CNAM IN for SIP trunks#

Caller Name Delivery (CNAM) provides a name associated with a telephone number. CNAM IN is the inbound service. It looks up the name associated with the caller ID of an incoming call and delivers the result to the receiving SIP endpoint. This can help agents and applications identify callers before answering or processing a call.

CNAM IN does not authenticate the caller ID or change the calling number. It is also separate from CNAM OUT, which provides a caller name for an outbound call. See Caller ID and CNAM OUT for outbound behavior.

How CNAM IN works#

CNAM lookup is an optional inbound SIP trunk service. Enable CNAM Lookup is disabled by default and applies to calls with a United States caller ID. When the setting is enabled, DIDWW queries a remote CNAM database and handles the result as follows:

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flowchart LR
    CALL["Incoming call with<br/>United States caller ID"]
    SETTING{"Enable CNAM Lookup<br/>enabled?"}
    LOOKUP["Query remote<br/>CNAM database"]
    RESULT{"Name returned?"}
    NAME["Add caller name to<br/>SIP From display name"]
    UNAVAILABLE["Use Unavailable as<br/>SIP From display name"]
    NUMBER["Use caller ID as<br/>SIP From display name"]
    LOG["Populate Source Name<br/>in inbound call logs"]
    ENDPOINT["Deliver call to<br/>SIP endpoint"]

    CALL --> SETTING
    SETTING -->|Yes| LOOKUP --> RESULT
    SETTING -->|No| NUMBER --> ENDPOINT
    RESULT -->|Yes| NAME --> LOG --> ENDPOINT
    RESULT -->|No| UNAVAILABLE --> ENDPOINT

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    classDef decision fill:#fef3c7,stroke:#facc15,color:#1f2d3d,stroke-width:1.5px

    class CALL,ENDPOINT endpoint
    class LOOKUP,NAME,UNAVAILABLE,NUMBER,LOG process
    class SETTING,RESULT decision

    linkStyle default stroke:#0066cc,stroke-width:1.5px

When Enable CNAM Lookup is enabled, an additional charge applies to each call from a U.S. source number. The rate is shown in the trunk settings when you enable the setting. CNAM IN charges appear in the CNAM IN (USD) field in inbound call logs.

SIP delivery#

DIDWW places the CNAM result in the display-name portion of the SIP From header. The caller ID remains in the user part of the SIP URI.

Lookup state

SIP From header

Lookup disabled

From: "12899230448" <sip:12899230448@46.19.213.14>;tag=example

Lookup successful

From: "KRIS TOTAL" <sip:15203981500@46.19.213.14>;tag=example

Lookup unsuccessful

From: "Unavailable" <sip:15203981500@46.19.213.14>;tag=example

In a successful result, KRIS TOTAL is the caller name and 15203981500 is the caller ID. The same retrieved name appears in the Source Name field in inbound call logs.

Trunk Group behavior#

When a Trunk Group contains at least one trunk with Enable CNAM Lookup enabled, DIDWW performs a lookup for every incoming call routed to the group. Each call from a U.S. source number incurs the CNAM lookup charge, even when the selected trunk does not have the setting enabled. The caller name is delivered only through trunks that have Enable CNAM Lookup enabled.

Important

Review every member before enabling CNAM lookup on a trunk in a Trunk Group. Enabling the setting on one member changes lookup and billing behavior for calls routed to the entire group.

Availability and limitations#

  • CNAM IN lookup applies to incoming calls with a United States caller ID.

  • CNAM lookup is also available on phone.systems™ trunks. See Additional Services in the phone.systems™ trunk settings reference.

  • The lookup result depends on the information available from the remote CNAM database. A name is not returned for every caller ID.

  • CNAM IN does not verify that the calling party owns or is authorized to use the caller ID. For caller-ID authentication information, see STIR/SHAKEN for inbound calls.

  • The receiving SIP system must support and preserve the display name in the SIP From header to present the caller name to users or applications. How the name is presented depends on the receiving system.

Configuration reference#

Configure Enable CNAM Lookup under Additional Services when creating or editing an inbound SIP trunk. For the field definition and default value, see Additional Services in the SIP trunk settings reference. To enable CNAM lookup on an existing trunk, see Manage SIP trunks or Manage phone.systems™ trunks.