Porting reality – the real deal behind UK telephone number portability

A porting primer for users of UK geographic and non-geographic telephone numbers

All UK numbers are issued in ranges by Ofcom to Communication Providers (CPs). Numbers generally begin ‘0’, and ranges are generally of 10,000 numbers, but certain numbers are issued in ranges of 100,000 numbers and some of 1,000 numbers. Numbers beginning ‘1’ are issued individually. Upon receipt of a number allocation, the CP becomes responsible for arranging the termination of all calls made to numbers in that range.

CPs choose, and may change, the chargeband applicable to each range that they hold, with the exception of numbers beginning 01,02,03 and 080.

 CPs arrange for ranges to be terminated by a network operator (NO). They may be a NO themselves (such as Syntec), or a CP (e.g. Vonage)  arranging for their numbers to be hosted by a NO (e.g. Gamma).

 CPs assign individual numbers (or blocks of numbers) to number-users.

 There are nearly 600 range-holding CPs in the UK and approximately 100 network operators who terminate ranges from the UK PSTN. The number of the former is increasing and of the latter decreasing.

How do calls get connected, and what changes when a number is ported?

The originating CP needs to get a call to the terminating CP. It does this by looking up the NO (not CP)  associated with the number-range within which the dialed number falls, and then routing the call to the relevant NO. If the originating CP has an interconnect with the target NO, it will most likely send the call direct to that NO. If it does not, it will send the call to a transit NO, preferably one that has a direct interconnect with the target NO. BT Wholesale is required by regulation to act as a transit NO to all other UK NO’s, and to charge rates for so acting which are regulated by Ofcom. The other major transit NOs in the UK are Vodafone Fixed Line and Virgin Media Wholesale.

When a number is ported, responsibility for terminating calls to that number is transferred from the range-holding CP (the exporter), to the gaining CP (the importer). A porting agreement needs to exist between the exporter and the importer, and a number portability transit path needs to exist between the NO by whom the range is built on behalf of the exporter, and the NO by which calls to the ported number are to be received on behalf of the importer.

In the UK, one of the earlier countries to introduce number portability, it was decided that it was too complex and expensive for the originating CP or NO to be expected to have knowledge that a number had been ported, or by whom it had been imported. Therefore all calls to ported numbers are still sent to the range-holding CP’s NO, and then forwarded on by the exporter’s NO to the importer’s NO.

So what’s the problem with ported numbers?

So whilst the number user of a ported number will now deal with the importer for incoming call management and accounting, there are two major drawbacks:

  1. All calls to the ported number will have to pass through the exporter’s network as well as the importers network (although the exporting NO and CP has lost their commercial benefit in carrying those calls). In the event of a fault, particularly an intermittent or quality-of-service fault, the number user may find it impossible to determine whether the exporter or the importer is the cause of the fault, and if the importer insists that it is the exporter that is responsible, no-one has any commercial leverage to cause action.
  2. Unless the number is at a fixed chargeband (01/02/03/080), the chargeband for the number will continue to be controlled and potentially changed by the exporting CP, but the exporter has no obligation to provide advance warning to the importer about such changes (unless such warning is negotiated in addition to the industry standard porting agreement), and so the number user risks commercial disadvantage and risks mis-advertising of call costs and resultant regulatory transgression.

On-porting or re-porting a ported number

When a number is supposedly on-ported, i.e. responsibility for termination is transferred from the importer to a third CP, readers should note that what actually happens, both from a commercial and a call-flow perspective, is that responsibility for call termination is firstly passed back from the old importer to the exporter, such that the original porting is canceled, and then a new porting is set up from the exporter to the new importer. Number users should note that the gaining CP must have a porting agreement with the exporting CP, which will only be the same as the losing CP if the number has never been ported.  

Depending on the efficacy of the CPs and NO’s systems and networks involved, there are obviously potential delays in on-porting, and the number-user needs to have arrangements in place for the exporter to handle calls mid-process. This may be difficult to arrange as the period of service could be anywhere between a few minutes and a coupe of days, and the exporter clearly has no commercial incentive to assist. If the process goes wrong, there are potentially six organizations where something has gone wrong (exporting CP, exporting NO, losing CP, losing NO, gaining CP, gaining NO), with only two of which the number-user will have a current commercial relationship. Also, remember that the gaining CP and NO may have no agreement at all with the losing CP and NO.

And what about migrations, IPExchange?

The IPExchange platform operated by BT Wholesale can add to the confusion over porting, as it doesn’t follow the same rules as the rest of the industry. In summary, ranges hosted on the IPExchange platform are treated as belonging to BTW, not the range-holding CP, for the purposes of exporting. Similarly, numbers to be imported onto IPExchange are imported (from the exporting CP’s viewpoint) by BTW, not by the gaining CP. In both cases BTW (wearing its unregulated hat) is the NO as well as the CP.

In complete contrast, for a number-range migration, termination for an entire Ofcom-allocated range is transferred from one NO to another NO. The range is normally only transferred from one CP to another where the CPs are the same as the NOs, and the range is being used exclusively for a big organization such as a government department or major corporate. In this case all the NOs change their data-builds and after the migration, all calls are sent to the new NO, and the old NO ceases to have any involvement with the range.

So what are the alternatives?

Syntec does not normally encourage the use of number portability. We would usually recommend that numbers are retained with or returned to the original range-holding CP and then calls are delivered to target numbers provided by the gaining CP. Where appropriate number change announcements may be used to migrate traffic to new numbers with an eventual withdrawl of service, or the original numbers may be retained in use indefinitely. Whilst this arrangement leaves the number-user dealing with more than one CP, it does ensure total traceability in the event of faults – if the fault persists when calls are made to the target number, the fault lies with the gaining CP; if the fault only registers when calls are made to the original number, then the fault lies with the range-holding CP. And the number-user will have a commercial relationship with both CPs, so should be likely to get prompt attention to the fault as well.

 Syntec does not consider that it would be commercially viable for a firm of its size to establish and maintain porting agreements with the near 600 UK communications providers, and so has chosen to work with two of the largest UK CPs to provide importing facilities. Where number-users insist upon actual importing of numbers to Syntec, and quality and reliability is key, we use tdm-based porting arranged by Virgin Media Wholesale. This has proven unusually robust, but is not as competitive a solution as IPExchange, which is our preferred solution for cost-sensitive imports.

 Since formation in 1998, Syntec has not yet been required to export any of its numbers, but will establish a porting agreement with any UK CP where a number-user requires it, as is required by statute.

 These notes do not apply to some mobile numbers (generally those operated by O2, Vodafone, Three and BTM (which was EE, which was Orange and T-mobile)) where industry arrangements extend beyond those described above.

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