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1、Chapter 2 Multimedia Networks: Requirements and Performance Issues,Prof. Guohui Li School of Information System and Management National University of Defense Technology Spring 2010,COURSE 600-081205602,2019/5/24,MMCN-Chapter2,2,Chapter 2,2.1 Distributed multimedia applications 2.2 Peer-to-Peer and m
2、ulti-peer communications 2.3 Performance parameters 2.4 Quality of Service 2.5 Multimedia transmission requirements 2.6 Summary,2019/5/24,MMCN-Chapter2,3,2.1 Distributed multimedia applications,Issues To make the discussion of multimedia transmission requirements more concrete, we start by discussin
3、g a few commonly used multimedia applications. How do these applications work and what characteristics are there for these applications.,2019/5/24,MMCN-Chapter2,4,2.1 Distributed multimedia applications,1. Audio and video streams Streaming audio and video applications (e.g. Realplayer, Winamp, etc.
4、live radio and broadcast) enable you to listen to or view program as it is being transferred. During their travel across the network, the packets suffer variable delays. The destination buffers a few packets before it starts playing them back as an audio or video stream. The buffering absorbs the de
5、lay fluctuations.,2019/5/24,MMCN-Chapter2,5,2.1 Distributed multimedia applications,2. Video conferencing For conversations, the one way delay is barely noticeable if it is less than 100 ms. Beyond 350 ms, the delay makes the conversation unpleasant. Small delay requirement of voice implies that voi
6、ce samples must be placed in small packets. Packetization will introduce some of delays that add to overall end-to-end delay.,2019/5/24,MMCN-Chapter2,6,2.1 Distributed multimedia applications,3. World Wide Web-WWW WWW is a distributed application that enables you to navigate through a set of hyperli
7、nked documents, called Web pages. Each Web page may contain text, pictures, audio clips, video clips, and possibly links. When you browse the Web, you initiate a sequence of file transfers according to HTTP. Actually, audio/video stream, video conferencing, video on demand can be Internet applicatio
8、ns.,2019/5/24,MMCN-Chapter2,7,2.2 Peer-to-Peer and multipeer communications,Three basic modes Unicast: there are two communicating partners, or peers, and also called peer-to-peer mode. Multicast: involves 1 to n communications, or peer-to-multipeer. e.g. one speaker, many participants in video conf
9、erencing and distance learning. Broadcast: 1 to all destinations over network. e.g. LAN, wireless network.,2019/5/24,MMCN-Chapter2,8,2.3 Performance parameters,How to decide whether a network will be able to carry multimedia traffic or not?,2019/5/24,MMCN-Chapter2,9,2.3 Performance parameters,Soluti
10、on: 1. A set of parameters are used to state clearly what the application needs from network. 2. A similar set of parameters are used to specify what the network can provide.,2019/5/24,MMCN-Chapter2,10,2.3 Performance parameters,SAS factors - Synchronization accuracy specification Delay; Delay jitte
11、r; Delay skew; Error rate. Traffic synchronization parameters Throughput; Burstiness. NPP - Network performance parameters Network throughput; Networking delay; Delay variance; Error rate.,2019/5/24,MMCN-Chapter2,11,2.3.1 SAS factors,Review: (multimedia system) Asynchronous system there is no well-d
12、efined timing relationship between the objects of one or more stream(s). inter-stream: between streams. intra-stream: within a stream.,2019/5/24,MMCN-Chapter2,12,2.3.1 SAS factors,Synchronous and isochronous systems well-defined temporal relationships exist between objects. isochronous : equal time;
13、 it is applicable when one stream is considered at a time. (intramedia) synchronous: same time; it is applicable mainly to the temporal relationship between two different media streams. (intermedia),2019/5/24,MMCN-Chapter2,13,2.3.1 SAS factors,isochronous stream: has equal time gaps between consecut
14、ive objects. synchronous stream: interstream synchrony implies that time gaps between related objects are equal to a constant T. Mostly often, T = 0.,Isochronous stream,synchronous streams,T,audio,video,audio,2019/5/24,MMCN-Chapter2,14,2.3.1 SAS factors,1. Delay factor Delay factor is used to measur
15、e the end-to-end time delay, which means the time it takes to transmit a block of data from the sending to receiving end. It comprises: Propagation delay: a physical parameter denoting the propagation time required to send a bit from one site to another. It is dependent only upon the distance traver
16、sed. (e.g. satellite link) Transmission delay: the time required to transmit a block of data over network. It is dependent upon the bit rate of the network and processing delays in the intermediate nodes (routing and buffering).,2019/5/24,MMCN-Chapter2,15,2.3.1 SAS factors,Network delay : composed of the propagation delay and transmission delay. Interface delay: the delay incurred between the time that a sender is ready to begin sending a block of data and time that the netwo
