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 protocolReal-time data transportRun on top of UDP

Support multicastDelay is better

than reliability Multicast/UnicastNo 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

participantsEach session is a pair of transport addresses

AudioAudioVideoVideo

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 RTPFeedback 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 sentnumber 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 deliveryPacket lost, jitter, timestamps (RTT)

Sender Report (SR) active sendersIntermedia synchronization, number of bytes sent

SDES, BYE, APP

RTCP Services

QoS monitoring and congestion control Feedback for quality of data

Source identification Canonical Namesunique 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 serverRTSP

pres. desc,streaming commands

RTP/RTCPaudio/video content

Presentation

descriptor

HTTPpresentation descriptor

RTSP Methods

OPTIONSC S

determine capabilities of server/clientC 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

RTSPserver

datasource

media player

AVsubsyste

m

RTSPclient

RTSP OK

RTSP PLAY

RTSP OK

RTP AUDIO

RTP VIDEO

RTSP TEARDOWNRTSP OK

get UDP portchooseUDP port

RTSP SETUP

Default port 554

RTCP

TCP

UDP

RTSP FeaturesApplication level protocolSyntax and operations similar to HTTPUse methods (SETUP, TEARDOWN)Servers & clients can issue requestsSupport multiple system platforms

Questions…?