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Re: Smoking gun in CA
Centrex is a different situation. This is something that did take me a while to
confirm. Centrex can support flat rate because there is no scarce shared
resource. But it only works in a limited way.
In Centrex, and in particular Centrex extensions which is what the Bells use to
compete with PBXs, there is no "scarce resource". In a Central Office, there is
effectively a one to one connection between the CO switch and the customer's
phone. When the CO is used like a PBX to connect extensions within a centrex
customer's facility, there is no shared resource consumed.
There is an independent wire between all the customer's extensions to the CO.
In the CO switch, there is a cross point switch that can connect
any extension to any other extension that is physically connected to the
switch. That is why you can only create Centrex Blocks (an aggregation of
extensions for one customer) in one wiring center (ie one CO) and not create
extensions that are in different COs.
[Note: In the past I had gotten mixed messages if the cross point switch is
truely not a scarce resource. I've had some Pac Bell and ATT (the switch maker)
tell me that it is not and there are enough cross points to connect every CO
customer line to another customer line on the CO. I've had others in the past
tell me its not true. At this point, there are more people telling me its true
than not! So I am assuming that there are enough cross points]
In the centrex or non centrex situation, there could theoretically be flat rate
if all the customers were on the same CO switch as the ISP provider. This is
rarely the case though. But usually the ISP is on a different switch and so
the phone call from the customer to the ISP must be routed over the scarce
resource of inter-switch trunks.
Now in some areas, ISPs are taking advantage of the Centrex situation and
creating their own Centrex Blocks that they connect thier customers too. It
only works if the ISP POP is directly connected to the same CO switch as their
customers. In some dense areas, this does indead make sense. It adds to the
cost of the ISP as they will need to buy PRI's to each CO they want to accept
Centrex customers from.
Robert J. Berger - CTO / VP of Engineering
InterNex Information Services, Inc. 2302 Walsh Rd. Santa Clara, CA 95051
Voice: 408-327-2290 Fax: 408-496-5484