However, we will say that the URI
is resolved into an IP address using a service called the Domain Name System (DNS).
The concept of identifying subscribers extends to their devices as well. It is important
for telecommunications service providers to be able to validate that the device
Addressing in the IMS 89
accessing their network is authorized, and the subscription is current and legitimate.
This is to prevent service theft.
But identifying devices also helps deliver unique services based on the device type.
For example, a subscriber may wish for e-mail to be sent to his or her Blackberry, but
for voice calls to be sent to a separate cell phone. The subscriber may also wish to have
personal calls sent to a different cell phone.
This need alone drives the requirements for multiple identities within the IMS model
as we will discuss in this chapter. These identities also provide a lot of flexibility for the
subscriber. For example, a subscriber can have one identifier for personal use, while
maintaining another identity for business use. All of their identities are supported by
the same service provider, who then manages the routing of calls and e-mails to the
various identities based on their profiles.
All of these are supported through one subscription, rather than forcing a subscriber
to have multiple subscriptions for different needs.
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