The voice traffic still needs to be packetized, and network growth needs to be supported
without significant investments in legacy network equipment. The purchase of additional
legacy switching nodes does not make sense if there is a long-term plan to convert to IP,
and VoIP can support the voice network as the operator begins its migration to IMS.
The transition at this first step is usually at the tandem level (back in the core of
the network). Then as subscribers are added, or legacy equipment needs replacement,
those replacements are achieved using VoIP deployments (MG/MGC). This now takes
care of packetizing the voice portion of the network and supports slower markets even
after IMS is fully deployed. The operator can then slowly begin retiring those legacy
switches and replace them with media gateways, while extending the reach of its IP
facilities to all of their markets.
Of course, we would be foolish to think that voice is the only reason to migrate to an
IP infrastructure. Data is a natural fit for the IP backbone (since this is what IP was
developed for), but video can be delivered over the IP network as well.
At this point, the operator has implemented IP in the core backbone, migrated its
signaling to SIGTRAN/SS7, and begun deploying VoIP at the core, and then the edge of
the networks to support packetized voice. Now all that is left are the service platforms
and the operator is ready to declare itself a convergent network, right?
Wrong.
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