Talk:Director telephone system

STD section
I think the page content concerning the STD system should be moved to the STD page. Denham062 2007-01-04T04:32:04 (UTC)


 * Agreed and implemented. Kbrose (talk) 19:41, 1 May 2013 (UTC)

Beta Working and hypothetical working
Sorry - I don't know where exactly to add this section. I only have experience / knowledge of the London system.

Beta working was used, for example, on Highams Park exchange in the 1980s. The code translation for 523 was the same as for 527 plus a 9 and the 9 stepped out on the first numerical selectors of the 527 block. Thus dialling 523 1234 was theoretically the same as dialling 527 91234. This 8 digit number wouldn't have worked within the London director area, because the system stored the first seven digits dialled, but from outside that area (maybe not from anywhere) I believe it would have worked if one dialled 01 527 91234 instead of 01 523 1234. I seem to remember testing it. Maybe someone with better knowledge than me could verify, but as the registers had to cope with cope with 9 digits after the 0 it worked.

Hypo working was when more than one code was provided with the same translation. This was deployed for 598 (either Goodmayes or Seven Kings exchange - they shared the same area) and for 709. 709 worked hypothetically on 220 in the mid 1980s. Thus dialling 220 1234 or 709 1234 produced the same results. I assume this was so that 709 could be later worked normally without number changes for those subscribers allocated 709 numbers. I can see that this would be useful for introducing a DDI range with its own code, or for working a code out of area pending a new exchange being brought into service.

[709 1234 (= 220 1234) used to ring out in my office in Docos House - a BT office building in Aldgate. We used to get calls in error for Islington Council which had 226 1234, presumably because of badly printed/written 6s looking like 0s, and also for 222 1234 - London Transport (now TfL), plus the inevitable minicab firm.] — Preceding unsigned comment added by 81.108.89.77 (talk) 16:56, 24 May 2014 (UTC)

What you are calling Hypo working was probably down to economics. For example in Birmingham there was little overlap on level 3 and level 9 so that with careful allocation of codes you could use the same BC switch for these levels which they did in Birmingham. So the translation for 385 was the same as 985. You saved space and equipment. I can't remember any other "economies" in Birmingham and I have no knowledge of other Director areas. I would love to get hold of translation lists for the Director areas. 86.27.29.50 (talk) 18:37, 4 July 2017 (UTC) G1CBK

Lead Section
I started my telecoms career in Birmingham so I am familiar with the Director system. The first paragraph actually describes why tandem exchanges were used. The real reason for using Directors was the need to keep the exchange codes the same wherever the exchange was. A Director system is just a very large linked numbering scheme.

In a Non Director linked numbering scheme the code shown was the routing digits in the case of Dudley charge group level 1 were services, 2 was Dudley, 3 and 4 were available, 5 was Dudley, 6 was Cradley Heath, 7 was Brierley Hill, 8 was available, 9 had limited availability (99 was reserved for 999) and 0 was STD. Kingswinford numbers also started with 7 so there was a prefix needed to dial to or from Kingswinford. Levels 3, 4 and 8 had ten numbers and 9 had nine. That's thirty nine codes available, but by putting a second selector on a level, say 4, increases that level from ten to a hundred codes. Kingswinford would dial 7 for local numbers but, as stated earlier, needed a prefix to dial other exchanges, especially Brierley Hill which also started with 7. There would be a small number of exchanges, twenty or so, in a linked numbering scheme.

Now if you have a large area that you want to group together a Non Director linked number scheme is too cumbersome. For a start London had over two hundred exchange codes in the seventies and Birmingham had close to a hundred. The number of routes needed, even with Tandems, was huge. So they came up with the Director system. Each exchange was allocated a three digit code and a four digit number. The three digit code is used by the Directors to work out the routing digits which could be up to six. Level 385 was Dudley, but it's routing digits would be different from each exchange. It was a local route from Blackheath, but would go through Tandems from others. There were four in Birmingham (Midland (levels 2,3 and 6), Selly Oak (level 4), Tipton (level 5) and Sheldon (level 7)). So a caller in Shirley would dial 559 for Blackheath and would be routed through Sheldon Tandem, Tipton Tandem and then to Blackheath. But would probably go direct if the same caller wanted Chelmsley Wood.

So the benefit of a Director system is that the routing digits are transparent to the caller who would dial the same exchange code no matter where they were in the Director area.

If it's agreeable then this explanation could be used or I would try and explain it better. 86.27.29.50 (talk) 17:40, 4 July 2017 (UTC) G1CBK