Path: utzoo!telecom-request Date: 21 May 91 14:16:06 GMT From: Toby Nixon Newsgroups: comp.dcom.telecom Subject: Re: It Still Don't Network ... or? Message-ID: Organization: Hayes Microcomputer Products, Norcross, GA Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 387, Message 5 of 11 Lines: 89 In article , hpa@casbah.acns.nwu.edu (H. Peter Anvin) writes: > A few questions about ISDN: I will answer as best I can, not being an employee of an operating company but an employee of a company that manufacturers ISDN terminal adapters. > 1. Is is feasible/not feasible to use ISDN as a link in an IP or Ethernet > network? Yes, if you can find somebody else with ISDN at the other end, and to the extent that it makes sense to have these connection be switched instead of leased. Bridging Ethernets over ISDN will be a major application (just as it already is for Switched 56k service). > 2. Is ISDN a worldwide standard, or another one of them "we decide what we > want" USA standards? The ISDN standards are being developed in the CCITT, so they are "worldwide". Eventually, when Signalling System 7 is implemented on international circuits, you'll actually be able to use ISDN on these circuits. Each country does specify which subset of ISDN options it will actually support; the T1S1 standards committee and the ISDN-1 industry group have been doing this in the USA. > 3. Does the 64 kbit/s B-channel rate over ISDN include error correction? No. The 64kbps is "clear channel". You certainly CAN run an error correction protocol on top of it, such as V.120 terminal adaption or X.25, but the basic service is not error-corrected. That makes sense, since error correction is neither necessary nor desirable for circuit-switched voice traffic (because the human ear filters out occassional noise, and the delay of error correction would be worse than the noise itself). > 4. Does the D-channel protocol include service identification (say IP, > video, voice, modem)...? Yes. > 5. Is is possible to call a POTS line with a modem from an ISDN connection? Yes, but exactly how that is accomplished varies. Hayes terminal adapters, for example, provide an analog phone jack into which a modem can be plugged, to allow you to communicate with remote PSTN modems through an ISDN voice call. Another way is through a modem pool at the ISDN-PSTN gateway (switch), to which you connect using V.120 or some other adaption protocol. T1S1 and CCITT Study Groups XVII and XVIII are currently looking at expanding the Q.931 protocol to accommodate automatic fallback from ISDN terminal adaption protocols to PSTN modulations, if the station called is turns out to be on the PSTN; this would be useful for interworking with both PSTN data modems and fax machines. We envision devices that would have a DSP implementation of a modem that speaks directly to a B channel (called a "digital modem"), built right onto the terminal adapter. This would help the transition from PSTN to ISDN. > 6. What are typical rates for ISDN? Is it billed per minute or per block? That is still very much open. Current ISDN services are B-channel circuit switched (which are charged by the minute) or D-channel packet-switch (which are often FREE on the same switch, depending on the RBOC, because they haven't really figured out how to charge for it yet). Charges for frame relay service are still being discussed. Charges for packet switched services, once these are provided other than point-to-point (i.e., by gateways to the PSPDNs), will probably be by segments or characters, as they are on the PSPDNs now. I haven't done much research on ISDN charges, but my understanding is that the time-and-distance charges for circuit-switched ISDN connections are identical to PSTN charges. Since most PSTN connections are circuit-switched 64kbps digital connections anyway, this makes perfect sense. Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net [Moderator's Note: A new mailing list is getting started, devoted to the topic of ISDN. I received a note on it today, and will run it here soon, so watch for it if you would like to join an interesting new group devoted to this topic. PAT]