CNAM (Caller Name) is the short name some North American networks associate with a telephone number and may display next to Caller ID. It is a database lookup, not a field the caller transmits during call setup the way the calling number is. The classic payload is 15 characters, a limit that comes from the storage and query formats used with the Line Information Database (LIDB) and the bureaus that grew around it.
LIDB was built in the Bell System era for alternate billing (calling cards, collect, third-number billing). CNAM was layered onto that infrastructure and onto later competitive CNAM databases. A terminating carrier that wants a name issues a dip (historically TCAP over SS7, today often an IP query to a CNAM provider) against the number. If nobody dips, nobody sees a CNAM name.
CNAM is not guaranteed
- The originating party does not push the name in band with the call. The terminator must query.
- Not every terminating carrier dips every call. Dips have a cost, and some networks skip them, cache aggressively, or dip only for certain trunk groups.
- A number may have no record, a stale record, or a record at one bureau that another bureau does not carry.
- Wireless and VoIP terminations vary widely in whether they perform CNAM at all.
- There is no cryptographic binding between the 15-character string and the caller. CNAM is not STIR/SHAKEN.
Contacts override CNAM on smartphones
If the incoming number is stored in the handset’s address book, the device shows the contact name. That local label replaces whatever CNAM the network might have supplied. For anyone calling a customer who already saved the number, CNAM is irrelevant. For anyone calling a stranger, CNAM only appears if the terminator dipped and a record existed.
CNAM vs branded calling vs the contact name
| Display source | Length / format | Where it lives | Authenticated? | When it shows |
|---|---|---|---|---|
| CNAM | Classically 15 characters (NANP LIDB-era limit) | LIDB or a CNAM bureau, queried by the terminator | No | Only if the terminator dips and a record exists |
| Smartphone contact | Whatever the user typed | The called party’s address book | No (user-controlled) | Whenever the number matches a contact; overrides CNAM |
| STIR/SHAKEN attestation | A / B / C, not a name | SIP Identity header, verified at the terminator | Yes (signature over the number) | Feeds analytics and some branded-calling products; not the 15-character CNAM string |
| Caller ID number | Typically 10-digit NANP national number | CPN / SIP From or P-Asserted-Identity | Only if signed (STIR/SHAKEN) | Almost always, unless presentation is restricted (*67) |
Updating a CNAM record
The party that controls the number (often the DID provider or the serving LEC) submits a CNAM listing to their CNAM provider. Propagation across bureaus is not instantaneous and is not universal. A change that appears on one terminating network may lag on another, or never appear at all. International callers outside the NANP generally never see North American CNAM at all.