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- └────────┬─────────┘ ║ File 33 ║ └─────────┬────────┘
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- └────────────────║ UK Telephone System ╟────────────────┘
- ╚═════════════════════╝
-
-
- Telephone services in the UK are provided by the following
- organizations:
-
- British Telecom
- Mercury Communications
- Hull Telephone Company
- Vodaphone
- Cellnet
-
- For historical reasons, BT allocates area codes. This will change in a
- couple year's time.
-
- The bottom level of the BT system is the "Junction Exchange" (JX in
- this document). A JX is a unit which handles 10,000 subscriber
- numbers, numbered 0000 to 9999. A number may have several lines
- attached to it (hundreds in some cases). These four digit numbers are
- called LNs (Line Numbers) in this document.
-
- In a few rural areas, some subscriber numbers are three digits. The
- appropriate JX thus takes some LNs as being three digits, and some
- (possibly none) as four. Such JXs are being phased out. [This should
- be distinguished from the case where all LNs in a group of ten go to
- the same subscriber, and are interconnected. For example, Basildon
- hospital officially has the LN 2811. In fact, all of LNs 2800-2899 go
- to the hospital switchboard, and the JX will route the call as soon as
- it sees "28".]
-
- JXs are grouped into "Area Codes" (AC). Each JX has a one or two digit
- number within its AC - one digit numbers are being phased out. The
- exception is in "all-figure areas", where each JX has a three digit
- number. These numbers do not begin with 0 or 1.
-
- Each area code has a number. For most area codes, this is three
- digits, but for all-figure areas, it is two digits.
-
- The "number-space" for area codes is used as follows. All normal area
- codes begin with a digit from 2-9. The area codes for the all-figure
- areas are:
-
- Birmingham 21
- Edinburgh 31
- Glasgow 41
- Liverpool 51
- Manchester 61
- London inner 71 (new)
- London outer 81 (new)
- Tyne & Wear 91
-
- Of the 720 three-digit codes, about 600-650 are in use (I do have a
- complete table in numerical order, but it's not in machine-readable
- form). Certain codes have special meanings:
-
- 345 Calls charged at L rate irrespective of distance
- 482 Hull Telephone Company
- 800 Free calls
- 831 Vodaphone
- 836 Vodaphone
- 839 Calls charged at m rate irrespective of distance
- 860 Cellnet
- 898 Calls charged at m rate irrespective of distance
-
- Mercury has been allocated fifteen JXs in the 71 AC and the same
- fifteen in the 81 AC. I believe that all Mercury subscribers have
- numbers in this AC, irrespective of location.
-
- Area code 1 was used for London (both inner and outer) until 0001 on 6th May
- 1990; I am unaware of any plans for it. Area code 10 is obscured by the
- international access code. No area codes begin with 0 (but see below).
-
- From any BT subscriber, you can call any number by:
-
- 0 + area code + JX number + line number
-
- For example, anyone can call me by 0-954-78-0223. In addition, there are
- certain special codes:
-
- 010 international access
- 0001 equivalent to 010 350 1 [Dublin]
- 0055 from London only; calls charged at L rate
- 0066 from London only; calls charged at a rate
- 0077 from London only; calls charged at m rate
-
- Service codes begin with a 1:
-
- 100 operator
- 144 BT credit-card calls
- 151 fault reporting
- 153 international directory
- 155 international operator
- 192 directory
-
- Area codes are further grouped into "Charging Areas" (CA). For example:
-
- London CA: 71, 81
- Cambridge CA: 220, 223
- Madingley CA: 954
-
- The exception is the Tyne and Wear AC, which is three CAs (JXs [24]??,
- JXs 3??, and JXs 5??). This AC replaced three separate ACs (whose
- numbers I have forgotten), each of which had its own CA.
-
- BT has five charging rates for UK calls, and seven for international.
- The UK rates, in increasing order of cost, are L, a, b1, b, and m (m
- is more expensive than I, which is the cheapest international rate).
- Rates also vary by time:
-
- peak = M-F 0900-1300
- standard = M-F 0800-0900 and 1300-1800
- cheap = all other times
-
- (these do not apply to international calls).
-
- All calls within a CA are at rate L, as are those to "neighbouring"
- CAs. Each CA has a nominal centre. For all other calls, if the CA
- centres are within 56km, the call is at rate a, and otherwise it is at
- rate b. Rate b1 replaces rate b where BT feels under pressure from
- Mercury (London CA to Cambridge CA is b1, but to Madingley CA is b).
- Rate m ("mobile") is only used for calls to Vodaphone, Cellnet, and
- the special area codes. Hull is treated as a normal CA. Calls from BT
- to Mercury are charged as normal calls to the London CA.
