An Introduction to Transmission Media Networking An Introduction to Transmission Media

Transmission Media There are several different types of transmission media that are used in modern day networks. Various networking situations and requirements may require distinctly different cable types. Considerations when deciding on type of cabling include: Speed/Transfer rates Distance/size Ease of installation Resistance to interference Cost Number of nodes supported

Types of Transmission Guided Unguided Twisted Pair Coaxial Fibre Optic Medium more important than the signal Unguided Atmosphere Outer Space Signal more important than the medium

Frequency of Transmission

Twisted Pair UTP & STP Unshielded Twisted Pair (UTP) Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference Shielded Twisted Pair (STP) Metal braid or sheathing that reduces interference More expensive Harder to handle (thick, heavy)

Unshielded Twisted Pair (UTP) Twisted pair is made of two copper wires which are covered by plastic. The two insulated wires are twisted together to form the communication line. The purpose of twisting the wires is to avoid electrical interference. Twisted pair should be familiar to us, since it is widely used in our telephone networks either in the home or the office. Twisted pair can be combined into a cable that may consist of two, four, fifty, or hundreds of pairs. Twisted pair is the basis of transmission media. It supports most of the local telephone networks and modern computer networks.

Shielded Twisted Pair (STP)

Shielded Twisted Pair (STP) Twisted pair wire is placed inside a thin metallic shielding, similar to aluminium foil, and is then enclosed in an outer plastic casing. The shielding provides further electrical isolation of the signal-carrying pair of wires. Shielded twisted pair wires are less susceptible to electrical interference caused by nearby equipment or wires and, in turn, are less likely to cause interference themselves. Because it is electrically "cleaner," shielded twisted pair wire can carry data at a faster speed than unshielded twisted pair wire can. The disadvantage of shielded twisted pair wire is that it is physically larger and more expensive than twisted pair wire, and it is more difficult to connect to a terminating block.

Coaxial Coaxial cable contains two conductors, which are insulated from one another. The inner conductor is covered by the dielectric. The outer conductor is covered by a shield. Cable TV is one of the most widely applications of coaxial cable which connects the home viewers to the cable companies. There are many applications for coaxial cable, local networks, short-run computer system links, and long- distance telephone transmission are the important applications of coaxial cable.

Coaxial In a local network, coaxial cable can support different types of traffic and data communication. In the transmission of data between different computers, coaxial cable can serve high speed input and output channels for computer systems. By using frequency division multiplexing ( FDM ), a coaxial cable can carry more than 10,000 channels at the same time.

Fibre Optic The optical fibre contains three parts. The inner most part is the core, which contains one or more thin fibres that are made of plastic or glass. Each of the fibres in the core is covered by the cladding. The cladding is a glass or plastic coating which has different optical properties from the core. The outer most part of the optical fibre is made of plastic or Kevlar, which is called the jacket. The purpose of the jacket is to prevent the destruction from the environment.

Fibre Optic There is a light-emitting diode ( light source ) on one side of the fibre and a photodiode ( light-sensitive receptor ) in the other side of the fibre. The fibre optics equipment transmits the light pulses from one side to the other through the plastic or glass. Because of the better performance and the greater data rate of optical fibre, the application of optical fibre has increased dramatically in long-distance communication and military application.

Fibre Optic Lots of different cable sizes and bandwidths

Terrestrial Microwave Terrestrial microwave transmission is another way of transmitting the data. A pair of microwave antennas which are fitted on the top of towers will transmit signals through the air. The shape of microwave antenna is similar to a dish and is about ten feet wide. The microwave antennas are usually in high places in order to achieve better transmission effect. Terrestrial microwave is used as an alternatives of coaxial cable and optical fibre, since terrestrial microwave transmission needs less repeaters than that of coaxial cable. The voice transmission, television transmission, and the short point-to-point links between building will be the major application of microwave transmission.

Terrestrial Microwave

Satellite Microwave Signals are bounced off satellites from one ground station to another allowing data to be sent round the globe The most important applications for satellite communication is long-distance telephone transmission, private business networks, and television distribution.

Satellite Microwave

Other Transmission Methods Infrared Initially used in remote controls portable - no antennae required inexpensive limited range sensitive to orientation of transmitter to receiver Laser • Use of light to carry information through the air (no fibre required) • A laser bean will stay focussed over a long distance • Requires a straight line of sight and can easily be blocked (e.g., by fog).

Conclusion range capacity to carry information cost directionality We use various transmission media with different properties in terms of: range capacity to carry information cost directionality reliability (noise and blocking)