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Summary of ISDN Information

14 May 1997 (Revised 1 August 1997)

This page was originally prepared to support a little presentation I was asked to give to the technical support staff members at GOL, during my brief stint there. It's intended to collect various kinds of background information about using ISDN with your Internet connection. Many providers these days are buying ISDN-capable equipment, and many of them just allow customers to use the additional speed (up to 64K) without any additional charges. There are several sections that could be substantially revised, but since the data would just get stale again, it's probably easier just to suggest that you send me email if you have more questions.

There are two sections here, one describing ISDN in general, and a table of various kinds of TA information. Some kind of disclaimer about as-isness and no guarantee of suitability and all that legal babble should go here, but I was too busy to talk with the lawyers.


ISDN is a relatively new service offered by NTT. Actually, the idea and standards have been around for quite a while, but it only became available a few years ago, and NTT is only now starting to market it aggressively. It allows a variety of new telephone services using the existing copper-wire-based phone system.

Basic ISDN service involves a single pair (two wires) using digital coding to carry two data channels and one control channel. The data channels are called B channels, and each B channel can carry one voice call or one digital data signal. (The control channel is only used for dialing and some support functions, and is basically unimportant here.)

For most residential users, ISDN doesn't make that much sense. There are a couple of cases when it can be better than regular phone service, however. If you have two phone lines in your home, then one ISDN line can do the same work for less money. The equipment needed to use the ISDN line is actually less expensive than the street value of the 'used' telephone line permission fee that you paid to NTT for each line, so selling off one of the lines may actually generate a profit, as long as there are not special construction fees required.

While ISDN does give you the capability of two phone lines, it can be a little hard to use both of them effectively because the equipment at each end will tend to switch things around a bit looking for a free channel. If you want to use one line only for faxes, you can pay extra for the second phone line, but you can't be sure that the fax calls will arrive correctly, because if one of your B channels is in use, the equipment will tend to use the other B channel. In practice, this sort of thing usually doesn't cause too much problem, and if you have a new computer with the capability to automatically switch to fax mode as required, then you can just send and receive voice calls and faxes on the single number, or connect to the Internet, while still being able to call out (but only two things at a time).

If you can actually get one of the apparently hypothetical ISDN phones or true ISDN fax equipment, you can get a lot more capabilities, but mostly that equipment doesn't seem to be around. For example, you can assign (and pay for) a bunch of phone numbers, and your ISDN phone can tell you which one is being called. This might be useful if you wanted to run several businesses with separate phone numbers, kind of like a small PBX. The ISDN faxes can send very quickly, but only to another ISDN fax. So all in all, it seems like the main users of ISDN are just computerists who want more bandwidth to the Internet.


This table is just a general description of some of the TAs I've run across over the last year or so. A very idiosyncratic selection and description, to be sure, and I've tried to be generous about skipping what I can't recollect. And most of it should be checked with the manufacturers, too. These links go directly to the relevant TAs: MN128, IT55, IT45, IT35, ComStarz, TA/2A, Brain, PCM-CIA Cards, INS Mate 1, INS Mate V-5, Suntac....

ISDN Terminal Adaptors (TAs)
TA Name Maker Speeds Customer-Oriented Description (as for making a recommendation of a suitable TA)
OEM Names (Vendors) Analog Ports
General Comments and Installation Notes (by platform)
MN128
MN128 B.U.G. 38.4K to 128K Probably the best device on the market. Maker has very strong engineering focus and high quality standards. Comes in two versions, with and without an external DSU. Includes all software and cables for all major computer types.
(NTT TE) 2
Powerup diagnostics are excellent, checking itself and each channel separately. Even includes a little tester that can tell whether or not a phone line is ISDN, though it can't tell if the ISDN is wired backwards... Very adequate status indicator lights. Starting default is 64K synchronous. In MP mode still having problems with 128K (as of 14May97).

Windows 95

Standard .INF file. Very troublefree.

Windows NT

Kind of tricky with NT 3.51 and RAS.

Windows 3.1

Includes .CMD files for Trumpet.

Mac

Includes Mac disks and adapter for cable.
IT55
IT55 NEC 38.4K to 128K Another very good device. Maker has strong engineering focus and lots of computer experience. Comes in two versions, with or without an internal DSU. Includes all software and cables for all major computer types.
INS Mate 3 (NTT) 3
Status lights are a bit limited. Can run on batteries.

