Figure 15.4 Personal mobility exampleThe example for personal mobility shown in Figure 15.4 also illustrates that
users can have more than one SIP account for communications (for example,
an account in the workplace and separate account for private use). The user
can technically register the various communication devices with the account
of their choice within the policy constraints of the account administrator. The
enterprise administrator policy may allow, for example, registering only
company-issued devices, while public service providers with restrictive poli-
cies may limit the user for one single device so that they can charge extra for
each new user device. G2 mobile phones and PSTN phones and fax machines
require static registrations, since they are not enabled for presence.
Session mobility to move an established session from one device to another
can also be easily supported by the SIPREFERmethod [12]. The more interest-
ing handling of session mobility is, however, when the handover from one
device to another must be accomplished in a seamless way, so as not to cause
any gap in the received media (missed sentences in conference, missed text in
an IM session, or missed audio and images in an RTSP session). A scenario for
seamless session mobility for streaming media is shown in Figure 15.5 [13].sip.example.comPrivate accountReach Alice
(Alice can be anywhere)SearchWork accountsip.corp.com[email protected][email protected][email protected][email protected]tel:[email protected]tel:[email protected]tel:[email protected]260 Chapter 15