Inter-Exchange Carrier

Interexchange carrier (IXC) is a U.S. legal and regulatory term for a 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 IXC carries traffic, usually voice traffic, between telephone exchanges. Telephone exchanges are usually identified in the United States by the LATA indicated by three-digit area code (NPA) and the first three digits of the phone number (NPA-NXX) within the LATA. Different exchanges generally cover different geographic locations, connected as separate central offices (COs, also called "wire centers").

IXCs originally carried voice traffic on analog lines, but voice traffic has since become largely 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 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). To give telephone users the possibility of opting for a different carrier on a call-by-call basis, Carrier Access Codes (CAC) were devised. These consist of the digits 101 followed by the four-digit CIC. The CAC is dialed as a prefix immediately before dialing a long-distance phone number.

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