Inter-Exchange Carriers (IXC)

Inter-Exchange Carrier (IXC) networks are used to link telephone networks within geographical service area to each other. AT&T, Sprint, MCI, and Qwest are examples of well-known IXCs.

In order to provide the bandwidth necessary to carry the volume of long-distance voice and data traffic at reasonable cost, most IXCs have deployed large bundles of fiber-optic cables that interconnect their switching systems. Burying thousands of miles of fiber cable is costly. However, each pair of fibers is capable of providing many Gbps of bandwidth.

The explosion of the Internet and the demand for advanced multi-media services continues to drive the demand for increased bandwidth at low cost. To increase the capacity of fiber cables, new fiber optic technology has emerged. By utilizing a technology known as dense wavelength division multiplexing, DWDM, each fiber can carry 80 or more separate light-waves. As of 2001, some DWDM technologies were capable of providing over 1 Tbps (1,000 Gbps) of bandwidth, enough to transmit in one second the contents of 150,000 encyclopedias. Advances in optical networking equipment and light-wave amplification technologies will continue to add bandwidth the fiber networks.

Picture on top shows the typical inter-exchange carriers (IXCs) connections. This diagram shows that there are many different IXCs. Each of these IXCs must interconnect to the local telephone companies at a defined point of presence(POP)...

Local Exchange Carriers (LEC)

Local exchange carriers (LECs) or post and telegraph and telecommunications (PTT) companies provide telephone services directly to residential and business customers located within a localized geographic area. Typically, these telephone companies provide services via copper lines that extend from a local carrier’s switching facilities to the end customer’s premises equipment (CPE). This is referred to local loop.

Until the early 1990’s, most countries had a single company that provided local telephone services. This company was either owned or highly regulated by the government. To increase competition and reduce telephone service prices to consumers, some governments have begun to allow other companies to provide basic (local) telephone service. These competitive local exchange company (CLEC) or competitive access providers (CAPs) provide alternative connections to the public switched telephone networks (PSTN). The established telephone companies are now called the incumbent local exchange carriers (ILECs),

Traditional incumbent local exchange company (ILEC) may be connected with one or more competitive local exchange companies (CLECs) who provide local telephone service in a defined geographic area. End customers (the houses) in the geographic area are connected to the End Office (EO) switching center by copper wire (local loop). The local loop length is approximately 1k to 10k feet from the EO. Rarely will the distance of the local loop exceed 20k feet.

The end office interconnects calls between local customers. Each end office switch can usually supply service up to 10,000 customers. In larger areas (such as a city), established LECs may have several EO switches. The EO switches are interconnected using a higher level tandem switch. If is a significant amount of calls regularly processed between end offices, they may be directly connected via high-speed communication lines (trunks).


Figure 1.7 shows that CLECs must be connected to the ILEC to allow calls to be routed between the different networks. There may be several CLECs in a specific local telephone service area.

Local Telephone Service Networks

Local telephone service areas are connected to each other by inter-exchange switches. These higher level (meaning above tandem) are often operated by long-distance service providers called inter-exchange carriers (IXCs). The IXCs interconnect their long distance switches to the local network through a point of presence (POP). The POP is the toll center that allows separation of billing for local and long distance service.

There are several other types of competitive access companies that are starting to provide local telephone service. These include cable television companies, Internet telephony service providers (ITSPs) and wireless local loop (WLL) providers.