Data Communication and Networks

Data transmission refers to the transmission of data from one location to another. Any type of data that is either analog or digital is transmitted along telecommunication lines, satellites and cables.

The basic components of data communication are

A central computer

Terminal devices

Telecommunications line (a) and (b)

A hardware device called Modem; an acronym for Modulator and Demodulator is a device that transforms digital signals into a form suitable for transmission on the telephone lines.

To establish a link between two stations, the source and the destination, two modems are required. A modem at the source will modulate digital signals into analog, transmittable through the telecommunication line, while the modem at other end (destination) will demodulate the analog signals of the telecommunication line back to its originals form (digital).

Telecommunications or data communication make use of various devices to achieve the transmission links. Common device for telecommunication include; (1) Transmission channels (2) Acoustic couplers (3) Modems (4) Communication adaptors (5) Multiplexers (6) Cluster controllers (7) Concentrators (8) Front-end processors.

Transmission Media are the materials or technologies that are used to establish the communications channel. Two types of transmission media include those that use some type of physical cabling and those that use wireless technology.

Cable channels comprises: Twisted pair cable, Coaxial cable and Fibre optics cable. They physically link the devices together to enable transmission. They are referred to as guided communication media.

The wire or network cable is referred to as bounded media because the signal travels through a physical media shielded on the outside (bounded) by some material. The type of cable used depends on different things. Does your building have existing cable? How many devices do you want to network? What speed do you need? Which network topology (such as Ethernet, Token Ring etc) do you plan to use?

Bounded media are made of a central conductor (usually copper) surrounded by a jacket material. Bounded media are great for LANs because they offer high speed, and security, and low cost. However, sometimes they cannot be used due to distance limitation.

Some of the characteristics you will look at for each cable type include the following:

Cost: Cost can be an important consideration when deciding on a network cable.

Installation: One reason fiber-optic cable was so expensive was due to the UTP cable is easier to install.

Bandwidth: Normally, cable speed is referred to as bandwidth and is an important characteristic of a media type. Bandwidth is usually measured in bits per second.

Attenuation (Maximum Distance): Attenuation is the fading of the electrical signal over distance. The maximum cable distance may also be another consideration.

Immunity to Interference: This last property is how well the cable holds up against, normally electromagnetic interference, or EMI. EMI could play a big part in which cable type you use, depending on the location.

Coaxial (coax) cable gets its name because it contains two conductors that are parallel to each other, or on the same axis. The center conductor in the cable is usually copper. The copper can be either a solid wire or a stranded material outside this central conductor is a nonconductive material. It is usually a white, plastic like material, used to separate the inner conductor from the outer conductor. The outer conductor is a fine mesh made from copper. It is used to help shield the cable from electromagnetic interference (EMI). Outside the copper mesh is the final protective cover.

Coaxial cable is a good idea for a borne network because it is easy to install and no hub is needed.

The actual network data travels through the center conductor in the cable. EMI interference is caught by the outer copper mesh. Coax cable should be ground at one end to dissipate this electrical interference. Do not ground it to a computer on the network but to something like a wall outlet ground.

The different types of coax cable vary by gauge and impedance. Gauge is the measure of the cable's thickness. It is measured by the Radio-Grade measurement, or RG number. The higher the RG number, the thinner the central conductor core; the lower the number, the thicker the core.

Coax cables vary in a measurement known as the impedance (measured in a unit called the ohm), which is an indication of the cables resistance to current flow.

Here are the most common coaxial standards:

50-ohm RG-7 or RG-11: used with thick Ethernet 50-ohm. RG-58 used with thing 93-obm RG-62: used with ARCNET