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

Overview
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.

Network Control

Network control is the transmission of signaling messages that perform call-control functions such as supervision, call setup routing, provisioning (authorizing) of services, and call processing control. Networks are either common to all users or privately leased by a customer for some specific application. The term “network” also refers to a group of two or more broadcast stations or cable systems interconnected physically and organizationally so as to broadcast the same program schedule simultaneously without any switching functions.

In the early telephone systems, network control routing of a telephone connection was manually monitored and processed by human operators. Human operators would supervise the call by listening for request tones (ringing sounds) and manually coordinate the connection by talking to end customers (who originate calls) and other operators (for cross-connections). When the call setup process had been agreed (all the switching points established), the connection was made through physical connections (patch panels).

To provide for more efficient network control, telephone control signals (tones) were created to allow the transfer or call control information on the same audio lines as the voice signals for call setup. These control tones would either be mixed with the audio or temporarily replace the audio signals. This type of audio signal control is called in-band signaling.

As the design of telephone networks advanced, it was necessary to add more intelligence to the call setup (e.g., automatic forwarding of telephone calls), it became necessary to shift the control signaling to circuits outside the audio path. This allowed more rapid call setup and better overall control over the communications connection. When the control signals are separated from the actual communication channel, these are called out-of-band signaling.

Provisioning of a network is a process within a company that allows for establishment of new accounts, activation and termination of features within these accounts, and coordinating and dispatching the resources necessary to fill those service orders. Provisioning involves customer care and billing systems.

Picture below shows how different types of networks can be controlled. This diagram shows that a network can have no control (distribution only), can use intelligent databases to control dumb switches, or it can use intelligent switches to route information through a dumb network.