Calling Line Identification (CLI) facilities provide information to the recipient of a telephone call about the party making the call. CLI Data consists of the caller’s line identity along with a privacy marking, which indicates whether the number can be shared with the recipient of the call. It is exchanged between communications providers involved in the connection of the call and can also be used in regulatory and enforcement action, for example, to identify the sources of nuisance calls. CLI Data needs to be provided correctly and delivered across networks accurately. As individuals have the right to withhold their CLI to maintain their privacy, it is also important that CLI Data is passed on reliably so that the privacy of individuals can be respected.
General Condition C6 requires communications providers to provide CLI facilities, unless they can demonstrate that it is not technically feasible or economically viable to do so. Where CLI is provided, it must include a valid, dialable telephone number which uniquely identifies the caller. This document sets out guidance on how CLI Data should be carried through different networks and the responsibilities of different parties involved in the routing of a call. Its aim is to ensure that communications providers improve the consistency of CLI Data presented to consumers, whilst also complying with statutory requirements on the privacy rights of individuals making and receiving calls.