If not, then the subscriber??™s
device must connect through a media gateway controller, which can convert the signaling
(call control) to SIP for communicating into the IMS. Following are several examples
of how this is accomplished.
In a wireline network, if a subscriber is using a PC or other stationary device to access
the IMS, the device must first secure an IP address. This process is started once
the device is activated (turned on). If the PC is connected to a local area network (LAN),
the LAN would assign the IP address (or the address could be hardwired to the location).
In a service provider??™s network, the connection may be through a DSL or ISDN
connection, where the network then provides the IP connectivity and the IP address is
assigned dynamically. The mechanics for how the device is assigned an IP address is
really outside the scope of this book, so we won??™t go into details about dynamic address
assignment.
Once the device has obtained an IP address, it must then learn of the closest IMS
network access. This is assuming that the device supports SIP and IMS procedures. If
the device does not support SIP, then interworking procedures are used to connect.
Interworking means using processes such as media gateway controllers (MGCs) for
converting from SS7 (for example) to SIP. The MGC is then responsible for managing
the connections on both sides of the MGC.
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