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Using the SIP Proxy Service

Note: This topic applies to the Hearst Release.

The Smoothwall supports a proxy to manage Session Initiation Protocol (SIP) traffic. SIP is often used to set up calls in Voice over Internet Protocol (VoIP) systems.

SIP normally operates on port 5060, and is used to set up sessions between two parties. In the case of VoIP, it is an RealTime Protocol (RTP) session that is set up, and it is the RTP stream that carries voice data.

RTP operates on random unprivileged ports, and, as such, is not NAT friendly. For this reason, the Smoothwall’s SIP proxy ensures that RTP is also proxied, allowing VoIP products to work correctly.

The Smoothwall’s SIP proxy is also able to proxy RTP traffic, solving some of the problems involved in setting up VoIP behind NAT.