There are 20 ring groups and they can all be used in any order (groups 11 to 20 are slightly different to the other groups).
The groups allow you to organise your extensions e.g. the extensions you want to ring when someone calls you can all be put into a group and the system can be programmed to ring this group when someone calls.
The number of extensions programmed in each group can be from a single extension up to 15 extensions.
In default, group 1 is programmed with extensions 201 to 207 and all the other groups are programmed with extension 201 only.
All groups must be programmed with at least one extension. The default ringing setting is for all lines to ring group 1 when someone calls you, so extensions 201 through to 207 will all ring if they are free.
Each group is given a number on the system (similar to how each extension is given a number), group 1 is 180, group 2 is 181 and so on until group 20 is 199. So, on a defaulted system if an extension dials 180, extensions 201 through to 207 will ring if they are free. If an extension dials 194, extensions in group 13 will ring if they are free (in default this would be extension 201 only).
DDI numbers can be programmed to ring a group. The group can be set up with the extension(s) you want to ring when someone calls the DDI number.
If a group has a mailbox enabled, extensions in the group can divert calls for the group using the Group divert feature to the mailbox (divert all calls, divert on busy and divert on no reply). The mailbox number for the group is the same as the group number (180 to 199).
As mentioned previously groups 11 to 20 have an additional feature. These are used to allow single digit dial though of auto attendant.
Further information can be found in the BT Quantum Administrators Guide.