Skype - 2.0 Guide de l'utilisateur télécharger pdf (Page 10)

Page 10 IT Administrators Guide

Are allowed by your specic Group Policy Object (GPO)

Only a very small percentage of Skype users in your network (if any) become supernodes,

mainly because the majority of users have no public IP address. You can also deliberately

prevent your users from becoming supernodes by using your Skype GPO Editor. For more

information, please see 2.4 Skype client configuration and policies.

Relay nodes are nodes outside your network. They relay media and signalling information

between nodes that otherwise can’t reach each other, normally because of rewall

permissions or problems traversing NAT. Relay nodes aren’t party to the communication

content and can’t view or decipher it.

Figure 1: Skype uses three kinds of peer nodes – ordinary nodes, supernodes, and relay nodes.

Our web-based Skype Manager is used for account management.

2.1.2 Operation

To see how Skype works and how it can be optimized for your network, we will look at

how call establishment (common to voice, IM and video sessions) works. Under normal

circumstances, a Skype client is an ordinary node in the P2P network. When Skype starts

up, the node binds listening sockets for random high (higher than 1024) TCP and UDP

ports. This is on port 443 for TCP/UDP and port 80 for TCP. It also uses UDP 443 to test

network connectivity.

The Skype client needs TCP connectivity for signalling information. It strongly prefers UDP

connectivity for stream (voice/video/le transfer) communications. If UDP is unavailable,

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Skype - 2.0 Guide de l'utilisateur Page 10