Real-Time ProtocolsRTP/RTCP/RTSP

Heba El-Dreamly– Ola nijam-

Real-time multimedia streamingReal-time multimedia applications

–Video teleconferencing–Internet Telephony (VoIP)

–Internet audio, video streaming

(A-PDUs)

Streaming performance requirements–Sequencing

–to report PDU loss –to report PDU reordering

–to perform out-of-order decoding

–Time stamping and Buffering –for play out

–for jitter and delay calculation

–Payload type identification–for media interpretation

–Error concealment –covers up errors from lost PDU by using redundancy in most-adjacent-frame

–Quality of Service (QoS) feedback – from receiver to sender for operation adjustment

–Rate control –sender reduces sending rate adaptively to network congestion

Ideal Timing – no jitter

00.00.00

00.00.10

00.00.20

00.00.30

00.00.11

00.00.21

00.00.31

Send time

Play time

30 se

cond

s

First RTP-PDU

Second RTP-PDU

Third RTP-PDU

application

Reality – jitter

00.00.00

00.00.10

00.00.20

00.00.30

00.00.11

Send time

Play time

00.00.21

00.00.25

00.00.35

00.00.37

00.00.47

delay

First RTP-PDU

Second RTP-PDU

Third RTP-PDU 00.00.40

Fourth RTP-PDU

00.00.41

00.00.51

How does Sequence number and Timestamp help?

Audio silent example:

Solution:

–After receiving no PDUs for a while, next PDU received at the receiver will reflect a big jump in timestamp, but have the correct next seq. no. Thus, receiver knows what happened .

– Why might this cause problems? sender

rece

iver

silent

Seq no.1, Tmpst 100Seq no.2, Tmpst 200Seq no.3, Tmpst 300

Seq no.4, Tmpst 600Seq no.5, Tmpst 700

Consider audio data– What should the sender do during silent?

Not send anything

Receiver cannot distinguish between loss and silent

RTCP

Why not UDP?

UDP offers datagram-like serviceConnectionless , Unreliable ,

Unordered No Flow , Error , Congestion

controlPort numbers

RTP + UDP usually used for multimedia services

Why not TCP ?

TCP does retransmissions unbounded delays TCP does not support multicast

TCP congestion control (slow-start) unsuitable for real-time transport (A-V media)

TCP(till now)

RTSP

Protocol stack for multimedia services

RTP RTCP

AVTCORE is to maintain the core RTP/RTCP specifications

AVTCORE will provide architectural guidance for extending the protocols and

guidelines for their proper use.

AVTCORE will coordinate closely with the Security Area

while working on maintenance and enhancements to the SRTP Profile.

When watching video clips on the Internet or listen to audio clips such as radio and others, as well as review in the games online, we need to Transmission control protocol, reception and transfer data in real time or in other words, the flow of data directly.

RTP: Introduction

The Organization for the development of IETF protocol called Real-time Transport Protocol or Acronym RTP.

RTP Control Protocol (RTCP) RTCP specifies report exchanged between sources and

destinations of multimedia information

receiver reception report

sender report

source description report

Reports contain statistics such as the number of RTP sent, number of RTP lost, inter-arrival jitter

Used by application to modify sender transmission rates .

Actually the RTP protocol consists of two parts, one is the same protocol and the other part is the RTCP protocol, where he works alongside. While working RTP protocol to transfer data and arrange them when they arrive in the wrong sequence, RTCP organizes this process by transferring control information, such as the synchronization of multiple transport channels and monitor the process used for QoS quantity of information or the Bandwidth occupied equal to 5%

All RTP sent to an even-numbered UDP port, 2p

All RTCP sent to UDP port 2p+1

All RTP and RTCP are sent to same multicast group

Of the basic things that have been taken into consideration when designing this protocol is the support for many formats, including

(H.264, MPEG-4, MJPEG, MPEG)

Real-Time Streaming Protocol (RTSP)

Application layer protocol (default port 554)Usually runs on RTP for stream & TCP for controlProvides the control channelUses out-of-band signalingUsable for Live broadcasts / multicast

Also known as “Network remote control” for multi-media servers.

web browser

media player

Web Server

Web Server/Media server

RTSP Overview

RTSPpres. 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