Interoperability also means providing a common infrastructure to support the service,
from ordering to provisioning and ultimately billing, again fully integrated with
all the other service platforms being used to deliver services to consumers.
This is the spirit of the IMS. It??™s about more than enabling all these different media
types and providing the delivery infrastructure. It??™s about enabling all of the various
entities within the network to work together, seamlessly and ubiquitously.
In this chapter we will look into how subscribers gain access to the IMS network and
the registration process. We will then look at session establishment and management.
This will give you a better look at how IMS and SIP can be used to control everything
that a subscriber does in your network.
Accessing the Network
First of all, access means many different things to a subscriber. It might mean using
a PDA with an 802.11b application to access the Web and download music files,
or it might mean using a cell phone to make voice calls. It might even mean picking
up the phone at home and placing calls, or using a broadband connection to surf the
Internet.
The method of access into the network becomes transparent to the IMS, because
there is no transport of actual bearer traffic within the IMS. The voice, the data, the
video, and everything else being delivered to the subscriber takes a different path, using
the access method for delivery.
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