What is a CLLI?

CLLI stands for, "Common Language Location Identifier," and is pronounced as "silly," believe it or not. A CLLI uniquely identifies a particular piece of telecom equipment. Every telephone exchange (the second three digits in an American phone number) has a corresponding CLLI for its switch.

What's the point of all this? Telephone companies use it to determine the distance between two callers, so they know if the customer needs to be charged for a local call or a long distance call. And if a group of callers report problems with their service, the phone company knows which CLLI is likely the source of the culprit. Furthermore, they assist service providers in saving money when they have to build out or expand a network. If you can route the calls for certain region (or large organization) through one CLLI, you can save an enormous amount of money while still providing quality service.

A CLLI can be either 8 or 11 characters long and is broken down as follows:

  • Characters 1-4: City abbreviation
  • Characters 5-6: State or province
  • Characters 7-8: Office location
  • Characters 9-11: Which piece of equipment at that office

The term CLLI was originally coined by Bell Research, but now is maintained by Telcordia, their official successor (who, incidentally, was acquired by Ericsson).