3G and SIP

The 3GPP (Third Generation Partnership Project) is producing globally applicable Technical Specifications and Technical Reports for a third generation mobile system. The group is using IP technology end-to-end to deliver multimedia content to mobile handsets so IETF protocols are a must. The call control and signalling function will be fulfilled by SIP.

• 3G is dedicated to using SIP for call control
• SIP from terminal to network
• SIP between network call nodes
• All IP multimedia call signalling will be performed via SIP

Users will be identified by SIP URLs and/or E.164 numbers, the numbering system of the telephone system. The bearer system (GPRS or mobile IP) will manage micro-mobility. This is the movement of the mobile user from one base station to another. Macro-mobility, the movement of the mobile user from one domain to another, will be handled by SIP. SIP will route signalling so that services are available from the originating or terminating network

3GPP has identified the Call State Control Function (CSCF) in the network. This is the equivalent of a SIP server. There will be three different kinds of CSCF:

• Proxy CSCF - this is the first point of contact in a visited network and will find the user's home network and provide some translation, security and authorization functions
• Serving CSCF - controls sessions, acts as registrar and triggers and executes services. The serving CSCF will access the user's profile. It can be located in the home or visited network
• Interrogating CSCF - the first point of contact in the home network. It assigns the serving CSCF, contacts the HSS and forwards SIP requests.

As SIP is rolled out as part of the 3G initiative, millions of SIP calls will be made.