NETWORK TRANSMISSION MEDIA
The physical channel that connects network components, such as nodes and printers, is known as the transmission medium. The transmission medium determines the speed and connectivity and; as a result, the overall performance of the network and the investments required to set up the network.
The types of transmission media include:
- Cables: Cables connect networks over relatively short distances. The different types of cables that can be used to set up networks include twisted pair cables, coaxial cables, and fiber optic cables.
- Wireless: Wireless transmission carriers connect mobile computers, such as laptops and personal digital assistants (PDAs), over a network. Various types of wireless transmission media include infrared, radio wave, and microwave transmissions.
Cables are the conventional media that are used to set up networks. When deciding on the type of cable to be used, you need to consider factors, such as the environment in which the cabling is to be implemented and the overall speed requirement of the network. After determining the requirements, you can choose the cabling that suits your requirements.
One of the major concerns in cabling is the environment in which the cables are set up. Some areas, such as factories and power plants, might generate electro-magnetic radiations, which may corrupt the data transmission. The disturbances are referred to as electro-magnetic interference (EMI). In electro-magnetic sensitive areas, the type of cable used should be such that transmissions are protected against EMI or are at a distance from radiations. In addition, other factors, such as the characteristics of the cable and network requirements, determine the type of cable that should be selected to install the network.
Twisted-pair (TP) cables are the most widely used cables for setting up networks. A twisted-pair cable uses copper wires, which are good conductors of electricity. However, when two copper wires are placed in close proximity, they interfere with each other's transmission, resulting in EMI (electro-magnetic interferences), known as crosstalk. In a twisted-pair network cable, multiple pairs of wires are twisted around each other at regular intervals. The twists negate the electro-magnetic field and reduce network crosstalk.
Twisted-pair cables are easy to set up, economical, and widely available media for network transmission. However, this media cannot be used in areas where network security is crucial or the network setup is close to electronically-sensitive equipments that may prove to be potential sources of EMI.
Twisted-pair cables are of two types:
- Unshielded Twisted Pair Cables (UTPs)
- Shielded Twisted Pair Cables (STPs)
Unshielded Twisted Pair Cables
Unshielded Twisted Pair cables are the most commonly used cabling media. This type of cabling is generally used in telephone systems.
UTP cables consist of a set of twisted pairs that are covered with a plastic jacket, as shown in the following figure:
|Unshielded Twisted Pair Cable|
However, this plastic jacket does not provide any protection against EMI. To ensure that data transmission is not disrupted due to EMI, UTPs are not installed in close proximity to electro-magnetic devices.
Another problem related to these cables is that the signals the UTPs carry undergo rapid attenuation. As a result, the recommended length of these cables is not more than 100 meters.
Although UTP cables are sensitive to interference, they are highly economical and widely available as compared to other cables and transmission media. In addition, UTP cables are easy to install. All these factors have contributed to the popularity of UTPs in the field of networking.
Due to their wide availability, UTP cables have been standardized by Electrical Industries Association (EIA) and are available in various categories called CAT ratings.
Shielded Twisted Pair Cables
Shielded Twisted Pair cables consist of multiple twisted pairs (TPs) surrounded by an insulator shield. This shield serves to protect the copper-based core from EMI. This insulator shield, in turn, is covered with a plastic encasement, as shown in the following figure:
|Shielded Twisted Pair Cable|
STP cables are protected against EMI by two layers. As a result,they are less sensitive to EMI and interference. However, STP-cable shielding should be grounded to prevent interference in the cable. In addition, compared to UTP, STP cables offer higher transmission rates – from 16 Mbps to 155 Mbps.
Despite high transmission rates, STP cables have a number of limitations. They are expensive and not as widely available as UTP and coaxial cables. STP cables are not implemented commonly on large networks because of its incompatibility with the normal telephone cabling. They are mainly restricted to the Token Ring LAN setup.
Part2 will deal with Token Ring and, and other types of cables existing on the networking industry.
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