A network entity comprising an input for receiving from a given IP device, a session initiation message for initiating a communication session over a packet based network via a session initiation message generated according to a particular session initiation protocol and a processing entity. The processing entity is operative for detecting a characteristic associated with the given IP device, determining, at least in part on the basis of the characteristic associated with the given device, a given interface module from a plurality of interface modules for processing the session initiation message generated according to the particular session initiation protocol and causing the first session initiation message generated according to the particular session initiation protocol to be processed by the given interface module for converting the first session initiation message into a second session initiation message generated according to a pre-determined session initiation protocol.