The Real Time Streaming Protocol (RTSP) is used to establish and control timesynchronized streams of continuous audio and video. Sources of data can include both real-time and stored clips. During an RTSP session, an RTSP client may open and close many reliable transport connections to the server to issue RTSP requests. Alternatively, it may use a connectionless transport protocol, such as UDP. The streams controlled by RTSP may use RTP, but the operation of RTSP does not depend on this protocol. RTSP is not typically responsible for the delivery of the data streams, although interleaving of the media stream with the control stream is possible.
Internet streaming media requirements :
- retrieval of media from media server
- video-on-demand ➠ unicast
- near video-on-demand ➠ time-staggered multicast
- live events (Mbone-style) ➠ multicast
- remote digital editing ➠ queued play lists, recording
- remote device control
- integration with conferences
- transport, content, description-neutr
The Real Time Streaming Protocol features :
- “rough” synchronization (fine-grained ➠ RTP sender reports)
- virtual presentations = synchronized playback from several servers
- ➠ command timing
- load balancing using redirection at connect, during stream
- supports any session description
- device control ➠ camera pan, zoom, tilt
- caching: similar to HTTP, except “cut-through”
RTSP protocol design :
- similar design as HTTP (TCP + UDP, HTTP, …)
- HTTP = “the Internet RPC protocol”
- supports any session description
- control “tracks” (audio, video) and “presentation” (movie)
- remote digital editing
RTSP sessions :
- TCP connection 6= RTSP session ➠ session maintained by identifier
- one TCP connection per session ➠ firewalls, bidirectional
- one TCP connection per ≥ 1 command ➠ no server state
- UDP
- multicast, low latency
- ➠ “passing around the remote”
- ➠ limit server connection state (live events!)
RTSP and HTTP: similarities :
- protocol format: text, MIME-headers
- request/response = request line + headers + body
- status codes
- security mechanisms
- URL format
- content negotiation
RTSP protocol design :
- server state needed
- different methods
- server −→ client
- data carried out-of-band
- avoid HTTP mistakes:
- – relative request paths
- – no extension mechanism
- – 8859.1 coding