCP

  16. Real-time Transport Protocol Summary • Services: • payload type identification • sequence numbering • time stamping • delivery monitoring • mixers & translators • Goals : • lightweight • flexible • protocol-neutral • scalable • separate control/data • secure

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