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Caller ID

Foreword
I have little direct knowledge of Caller ID (known also as Caller Line Identification, CLI, CLID or Caller Display) so will immediately give you the Caller ID FAQ at ainslie.org.uk as a most astonishingly thorough run-through of the subject, although now out of date. This page will confine itself to modem-specific links.

The page has been inspired by Mike McMullan, who both got his Pace 56K ISA working with CLID under Windows XP & then also sent some links through to me. Thanks, Mike.

I'm amazed that support for UK CLID is so patchy - effectively invisible. As modems have become so ubiquitous the manufacturers need to fight for an edge. I would have thought that CLID support is one obvious edge to lift their model above the rest. Whilst writing this article (Apr 2002) my mouse finally packed up & my only supplier at that time of night could be my local PC World. I decided to also finally replace my Motorola soft (spit) modem. The eager young assistant just looked at me blankly when I asked for a modem with UK CLID support.

What it is, How it works, and Requirements
In about 1986 I moved into my current house and, not long after, had reason to call the local Gas company. The lady that answered the phone waited a few moments, then greeted me by name and told me my address. This was impressive as I hadn't told her either fact. It was the integration of telephone, Caller ID & computer system that allowed all this, bringing up my account details on her screen within a few seconds of her telephone ringing, before even picking up the phone to talk to me. 20 years later, even my own company's systems cannot achieve this. Yes, the caller's number appears on my telephone, but the telephone system & the computer system are unaware of each others existence.

US Patent 4,582,956 was filed by Carolyn A Doughty of AT&T Bell Labs (now Lucent Technologies) on 12 July 1983 and granted on 15 April 1986. It was a “Method and apparatus for displaying at a selected station special service information during a silent interval between ringing”. Because of the size of the American market, the Bellcore standard is the principal CLID protocol found in modems. It sends the data 500 ms after the first ring tone and uses the 1200 baud Bell 202 tone modulation. Naturally, other countries have developed different protocols. Use of Bell 202 tones prevents BABT approval on the UK phone system, so BT wakes up the display with a line reversal, then sends the data as CCITT V23 modem tones. Some other countries choose a protocol which is almost the Bellcore standard, but varies in it's details just enough to prevent Bellcore hardware/software from detecting it.

Digital telephone exchanges contain a separate call data circuit in addition to the speech/data circuit. The first carries signalling information (ring tones, busy signals etc) whilst the second carries the actual speech and/or modem tones. With ISDN lines, the first is the D channel, whilst the latter is the B channel(s). CLID info is carried on the first system, in between the ring tones, and a digital exchange is the first requirement for CLID to work.

Signalling System 7 (SS7) is the standard for this call data circuit. It has been adopted internationally, and this allows digital exchanges throughout the world to communicate, and therefore for the CLID info to be communicated from exchange to exchange. At your local exchange, this SS7 info is translated into your telecom's local variant of CLID. The first requirement above therefore becomes updated to, the two parties must be on digital exchanges, that are linked by SS7.

Your local service is the next hurdle. The connection from the telephone exchange to your home/business is known as the Local Loop. Obviously, if your local exchange is not digital, you cannot receive CLID signals across your local loop at all. In addition, if your caller is not on a digital exchange you also cannot receive their CLID. Further, if the call between the two of you is routed via SS7-incompatible equipment you cannot receive it. However, even if all of the proceeding is correct, unless your Telco propagates the signal through the local loop to you, you still will not receive it. In the UK, British Telecom has made a habit of treating everything beyond the basic provision of a telephone as an opportunity to wring as much money as possible out of it's subscribers. Caller ID therefore becomes one of the “Select Services” and is an extra charge.

Your local wiring is the next hurdle. Just as with modem communication itself, the polarity of the line, existence of smart boxes, DACS boxes & many other things can affect CLID devices. See Caller ID FAQ #5 for a more thorough run-through.

The final hurdle is compatibility between your Telco's CLID standard & your hardware/software combo. Life is easy if you are American (not Canadian) as yours is the default for modems. The good Lord help you if you are not...

First, all of the above sections need to be working, so that your local exchange presents the CLID to the modem. Next, your hardware (the modem) needs to be compatible with your Telco's CLID standard to be able to collect the signal, and then the software (first the modem drivers and then the operating system telephony APIs and then the telephone-software) needs to be able to decrypt the signals. This is a long, long chain from the person that calls you to your computer screen and a break at any one point will leave you with nothing on the screen.

Next, there is more than one UK (local-loop) CLID standard:

Modem Compatibility
Getting the CLID to appear on a computer screen in the UK is possible, but very difficult. For a more thorough run-through of other countries see Caller ID FAQ #18 for analogue modems & Caller ID FAQ #19 for ISDN.

With UK Cable Companies, an ordinary modem that supports Bellcore CLID may work, but will need to handle the slight differences between the Cable standard & true Bellcore. No further info is currently available.

There are just 3 modem manufacturers that have ever supported UK BT CLID. One has gone out of business, one in to Chapter 11 bankruptcy & the third is ignorant of its modem's capabilities in this area. Sigh.

With ISDN, Caller ID is available on the analogue ports of the BT Home Highway box, and on the digital lines of Business Highway. There have been reports of people getting a BT engineer to add it to Home Highway unofficially.
Software Compatibility, TAPI & TSAPI
Having somehow persuaded the Caller ID info to be collected by the modem hardware it will then be necessary to have software that can decrypt and use it when the phone rings. There are two aspects to this
  1. The Operating System (OS)
  2. The Communications Software
1 The Operating System (OS) The modem will present CLID info at the Communications (COM) port. If this is all that the COM port is being used for - essentially as an answering machine - that is fine, but usually the modem is also wanted, as just one example, to be able to browse the internet. However, if a CLID program is set to listen for the modem directly on it's COM hardware that port will be fully occupied by the software & unavailable for use by anything else. This is a common OS problem and is properly handled by a piece of OS ‘middleware’ which will itself listen at the COM port and also broker requests from the various programs which want access to the port. Next, the modem drivers need to be aware of this middleware, and direct their system calls to it rather than directly to the hardware. As a footnote, Microsoft seem to be repeating their experience of Windows 95 with Windows XP, but in a different way. Windows 95 was a horrible hybrid of 16-bit & 32-bit software produced to kill off DR-DOS (it succeeded in this) by “integrating” MS-DOS into the GUI (Windows 3.1) software. Then, incidentally, Windows 98 was produced to kill off Netscape (it effectively succeeded in this) by “integrating” Internet Explorer into the OS. Windows 95 was an abortion of an operating system which finally got (mostly) useable by 98 & moderately good by Windows 98 Second Edition (three tries, just like Windows 3.1x). Then they tried to get rid of the 16-bit software (DOS) by hiding it (Windows Me) and then finally with Windows XP, a true 32-bit OS, which tries to kill off everything else by integrating everything into the OS - cynical, sorry. Critical Updates are appearing on the Windows Update site at a rate of knots as Microsoft attempt to fix all the problems found with XP, just like 95. Give them another couple of goes - and probably 10 years in total - and Windows may be a decent OS.

2 The Communications Software See Caller ID FAQ #26 & Caller ID Software for more info. I've had a quick look at Wave Caller-ID but cannot offer any reviews.

Troubleshooting
This will concentrate on modem aspects and will assume that CLID is being received at the modem.

The simplest way to check is with Talkworks Call Display (FTP 743 KB) (win95/98/Me) - a piece of Freeware from Symantec which gives a popup window to tell you an incoming number (this utility no longer links anywhere from the Symantec site). If this works, everything is fine. If not, it will be necessary to check directly at the modem: