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The access network is the portion of a telecommunication system that is closest to the end consumer. These networks connect end users to local service providers, who then connect them to regional providers, which will then connect to different providers, and so on, until the user reaches the area necessary to connect her communication session. In most cases, the access network is invisible to users. Rather than bill users directly, the network will bill the companies the users connect to; those companies then turn around and bill the user.
Telecommunication systems, especially those in the United States, are a very complex affair. There are small local systems sandwiched between large exchanges, and all of it is connected through the Public Switched Telephone Network (PTSN). Any given area may have dozens of different exchanges in operation over the same systems. The overall goal of these systems is to allow users to talk to each other, regardless of location or carrier, simply by dialing a number.
From the user’s standpoint, the process begins with the access network. This system is the physical connection made between users and the local switching hub. If the access network were viewed on its own, it would be like a giant web covering an area and converging on a single location. Every wired phone in the area connects to this web, and the convergence point is the Local Exchange Carrier (LEC). The LEC then connects to one or more Interexchange Carriers (IXC) to route calls out of the local area.
The relationship between all of these systems is important to the user, but likely invisible in use. For instance, if a call originates and ends within the area of a single LEC,then it is defined as a local call; calls that terminate outside are long-distance. If a user makes a long-distance call, then he will use his own access network and his regional LEC, one or more IXCs and the LEC and access network of the person he is calling. All of the transitions should be seamless, but problems like faint calls or unexpected disconnects are the result of the complexity.
Using all these different exchanges costs money, and the end user ultimately pays for the time on these networks. The individual exchanges keep track of time spent on the systems and bill each other accordingly. For instance, the owner of the access network and LEC will bill the IXC for calls made by a specific user. The IXC, which is what people traditionally call their phone company, will then bill the user based on usage.