Network Topologies

It is essential when choosing an intranet for a company to select the topology that best fits the company's needs and financial requirements. If a mistake is made in the topology selection, rearranging computers or changing topologies is both difficult and expensive. The three most common topologies used to connect an intranet are the bus, star, and ring topologies.

A bus topology is the least complicated network configuration; it makes use of a single transmission medium called a coaxial cable. In most instances the cable is many different lengths joined by a T-connector which allows the cable to divide into various directions enabling other computers to be connected to the network. Specific hardware is then needed to terminate the coaxial cable ends so that signals traveling to the end of the bus will not return as repeat data transmissions. The bus topology uses the smallest amount of wire and hardware making it fairly inexpensive and permits for a relatively trouble-free installation. One merely connects the cable and T-connector from one computer to the next and then terminates the cable at both ends.

There exist several limitations with a bus topology. There is a limit to the number of computers that can be connected via a bus topology: the strength of the signal weakens as it travels along the cable, so if more computers need to be added to a network using a bus topology, a repeater will be needed at fixed intervals to strengthen the signal. A major problem with the bus topology is that were the cable to break at any point along the bus, the computers on either side of the break will lose their termination, causing the signals to repeat and corrupt data. Additionally, if the intranet has a bad network interface card, a card inside the computer providing a connector to plug into the network cable, the whole network will function improperly due to noisy signals.

The star topology is a computer network connected via cables to a central system called a hub, (picture a wagon wheel): there are no direct connections between any of the computers, although multiple hubs can be added to increase the number of computers that may be connected to the network. The star topology consists of shielded twisted pair wire (STP) or unshielded twisted pair wire (UTP). Due to the high cost of STP wire, most networks use UTP; however, STP wire must be used if the distance between the hub and the node exceed 110m. Since each computer is connected to the hub by a single cable more cable is used in a star topology than a bus topology network. The hub also adds an additional charge. Regardless of the higher cost of the additional wiring and hub the star topology is becoming more popular in current networks.

A significant advantage to using a star topology is a breakdown n communication between the hub and any one computer does not have any effect on other computers in the network. Additionally, because the data must travel through the hub during transmission, the network administrator is able to monitor the status of all the connections. Tragically, if the hub breaks down, the whole network goes down.

The ring topology is the most expensive of the three topologies. In a ring topology the network has no end, but forms a continuous ring from one computer to another. A ring topology enables more computers to be connected to the network than either of the previous two topologies. Each node can amplify and purify the data signal prior to sending it on to the next, producing less signal loss as the data travels along the ring.

The ring topology is often used to cover a large geographic location where use of a star topology would be complicated. Problems arise with the ring topology if a break arises anywhere along the ring, resulting in a stop in all network communications; a backup path may be employed for just such occasion to prevent the network from going down. A major drawback of ring topology: any user can access circulating data as it passes through his or her computer creating a sticky situation regarding confidentiality issues.

The high points of each system are as follows: the bus topology is the least expensive, is fairly reliable, is not useful for geographic coverage, and it is difficult to troubleshoot; the star topology is moderately expensive, fairly reliable, able to cover some geography, and is the easiest to troubleshoot; and the ring topology is quite expensive, fairly reliable, fairly easy to troubleshoot, but its shining glory is its ability to cover geography. Keeping these network topology features in mind, it is easy to understand why one must have a thorough understanding of the company's needs to prevent costly errors.