More about Calling Line ID and Calling Party Name

CallerID consists of two user-facing pieces of information:

  • A phone number (typically referred to as CLID or calling line ID).

  • Calling party name (typically referred to as CNAM).

When a call is made, the CLID (phone number) is routed to the destination's carrier (also known as the terminating carrier). The CNAM information for the call may or may not be routed with the call because as this information depends on how the country/region has implemented CNAM (if at all). The reliability of CNAM delivery with the call varies depending on the country/region and carriers that handle the call--either as an intermediary or a terminating carrier.

CLID & CNAM transmission is the responsibility of the terminating carrier. The terminating carrier must support CLID & CNAM functionality as well as provide up-to-date records for both values. Microsoft reliably provides CLID values when originating calls, but those values may not be kept intact once they pass through an intermediary carrier or the terminating carrier. If the CLID value is changed, omitted, or truncated by the intermediary or terminating carrier, Microsoft has little to no recourse in correcting such problems in the public telephone network.

Inconsistencies in CNAM can be caused when the intermediate or terminating carriers delay refreshing the CNAM information in authoritative databases--as in the case of the United States. In countries/regions where there are no authoritative databases for CNAM, individual carrier practices can also cause problems with CNAM information arriving intact with the call. Microsoft currently does not support originating CNAM information in countries/regions other than the United States.