The originating network can withhold the calling number from the callee’s display while still completing the call. The digits travel as Calling Line Identification (CLI), but they are marked so the destination must not offer them to the called user.
That is an ITU-T supplementary service for the calling party, specified for Signalling System No. 7 in Recommendation Q.731.4. It is the counterpart of Calling Line Identification Presentation (CLIP). When both apply, restriction takes precedence, and a presentation subscriber receives an indication that the identity is not available due to restriction rather than the digits themselves.
How Restriction Is Signalled
On invocation, the originating exchange notifies the destination that the calling number is not allowed to be presented. The number is not removed from the call. It is flagged, then stripped from what the called user’s installation is offered.
- Presentation indicator: the originating exchange sets address presentation restricted on the calling party number, and on the generic number if present, as those parameters are passed across the network.
- Call offering: the destination local exchange omits the number and any calling-party sub-address from the offering to the called user’s installation.
- CLIP interaction: a called user who subscribes to presentation is told that the identity is not available due to restriction. Restriction wins unless an override category applies.
- Packet voice: on Voice over Internet Protocol (VoIP) trunks that use Session Initiation Protocol (SIP), the same intent is typically a privacy flag on the display identity. A network-asserted identity can still be present for the carrier.
Subscription Options and Override
Restriction hides the number from the callee, not from the network. Carriers still route, bill, screen, and, where required, intercept the call with the real calling number in hand.
- Permanent mode: restriction is active for every outgoing call on the subscription.
- Temporary mode: the line has a default of presentation allowed or presentation restricted, and the user can reverse that default for a single call.
- Override category: as a national option, certain called users (typically police or emergency services) may still receive the number. On a call that originates in one network and terminates in another, the destination network’s rules apply.
- Interworking: when the call leaves the originating digital network, including a handoff to the Public Switched Telephone Network (PSTN), the restriction indication may not reach the destination. Some originating providers also decline to send the number to other networks at all.
- Name lookup: Caller Name Delivery (CNAM) is a separate database dip keyed on presented digits. If the digits are withheld, the name is withheld with them.
- Attestation: Secure Telephone Identity Revisited / Signature-based Handling of Asserted information using toKENs (STIR/SHAKEN) can still sign the number the originating provider authorized. A signature does not put the digits back on the handset.
Restriction Versus Presentation
CLI is the identity in signalling. CLIP is the called user’s right to see it. Restriction is the calling user’s right to stop that display.
| Service | Full Form | Effect |
| CLIR | Calling Line Identification Restriction | Withholds the calling number, and any calling-party sub-address, from the callee’s display |
| CLIP | Calling Line Identification Presentation | Offers that number to a called user who subscribes to presentation |
| CLI | Calling Line Identification | The calling number carried in signalling, whether or not it is shown |