Statement: Guidelines for Calling Line Identification Facilities

Published: 19 September 2017
Consultation closes: 14 November 2017
Status: Closed (statement published)

Statement published 26 April 2018

Calling Line Identification (CLI) data consists of a number that identifies the caller and a privacy marking, which indicates whether the number can be shared with the recipient of the call. It can give the recipient of a call information about the party making that call. CLI Data can also be used for other functions, such as call tracing to identify the sources of nuisance calls or as a reference to help identify the location of a caller in emergency situations. For this to work effectively, the CLI Data must be accurate.

In Autumn 2017, 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. We also published a consultation on changes to the CLI guidance to reflect the new requirements in the GC.

Following responses to this consultation, we have updated the guidance on CLI facilities. The updated guidance document clarifies the definition of a valid and dialable CLI for CPs in different parts of a telephone call, based on what is technically possible today. Originating providers are responsible for ensuring that accurate CLI Data is provided with a call. Transit and terminating providers are expected to check that the number provided with a call is from a valid number range. For calls that originate on a network outside the scope of these requirements, the CP at the first point of ingress is responsible for ensuring that the call is populated with valid CLI Data, replacing the information with a number that has been allocated to them for this purpose where the original number is not valid or is missing. The updated guidance also clarifies the options available to CPs to prevent calls with invalid or non-dialable CLI from being connected to the end user.

To support these recommendations, we have made numbers in the 08979 range available to allocate to CPs to use as inserted Network Numbers where no number is present or they suspect that the incoming CLI is not reliable.

Update 30 July 2018

In April 2018, we consulted on further changes to the guidelines for CLI facilities. The revised guidance on the provision of CLI facilities and other related services (PDF, 296.7 KB) will apply from 1 October 2018, the same date that the new General Conditions come into effect.

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Jill Faure
Riverside House
2A Southwark Bridge Road
London SE1 9HA
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