This FAQ covers questions for
basic installation and operation of ISDN in the UK
with an emphasis on Microsoft Windows NT Remote Access operation.
Q1. What does an ISDN line provide compared to
my normal telephone?
Q2. How much faster is ISDN than a modem over a
normal line?
Q3. What does ISDN cost?
Q4. What about call charges?
Q5. What about International Dialling/Call charges?
Q6. Why does it cost so much in the UK?
Q7. What else does ISDN provide that I can’t
get with my normal telephone line?
Q8. Can I get Caller Line ID facilities
Q9. Is the D-Channel supported for data?
Q10. What equipment do you need for basic ISDN?
Q11. What standards exist for interoperabilty of
ISDN Equipment?
Q12. Can I use ISDN hardware which isn’t
designed for the UK ISDN?
Q13. How do I have multiple calls going on the
same ISDN line?
Q14. Can I use a normal telephone or fax on an
ISDN line?
Q15. How usable is a wide area network over ISDN?
Q16. How do I go about getting ISDN installed and
what installation options should I consider?
Q17. What UK Internet Service Providers offer
ISDN?
A1. Your normal telephone is analogue whereas ISDN is digital. Overall you get much higher bandwidth with ISDN so you can transfer data more quickly and more reliably.
A2. The fastest transmission over a normal telephone line is 28,800 bits per second. You can achieve 128,000 bits per second over ISDN so it is theoretically 4-5 times faster over ISDN. Practically ISDN is better than this because it doesn’t suffer from the noise limitations of analogue telephone lines.
A3. The BT ISDN-2 service is £400 or installation and £84 rental per quarter (all plus VAT).
A4. ISDN call charges are the same as for your normal line except that international calls are more expensive. Calls are charged separately for each of the ISDN B channels (there are two B channels hence the name ISDN-2). If you use both channels at once you are effectively making two calls, so you get charged twice.
A5. ISDN international call charges are at a higher rate than residential international calls Calls are again charged separately for each of the ISDN B channels. To guarantee an international call at 64K on the B-Channel you prefix the number with 000. If you just prefix the dialed number with 00 then you may get 64K bandwidth on the B-Channel, but you may not. Prefixing the dial code with 000 will cost you up to 50% more than the same number prefixed with 00.
The moral is that if you want to make an international voice call then use prefix with 00 as it will be cheaper. If you need 64K on the B-Channel then try 00 first, you may be lucky. If you want guaranteed 64K on the B-Chanel prefix with 000.
A6. You really need to ask BT about their charging policy, but I suspect it fits in with their overall pricing strategy for "private" circuits.
A7. Data transfer reliability, multiple calls on a single ISDN line, separate channel numbering and multiple subscriber numbering (MSN) are the main features.
A8. If you don't want your outgoing number details to be available to other people then BT can restrict you number from going out. BT will do this for free if you dial 152 and tell them, otherwise your number is available to others by default.
If you want to see the number of the person calling you then Caller Line ID will cost you a £10 one off fee and £3.40 quarterly rental thereafter. The £3.40 charge applies to each separate number, eg. if you have separate channel numbering it costs £6.80, MSN costs £3.40 (for the whole block) and if you had several ISDN-2 circuits under the one number it still costs only £3.40 (what a bargain!).
A9. Not in the UK at the moment. BT plan to have additional facilities for the D-Channel next year. We will have to wait for the ability to have "nailed-up" circuits and be able to use all three ISDN channels for data transfer.
A10. The equipment you can get ranges in price from a few hundred pounds to a few thousand pounds. For basic remote access applications there are plug-in cards for your PC such as the Digiboard PC/IMAC, standalone boxes called a Terminal Adapter (TA) which you connect to your computer serial port using RS-232, and TAs which you can connect onto to a network connection.
A11. V.110, V.120, Multi-point PPP, CAPI, etc, - loads of 'em. At the moment a lot of work is being done to sort out interoperability problems and eventually different manufacturers’ equipment will connect together properly. For plug-in PC cards for Windows NT the Digiboard PC/IMAC and PCiMAC/4 work extremely well, but don’t expect them to talk to anything else. Digiboard however, are the only ISDN vendor in the Windows NT hardware compatibility list. For more info on ISDN standards try our ISDN Favourite Links.
