MAP supports all of
the wireless-specific functions such as the authentication and registration processes.
So in a wireless network today, there is SS7 communication between the mobile
switching centers (MSCs) and the base station subsystems (BSSs), as well as from MSC
to MSC. SS7 is also used to communicate to the Public Switched Telephone Network
(PSTN) when a call is routed between wireline and wireless domains.
Architecture of the IMS 7
The switches and the base stations communicate the location of a subscriber device
as they roam from cell site to cell site, providing the location data to the Home Location
Register (HLR) and the Visited Location Register (VLR). The HLR is a more static database
providing the subscription data as well as identifying the serving MSC. The VLR
is a more dynamic database identifying the cell site serving a subscriber device.
Something else IMS inherits from wireless networks is the concept of home and
visited networks. In the wireless network, subscribers are assigned to a ???home??? network,
which becomes the location of their subscriber data (provisioned in the network
database function HLR). Whenever a subscriber roams outside of their network, they
are considered as ???visitor.??? Their location is tracked through the same databases in the
home network to allow the network to track and authorize access to specific services
such as messaging.
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