On Jan 25, 2008, at 6:05 AM, Stephane Bortzmeyer wrote:
On Fri, Jan 25, 2008 at 10:42:44AM +0000, Roland Perry <lists@internetpolicyagency.com> wrote a message of 15 lines which said:
in the UK it [phone number portability] 's done with something similar to DNS. The telephone system looks up the first N digits of the number to determine the operator it was first issued to. And places a query to them. That either causes the call to be accepted and routed, or they get an answer back saying "sorry, that number has been ported to operator FOO-TEL, go ask them instead".
What happens when a phone number is ported twice, from BAR-TEL to FOO-TEL and then to WAZ-TEL? Does the call follows the list? What if there is a loop?
The solution you describe does not look like the DNS to me. A solution more DNS-like would be to have a root (which is not an operator) somewhere and every call triggers a call to the root which then replies, "send to WAS-TEL".
There is a shared root in the US SS7 system. The security of said root follows a rather interesting model. At least until fairly recently, any "trusted" carrier (LEC, ILEC, RBOC, or IEC) could put pretty much whatever they wanted into the database. Of course, the consequence of getting caught with your hand in the cookie jar there was sufficient that it tended to prevent invalid entries other than by accident, but, still, it was a remarkable trust model for such an industry. Owen