TABLE OF CONTENTS Since IP is a network layer protocol, it may appear natural to handle mobility at the network layer. Indeed, this is how Mobile IP does it. However, there are alternatives, towards which we now turn our attention. We note that elements of SIP mobility (to be introduced next) are finding their way into specifications being developed in 3GPP and 3GPP2 (see Chapter 12 for an example).
SIP, as discussed in Chapter 5, is used for initiation and management of sessions such as multimedia-over-IP sessions. SIP can also be used to support mobility management. It is powerful enough to support not just terminal mobility, but also personal, session, and service mobility [6]. SIP mobility management can be divided into presession mobility management and midsession mobility management, depending upon whether the subscriber is in a SIP-managed session or not.
Presession mobility (also known as out-of-session mobility) capabilities provided by SIP include the following:
Ability to register a SIP user's presence in his or her current location;
Ability to register and map one SIP address to several devices (known as forking);
Ability to register and map several SIP addresses to one location.
These capabilities allow SIP to support presession terminal mobility, and also personal mobility and service mobility. Presession terminal mobility occurs when a terminal moves and obtains a new IP address. SIP registration is used to update the bindings at the SIP location service (the SIP application in the terminal...
