Summary of Skype

Skype is a popular VoIP (Voice over Internet Protocol) Software Client that allows users to make “free” computer to computer calls over the internet. Users may also call traditional telephone lines on the Public Switch Telephone Network (PSTN) and be called by traditional phones through Skypes SkypeOut and SkypeIn services. Skype also contains File Sharing, Instant Messaging, Conference and Video capabilities.

Skype uses a node-base Peer-to-Peer Model, where individual clients perform some processing tasks on behalf of the network [1, 2]. This model allows for "Supernodes " to be created. Supernodes are where individual computers begin to route a sizeable amount of 3^rd party traffic, 200MB per hour has been detected on the ANU ICN, from the Skype network. Janet has measured a supernode over a 24 hour period to log 319,314 flows to and from 38,366 IP addresses [3].

Due to Skypes proprietary code, it is unknown how supernodes are chosen. From various tests and discussion it seems that supernodes are chosen based on a number of factors such as the bandwidth of their connection, computing resources and up time on the Skype network.

This is particularly pertinent to the ANU network as machines have 100Mbps connections, are on 24 hours a day and the hardware is kept up-to-date. Experience has shown that University machines are particularly susceptible to becoming a supernode if suitable firewalls are not installed.

If you have contacted your LITSS and you have been informed by them that
your local area is protected from Skype supernodes, and you wish to proceed
with the Skype installation then you MUST follow these instructions

Return to skype policy home page

References

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1. Baset, Salman A. and Schulzrinne, Henning (2004) An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol. Department of Computer Science, Columbia University, New York.

2. Skype (2005) Skype Guide for Network Administrators. Version 1.0.1 April 2005 http://www.skype.com/security/guide-for-network-admins.pdf [Last Accessed 20th November 2006]

3. Ukerna and JISC (2006) Skype and JANET March 2006 http://www.ja.net/development/voip/skype&janet.pdf [Last Accessed 13th November 2006]