# SIP Protocol Agent

The Session Initiation Protocol (SIP) Protocol Agent can be used with Engines to handle multimedia connections that use SIP as their transfer protocol (such as VoIP).

Using the SIP Protocol Agent allows SIP to be used across a Engine that uses NAT. SIP uses TCP or UDP port 5060 to initiate the connection, after which the traffic is allocated a dynamically assigned port. The Protocol Agent tracks the actual ports used, so that the whole range of dynamic ports does not need to be allowed in the Engine Policy.

The SIP Protocol Agent can be configured to force the client or server address used within the SIP transport layer to also be used for the media stream carried over SIP (by default, enforced for both the client and the server).

This Protocol Agent has parameters you can set in the Service properties. This Protocol Agent is not available on IPS engines or Layer 2 Engines.