The document discusses multimedia communication protocols including SDP, RTSP, and SIP. SDP is used to describe multimedia sessions to enable clients to join. RTSP establishes and controls media streams, allowing playback control like start, stop, and pause. SIP establishes, modifies, and terminates multimedia sessions like voice and video calls, using requests and responses.

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Multimedia CommunicationMultimedia Communication

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BackgroundBackground
The story so far….
 Video Coding–MPEG-4 …
 Audio Coding– u-Law, AMR …
 Packetization and Transport of media– RTP
 Transprot Control / QoS Feedback -RTCP
Next
 SDP – Description
 RTSP – Signaling
 SIP

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BackgroundBackground
SDP (Session Description Protocol)
How to describe a multimedia session?
RTSP – Internet VCR controls
Stop, Pause, Play, Fast Forward over the
internet

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SDPSDP
 Example : An existing live multicast session
Video and Audio streams
Transport - RTP/UDP/IP, Control – RTCP/UDP/IP
 A new client wanting to join the multicast session
 Needs to know
– multicast IP address and port
– Media streams in a session (e.g. video only or audio + video)
Payload format (e.g. MPEG-4 video, AMR audio)
– Initialization data for video and audio decoders
– Transport protocol used
– Other information ....
 Need a way to describe a multimedia session
– To enable new clients to easily join the session

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SDPSDP
 Session Description Protocol (SDP)
– IETF –RFC2327: www.ietf.org/rfc/rfc2327.txt
 For describing multimedia sessions
– To communicate the existence of a session
– To convey sufficient information to join a session
 Simple text format
 Defined to be general purpose
– Can be used for a wide range of network environment
– And applications

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SDPSDP
SDP includes:
 Session name and purpose
 Time the session is active
 The media comprising the session
 Information to receive media (addresses, ports, formats)
 Information about bandwidth to be used
 Contact information of a person responsible for the
session
SDP is used by other signaling / initiation protocols
 SIP : Session Initiation Protocol
 RTSP : Real-time Streaming Protocol

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SDPSDP

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SDPSDP

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SDPSDP
Example – Using SDP to join a multicast session
 Request SDP file via HTTP
 Retrieve information from downloaded SDP file
 Receive RTP streams on SDP specifed address & port
 Decode and display specified media

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RTSPRTSP
Now we can describe and transport media streams
But how to control these streams
 Start, Stop, Pause, Fast Forward, Rewind
 “Internet VCR”
Solution- RTSP
 Real Time Streaming Protocol
 Establishes and controls one or more countinuous media streams – such as audio and
video
 Similar in syntax and operation to HTTP/1.1
– Client–Server protocol
– Text based
 IETF RFC 2326
 www.ietf.org/rfc/rfc2326.txt
 www.rtsp.org

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RTSPRTSP
Example

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RTSPRTSP
Protocol Properties
 Media Transport Indepedent
– RTSP does not depend on the transport machanism used to carry
the continuous media
– Media transport can be via RTP or some other mechanism
 Transport-independent:
– RTSP may use UDP or TCP
 Control of recording devices:
– Can control both recording only and playback only devices,
– Or devices that can alternate between the two modes

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RTSPRTSP
Protocol Properties:
 Extendable:
– New methods and parameters can be easily added to RTSP.
 Easy to parse
 Multi-server capable:
– Each media stream within a presentation can reside on a different
server.
 HTTP- friendly:
– RTSP reuses HTTP concepts, so that the existing infrastruture
can be reused.

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RTSPRTSP
Protocol Operation
– Text based messages between client and
server
– Messages can be:
 Requests
 Responses

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RTSPRTSP

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RTSPRTSP

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RTSP – Decribe MethodRTSP – Decribe Method

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RTSP – Setup MethodRTSP – Setup Method

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RTSP – Play MethodRTSP – Play Method

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RTSP – Pause MethodRTSP – Pause Method

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RTSP – Teardown MethodRTSP – Teardown Method

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RTSP – Signal Timing DiagramRTSP – Signal Timing Diagram

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Summary of RTSP methodsSummary of RTSP methods

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SIPSIP
 Session Initiation Protocol
– Another session control protocol
– IETF RFC 3261 www.ietf.org/rfc/rfc3261.txt
 Protocol that can establish, modify and terminate multimedia
sessions
 Applications– IP telephony, multimedia conferences
 SIP, likeRTSP,
– Uses text-based request/response transattion model
 Requests contain Methods and Header fields
 Responses include 3 digit status codes, eg "200 OK"
– Is Transport layer independent
– Uses other protocols for media delivery (eg RTP)

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SIP MessagesSIP Messages
SIP AddressesSIP Addresses
 RFC 3261 defined SIP addresses in form of s
sip:user@domain:port
sip:user@host:port
 Default port is 5061

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SIP Message TypesSIP Message Types
SIP Invite
SIP Response

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SIPSIP
 SIP Methods
– INVITE, ACK, CANCEL : for setting up sessions
– BYE : for terminating sessions
– REGISTER for registering contact information
– OPTIONS : for querying servers about capabilities
 INVITE
– User agent client initiates a session with INVITE
– Invitation can be accepted by a user agent server
– Sip invitations convey session descriptions that allow
participants to agree on a set of compatible media types
– Offer/answer model
 ACK
– Response confirmation to INVITE

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SIP ResponseSIP Response
 Code range from 100 to 699, divided into several classes
1xx, 2xx, …,6xx:
– 1xx : the status.
– 2xx : the query was processed successfully.
– 3xx : the query was sent to another servers to further processing.
– 4xx, 5xx, 6xx: There are error in the query processing

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SIPSIP
ExampleExample

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SIPSIP
SIP supports user mobility
With proxy servers to help route requests
to user's current location
Registration function allowing users to
upload current locations for use by proxy
servers.

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SIPSIP

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SIPSIP
Respose ExampleRespose Example