> > 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 _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