Windows 95

Standard .INF file. Generally troublefree.

Windows NT

Kind of tricky with NT 3.51 and RAS.

Windows 3.1

Take the AT commands from the 95 .INF file.

Mac

Includes Mac disks and adapter for cable.
IT45
Aterm IT45 NEC 38.4K to 64K Good device. Predecessor of IT55. Maker has strong engineering focus and lots of computer experience. Comes in two versions, with or without an internal DSU.
INS Mate 2 (NTT)
FastWave (Omron)
2
Status lights are a bit limited. Can run on batteries.

Windows 95

Standard .INF file. Generally troublefree.

Windows NT

Kind of tricky with NT 3.51 and RAS.

Windows 3.1

Take the AT commands from the 95 .INF file.

Mac

Don't know about Mac installation for this one.
IT35
Aterm IT35 NEC 38.4K to 64K Good device. Predecessor of IT45. Maker has strong engineering focus and lots of computer experience. Requires external DSU. Probably no longer available.
FastWave (Omron) 1
Better status lights than successors, but confusing modes.

Windows 95 & NT

May have been off market before these systems became popular.

Windows 3.1

Initializations explained in manual.

Mac

Works with Mac, but critical dependence on PPP version.
ComStarz
ComStarz NEC Probably can't recommend this one.
These were some of the earliest TAs available, but they seemed rather difficult to configure, and I had very poor luck making them work properly. That may have been due to my inexperience with ISDN--first TA I ever met--, or with their being designed for earlier types of ISDN equipment and maybe even different protocols and services. Though NEC is continuing to make various models in this product series, they seem to be pretty rare in the field, which makes me think they are special purpose devices, perhaps only suitable with a few networks.

Windows

Manuals seemed to be pretty extensive, but not very illuminating....

Mac

Wouldn't want to try it...
TA/2A
Oki TA/2A Oki 38.4K to 64K Not a terrible device. Models with and without internal DSUs. Probably no longer available.
2
One of a series of big gray boxes. Some of the earliest TAs available.

Windows 95 & NT

May have been off market before these systems became popular.

Windows 3.1

Initializations explained in manual. Only does 38.4 asynchronous.

Mac

Works with Mac at 38.4 or 64K, but 64K uses special port driver, special cable, and requires a lot of dip switch twiddling, too.
INS Mate 1
INS Mate 1 Yes? Not for regular users.
(NTT) 1
One of a NTT's first offerings. Seemed to work rather like an Ascend Pipeline router and configured through remote terminal windows. Didn't seem to be capable of handling dynamic IP addressing.

Windows

Extensive manual, but also unenlightening.

Mac

Very unlikely.
Brain Internal TA
Brain Brain 64K 38.4K? Workable, but....
0
Early internal TA for PCs.

Windows 95 & NT

Targeted for these platforms, but somewhat problematic drivers. Went through several versions and a lot of wasted time before it worked properly.

Windows 3.1

Possible. Theoretically.

Mac

Impossible.
PCM-CIA Cards
PC Card TAs 38.4K to 128K Varies widely.
0
Wanted to include something about these, but they vary pretty widely. Usually they work pretty well.

Windows 95

Several unusual problems can come up with these under 95, though it is usually possible to make them work, eventually. They are very dependent on having the proper .INF files, and there are sometimes problems with specific laptops. Sometimes there seem to be cases where conflicts are not detected properly by 95, and manual configurations of the resources will help. In cases where a machine has been upgraded or a DOS-based PC-card slot controller program has been installed, it can interfere with 95's handling of the PC-card slots, and this can be especially messy to fix.

Windows NT

Supported, but don't know how well.

Windows 3.1

Another theoretical possibility.

Mac

Supported but unusual, and don't know how good the support is.
Copyright 1997 by Shannon Jacobs. Must be a work of fiction?
I think that means you're allowed to freely use the ideas here, but not my precise expression of these ideas. And if you want to SELL them, then I definitely want a cut!

Feel free to send me your comments or suggestions, and if I work them in, I'll include colored acknowledgements, too. [But so far, no one has sent me anything. :-( ]


Copyright ©1996-2000 by Shannon Jacobs My weird disclaimer
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