That's quite a hypothesis. But let's run with it.
The total number of "physical" trunks would be arbitrary. Contained within a single physical trunk you can have any number of private or permanent virtual circuits (PVCs), each with their own function. Or, in a more open scenario, each application could be riding over the larger trunk in IP mode, or in a purely contention-oriented mode. It's entirely up to how they would elect to engineer it.
In the PVC sense, individual virtual circuits (which are merely predefined packets per application between predefined end points, H-E to a given Central Office, say) would "point" the voice traffic to the core systems which are designated for a particular service. In the case of local telephone service, IP voice would come off the head end and then be routed locally within the head end to the PVC which goes to SBC's switching office, conceivably, where it would first go through a VoIP gateway process, or directly onto one of their softswitch platforms (if they were so provisioned). These processes would originate in the local h-e router, or routers.
Or, it could be routed directly via IP-only, sans ATM PVCs, into some VoIP-PSTN cloud (such as ITXC's) with only SBC's surveillance and monitoring through network management tools to satisfy their accounting requirements for billing and auditing purposes. Again, it's an arbitrary call, often dictated by the individual carrier's policies with regard to security, billing requirements, and traffic management philosophies, not to mention their other overall architectural considerations, as well.
Of course, carriers being carriers, they may elect to put in a separate physical layer pipe (or 'bone, as you call it) for each type of application for reliability purposes. In this case, SBC would have an ATM (most likely) link going between themselves and the TWX regional head end where the remote h-e's fall under a virtual clustering arrangement; and TWX could conceivably continue to have their own pipe to ATT's cloud, etc.
But, it needn't be this way, necessarily, given the attributes of IP networking. However, it often will be this way, which calls to mind my earlier observations of last night where I discussed how carriers are increasingly avoiding the sharing aspect of the 'net, causing a high level of redundancy in routes and other expensive resources as they continue to isolate themselves, on multiple levels, from the larger pool. |
