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 MCI (before its absorption by Verizon), Sprint and the former AT&T (before its merger with SBC in 2005) in the United States. It is defined as any carrier that provides inter-LATA communication, where a LATA is a local access and transport area.
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 (NPA) and the first three digits of the phone number (NPA-NXX). 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 between an IXCs and COs are ATM links carried on optical fiber.
Carrier identification code
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 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 dialing a long-distance phone number.
In popular usage, CACs are often referred to as "dial-around codes" (because they allow dialing 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 trunks.
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.
Although CAC are no longer used, PIC and CIC are still common. An example of a 10-10 Dial around could be as follows. I may have AT&T as my assigned long Distance Carrier with my Local Exchange Carrier (LEC), also known as a regional Bell Operating Company (RBOC). The PIC for AT&T is 288. If there should be a public offer to have long distance calls to NY be at a special rate, the caller would dial 1010 followed by the offering telco's CIC and then the 10 digit number. This would circumvent the AT&T billing and be billed through the CIC. This allows making LD calls with different carriers without changing the assigned PIC on the account. This feature gave rise to slamming and the lesser known cramming technique of telephone fraud.
In telephone slamming a customer's assigned long distance carrier on their account is changed without their authorization. Some LD companies, known as switchless resellers, have contacts with LD Carriers to use their transmission lines and infrastructure. With cramming, your calls may still be going over the AT&T network (288) but some LD reseller will be billing you for the calls. Although the PIC on your account has never changed from 288, another company is billing you for LD calls going through their CIC. An LD company could tell AT&T that any calls from this 10 digit phone number (known as an ANI) be sent to them for billing. AT&T will pull those calls on a monthly basis and send the call tapes. It is then up to the LD Company to either bill them directly or on their Local Telephone bill.
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