bcousert%zardoz.uucp@ics.uci.edu> (04/23/91)
Could someone briefly describe in laymen's terms what ISDN is? Also, is ISDN fast enough for real-time video? Bill Cousert share!bcousert@CPD.Com
Johnny Zweig <zweig@cs.uiuc.edu> (04/26/91)
share!bcousert%zardoz.uucp@ics.uci.edu (William Robert Kent Cousert) writes: > Could someone briefly describe in laymen's terms what ISDN is? Also, > is ISDN fast enough for real-time video? The wires going to your house can carry digital signals at about 150,000 bits per second without much problem. So if you digitize your voice (at 64,000 bits per second) you can have two voice channels on one pair of ordinary copper wires, with room to spare. "But how are we ever going to convince people to toss out their $20 analog phones and buy $300 digital phones?" the question arises. "Aha! If we make it an Integrated Services Digital Network (ISDN), we can let people do all kinds of crazy stuff besides just talking, like faxing, email, running home security, and so forth ... That's the ticket!" So there you are. And no, the basic rate ISDN service (the one that does not require coax or optical fiber into your house) is not fast enough for anything but the high-compression/slow-scan type video. I wouldn't want to watch "Monsieur Hire" over the phone just yet. Johnny ISDN
"Fred R. Goldstein" <goldstein@delni.enet.dec.com> (04/26/91)
In article <telecom11.303.8@eecs.nwu.edu>, share!bcousert%zardoz.uucp@ ics.uci.edu (William Robert Kent Cousert) writes... > Could someone briefly describe in laymen's terms what ISDN is? Also, > is ISDN fast enough for real-time video? Okay, you asked for it. I'll try to be brief. ISDN is the all-digital evolution of the telephone network. It provides a standard set of services over a standard set of interfaces, with a goal of reducing the total number of interfaces from what we need in an analog world. ISDN's main stock in trade is the 64 kbps channel, used to carry digitized voice. (Already the network is mostly digital between COs; ISDN provides a digital local loop too.) It can also carry 64 kbps data, of course, which makes ISDN a lot nicer than a modem for long-haul data use. And it provides access to X.25 packet services, which may make X.25 a lot more accessible in the US market. The Basic Rate Interface (BRI) has two 64 kbps B channels and a 16 kbps D channel; the D channel carries the signaling protocol (a set of messages that takes the place of off-hook, ring voltage, etc.). The D channel can also carry X.25 in its spare time. The Primary Rate Interface (PRI) has 24 channels of 64 kbps apiece, with the "23B+D" combo being common, but higher-bandwidth "H" channels (384, 1472, 1536 kbps) also being possible. Think of the BRI as a phone line and the PRI as a PBX trunk and you'll get the "common" use. With some effort, a BRI can support compressed 112 kbps video, and a PRI can support 384 kbps video. AT&T already provides PRI service from its POPs (including switched 384k); local Bells are fairly slow to offer BRI, though it exists in some areas. That's the tip of the iceberg. (I have a book on the subject coming out in a few months, and even that's just a summary.) Fred R. Goldstein Digital Equipment Corp., Littleton MA goldstein@delni.enet.dec.com voice: +1 508 952 3274 Do you think anyone else on the planet would share my opinions, let alone a multi-billion dollar corporation?
phil@ucbvax.berkeley.edu> (04/27/91)
In article <telecom11.303.8@eecs.nwu.edu> share!bcousert%zardoz.uucp@ ics.uci.edu (William Robert Kent Cousert) writes: > Could someone briefly describe in laymen's terms what ISDN is? Also, > is ISDN fast enough for real-time video? A fairly good aricle describing ISDN and the various Acronyms associated with ISDN can be found in the March 1 issue of EDN. The only major omission in the article (warning - a commercial is coming) was leaving out Motorola as a source of ISDN IC's in the list near the end of the article (pages 80-88). Of course you can also wade through the CCITT, ANSI, and BELLCORE documents to get the actual specs for this service. << Usual Disclaimer >> Phil Weinberg @ Motorola Semiconductor, Sunnyvale, CA 94086-5395 UUCP: {hplabs, mot,} !mcdcup!phil or phil@sjc.mcd.mot.com Telephone: +1 408-991-7385
ac220@cleveland.freenet.edu (Rich Szabo) (04/28/91)
I am sketchy on how ISDN interacts and co-exists with Plain Old Telephone Service. Does an ISDN line have a "phone number?" If so, what happens if I dial this number from a Plain Old Telephone? Can an ISDN line be used as a voice line so that I don't need a POTS line in addition? Rich Szabo 216-662-1112 internet:ac220@cleveland.freenet.edu rszabo@attmail.com <-- Real Soon Now, so they say
tnixon@uunet.uu.net> (04/30/91)
