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Summary of findings

The key question addressed in this report is whether it is reasonable to ask operators to carry out finer digit analysis, thereby allowing numbers to be allocated in smaller blocks. This question is examined for geographic, non-geographic and mobile numbers and the answer, in each case, is that the wholesale implementation of finer digit analysis is possible but that this is not without consequence.

At the heart of this issue is the amount of available data decode resource. The allocation of smaller number blocks requires a deeper analysis of digits to route a call and this analysis consumes decode resource. All network switches have a finite decode capacity and, in the case of the long established System X and Ericsson AXE 10 systems, it is not viable to upgrade that capacity.

In order to establish the technical limits of installed network equipment and the extent to which finer digit analysis will likely test those limits, detailed input has been sought from operators. The bulk of this report is an analysis and discussion of the input received. Of particular relevance to the main question are the facts that:

• The available decode resource on both System X and AXE 10 switch (which represent the limit on finer digit analysis for both geographic and non-geographic numbers) is constrained and not extensible but is nonetheless adequate to support many more number conservation areas.
• The way in which decode resource is consumed in these two types of switch varies significantly with the majority of System X decode blocks used by local subscriber decode and the use of AXE 10 decode lines most affected by non-geographic ranges.
• This variation means that the ability to support many more conservation areas could quickly be compromised by other regulatory measures that compete for data decode resource. In particular, the way in which AXE 10 decode is organized make it vulnerable if there is an expansion in the use of non-geographic numbers. The most pressing limit on System X switches appears to be the availability of the destination categories used to select an appropriate path once decode is complete.
• The decode space available to mobile network operators poses no barrier to the allocation of smaller number blocks but the attendant requirement to analyse an extra digit of the dialled number would require time so that foreign operators are made aware of the change in the UK plan.

Given the above, it is clear that there is no overarching technical reason to limit the introduction of finer digit analysis. However, because number conservation is not insulated from other regulatory measures, the utilisation of decode resources needs to be managed as a whole. The fact that there is a different sensitivity to particular changes between the installed network equipments underlines the need for this. A regular audit of the cumulative effects of regulation is therefore recommended as a sound basis for overall policy.

The full document is available below:

• Finer Digit Analysis of Telephone Numbers for Routeing Purposes [pdf]
  Full print version (149 Kb)

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