Inter Exchange Networks

Inter-exchange networks (IXCs) are telecommunications networks that connect local exchange carriers (LECs), competitive local exchange carriers (CLECs), local post, or telephone and telegraph (PTT) with each other. IXCs provide long distance bearer service communication and may provide other value-added teleservices. IXC’s are regulated by governmental commissions but are not usually government-owned. In other parts of the world the government may own and operate LECs and PTTs.

Some IXC’s provide interconnection for the Internet through their high-speed links and switching nodes. IXC networks use meshes of microwave, fiber, copper, coaxial cable, and satellite links to interconnect their switching systems.

Figure 1 shows a diagram of an inter-exchange carrier network. This diagram shows that the IXC interconnects LECs and CLECs with teach other through POP switching points. Access lines connect the IXC POP switching centers with LEC and CLEC tandem switching systems. These interconnection lines are typically dedicated high-speed carrier transmission lines such as DS3 or OC3 lines.

Figure 7.1: Inter-Exchange Carrier Network

IXC networks use high-speed switching systems to interconnect high-capacity transmission lines. End users connect to IXC networks either through local telephone systems or through direct connection using customer provided equipment (CPE). Network interconnections are the points where IXCs connect to other networks. Transmission lines transport signals through the IXC network. High-speed switching systems provide interconnections between transmission lines and individual channels on those transmission lines. IXCs have multiple types of international interconnection issues to adapt telecommunication formats between different types of systems.

The overall operation of services, switches, and transmission lines in an IXC is coordinated by network operations centers (NOCs). NOC’s continuously monitor the status and performance of all network nodes and links. If a network transmission or equipment fails, most networks will automatically reconfigure to (reroute) communication lines or automatically switch to backup systems. Practically all network components have redundant assemblies that will automatic switch into service on detection of equipment failure. Multiple routes are required between all switching facilities. These facilities are hardened with all support systems such as power, water, local emergency access, security redundant, and sabotage-proof.

NOC’s management systems are usually distributed to multiple locations. These management centers contain information related to addressing, routing, and reroute scenarios. These regional centers are capable of distributing the network configuring information to remote switching nodes through communication links. Through this application of decentralized control and operations combined with an extensive data base maintenance and support activity, the utilization, efficiency, and security of network capacity can be maximized.

The actual placement of circuits and switching equipment is confidential information when viewed as an operational system. This is because of the critical nature of this type information to all countries. Major damage to a country’s telecommunications infrastructure could easily cripple an area or even a whole country. Telecommunications is considered a vital part of national security and special requirements exist to the protection and reliability of telecommunications networks.

Network Interconnection Points

IXCs connect to LECs, CLECs, PTTs, and other networks through access lines and network interconnection points. Network interconnection points link networks to an IXC through the IXC’s point of presence (POP). POPs are the switching points in an IXC network that are located on the edge of the network (end switching points). A POP can be a switching location (like an end office (EO) where direct access to the IXC’s high-speed infrastructure is available. POP’s can also be simply access nodes (multiplexers) that are co-located with the LEC/CLEC for convenience and logistics.

Some IXCs connect directly with end users to provide high-speed communication services. When an end user directly connects to an IXC, facilities such as T-1’s may be installed directly tying the customer to the IXC’s POP without connecting through the LEC, CLEC or PTT. This is often the case when a business contractually receives discounts for the amount of long distance the IXC can bill to the customer business per month.

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