[Asterisk-Users] Re: How to generate "ringing tone" to a calling party.

[Rich Adamson]

> > Examples:
> > 1. two-wire analog pstn lines: as soon as current draw is sensed by
> > the central office, answer supervision is generated by that "central
> > office", period. It has nothing to do with whether * handled it or
> > whether an analog phone is hanging on the end at the customer's
> > location. There is no such thing as one-way audio or grace periods.
> > 2. Trunk lines from the Central Office to a customers site: can be
> > configured at the central office in many different ways and is
> > dependent on the "service" requested/provided. One-way audio, grace
> > periods, etc, are oftentimes dependent upon exactly which Central
> > Office switch the telco is using (eg, Nortel, Siemens), and whether
> > the telco "chooses" to support those options.
> > 
> > A PRI is considered a trunk line; a BRI is not. An ordinary analog
> > pstn fxo interface is not a trunk.
> 
> Early audio b->a is an option in isdn. It is quite common in 
> EuroIsdn-land. Even on a bri. There seems to be a large difference in 
> mindset between US and European countries. In the US isdn is just a fancy 
> form of the old trunk lines. You pay for everything you want enabled. In 
> some (most?) EuroISDN-countries a lot if stuff is considered basic isdn 
> setup and has no extra cost associated with them. Reverse audio, caller 
> id, etc.

Exactly. The US implementation has lots of different exceptions and a
fair number of differences relate back to what the US telco marketing
_thought_ were options vs standard features, and therefore what the
telco engineers and switchman _think_ are industry standards. However, 
there are differences in what the central office switch vendors 
support in terms of electable options as well. Siemens, as one example, 
is very different from Nortel or ATT switches, etc.
 
> Isdn can certainly emulate old copper wires with their limitations. I 
> guess it is up to how greedy the pstn provider is, or what they can get 
> away with.

When ISDN was first introduced in the US a looong time ago, the telco
engineers and marketing folks thought they had the best thing since
sliced bread for both data & voice. They all got into attending x.25
and isdn classes, tried to put together marketing/sales plans to take
over large corporate data & voice networks, and soon found out that
corporate america was not interested in their antiquated star-configured,
C.O.-based, essentially-point-to-point stuff they were trying to sell.
On top of that, many of the telco marketing/sales types were attempting
to sell the stuff as "telco managed networks" when they didn't have a 
clue that managing large-scale end-to-end network resources meant 
something far more then simply detecting when their last-mile circuit 
failed, and didn't even do a acceptable job of that.

For the non-US people reading this, keep in mind at that time there
were the major Bell operating companies, _many_ very large independent
telephone companies, and literally 1,000's of small independent telco's
in the US. (Just the state of Iowa had over 600 _independent_ telcos
at one time.) Each of those were running off trying to do their own
thing in terms of marketing/sales/engineering/pricing setting their 
own standards in terms of what they were going to support. Not cool.

When the telco's introduced the stuff to corporate america, they were
competing against IBM's SNA and other established networks that were
far more sophisticated then what the telcos were attempting to peddle
for data. IBM (and others) purposefully drug their feet implementing 
any sort of scalable mainframe interfacing primarily to protect their 
installed base that had generated a very substantial revenue stream 
for them. Larger voice users already deployed virtual private voice
nets and had reduced their voice costs well below isdn pricing, and
the majority of installed pbx's didn't have isdn capability.

Judge Green had not yet broke up the US Bell system, and the majority 
of independent telco's didn't want to disturb the voice revenues by
doing anything they didn't understand (eg, isdn for voice).

Thus was born the US ISDN acronym: It Still Don't Work

That all comes from 21 years of working for the fifth largest independent
US telco outside the Bell system, partially as a central office and
transmission engineer and later as the director of their corporate
internal data-voice network. Very experienced on both sides of that story 
back then. Try that one for political pressure: NO, we can't use or
help promote our own isdn & x.25 networks. Why? at the time they could
not truly provide connectivity between any _two_ of 100's of nation-
wide sites that were needed. And, all of their offered interfaces were
slow-speed RS232 when we already were running 56k sdlc stuff or better.
It would have been a total fork-lift of equipment to move back to their 
data interfaces, and a total fork-lift of our pbx's since they didn't
have isdn support. The isdn & x.25 protocols were not the problem; 
their marketing, engineering, and pricing followed by their "regional" 
implementations were the problem. (They were selling a solution without 
an understand of the requirements/problem. How unique!)

Non-US countries were not in that same boat for lots of different
reasons, one of which was the influence that government owned/sponsored
telco's had on setting/implementing their country standards. The
majority of those didn't have the embedded base of networks to compete
against. ISDN (pri's & bri's) were definitely a step up and had value.

The US telco's still don't really understand the value (some twenty
years later), and the majority have antiquated pricing schedules that
ensure no one will buy their service. (That's why BKW, I think it was,
was having an issue with his local telco pricing for isdn facilities.)

Now with the US telco revenues dropping like rocks, senior managers are
looking for ways to cut expenses. One of their common internal choices 
has been to dump their isdn investments & staff, as their costs far
exceed their sales revenue on paper. (Let's see, was that the chicken 
or the egg.)

So, finding anyone in a US telco's staff/support ranks that has a 
clue what their technical capabilities happen to be in terms of isdn,
features, options, etc, is truly painful if not non-existent. If one
can actually find that technical person(s), he/she is strapped to
what they are authorized to support via artificially restrictive
pricing schedules/tariffs/company standards, etc. All of the major 
forecasts in the US show isdn deployments decreasing, not increasing 
as a result. (There truly are 1,000's of US central offices that don't
have isdn capabilities today.)

Let's see (back on topic finally), would you guess that a US telco is
going to implement "an early audio b->a option for a bri" because 
their customer asked for it? There are some but very few would even
have a clue, and it ain't going to get any better.

Rich