Multimedia Over IP: RTP, RTCP, RTSP “Computer Science” Department of Informatics Athens University of Economics and Business Λουκάς Ελευθέριος

Problem & Solution  Problem: Multimedia Networking is not a trivial Task  High bandwidth requirements  Real-time, bursty traffic  Solution:  Expensive solution – ATM networks  Rational solution – Internet

Rational Solution – Internet  Issues must be solved  Enough bandwidth  Protocol support multicast  reduce traffic  Resource reservation (real-time applications)  Guarantees for timing issues (packet switch network)  Integrated Service Model  RSVP  RTP  RTCP  RTSP Working foundation for real time services

Content  Real-time Transport Protocol (RTP)  Real-time Control Protocol (RTCP)  Real-time Streaming Protocol (RTSP)

Real-time Transport Protocol (RTP)  IP-based protocol  Real-time data transport  Run on top of UDP  Support multicast  Delay is better than reliability  Multicast/Unicast  No QoS guarantees

RTP Packet Format  Payload Type (7 Bits)  Multimedia data type  Sequence Number (16 Bits)  Frame re-construction  Error detection  Timestamp (32 Bits)  Play out data in correct rate  Synchronize different streams (audio, video data)  Source Identification (32 Bits)  Who is talking… (conference)

RTP Session  RTP Session: IP address + RTP port + RTCP port  RTP session sending/receiving RTP data group of participants  Each session is a pair of transport addresses Audio Video

Content  Real-time Transport Protocol (RTP)  Real-time Control Protocol (RTCP)  Real-time Streaming Protocol (RTSP)

Real-time Control Protocol (RTCP)  Control Protocol-conjunct with RTP  Feedback for data quality, information for memberships  Report PDUs between sources/destinations  receiver reception report  sender report  source description report  Reports contain statistics  the number of RTP-PDUs sent  number of RTP-PDUs lost  inter-arrival jitter  Used by application to modify sender transmission rates and for diagnostics purposes

RTCP Message Types  Recevier Reports (RR)  not active senders  Feedback of data delivery  Packet lost, jitter, timestamps (RTT)  Sender Report (SR)  active senders  Intermedia synchronization, number of bytes sent  SDES, BYE, APP

RTCP Services  QoS monitoring and congestion control  Feedback for quality of data  Source identification  Canonical Names  unique identifiers  Inter-media synchronization  Sender/ Receiver  Control information scaling  Limit the control traffic

RTP Features  End-to-end delivery service for real-time data  No mechanism to ensure timely delivery  Depends on RSVP to reserve resources  No reliability, No flow/congestion control  Timestamps, sequence number  Implemented with applications  RTP/RTCP reports provide flow/congestion control  Is not complete, is open to add new formats

Content  Real-time Transport Protocol (RTP)  Real-time Control Protocol (RTCP)  Real-time Streaming Protocol (RTSP)

Real-time Streaming Protocol (RTSP)  Client-Server multimedia presentation protocol  Support streaming over IP network  Work with lower–level protocols (RTP, RSVP)  Network Remote Control (PLAY, PAUSE, STOP)  Transport methods: Unicast /Multicast  RTSP Operations  Receive media from server  Invite media server to conference  Add media to an existing presentation

RTSP Overview web browser media player Web Server Web Server/Media server RTSP pres. desc,streaming commands RTP/RTCP audio/video contentPresentation descriptor HTTP presentation descriptor

RTSP Methods OPTIONS C  S determine capabilities of server/client C  S DESCRIBE C  S get description of media stream ANNOUNCE C  S announce new session description SETUP C  S create media session RECORD C  S start media recording PLAY C  S start media delivery PAUSE C  S pause media delivery REDIRECT C  S redirection to another server TEARDOWN C  S immediate teardown SET_PARAMETER C  S change server/client parameter GET_PARAMETER C  S read server/client parameter

RTSP Session media server RTSP server data source media player AV subsystem RTSP client RTSP OK RTSP PLAY RTSP OK RTP AUDIO RTP VIDEO RTSP TEARDOWN RTSP OK get UDP port choose UDP port RTSP SETUP Default port 554 RTCP TCP UDP

RTSP Features  Application level protocol  Syntax and operations similar to HTTP  Use methods (SETUP, TEARDOWN)  Servers & clients can issue requests  Support multiple system platforms

Questions…?