A12. When BT install your ISDN line they will provide a box having two RJ45 8-pin connectors which they will mount on your wall. Your ISDN equipment plugs in to this box which houses a Network Termination unit. The Network Termination unit basically converts the analogue telephone line fed into your premises, to a digital connection (called an S-bus). You cannot connect equipment with a built-in Network Termination unit (often called an NT1) to the ISDN-2 wall socket. For UK operation the equipment should have a European CE approvals sticker.
A13. One ISDN line has two separate 64kbps B channels and a single 16Kbps D channel which is mainly used for call setup and signalling. You can have a maximum of two calls at once; one on each of the B channels, or a single call using one B channel, or a single call using both B channels giving you up to 128000bps throughput (using both channels in parallel is known as "bonding").
A14. Yes, but they use analogue technology so you need to connect them to ISDN via an analogue-to-digital converter. The most popular route is to use a TA which also has two analogue ports (often called POTS Plain Old Telephone Service ports). You can allocate separate telephone numbers to each analogue ports and put a telephone on one port and a fax/modem on the other. The Dataflex Desktop Diamond and Racal DAP 6200 units provide these features.
A15. Very. OK this is subjective - but we find ISDN for remote access is reliable and much more practical than a dial-up modem.
A16. Only BT install ISDN (more correctly ISDN-2) in the UK. Here are the basic steps:-
1. Before contacting BT decide on what numbering scheme you want; "single number", "separate channel numbering" or "Multiple Subscriber Numbering" (MSN). If you change your mind later on BT will charge you accordingly and they don’t normally point the out the options.
(i) Single number: you can have the same single number for both B channels (two callers can dial you on the same number simultaneously). BT doesn’t charge extra for this.
(ii) Separate channel numbering: you can accept calls on two different numbers at the same time, which is good if you just want one for data and one for voice for example. BT doesn’t charge extra for this.
(iii) MSN: BT will allocate you a block of ten consecutive numbers. If you add equipment that supports MSN you will able to allocate up to ten different numbers for different appliances such as voice, fax, modem, remote access, another telephone, etc. BT will charge about another £10 per quarter + VAT for this service (but what the heck you’ve already paid 400 quid...
(iv) Also decide if you want to restrict your number from being available to others and if you want to have Caller Line ID facilities - see Q8. Can I get Caller Line ID facilities above.
2. Call the BT ISDN helpline on 0800-181-514 and check the following:
(i) Find out if your local exchange has the necessary ISDN equipment. If BT say they can’t check this without first having a purchase order from you, either get stroppy with them until they agree to do it, or speak to another person on the helpdesk. BT should be able to give you this information within a few hours. It's worth realising that ISDN-2 is a viewed by BT as a business only service rather than residential, but anyone can get it and purchase orders aren't mandatory.
(ii) At the same time, ask BT to find out if your local exchange uses "I-MUX" or "Line cards" for ISDN. This is just for your own future information; if they have line cards then it is generally better because BT will be able to remotely test your connection to the box on the wall (in this case an "NTE8" complete with a green light). This feature isn’t available on the IMUX and your wall mounted box will be a type "NTE6". In the future should you have a fault and be on an I-MUX you will to wait longer whilst an engineer does some tests. With the Line Cards, when you report a fault on 154 the operator will be able to test the line while you wait, after which you still may have wait in for an engineer, it's just they will be more certain of what's wrong!
3. All being well you can now go back to BT business sales on 152 and order your ISDN-2 service telling them what type of numbering you want. Also tell them who will be paying; either yourself or your business. They will confirm the transaction by sending a form for you to complete, and installation is around about 7 working days. Good luck!
The BT ISDN help desk seem to be more knowledgeable than a few months ago so hopefully installation is easier these days. Please let us know if you're having problems (or if you find them to be really good) so we can keep this bit of the FAQ up-to-date.
A17. In the UK most ISP's say they offer an ISDN connection. In practice a lot of them are just thinking about it and for the few that *actually* offer ISDN there is a great variation in price and capabilities.