Number portability¶

Table of contents
Number portability

General informtion¶

Number portability — is a feature to allow completely preserve owned telephone number, including prefix, after changing telephony provider.
Usually number portability is relevant to mobile subscribers (mobile number portability, MNP).

Along with the spread of mobile telephony, developed the idea that subscriber should be able to preserve his telephone number after moving to a different operator.
It was believed that it would make competition between operators stronger.

Thus from the end of 1990s — start of 2000s in many countries, starting from UK and Netherlands, a requirement for operators to provide number portability on customer request has been introduced.

This requirements differ in different countries.
In some countries one can port number only in the boundaries of his region.
Almost nowhere (besides USA and Canada) a landline number couldn't be ported to mobile and vice versa.
A number portability procedure could be free of charge according to law or could require paying commission, and could last from several minutes to several days.

Difficulties¶

Provision of number portability could be a technically complex task.
To originate a call, one need to know where to direct it.
Telephony numbers are usually allocated by large blocks, thus by number one can determine operator, which should accept a call.
In case if number has been ported, it becomes harder to determine operator.
This complicates not only routing, but also a calculation of call cost (billing).

Also process could cause additional difficulties on subscriber's side, connected with that it's became harder to determine, to which operator belongs dialled number, and, due to that, it's harder to determine the cost of planned call.

Solutions¶

A task of routing the ported numbers is solved by different ways.

All calls could be directed to a common center with common database of all phone numbers.
Calls could be directed to «standard» route.
The accepting operator either accept a call, or responds, that number has been ported, and then a query to central database is done.
Calls could be routed to standard route.
The accepting operator checks the number, and if it's ported, then tells a new route for it.
In this case a centralized database is not needed.