The IMS: IP Multimedia Concepts And Services, Second Edition

3.3. Mechanism to register multiple user identities at a go

SIP allows one public user identity to be registered at a time;so, if a user has more than one public user identity, then she has to register every public user identity individually. This may be frustrating and time consuming from the end-user perspective. Obviously, registering four public user identities would consume four times as much radio resource in the case of Universal Mobile Telecommunications System (UMTS) than registering one public user identity. It was for these reasons that Third Generation Partnership Project (3GPP) developed a mechanism to register more than one public user identity at a time. This concept is called "implicit registration".

Figure 3.2. Example of implicit registration sets.

An implicit registration set is a group of public user identities that are registered via a single registration request. When one of the public user identities within the set is registered, all public user identities associated with the implicit registration set are registered at the same time. Similarly, when one of the public user identities within the set is de-registered, all public user identities that have been implicitly registered are de-registered at the same time. Public user identities belonging to an implicit registration set may point to different service profiles. Some of these public user identities ...