3 Calling Line Identifier (CLI)

3 Calling Line Identifier (CLI)

3.1 Measures : Conditions of Use of the CLI as of August 1, 2019

a) Conditions of Use of a Number as a Calling line Identifier (CLI): The telephone number used as CLI or Message Sender ID must:

  • be in accordance with the structure of the National numbering plan defined in this Decision;
  • belong to a part of the plan that has been allocated by the Authority;
  • be attributed to an operator and assigned to a user;
  • allow, during the period of assignment or use of the telephone number, the user at the origin of the call or message, or the entity he represents, to be re-contacted.

In addition, where the recipient of a number is a separate person from the person wishing to use that number as a CLI or message sender, the use of that number as a CLI or message issuer must be previously authorised by the party to which this number has been assigned.

b) Territoriality condition: When the numbers used as CLI or message sender ID are geographical (01-05) or non-geographical (09) numbers, calls or SMS/MMS messages shall not be issued by end-users located outside the French territory or conveyed through an incoming international interconnection, unless the attributor, the depositary of the number or the receiving operator of the number after a porting (hereinafter referred to as the “operator of the number“) used as a CLI or message sender ID is able to guarantee, in particular to other operators, that the conditions of use defined above are respected, call-by-call and message-by-message. The exception allowing the operator operating a number to certify compliance with the conditions of use can be implemented now through VoIP solutions for which the operator is able to authenticate the calling user located outside French territory before routing his calls to other operators through its National interconnections. This can be applied for nomadic users on occasional trips abroad or for call centres located abroad wishing to make calls by presenting the number of their client. In the longer term, work on the so-called “STIR/SHAKEN” solution to deploy an interoperable trusted solution to prevent CLI or message ID sender spoofing could enable operators to fully benefit from the exception.

Role of Operators in Verifying the CLI

When an operator allows his customers to change the identifier of the caller or issuer presented to the called party, it is his responsibility to ensure compliance with the conditions of use and, where appropriate, territoriality for French numbers actually used as CLI or message sender ID. For this purpose, ARCEP recommends to operators who offer offers allowing customers to choose as a caller or issuer identifier a different French number than the number assigned to them for their telephone line:

  • to ensure, contractually and technically, that the use of the number chosen as CLI or message sender ID by an end user has been previously authorized by the assignor;
  • to be able, contractually and technically, to require the calling end-user at any time to always have the authorization of the number allocator to use as a CLI or message sender ID;
  • to be able, contractually and technically, to suspend without delay the service allowing the modification of the CLI or message sender ID to end-users who do not respect the conditions of use and, where appropriate, of territoriality.


Incentive for the insertion of the right of interruption for non-respect of the calling party’s identification in National interconnection contracts

In order for these rules to be applied effectively to protect consumers, it seems reasonable that are implemented very quickly, even in real time, by the operators on the networks on which the call and SMS / MMS message flows (hereinafter “message”) flow. Thus, ARCEP recommends operators who find that the conditions of use or, where applicable, territoriality are not respected for calls or SMS / MMS messages sent from their networks, transiting through them or terminated on their network. these, to take the necessary measures, for example by implementing on their network technical devices and by inserting clauses in their contracts, allowing them to interrupt their routing.

Incentive to the insertion of the right of cut for non-respect of the caller’s identification in international interconnection contracts

As regards in particular calls or messages received via an incoming international interconnection, ARCEP considers that the operators are a priori justified in interrupting the routing of calls or messages containing a geographical or non-geographic number as a caller or sender identifier, since these calls or messages do not respect the territoriality rule, that is to say, where there is no indication that the number operator (the successful tenderer, the depository or the receiving operator of the number) certifies that these calls or messages comply with the conditions of use. In this respect, the operators can in particular program their international interconnection equipment with default blocking rules for calls and messages comprising geographical and non-geographical numbers as call or issuer identifier.

Incentive to inform other operators of cut-off measures due to non-compliance with the CLI

In addition, in the event that an operator becomes aware of the use as CLI or Message Sender ID number of messages of which it is attributed or that it operates on behalf of one of its end users not satisfying the conditions of use or, if necessary, of territoriality, the Authority recommends to this operator to inform the other operators as soon as possible and invite them to take the necessary measures to stop this use for calls and messages sent from their networks, passing through them or terminated on them. In general, it is desirable that the operator who interrupts calls or messages concomitantly informs the operator who transmitted them to identify the origin of any malfunctions.

Incentive to inform ARCEP of the cut-off measures due to the non-respect of the caller’s identification

Finally, in order to allow the Authority to assess the implementation of these recommendations, it invites the operators to keep it regularly informed of the filtering actions that they implement in application of its recommendation, the filtered call volumes and their origin.

3.2 Implications

Regarding the conditions of use of a telephone number as a CLI, European countries can be classified into two categories: on the one hand the United Kingdom, which has always been very flexible on this issue; on the other, Germany, Switzerland, Austria, Italy, Spain and Portugal, which have always been much more rigorous in this area. With decision 18-0881, France, which until now had an attitude as flexible as the United Kingdom, takes a step towards the rigor of the continental countries. Nevertheless, the compromise reached to move from the previous regime to the new one requires operators operating a number to be able to answer complex questions that other operators might ask them:

  • Basic calls must be made by a user residing in the national territory and presented via a national interconnection to the recipient’s operator or his forwarder.
  • Basically, if the number presented is assigned to a third party in relation to the calling customer (or sender of the message), the originating operator must be able to prove that the third party has given his consent to the presentation of his number by the calling party.
  • If the call or message reaches the recipient’s operator via an international interconnection, the operator using the number presented by the calling party must be able to certify, call by call or message by message, to the recipient’s operator or to his forwarder, that the number is reachable in the event of a call back and, if the number is presented by a third party in relation to the client, that this assignor has given the authorization to this third party to present the number to his square.

In the absence of supply of such guarantees, the transit operators or the attributed operator are entitled to break said calls, provided that they inform the other operators and ARCEP.

The decision of ARCEP does not define any response time for such requests. Depending on the volume of these requests and the level of demand of the applicants in terms of response time, the situation can quickly become very tense on this point between operators. It is regrettable that ARCEP has not invited operators to define SLA (service level agreements) on this point, nor has it encouraged operators to use common instances (notably the APNF) to develop common standards (numbers legitimately submitted by third parties or numbers likely to be legitimately presented via an international interconnection for example). It is not too late for operators to take charge of handling this issue properly, but no impetus is yet visible in this area.