GC C6: CLI Update



1st March 2019

by Ross McKillop

As those of you who attended SimCon will know, there’s been a few issues around General Condition C6 and the inconsistent interpretation of it across many CPs in the face of ambiguous guidance by Ofcom.

This came to the fore when receiving numerous complaints of the 08979 number being presented to the called party, largely by EE. Ignoring the fact that, as per the NICC Standard ND 1016, largely unchanged for 15 years, the Network Number (whether 08979 or anything else) should never be presented to an end user, this led to a tangential debate about the ‘correct’ use of the 08979 “Inserted Network Number”.

The Ofcom guidance states this was to be used where the CP doesn’t “reasonably trust” the CLI Data being provided, or where it’s not available, one example given of this is where a call originated from abroad.

The same guidance requires that “The Network Number must be one that has been allocated to the originating CP or a number that has been imported into their network” – this seems pretty unambiguous. We can only present numbers on our network as a Network Number.

However, Ofcom have since advised that the intention of the 08979 range was for it to be used only for calls originating internationally, although the guidance doesn’t reflect this. In any event, we find a number of networks (contrary to published guides and NICC standards) occasionally display the Network Number to the called party rather than the Presentation Number, resulting in a bad experience for the end user either because they see an unexpected number or, worse, the 08979 range which should never be visible to the public.

We also know it’s not just us, and this isn’t only affecting our customers! We published an article about 08979 to inform the public, and subsequently have received numerous enquiries about calls from other 08979 numbers – not those allocated to Simwood – and therefore have a good indication of other CPs experiencing the same issues.


As a result of this, today we’ve disabled some of the CLI rewriting measures on routes to networks where we know this is an issue, and as any more become apparent we will do the same.

As a result, if you’ve forwarded a call that originated from Vodafone (for example) and sent the Vodafone CLI over the Simwood network for onward termination, we’ll pass that call on with a Vodafone Network Number. We believe this completely at odds with the spirit of the rules, the effort to reduce consumer harm through CLI spoofing, and deprives us of the opportunity to provide useful information to other Communications Providers regarding the origin of the call by means of the Network Number as, for all intents and purposes, that call will have appeared to have originated from Vodafone.

We strongly believe our interpretation, and one that is shared by many other CPs, actually provides a more tangible benefit and achieves the aim of ensuring that the origin of calls can be identified and ultimately furthers the goal of reducing consumer harm from nuisance calls and spoofed CLI.

That, however, would require other operators to care about it.

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