Skype - 3.0 beta Guide de l'utilisateur télécharger pdf (Page 8)

Skype Network Administrator’s Guide Skype 3.0 Beta 8

2006-10-31 Document version 2.0 Beta

Instead of relying on centralized infrastructure and equipment, Skype relies on state-of-the-

art P2P networking technology to establish connections among Skype clients, as well as to

route calls, IMs, file transfers, and video between one Skype client and another.

Once installed, Skype is similar to any piece of end-user software. The Skype client runs in

the foreground while the user is making voice and/or video calls, sending/receiving IMs,

transferring files, etc. it. Otherwise, the Skype client runs in background, consuming

minimal computer and networking resources.

Skype P2P Architecture

Interaction between any pair of Skype users – any combination of voice, video, text chat,

or file transfer – are carried over an encrypted “session layer” that is established among the

communicating Skype users before messaging begins.

The Skype solution is composed of the Skype client and the underlying P2P network. The

Skype client is primarily a communications platform, and it also offers other essential

capabilities that integrate voice calling, instant messaging, person-to-person

videoconferencing, and file transfers into one seamless program.

The Skype client is tightly coupled to the underlying network and relies on an

authentication server, which is discussed in more detail later. And, unlike many P2P

applications, the Skype client (when downloaded from the Skype website) does not contain

any adware, malware, or spyware.

Intelligent Routing with Supernodes

When a Skype client is downloaded and installed, a user’s computer becomes part of the

Skype P2P network, which is composed of Skype network peer nodes, supernodes, and

relay hosts. Skype’s ability to act as a self-forming distributed network is the result of the

interaction among ordinary nodes, supernodes, and relay hosts throughout the network.

A supernode is a regular Skype peer node that, under a particular set of circumstances,

takes on additional responsibilities. Supernodes are responsible for detecting Skype clients

that are online, establishing connections among them, and transmitting signaling messages

to ensure encrypted traffic is routed efficiently.

Supernodes work in concert with one another to support the Skype directory service or

global index—a distributed database of Skype users. The Skype global index is, in part,

composed of a hierarchical system of available supernodes. See, “Skype Global Index”

later in this document for more information on supernodes.

The global index is not hosted on central servers. When a capable computer with a high-

speed connection to the Internet runs the Skype software, under certain circumstances, it

may automatically “come alive” as a supernode, and function as a temporary directory

index server for nearby Skype clients. Each supernode’s capabilities are based on the

computer’s available memory, bandwidth, and uptime characteristics.

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Skype - 3.0 beta Guide de l'utilisateur Page 8