Definition of Central Office

A Central Office is a building that telephone companies own to house their telecom hubs and switches. Every telephone area code and prefix (NPA-NXX) is assigned to a particular Central Office, and one Central Office is typically responsible for many area code prefixes and serves as the switching hub for consumer and business telephone lines within a certain geographic area or radius.

Each Central Offices has a unique 8-digit identification codes (COID), better known as a CLLI code.

Telecom companies understand the value of having contact data appended with the COID, because they can tune their marketing efforts to focus exclusively on customers that they know can be serviced by their network.

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