WAN Technologies: Dedicated-Circuit Networks
Basic Architecture
A dedicated-circuit network is a separate point to point data-communication route between communicating systems. It is available to employ at any time by a designated user. The circuit may be either physical or logical. The physical one is just a cable used to create permanent link between two devices. In such case the network is typically a leased line frequently used to create private wide area networks. Logically dedicated circuits exist as a virtual part of switching networks such as the Internet, frame relay and ATM networks.
Due to the fact that dedicated circuit is a used by only a dedicated user, it can offer a high level of round-the-clock connection stability as the bandwidth is dedicated and high level of performance. But as this type of connection is not supposed to be publically shared, the costs for its development can be significant as the marginal expenses of additional bandwidth and distance should be covered only by that single user. In addition there is one more difficulty – dedicated-circuit network connection is quite a complex task.
The architecture of dedicated-circuit networks includes three types: ring, star, and mesh. In ring architecture each computer is linked to the next forming a ring where data can be sent in both directions, preferring the one with a shorter path. The network is quite easy to establish though the working speed and stability of this type of connection significantly depends on every connected device. The point is that before reaching its destination the information passes through several computers. As the load on any of them is different there are often situations when some of the machines suffer from capacity lack causing delays in information transfer thus drastically increasing the time needed for information transmission. In addition, taking into account the fact that in case of transmission failure the information is sent through an opposite path, every overloaded computer increases to load on the other part of the system causing a negative snowball effect on the productivity of the entire network.
In star architecture all the devices are connected to a single computer through which all the information is transmitted. This type of connection is easy to administrate and appears to be faster that the ring one as all the information is transmitted by just one machine. Though it is very important to carefully estimate the capacity of the central computer as in case it is overloaded all the system will fall.
In mesh architecture all the computers (full-mesh) or a significant part of them (partial-mesh) are connected to each other. Such type of connection prevents the system from facing the problems the ring and star architectures do as there always are several paths for the information to travel through. However, the fact that each computes performs own routing increases the processing power needed for information transmission.
T-carrier services
T-carriers are the duplex digital channels, designed by AT&T Bell Laboratories specifically for the transmission of digital signals. Originally they served as domestic routes for telephone …
