TELECOM Digest OnLine - Sorted: Re: Phone Call Routing

Re: Phone Call Routing
8 Mar 2007 11:47:39 -0800

On Mar 7, 8:51 am, Sam Spade <> wrote:

> The switched public network has been around in its present form
> since the 1950s. There has been huge amounts of material published
> on the technical workings of the telephone system

Actually, the question is very reasonable. Since the 1980s the nature
of the public switched network has drastically changed and much of
that material is obsolete. Here's why:

1) Expense: The "trunk" (physical connection) between two central
offices was extremely expensive. It consisted of (a) switchgear on
the front end, (b) the physical wire, and (c) switchgear on the rear
end. Accordingly, trunks between offices rationed and carefully
planned -- just enough to meet demand but not more so. The phone
company worked hard to maximize capacity of the physical wire (carrier
circuits) and switchgear.

But after the 1980s the costs dropped dramatically. The head and
rear terminal equipment became cheap. Fiber optic with very high
capacity replaced copper and coax. Suddenly capacity was not a big an
issue anymore. Everything was so cheap there could be waste.

2) Politics: The old model had the Bell System handling everything.
The 1983 model had the local Bell companies handing off toll calls to
dedicated toll carriers (AT&T, MCI, Sprint, etc.)

But further deregulation allowed local companies access, too. Bell
(that is, successors to Bell) might own the physical line between your
house and the C.O., but once inside it was immediately handed off to a
new company that did the switching instead. (Bell had to spend a
fortune building extensions to C.O.s to house lockable rooms for new

Non-Bell companies might lease lines and switching from Bell or own
their own. Bell might lease stuff from non-Bell companies, indeed,
they often now sub-contract out repair and installation work. (If you
see a plain truck with a small stick-on Bell company sign instead of
fully painted, that's probably a sub contractor.)

3) Many people use their cell phone or cableTV phone as their line.
The routing is completely different for those systems.

4) New services: We have new stuff like DSL and FIOS.

So, the question of routing methods today is quite reasonable and
realistic. With so much deregulation, it is also relevant to know if
a given carrier, even a "main" one, is good to use.

> You would learn a lot more my doing a bit of research

Where would you suggest to research to get _current_ information
appropriate for a lay person?

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