In article <telecom11.309.3@eecs.nwu.edu>, ac220@cleveland.freenet.edu (Rich Szabo) writes: > I am sketchy on how ISDN interacts and co-exists with Plain Old > Telephone Service. Does an ISDN line have a "phone number?" If so, > what happens if I dial this number from a Plain Old Telephone? Can an > ISDN line be used as a voice line so that I don't need a POTS line in > addition? An ISDN Basic Rate Interface as two 64000bps bearer channels. Except for the analog local loops, POTS is based on exactly this same kind of channel! Once you get into the CO, you can connect a digitized 64kbps POTS PCM voice channel to an ISDN B channel, and talk just fine. You definitely don't need to keep a POTS line around once you have ISDN. Of course, there's a lot more you can do with that 64kbps channel in ISDN than in POTS -- clear channel 64kbps synchronous transfers, V.110 or V.120 terminal adaption, X.25, etc. When it's being used for 3.1KHz voice or voiceband data, the network knows this so that it can route you to POTS lines (it will reject attempts to connect those other call types to POTS lines). Also, if the network knows you're using the channel for voice or voiceband data, it knows it can do voice compression and multiplexing on the channel -- but this happens primarily on international calls (rarely on domestic calls). Don't tell the network you're using the circuit for voice and then use it for something else, because strange things will happen. 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
Johnny Zweig <zweig@cs.uiuc.edu> (05/01/91)
ac220@cleveland.freenet.edu (Rich Szabo) writes: > I am sketchy on how ISDN interacts and co-exists with Plain Old > Telephone Service. Does an ISDN line have a "phone number?" If so, > what happens if I dial this number from a Plain Old Telephone? Can an > ISDN line be used as a voice line so that I don't need a POTS line in > addition? Your local Central Office probably digitizes your POTS signal as soon as they get their (4ESS or higher) hands on it. ISDN phones actually have a number along with port-number like thingies I forget the name of that specify particular devices that may be connected to a single interface. But it should certainly be possible to call a seven-digit number and talk to your friend Joe down the street from POTS.
"24460-W. H. Sohl(L145" <whs70@taichi.bellcore.com> (05/01/91)
ac220@cleveland.freenet.edu (Rich Szabo) writes: > I am sketchy on how ISDN interacts and co-exists with Plain Old > Telephone Service. Does an ISDN line have a "phone number?" If so, > what happens if I dial this number from a Plain Old Telephone? Can an > ISDN line be used as a voice line so that I don't need a POTS line in > addition? The answer is absolutely YES. The ISDN line is an access technology that includes POTS if the line is ordered with the POTS capability. Major deployments of ISDN that have already occured and have been reported in the media include, McDonald's headquarters in Illinois, several major oil companies in Texas, and numerous other deployments around the USA. The estimate at this time is that there is around 100,000 ISDN lines installed. Most, if not all, of the installed lines are to business customers. Bill Sohl (K2UNK) || email Bellcore, Morristown, NJ || UUCP bcr!taichi!whs70 (Bell Communications Research) || or 201-829-2879 Weekdays || Internet whs70@taichi.cc.bellcore.com
bote@uunet.uu.net> (05/06/91)
Toby Nixon typed: > Rich Szabo writes: >> Can an ISDN line be used as a voice line so that I don't need a >> POTS line in addition? > You definitely don't need to keep a POTS line around once you have > ISDN. Unless the power fails at your location. Then, no more ISDN. OOPS! John Boteler bote@csense {uunet | ka3ovk}!media!csense!bote SkinnyDipper's Hotline: 703 241 BARE | VOICE only, Touch-Tone(TM) signalling
nagle@uunet.uu.net> (05/09/91)
csense!bote@uunet.uu.net (John Boteler) writes: > Unless the power fails at your location. Then, no more ISDN. > OOPS! No, ISDN sets can be powered from the phone line. The power situation is ingenious. Normally, you can draw (I think) 400ma off-hook from an ISDN line. This should be enough for a reasonable phone, and maybe a digital answering machine as well. If the CO has a power problem (maybe when commercial power is out) the DC polarity of the line is reversed, and you can then draw only some lesser amount of power. Maybe your dial light will go out. But the phone should still work. Now, which ISDN phones properly comply with the spec? John Nagle
Thomas J Roberts <tjrob@ihlpl.att.com> (05/13/91)
From article <telecom11.339.9@eecs.nwu.edu>, by csense!bote@uunet.uu. net (John Boteler): > Toby Nixon typed: >> Rich Szabo writes: >>> Can an ISDN line be used as a voice line so that I don't need a >>> POTS line in addition? >> You definitely don't need to keep a POTS line around once you have >> ISDN. > Unless the power fails at your location. Then, no more ISDN. Correction: Unless the power fails AND YOU HAVE MADE NO PROVISION FOR THIS. Then, no more ISDN. In every ISDN installation I have been involved with (either as user, or consultant, or designer/engineer - some 20,000 lines in all), battery-backed-up power has been supplied for the NT1s and the station sets. Most users want phones that work during a power outage. Tom Roberts AT&T Bell Laboratories att!ihlpl!tjrob TJROB@IHLPL.ATT.COM