CLLI code (COMMON LANGUAGE Location Identifier Code and pronounced silly) is an identifier used within the North American telecommunications industry to specify the location and type of a piece of telecommunications equipment or of a relevant location such as an international border or manhole location.[1] Originally, they were used by Bell Telephone companies, but since all other telecommunications carriers needed to interconnect with the dominant Bell companies, CLLI code adoption eventually became universal. CLLI codes are now maintained and issued by Telcordia, which claims trademarks on the names "Common Language" and "CLLI".[1]
CLLI codes are useful to telephone companies for ordering phone service, for rating of call detail records (and hence billing), and to assist in tracing calls. CLLI codes are associated with Vertical and Horizontal coordinates (frequently abbreviated to "V and H coordinates"), which were developed by AT&T researcher Jay K. Donald to provide a relatively simple method of calculating distance between two network locations.[2][3] Various mileage-sensitive services are priced according to the V and H coordinates associated with the two endpoints' CLLI codes.[3][4]
There are three formats for CLLI codes, but the most commonly used is the Network Entity format, an eleven-character format used to describe the location of network equipment. A CLLI code is composed of four sub-fields:[1]
Each of the fields is defined fairly precisely, but there is room for interpretation and there are therefore some possibilities for confusion as shown in the examples below:
HSTNTXMOCG0
This code shows two characteristics:
PTLDOR12DS0
Some telephone companies named their central offices, but did not reflect this name in the CLLI code, as in the above example with a numeric location code.
PTLEORTEDS0
The item to note in the above example is that Portland is usually abbreviated as "PTLD", but because of the relatively small number of possible combinations available in the two-character location code, the city abbreviation must occasionally be modified for locations added later, usually by incrementing the fourth character in the code.
DLLSTXRNDS1
Note that this location is actually in Richardson, Texas, not Dallas.[10] Apparently, the organizational structure of Southwestern Bell Telephone at the time considered Richardson to be within its own Dallas organization, although the cities themselves have always been legally separate.