Chapter 28

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Chapter 28

Real-TimeTrafficover theInternet


CONTENTS

• CHARACTERISTICS• RTP• RTCP


인터넷상의 실시간 트래픽인터넷상의 실시간 트래픽

실시간 멀티미디어 트래픽



In real-time traffic, if we ignore In real-time traffic, if we ignore propagation delay, propagation delay,

the production, transmission, the production, transmission, and use of data takes and use of data takes

place at the same time. place at the same time.



Example 1Example 1

An example of non-real-time multimedia traffic is the downloading of a video from the Internet. The video has already been made; it’s a finished product. A client HTTP is used to download the video from an HTTP server and the user views the video at a later time. The production, transmission, and use all happen at different times. Figure 28.2 shows this situation



비실시간 멀티미디어 트래픽



Example 2Example 2

Now let us consider an example of real-time multimedia traffic. Consider a video conference in which a camera is connected to a server that transmits video information as it is produced. Everything that happens at the server site can be displayed on the computer at the client site. This is both multimedia (video) and real-time traffic (production and use at the same time). Figure 28.3 shows the situation.



실시간 멀티미디어 트래픽


CHARACTERISTICSCHARACTERISTICS

28.128.1


28.1 28.1 특징특징

시간적인 관계


28.1 28.1 특징특징

지터 (jitter)서로 다른 지연시간으로 도착되어 새기는

시간적인 gap


28.1 28.1 특징특징

Jitter is introduced in real-time Jitter is introduced in real-time data by the data by the

delay between packets. delay between packets.


28.1 28.1 특징특징

타임스탬프 (timestamp)지터 해결방법으로 재생시간을 나타내는 시간정보

이용


28.1 28.1 특징특징

To prevent jitter, To prevent jitter, we can timestamp the we can timestamp the packets and separate packets and separate

the arrival time the arrival time from the playback time. from the playback time.


28.1 28.1 특징특징

재생 버퍼도착시간과 재생시간을 분리하기 위해 재생될

때까지 수신 데이터 저장


28.1 28.1 특징특징

A playback buffer is A playback buffer is required for real-time traffic.required for real-time traffic.


28.1 28.1 특징특징

A sequence number on A sequence number on each packet is each packet is

required for real-time traffic.required for real-time traffic.


28.1 28.1 특징특징

Real-time traffic needs Real-time traffic needs the support of multicasting.the support of multicasting.


28.1 28.1 특징특징

Translation means changing the Translation means changing the encoding of a payload to a lower encoding of a payload to a lower quality to match the bandwidth quality to match the bandwidth

of the receiving network. of the receiving network.


28.1 28.1 특징특징

Mixing means combining Mixing means combining several streams of traffic several streams of traffic

into one stream. into one stream.


28.1 28.1 특징특징

TCP, with all its sophistication, TCP, with all its sophistication, is not suitable is not suitable

for real-time multimedia for real-time multimedia traffic because traffic because

we cannot allow we cannot allow retransmission of packets. retransmission of packets.


28.1 28.1 특징특징

UDP is more suitable than UDP is more suitable than TCP for real-time traffic. TCP for real-time traffic.

However, we need the services of However, we need the services of RTP, another transport layer RTP, another transport layer

protocol to make up the protocol to make up the deficiencies of UDP.deficiencies of UDP.


RTPRTP

28.228.2


28.2 RTP28.2 RTP


28.2 RTP28.2 RTP

RTP 패킷 헤더 형식


28.2 RTP28.2 RTP

RTP uses RTP uses a temporary even-numbered a temporary even-numbered

UDP port. UDP port.


RTCPRTCP

28.328.3


28.3 RTCP28.3 RTCP

RTCP 메시지 유형


28.3 RTCP28.3 RTCP

RTCP uses an odd-numbered UDP RTCP uses an odd-numbered UDP port number that follows port number that follows the port number selected the port number selected

for RTP.for RTP.

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Chapter 28

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