Services are typically executed in an application server. The interface between the SIP server and the application server is based on SIP. However, certain operators may want to reuse the existing technology, and therefore, they may need to interoperate SIP with protocols such as CAMEL/Intelligent-Network or Open Services Architecture (OSA).
4. 3GPP Requirements on SIP
4.1. General Requirements
This section does not specify any particular requirement for SIP.