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Interexchange carrier
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 Corporation (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. From the telephone user's point of view, the long-distance company does not handle calls that do not have additional tolls. Calls made across phone circuits within the local geographic area covered by one local network are handled only by that one LATA, commonly called a 'local telephone exchange.' 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. In the United States interLATA usually refers to rated or 'Toll' calls between LATA within state boundaries, as opposed to interstate, or calls between LATA in different states.
== How it works ==
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, software code, that implement Session Initiation Protocol (SIP) and error correction. ITSPs can thereby connect between VOIP to POTS, computer to computer, computer to phone, and IP devices to other phone services.〔(【引用サイトリンク】url=http://www.ixc.ua/telecom-industry-concepts )〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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