In an ASP model, for example, the video server
may be located within a data center, along with an S-CSCF supporting video services.
All subscriptions for those video services would then be assigned to the S-CSCF in that
location. The decision of how to assign the S-CSCF then becomes based on the subscriptions
themselves, rather than where the subscription is located.
The other approach is to assign each S-CSCF according to geography. This is the
traditional telecom approach used in today??™s legacy networks with switches. This
model works well for traditional telecom operators, and in some networks it may make
the most sense. The S-CSCF is then assigned according to the location of the I-CSCF
that receives the request/response. The S-CSCF assignment is stored in the Home
Subscriber Server (HSS) for future reference.
For wireless and wireline operators, this model probably makes the most sense, given
that this is the model they are accustomed to today. Subscribers are assigned to resources
according to their home locations, and all services are supported network-wide
rather than in network segments.
The S-CSCF is assigned by the I-CSCF when a subscriber registers in the network.
The I-CSCF then stores this information (along with routing information) throughout the
lifetime of the registration. When the I-CSCF receives subsequent requests/responses, it
forwards them to the S-CSCF assigned on the basis of this information.
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