Community Research and Development Information Service - CORDIS

Viability of using a connection tracking helper for the SIP protocol

In the Torrent system proxies are used to help with the routing and the route pinning of packet flows of different types of service, and also to extract dynamic information about related data flows/connections from initial signalling flows/connections. While a proxy operates in the user space, there is an alternative mechanism of using protocol helpers in kernel space based on the netfilter framework and the connection-tracking framework. While a proxy usually has to be addressed explicitly and terminates signalling relations for security reasons, a connection tracking protocol helper operates transparently and does not interfere with the signalling relation. The protocol helper has to extract the same dynamic information as a proxy, and therefore requires capabilities for parsing (signalling) packets of the protocol it should help.

For the SIP protocol the viability of a connection tracking protocol helper has been investigated. The SIP protocol offers numerous options in the signalling, a number of protocol extensions, and also several application scenarios. It was possible to make a helper work for a specific client in a back-to-back setup for a control and a media connection with great difficulty. Due to this experience, a protocol helper can be considered to be a solution for simple protocols like HTTP or FTP, using only one or two related traffic streams. It cannot be considered to be a valid alternative for complex protocols with numerous related traffic streams. This holds especially true if additionally network address translation or complex call scenarios, as for instance in SIP, also need to be considered.

More information on the Torrent project can be found at:

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