U.K. regulator issues new rules to block spoofed calls

November 16, 2022

Ofcom, the UK regulator for communications services, instituted new rules designed to identify and block spoofed calls. It also updated its guidance for how service providers should work with Calling Line Identification (CLI) data. Let’s have a look.

Ofcam rules make frequent references to “CLI.” This acronym stands for Calling Line Identification, or Caller ID.

Rules modification

The modified rules appear in General Condition (GC) C6.6. (Changes highlighted in yellow.)

Current GC C6.6	Modified GC C6.6
Where technically feasible, Regulated Providers must: take all reasonable steps to identify calls, other than calls to Emergency Organisations, in relation to which invalid or non-dialable CLI Data is provided; and prevent those calls from being connected to the called party, where such calls are identified.	Where technically feasible, Regulated Providers must: take all reasonable steps to identify calls, other than calls to Emergency Organisations, in relation to which the CLI Data provided is invalid, does not uniquely identify the caller, or does not contain a Telephone Number that is dialable; and prevent those calls from being connected to the called party, where such calls are identified.

Current GC C6.6

Modified GC C6.6

Where technically feasible, Regulated Providers must:

take all reasonable steps to identify calls, other than calls to Emergency Organisations, in relation to which invalid or non-dialable CLI Data is provided; and
prevent those calls from being connected to the called party, where such calls are identified.

Where technically feasible, Regulated Providers must:

take all reasonable steps to identify calls, other than calls to Emergency Organisations, in relation to which the CLI Data provided is invalid, does not uniquely identify the caller, or does not contain a Telephone Number that is dialable; and
prevent those calls from being connected to the called party, where such calls are identified.

Here’s how the rule explains the phrase uniquely identifies the caller:

A number uniquely identifies the caller (which can be an individual or an organisation) where it is one which the user has authority to use, either because it is a number which has been assigned to the user or because the user has been given permission (either directly or indirectly) to use the number by a third party who has been assigned that number.

Here’s how Ofcam describes CLI in relation to Presentation Number and Network Number:

Where the Network Number and Presentation Number are the same, the number must be a valid number, which uniquely identifies the caller, and a dialable number. However, where the Network Number and the Presentation Number are different, then both numbers must be valid and uniquely identify the caller, however only the Presentation Number needs to be dialable.

CLI guidance

The CLI guidance sets out what is expected of providers for them to meet the requirements of GC C6. Here are the changes to the CLI guidance to accompany the changes to the rules:

Check that the format of a CLI is a 10- or 11-digit number
Use information that identifies numbers that should not be used as CLI
- Ofcom’s numbering allocation information
- The Do Not Originate (DNO) list
Identify and block calls originating from abroad that:
- Have an invalid or non-dialable CLI
- Are spoofing a UK CLI
Prohibit the use of 09 non-geographic numbers as CLI.

One might wonder how these guidelines handle legitimate calls to the UK originating abroad with a UK CLI.

The CLI guidelines address this with a reference to an industry standard, Guidance on blocking of inbound international calls with UK Network Number as CLI (NICC ND 1447).

The full statement describing the rules and guidelines is available at Improving the accuracy of Calling Line Identification (CLI) data – Statement on Changes

These rules and guidelines will come into force on 15 May 2023.

TransNexus solutions

TransNexus is a leader in developing innovative software to manage and protect telecommunications networks. The company has over 20 years’ experience in providing telecom software solutions including toll fraud prevention, robocall mitigation and prevention, TDoS prevention, analytics, routing, billing support, STIR/SHAKEN and SHAKEN certificate services.

This information will only be used to respond to your inquiry. TransNexus will not share your data with any third parties. We will retain your information for as long as needed to retain a record of your inquiry. For more information about how we use personal data, please see our privacy statement.