blocking scam calls

[#1]

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@paul_blitz wrote:

Do you ever get false positives? Or does your 'whitelist' generally stop that?

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Not that I know of. My familiy used to moan a lot when CLID didn't work, as they had to go through the screening process.

[#2]

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@Townman wrote:
All calls carry an originating CLI which might not be the Dane as the display (presented) CLI. These ought to raise alarm bells.

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Many genuine companies set up their systems so that any call presents the main switchboard number rather than the direct dial the call is made from, so that would create issues.

[#3]

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@orrery wrote: Many genuine companies set up their systems so that any call presents the main switchboard number rather than the direct dial the call is made from, so that would create issues.

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No issues at all.  The requirement is that the presented (displayed) CLI be a valid dialable number.  The presented CLI and the calling CLI being different should be a trigger for double checking that the presented CLI is a valid dialable number.

Given that this is an Ofcom requirement ... it is clearly not seen as an issue in the described circumstances.

See Statement: Guidelines for Calling Line Identification Facilities - Ofcom

"...we introduced a new General Condition (GC) C6 which requires Communications Providers (CPs) to provide CLI facilities, and ensure that the CLI Data provided with a call includes a valid, dialable telephone number which uniquely identifies the caller"

The detail in the referenced PDF is very interesting too...

• C6.2 Regulated Providers must provide Calling Line Identification Facilities, and enable them by default, unless they can demonstrate that it is not technically feasible or economically viable to do so.
• C6.3 Regulated Providers must inform Subscribers if Calling Line Identification Facilities are not available on the service they are providing to those Subscribers.
• C6.4 When providing Calling Line Identification Facilities, Regulated Providers must:
  • (a) ensure, so far as technically feasible, that any CLI Data provided with and/or associated with a call includes a valid, dialable Telephone Number which uniquely identifies the caller; and
  • (b) respect the privacy choices of End-Users.
• C6.5 Regulated Providers must not charge Subscribers any additional or separate fee for access to or use of standard Calling Line Identification Facilities.
• C6.6 Where technically feasible, Regulated Providers must:
  • (a) take all reasonable steps to identify calls in relation to which invalid or non-dialable CLI Data is provided; and
  • (b) prevent those calls from being connected to the called party, where such calls are identified.

It is quite evident that many CPs are failing to comply with GC C6 in full which has been a requirement since October 2018.