Interexchange carrier

An interexchange carrier (IXC), in U.S. legal and regulatory terminology, is a type of telecommunication company, commonly called a long-distance telephone company. It is defined as any carrier that provides services across multiple local access and transport areas (interLATA). Calls made on telephone circuits within the local geographic area covered by one local network are handled only by that intraLATA carrier, commonly called a local telephone exchange carrier. Local calls are usually defined by connections made without additional charge whether the connected call is in the same LATA or connects to another LATA with no charge. IntraLATA usually refers to rated or toll calls between LATA within state boundaries, as opposed to interstate, or calls between LATAs in different states. An interexchange carrier handles traffic between telephone exchanges. Telephone exchanges are identified in the United States by the three-digit area code (NPA) and the central office prefix, which is the first three digits of the local telephone number (NPA-NXX). Different exchanges, or central offices, generally serve different geographic areas. IXCs originally carried voice traffic on analog lines, but much voice traffic has since been digitized. Therefore, voice traffic is more typically a data stream and can be intermixed with data traffic such as uplinks for DSL. Most commonly, links between IXCs and COs are ATM links carried on optical fiber. For voice traffic transfer, IXCs use softswitches and VoIP protocols and error correction. ITSPs can thereby connect between VoIP to POTS, computer to computer, computer to phone, and Internet Protocol devices to other phone services. Each carrier (interexchange or local exchange) is assigned a four-digit identification code, the Carrier Identification Code (CIC) which was used with feature groups. The interexchange carrier to which calls from a subscriber line are routed by default is known as the Presubscribed Interexchange Carrier (PIC).