1. Real Time Protocol (RTP) 2006. 5. 16 김 준 seojey00@hotmail.com

2. 2 Agenda About RTP Data Transfer Protocol RTCP RTP Translators and Mixers SSRC identifier Security

3. 3 About Real-Time Protocol (RTP) Purpose Transmit protocol for real time packet  Audio  Video  Simulation data Function Provide end to end network transport function  For application transmitting real- time data Characteristics Not provide RSVP Not guarantee QoS. Suitable Protocol.

4. 4 Overview of RTP Application RTP UDP IP Physical Transport layer  RTP provide transport layer interface that extend UDP

5. 5 Data Transfer Protocol – Header Format  V : Version [2]  P : Padding [1]  X : Extension [1]  CC : CSRC Count [4]  M : Marker [1]  PT : Payload Type [7]  SN : Sequence Number [16]  Timestamp : [32]  SSRC identifier : Synchronization Source [32]  CSRC identifier : Contributing Source [32]

6. 6 Data Transfer Protocol – Session Session Based on Destination Address (IP and port). Each Stream translate each session.  Select encoding type  Timing and Sequence number Multiplexing multiple related source on same medium  Used one session by RTP mixer.  But used different SSRC number.  Considered Payload Type (PT)- RFC 1890

7. 7 Data Transfer Protocol – Modify RTP header Modify RTP header by profile PT field modified Used Payload section in packet  for specific payload type’ information Additional header field Additional functionality RTP header extension New functionality Independent payload type

8. 8 Real-Time Control Protocol (RTCP) Function Provide feedback on quality of data distribution Transmit identifier for RTP source,called CNAME Transmit rate control RTCP function need participants send control packet. Need the rate control for large number of participants. Detect total participants by received control packet.

9. 9 RTP Translators and Mixers Cloud Common network and transport protocol (e.g., IP/UDP) Multicast address and destination port A pair of unicast address and destination port Translator and Mixer connect two or more cloud. Translator Forwards RTP packets with their SSRC Mixer Combines the stream from on or more sources.  Change data format.  Forwards the combined stream. Used mixer’s SSRC identifier for timing

10. 10 RTP Translators and Mixers Intermediate system Situation of connection between high and low bandwidth Advantage  High performance Disadvantage  Receiver can’t control

11. 11 SSRC identifier - Collision resolution SSRC is required globally unique within RTP session Collision Resolution Source detect collision  Used RTCP BYE packet Receiver detect collision  SSRC value is equal  CNAME or is different  One accept, another discard  Then used RTCP BYE packet

12. 12 Security Application required security Confidentiality  Only intended receiver can decode packet  Used encryption such as CBC, DES - RFC 1423 Authentication and integrity  Not defined  They need key management infrastructure