CLI-based routing

As we near the mandatory changes to CLI handling in October, we’re seeing an increased number of tickets relating to routing issues where certain CLI is presented, e.g. presenting a Mongolian mobile CLI on calls to a Mongolian number fails, whereas a UK CLI works.

We’re finding downstream carriers (well, some of them!) are implementing the necessary changes for October and taking opportunity to lock down CLI generally. Thus, in our example above, they’ll reject our call with a Mongolian mobile CLI because we are not a Mongolian Mobile provider.

That seems perfectly fair and reasonable but a number of our customers would argue it is legitimate that they originate a call with a Mongolian mobile CLI where, for example, they’re call forwarding. We warn on invalid CLI and expect CLI to be representative of the caller, but do not presently reject calls based on a number type policy. The result is calls fail across different carriers all of whom are responding with different error codes or in some cases rejecting the calls with plainly disruptive error codes.

Therefore, effective immediately, we are now filtering our outbound routes based on CLI patterns we’ve learned to be acceptable! Thus, a CLI that is anything other than a UK land-line or NANP number (for calls to North America) will take a different route through more tolerant / less organised carriers.

The ‘correct’ solution of course for the call forwarding examples above is to set the mobile number as the presentation number, and ensure that an appropriate UK network number is set also. Support for this, however, isn’t widespread, but we will support setting both these individually from October.

This blog post serves two purposes:

- Please consider CLI when investigating issues for your customers. If you are not setting valid and appropriate CLI on calls, you will have problems come October.

- The days of setting any CLI in the world on any call are coming to an end. We welcome the changes in October but we expect that, even with network numbers set, CLI will still be filtered to some destinations.

It’s worth noting that if unusual CLI results in our primary routes being excluded, then your call may travel over a higher cost route to ensure the call completes with the CLI presented. As our rates are based on our ‘normal’ routes this may result in some loss-making traffic which, if sustained, may activate automatic loss prevention.