Transmission Medium
A transmission medium (plural media) is one which carries a signal from one computer to another. It is
also known as communication channel. Transmission medium can be wired or wireless.
Wired Transmission Media
The data signal physically gets transferred from the transmitting computer to the receiving computer through the wired transmission medium. Some of the wired transmission media are discussed below
1. Twisted Pair Cables
It is generally used for telephone communications in offices and also in modern Ethernet networks especially in LANs . For telephonic communication a Voice Grade Medium (VGM) cable is used but for LAN applications a higher quality cable known as Data Grade Medium (DGM) is used.
Types of Twisted Pair Cables
There are two types of twisted pair cables available. These are:
- Shielded Twisted Pair(STP) Cable.
- Unshielded Twisted Pair(UTP) Cable
2. Coaxial Cables
It is the most commonly used transmission media for LANs. It consists of solid wire cores surrounded
by one or more foil or wire shields, each separated by some kind of plastic insulator.
3. Optical Fibres
These consists of thin strands of glass or glass like material which are so constructed that they carry
light from a source at one end of the fibre to a detector at the other end. The light sources used are either
light emitting diodes (LEDs) or laser diodes (LDs). The data to be transmitted is modulated onto a light
beam using frequency modulation techniques. At the receiver’s end, the signals are demodulated.
Optical fibres offer a very high bandwidth and this makes it capable of multichannel communication.
The Optical fibre consists of three layers:
- Core -glass or plastic through which the light travels
- Cladding -covering of the core that reflects the light back to the core
- Protective (Buffer) coating-protects the fibre cable from hostile environments
Fibre Optic cable can be of two types:
- Single node fibre optic cable: It supports a segment length of up to 2kms and bandwidth of up to 100Mbps
- Multinode fibre optic cable: It has a segment length of 100kms and bandwidth of 2Gbps
Wireless Transmission Media
Wireless or unbounded or unguided media transport electromagnetic waves without using a physical
conductor. The signals are broadcasted through air or water and thus are available to anyone that has a
device capable of receiving them. Some of the wireless media are:
1. Infrared
Infrared communication requires a transceiver (a combination of transmitter and receiver) in both
devices that communicate.
2. Radiowaves
In case of radiowave transmission, certain radio frequencies are allocated to private/government organizations for direct voice communications. Each radio signal uses a different frequency and this differentiates it from others. The transmitter takes some message, encodes it and then transmits it with radio wave. The receiver on the other hand receives the radio waves and decodes it. Both the transmitter and the receiver use antennas to radiate and capture the radio signal. Radio transmission is widely used by delivery services, policemen,security personals etc.
3. Microwaves
This type of transmission uses high frequency radio signals to transmit
data through space. Like radio waves, microwaves can pass through obstacles viz. buildings,
mountains etc. Microwaves offer a line of sight method of communication. A transmitter and receiver
of a microwave system are mounted on very high towers and both should be visible to each other (line
of sight).It is generally used for long distance telephonic communications.
4. Satellites
Satellites are an essential part of telecommunications systems worldwide today. They can carry a large
amount of data in addition to TV signals.Satellite communication is a special use of microwave transmission system.Typical data transfer rates are 1 to 10 Mbps.
Satellites are especially used for remote locations, which are difficult to reach with wired
infrastructure. Also communication and data transfer on internet, is only possible through satellites.
Quick Review
Network: A collection of independent computers that communicate with one another over a shared network medium.
Node: A computer attached to a network.
Server: A computer that facilitates sharing of data, software and hardware resources on the network.
Network Interface Unit (NIU): A device that helps to establish communication between the server and
workstations.
Circuit switching: A technique in which a dedicated and complete physical connection is established
between two nodes for communication.
Packet switching: A switching technique in which packets are routed between nodes over data links
shared with other traffic.
Personal Area Network (PAN): A computer network organized around an individual person.
Local Area Network (LAN): A network in which the devices are connected over a relatively short
distance.
Metropolitan Area Network (MAN): A network which spans a physical area ( in the range of 5 and 50
km diameter) that is larger than a LAN but smaller than a WAN.
Wide Area Network (WAN): A network which spans a large geographical area, often a country or a
continent.
Internet: It is a network of networks spread across the globe, all of which are connected to each other.
Interspace: A client/server software program that allows multiple users to communicate online with
real time audio, video and text chat in dynamic 3D environments.
Channel: A medium that is used in the transmission of a message from one point to another.
Bandwidth: The range of frequencies available for transmission of data.
