The location is also the IP address assigned to the subscriber
device. In other words, the location identifies how to route sessions to the subscriber at
any moment in time.
This is why registration is so dynamic. Each time the subscriber changes locations,
the address assigned at the IP level is changed and must be updated within the registration
so that sessions can be connected properly. This is analogous with wireless
networks where the handset registers with the HLR/ VLR functions.
Figure 1.5 The HSS within the IMS
P-CSCF I-CSCF S-CSCF
HSS
18 Chapter 1
Also a part of the registration information is the subscriber data. The private user
identity and the public user identities are all stored as part of the registration data.
This allows the S-CSCF to provide full support to the subscriber device and any services
it wishes to use.
Services are identified by their service identifiers and are stored by public user identity.
As you will see in Chapter 3, public user identities can be assigned to multiple service
identifiers, based on the subscription. This information is stored in the HSS, and is
shared with the S-CSCF when the subscriber device registers with the network.
If a subscriber is to be barred from service access, the operator is able to bar the public
user identity or the private user identity associated with a subscription at the HSS.
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