Although quite new, SIP has already established itself as the way of the future for signaling in VoIP networks. Its strengths include the fact that it is far simpler than H.323 and is therefore easier to implement. Its simplicity, however, belies its flexibility and power. It can support all the features that are already supported by traditional telephony networks and more besides. In fact, SIP is the protocol of choice for the evolution of third-generation wireless networks, where it is expected that SIP-based mobile devices will become available and SIP-based network elements will be introduced within mobile networks.

As we shall see in the next chapter, SIP also fits very well with those protocols used for media gateway control and, as such, forms part of the overall architecture known as softswitch.