台北科技大学：《计算机网络》（英文版） NP04 28 Real-Time Transport protocol

Real-Time Traffic oⅴ er the nternet Chuan-Ming Liu CSIE NTUT Spring 04, TAIWAN

1 Real-Time Traffic over the Internet Chuan-Ming Liu CSIE, NTUT Spring ’04, TAIWAN

Real-time multimedia traffic Real-time Real-time Multimedia traffic multimedia traffic traffic

2 Real-time multimedia traffic

Real-Time Transport protocol o Real-time traffic v.S. multimedia traffic o Real-time communication is the almost simultaneous production and use of the data, ignoring the short delay in transmission

3 Real-Time Transport Protocol  Real-time traffic v.s. multimedia traffic  Real-time communication is the almost simultaneous production and use of the data, ignoring the short delay in transmission

Example 1 An example of non-real-time multimedia traffic is the downloading of a video from the Interne which has already been made Http Client Http Server Internet Http Request Http Response Audio or video data but not real-time traffic

4 Example 1 An example of non-real-time multimedia traffic is the downloading of a video from the Interne which has already been made

Example 2 Consider a video conference in which a camera is connected to a server that transmits video information as it is produced erver Client Internet Video frames are transmitted as they are produced

5 Example 2 Consider a video conference in which a camera is connected to a server that transmits video information as it is produced

Streaming Services o Unlike applications that transfer a fixed amount of data in each request or response, a streaming service provides a continuous, arbitrarily long stream of data o The stream of data is neither limited in size nor in the time it takes to transfer o The stream is theoretically infinite . or persists for a long time(hours)

6 Streaming Services  Unlike applications that transfer a fixed amount of data in each request or response, a streaming service provides a continuous, arbitrarily long stream of data  The stream of data is neither limited in size nor in the time it takes to transfer  The stream is theoretically infinite, or persists for a long time (hours)

Real-Time delivery o An application is classified as real-time if the data must be delivered with exactl the same time relationship as it was created o Streaming is often linked to real-time delivery because applications such as audio and video that are appropriate for streaming require real-time delivery

7 Real-Time Delivery  An application is classified as real-time if the data must be delivered with exactly the same time relationship as it was created  Streaming is often linked to real-time delivery because applications such as audio and video that are appropriate for streaming require real-time delivery

Real-Time Delivery(cont) o Two aspects to real-time delivery that protocol software is required to handle o Order: Incoming data must be played in exactly the same order it was created o Time To create an exact reproduction of the input signal, a receiver must know the exact time at which each packet was produced; the receiver converts the data back to analog forms and plays each piece of analog output at exactl the time that piece occurred in the input

8 Real-Time Delivery (cont.)  Two aspects to real-time delivery that protocol software is required to handle: ⚫ Order: Incoming data must be played in exactly the same order it was created ⚫ Time: To create an exact reproduction of the input signal, a receiver must know the exact time at which each packet was produced; the receiver converts the data back to analog forms, and plays each piece of analog output at exactly the time that piece occurred in the input

Contents o Characteristics O RTP O RTCP

9 Contents  Characteristics  RTP  RTCP

Characteristics o Time relationship real-time data requires the preservation of the time relationship between packets of a session o Jitter is introduced in real-time data by the delay between packets and can be solved using o Timestamp ● Playback buffer

10 Characteristics  Time relationship: real-time data requires the preservation of the time relationship between packets of a session  Jitter is introduced in real-time data by the delay between packets and can be solved using ⚫ Timestamp ⚫ Playback buffer