Interexchange carrier

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IXC redirects here. For the IATA airport codes see Chandigarh Airport

An IntereXchange Carrier (IXC) is a U.S. legal and regulatory term for a telecommunications company, commonly called a long-distance telephone company, such as AT&T, MCI and Sprint in the United States. It is defined as carriers which provide inter local access and transport area (LATA) communication.

An IXC carries traffic, usually voice traffic between telephone exchanges. Telephone exchanges are usually identified in the United States by the three-digit area code and the first three digits of the phone number. Different exchanges are generally in different geographic locations, such as separate central offices (COs, also called "wire centers").

IXCs used to carry voice traffic on analog lines, but these days, most voice traffic is digitized. Therefore, voice traffic is more typically a data stream. These voice data streams therefore can be intermixed with data traffic too, such as uplinks for DSL. Most commonly, links to and from COs are ATM links carried on optical fiber.

[edit] Carrier identification code

Each carrier (interexchange or local exchange) is assigned a four-digit identification code, the Carrier Identification Code (CIC). The interexchange carrier to which calls from a subscriber line are routed by default is known as the Primary 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 dialled as a prefix immediately before dialling a long-distance phone number.

In popular usage, CACs are often referred to "dial-around codes" (because they allow dialling around the PIC). Sometimes they are even called "PIC codes", though this term is inaccurate, since the code is being used to avoid the PIC, not to use its services.

When CICs were first introduced in 1983, they were only three digits long, and the CAC consisted of the digits 10 followed by the three-digit CIC. In 1998, the CIC had to be extended to four digits. Existing carriers' codes were prefixed with zero. Thus a pre-1998 CAC of the form 10-XXX became 101-0XXX. (See the FCC's FAQ on the subject.) Since the CACs starting with 10-10 are generally the oldest and best-known ones, CACs are sometimes referred to as "10-10 codes".

Use of CACs is popular with telephone users who wish to avoid paying a regular monthly fee for access to inexpensive long distance service. They can also be useful if encountering a 'circuits busy' condition when all long distance trunks are tied up; a CAC allows selection of an alternate carrier which may have other open long distance trunk lines.

As multiple competitive long-distance carriers have been permitted in countries other than the United States, schemes similar to the CIC/CAC have spread worldwide. They are now used in (among other countries) Canada, Germany, and Japan.

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