The transport of bearer traffic is the easiest. Once bearer traffic is packetized, moving it
through an IP infrastructure is much simpler (yes, I know I am oversimplifying things
here) than maintaining a TDM circuit-switched network.
36 Chapter 2
The voice is in a form that must be converted to packet before it can be sent through
the IP infrastructure. The IMS itself is not really a part of this, since the IMS is really
the call control portion of the network. The IMS itself is the architecture that allows the
various packet elements within the network to communicate all aspects of the sessions
and share this information between multiple entities.
The second challenge comes in the form of signaling, which is really session control.
Session control ensures that subscribers are able to access the same services they enjoy
in their home networks anywhere they connect. It is what ensures a subscriber is legitimate
and is authenticated prior to connecting to your network. Session control is about
maintaining complete control over every service you deliver in your networks, enabling
security, billing, and much more. Signaling and session control are how network entities
exchange information about a session in an effort to be able to support the session.
This means converting the signaling plane from SS7 to SIP after implementing IP
as the transport for the signaling network.
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