520251: Multimedia Systems

Multimedia

17 ¡กÑั¹นÂยÒาÂย¹น 2555

Delivering

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offline

online

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•TCP/IP•Internet Service Provider (ISP)•Dial-up•ADSL•3G

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•TCP/IP•Internet Service Provider (ISP)•Dial-up•ADSL•3G

629NETWORKING FUNDAMENTALSCHAPTER 16

Clients and ServersOnline distribution of multimedia over LANs or the Internet is almost always based on the client/server model of distributed computation. In this model, programs called servers “listen” on a communication channel for requests from other programs, called clients, which are generally running on a different machine elsewhere on the network. Whenever a server receives a request, it sends a response, which provides some service or data to the client. Requests and responses are collectively known as messages. Here, a message is a structured collection of data transmitted over the network. The messages exchanged by a client and server conform to a protocol – a set of rules governing the format of the data and the actions to be taken by a server or client when it receives a request or response.

The most popular form of online multimedia delivery is the World Wide Web, whose imple-mentation is an example of the client/server model. Web servers and clients communicate with each other using the HyperText Transfer Protocol, abbreviated to HTTP. HTTP is a very simple protocol designed for the fast transmission of hypermedia in the form of HTML or XHTML documents and CSS stylesheets, as described in Chapter 10, and the graphics, sound, video, animation and other sorts of data that go with them to make up Web pages.

Connection Type

Speed Text

20 kB

Graphics

100 kB

Multimedia

2 MB

Dial-up (V.90) 56 kbps 2.9 s 14.6 s 5 min

ADSL basic 512 kbps 320 ms 1.6 s 32.8 s

typical 2 Mbps 82 ms 410 ms 8.4 s

premium 8 Mbps 20.5 ms 102 ms 2.1 s

Cable typical 512 kbps 320 ms 1.6 s 32.8 s

premium 2 Mbps 82 ms 410 ms 8.4 s

Satellite† 512 kbps 860 ms 2.1 s 33.3 s

Leased line

T1 1.5 Mbps 109 ms 546 ms 11.2 s

T3 44 Mbps 3.7 ms 19 ms 381 ms

G3 phone 2 Mbps 82 ms 410 ms 8.4 s

Abilene 100 Mbps 1.6 ms 8.2 ms 168 ms

† Includes latency.

Typical download timesFigure 16.1.

apisake@gmail.com...................................................... © MacAvon MediaEx Libris

Client-Server Model

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HTTP (HyperText Transfer Protocol)

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Unicast - Multicast

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streaming áแÅลÐะ internet

television

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•FTP (File Transfer Protocol)•RSS•Podcasts

•Bit-Torrent (P2P)