SIP is the call control signaling protocol for
the IMS. It replaces SS7 in the control plane, supporting all forms of media in addition
to voice. This model is very similar to the Intelligent Network (IN), where SS7 is used
to communicate between network entities for the support of voice.
The IMS provides the same functions theoretically as the IN used today, except the
IMS supports more than just the voice services. It supports all media types and all services
within the network, using the same signaling and the same call control.
Again, it is not foreseen that the service providers of the world are simply going
to abandon their SS7 networks and start replacing them with SIP. This has never
been the case historically as new technologies came along. Certainly SS7 and the IN
were not implemented overnight. Operators took many years to implement their SS7
networks, implementing small portions of the network at a time, until eventually the
entire switching network was interconnected with SS7 signaling.
So far we have only discussed the transition of the voice transport and signaling
parts of the network. There is much more to a network than signaling and switching.
The support systems that are used to manage these networks is perhaps the most important
aspect of the business, because it is these support systems that allow an operator
to maintain profitability, secure the network from attack and unauthorized access,
and accurately bill for its services.
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