Computer Networks V

CONNECTIVITY MEDIA.

Some type of media is required in order to connect network components. Various types of cables exist for this purpose; as with most hardware, their price is related to their performance. Two PCs can be connected quite simply and cheaply by using a null modem cable. At the upper end of the spectrum, wireless and even satellite connections are used by large corporations and the military.

The earliest cable to become widely used is coaxial cable (nicknamed "coax"). As it is shielded and resistant to electrical noise, it has proven useful in factory situations. Twisted-pair cable, also called UTP (unshielded twisted pair), has replaced coax in most applications, as it is cost effective. Similar to telephone wire, noise problems prevented it from being accepted more quickly. Underwriters Laboratories rates UTP cable from Levels I through V based on performance. Levels I and II are only suitable for low grade or slower applications.

Fiber optics is the most expensive and the fastest of the cables. Fiber-optic technology has been shown to achieve speeds of several hundred gigabits per second (Gbps) or faster, although most commercial applications to date have settled for between 2.5 and 10 Gbps. Experts have theorized that multiplexing technology can push fiber-optic capacity into the terabits—or trillion bits—per second (Tbps). For these reasons, it is frequently used for high-volume backbones connecting network segments. Another benefit of fiber-optic cable is that it is immune to electrical interference.

Wireless systems are also used for connecting workstations with the file server. Microwave dishes are among the oldest means of connecting computers over long distances, though they are limited to line-of-sight transmissions and can be affected by weather conditions. Depending upon frequency, microwave equipment can transmit up to 30 miles. Another option is satellite transmission, which has been used to transmit price changes among stores in national retail chains.

Networks also require connectors to interface computing devices with the connecting media. While mainframes usually have connectors built in, most PCs require the addition of a network interface card (NIC). Larger, more powerful computers require more expensive connections due to the cost of their high-performance microprocessors and support circuitry. Such devices often implement the protocol to which electronic messages on the network must conform.