Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!killer!vector!nobody From: peter@hpqtdla.HP.COM (Peter Locke) Newsgroups: comp.dcom.telecom Subject: Re: FRG phone numbers Message-ID: Date: 18 Oct 88 17:32:55 GMT References: Sender: chip@vector.UUCP Organization: HP, Queensferry Telecomms (UK) Lines: 31 Approved: telecom-request@vector.uucp X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 164, message 1 >How does the CO know when it has all the digits? Does it time >out, or do prefixes carry implicit lengths? Neither, really, for most of the European networks. The old mechanical networks operated step-by-step signalling. This means that as you dial, different exchanges in the network interpret the digits you are dialling to determine the route, they connect you through to the next exchange and ignores the dialling. The next exchange now continues this interpretation until the end exchange rings the phone and - usually - any further dialled digits are lost. In the UK, for PBX direct extension dialling, the PTT fits a 'balck-box' in the end exchange which 'stores' further digits and then passes them on when the PBX connects - I don't know how they tell how many digits are needed. For the new CCITT SS#7 networks, as found in most European countries to some degree ( and all of Germany ), a call can be either step-by-step or block. We are used to step-by-step and it's benefits to us as users ( the network can give busy or bad number indications immediately, it doesn't wait till the whole number is dialled in ) and the CCITT#7 protocol has a Subsequent-Address-Message defined to ease implementation. ANSI does *not* have the SAM, so I guess either you're 'stuck' with block. So, in summary, we do not need time-outs to know if the user has entered all the digits. Effectively, the network 'finds out' by trying it. And no they do not need to be fixed length for the same reason. Now, when our national PTTs have *serious* competition, I think this will all change as the astute might have realized that step-by-step ties up equipment for longer than block. With equal access, the trunk providers will not be happy with step-by-step. I'm holding my breath !