-
- The real complications (you thought this wasn't enough ?) come when
- dialling calls other than by the full 0+ sequence. For this you need
- to know the subscriber number (SN).
-
- The one simple case is the all-figure areas. For each area, lines
- within the area are identified by seven digits (JX+LN), and calls are
- made by just dialling this number [in Tyne and Wear, calls *between*
- ACs must be prefixed with 90; this is being phased out].
-
- Everywhere else, we run into the "Named Exchange" (NE). An NE
- comprises a set of JXs, usually, but not always, in the same AC. A
- subscriber is identified by an exchange name followed by the SN, which
- is the LN with a prefix. The prefix can be empty, the last digit of a
- two digit JX, or the JX number. A catch to beware of is that sometimes
- two NEs have the same name but are distinguished by number length. For
- example, there is "Welwyn (six figure numbers)" and "Welwyn (four
- figure numbers)". These cover the same geographical area, but may have
- different ACs (these two don't). They are always in the same CA.
-
- As an example, the Madingley CA consists of:
-
- AC JX NE Prefix
- 954 78 Crafts Hill 78
- 954 21 Madingley 21
- 954 3 Swavesey 3
- 954 6 Willingham 6
- 954 5 Cottenham 5
- 954 4 Caxton (4 digits) none
- 954 71 Caxton (6 digits) 71
- 954 7 Elsworth none
-
- Calls to CAs other than at rate L are always dialled by the full 0+
- method. To call a subscriber on the same NE, it is just necessary to
- dial the SN. Other calls within the CA, and to CAs which are at the L
- rate, may have an alternate dialling method (not necessarily:
- Madingley to Huntingdon is rate L, but 0+ must be used; all calls from
- AC 71 or 81 to any other (or each other) must be dialled as 0+).
-
- Two alternate methods seem to be in common use: the "fan" method and
- the "slave" method (my names).
-
- The "fan" method is used at the main NE of a CA. Several prefixes in
- its AC are not used, but instead become dialling codes from the NE.
- For example, from Cambridge:
-
- 8 -> AC 220 (same CA)
- 91 -> AC 440 (different CA)
- 92 -> AC 767 (different CA)
- 93 -> AC 954 (different CA)
- 94 -> AC 638 (different CA)
- 95 -> AC 763 (different CA)
- 96 -> AC 799 (different CA)
- 98 -> AC 353 (different CA)
-
- These are then followed by the JX and LN. All other NEs in the same AC
- (not the same CA) can be called by dialling the JX and LN with no
- prefix (there are no cases of this in AC 223).
-
- [Amusing side-note. Someone blew it in specifying 8 -> AC 220. The JXs
- that were in AC 220 (21, 23, 24, 26, 27, 29, 5) did not occur in
- AC223. So there was actually no need for the dialling code. All of
- these except the last two have now been moved to Cambridge NE (and AC
- 223) by simply changing the SN, without changing the JX+LN
- combination. The others will come soon (I have already seen people
- using "Cambridge 29xxxx" phone numbers).]
-
- The "slave" method is used at all other NEs in the same CA, and
- possibly in other CAs (All of Madingley CA is a slave of Cambridge NE
- in this sense). Calls to the master NE are made by dialling a single
- 9 followed by the SN. All calls which are rate L, and which could be
- made from the master NE with a dialling code, are made by dialling 9
- followed by the sequence from the master NE.
-
- For example, from ACs 220 and 954, the following dialling codes exist:
-
- 9 -> AC 223
- 9+8 -> AC 220 (also used from Teversham (220 5) to West Wratting (220 29))
- 9+91 -> AC 440 (not available from AC 954)
- 9+92 -> AC 767
- 9+93 -> AC 954 (also see below)
- 9+94 -> AC 638 (not available from AC 954)
- 9+95 -> AC 763 (not available from AC 954)
- 9+96 -> AC 799 (not available from AC 954)
- 9+98 -> AC 353
-
- In addition, a slave NE may also have other dialling codes not
- beginning with a 9. For example, in AC 954, to dial from Caxton (six
- digits), Cottenham, Crafts Hill, Madingley, Swavesey, and Willingham
- to any number in the AC is done by JX+LN, without any code. On the
- other hand, to dial from Elsworth to Caxton (four digits), or vice
- versa, the route via Cambridge must be used (i.e. 9+93+JX+LN).
-
- One final note. Slave exchanges have operator service provided by the
- master exchange. This means that emergency service is "9+99". On
- master exchanges, it is thus simply "99" (! for UK readers).
- -JUDGE DREDD/NIA
-
- [OTHER WORLD BBS]
-