Charge group

From aa-asterisk.org.uk wiki

Each 01/02 geographic code is allocated a charge group, which is a nominal geographic place that the call is deemed to have originated for charging purposes. In the days of local, regional and national pricing, the charge group of a given dialling was used to work out what rate to charge.

When the Post Office designed the system, each charge group was placed so as to be approx 20 miles away from adjacent charge groups. This explains why some seemingly small places were allocated codes of their own even though this was not strictly necessary. However the system made it easy to work out how to price a call:

• Calls made to codes in the same charge group were always priced at local (L) rate, e.g. 01446 to 01446
• Calls made to codes in an adjacent charge group were always priced at local (L) rate, e.g. 01420 to 01256
• Calls made to codes which are 2 charge groups away from your charge group were priced at regional (a) rate, e.g. 01420 to 01483
• Calls made to any other charge group from your charge group were priced at national (b or b1) rate, e.g. 020 to 0121

These days retail tariffs tend to be charged at a flat rate regardless of the distance between the caller's charge group and the callee's charge group, but BT Wholesale still charge different rates to their wholesale customers depending on how many tandems the call needs to go through.

Note that it is not always the case that exactly one code is assigned to exactly one charge group. In some cases, multiple codes are assigned to one charge group (e.g. 01344 and 01276 are both part of the Ascot charge group), and in other cases multiple charge groups are assigned to one code (e.g. 023 covers both Southampton and Portsmouth charge groups, and 028 covers all of the charge groups in Northern Ireland.)

See also

• Area code
• Number format
• S-Digit
• F-Digit
• 0SABCDEF
• ELNS areas
• Mixed areas
• 01 numbers
• 02 numbers
• Conservation Area
• E.123
• Sabc.txt
• National Telephone Numbering Plan
• Regular Expressions for Validating and Formatting GB Telephone Numbers
• Local dialling rules for GB telephone numbers
• Errors in Cisco UK Numbering Plan Documents

External Links

• List of charge groups - there's the odd piece of out-of-date data and a few typos. Most problems are fairly obvious.
• Oftel's 2003 Users Guide to Numbering - The system is explained reasonably well around pages 7 to 10.