Transmission Media Guided/ Unguided

Transmission Media Guided & Unguided Media

Transmission Media Guided/ Unguided-:A satellite link and other communication media. Emailing, instant messaging and web pages all are dependent on communication that take place across and underlying computer network.

Networking is a technique which is used to make personal computer to multi user behaviour .Though the computers having single user multi tasking operating system or network operating system (NOS).By sharing the resources and peripheral devices more than one user can work at a single resources or device.

Need for Computer Network

The purpose of a computer network is to share resources:

  • You can play a CD music from one computer while sitting on another computer.
  • You may have a computer with a CD writer or a backup system but the other computer does not have it. In this case, you can burn CDs or make backups on a computer that has one of these but using data from a computer that does not have a CD writer or a backup system.
  • You may have a computer that does not have a DVD Player. In this case, you can place a movie DVD on the computer that has a DVD player, and then view the movie on a computer that lacks a DVD player. 
  • You can connect a printer ( or a scanner , or a fax machine)to one computer and let other computers of the network print (or scan, or fax) to that printer (or scanner, or fax machine). 
  • You can place a CD with pictures on one computer and let other computers access those pictures. 

Benefits of Computer Network

  • File sharing is the major advantage of a computer network. A person sitting at one workstation of a network can easily see the files present one the other workstation. It saves the time that is wasted in copying a file from one system to another, by using a storage device. 
  • Accessing remote files is another advantage of a computer network. People can access or update the information stored in a database, making it up-to-date and accurate. 
  • Internet services, e-mail and video conferencing are the great feature of a computer network. 
  • Another important benefit of a computer network is resources sharing. A number of people can share device like printer , modem etc for their personal computer in a family or in office. 
  • A computer network increase the storage capacity as there is more than one computer on a network which can easily share file,  so files can be stored or any computer in the network. 
  • Storing files in a server allows data to be shared easily. 
  • Fast and quick backing up of files. 
  • Software and resources can be easily managed. 
  • Network software have fast installation. 
  • Device can be shared easily. 
  • Accessing files from any workstation. 

Components of Computer Network

Network components are those major parts that are needed to install a network . Before that understand how data is transmitted on a network, is important to know various components that compose a network. 

Some of them are discussed below: 
  • Client Any computer that is part of a common network other than the server is called as client. 

  • Server Any computer that holds shared files, programs and the network operating system is called server. 

  • Network Cable These are the physical device through which various components of a computer network are connected with each other. This is also known as bus. 

  • Network Interface Card (NIC) It is also known as adaptor NIC regulates the exchange of data between the network and the computers. 

  • Protocol A set of rules is called protocol. Network protocol is standardised set of rules, used for transmission of data and/or establish  communication between them. 
  • Resources The hardware that are available to a computer on a particular network are known as resources. 

Types of Networking

The network is divided on various grounds .There are mainly the following types of them:-

  • Based on Transmission media: There are two types depending on the medium of data transmission – wired network and wireless network wire ( Twisted pair cable, coaxial cables , fibre – optic cable) and wireless (Radio, Microwave, Infrared ,Satellite) . 
  • Based on Network Size: These are mainly of three types depending on the network size. LAN, MAN and WAN ;
  • Based on Management method: It is also of two types depending on the network management method. Peer-to-peer and Client/ Server . 
  • Based on Topology (connectivity): Bus, Star, Ring, Tree and Mesh. 

Network Media (Transmission Media) 

This is actual physical environment by which data travels from one computer to another and it connects network device.The most basic hardware required for communication is the media through which data is transferred .There are several types of transmission media and the choice of the right media depends on many factors such as cost of transmission media, efficiency of data transmission and the transmission rate. 

It can be divided into two main categories these are:
  • Guided Media 
  • Unguided Media

Guided Media

The Guided media refers to the method of transmission of data over which signals can travel in a network. Examples of guided media include the following:

  • Twisted – Pair Wire 
  • Coaxial Cabling
  • Fiber – optic Cabling

Twisted – Pair Wire 

Twisted Pair Wire

A twisted pair consist of two insulated copper wires, typically about 1 mm thickness. The wires are twisted together in a helical shape. The purpose of twisting the wire is to reduce electrical interference from similar pair that are close by. Twisted pair wires are commonly used in local telephone communication and for digital data transmission over short distance up to 1 km .When many twisted pairs run in parallel for a substantial distance ,such as all the wires coming from a multistory apartment building to the telephone exchange, they are bundled together and placed in a protective sheath. The pairs in these bundles would interfere with one another if they are not twisted. Wire pairs are normally used to connect terminals to the main computer up to short distances from the main computer. Data transmission speeds up to 9600 bits per second can be achieved if the distance is not more than 100 meters. 

  • Being the oldest method of data transmission, trained manpower to repair and service this media of communication are easily available. 
  • In a telephone system, signals can travel several kilometres without amplification when twisted pair wires are used. 
  • This media can be used for both analog and digital data transmission . The bandwidth depends on the thickness of the wire and the distance travelled but several megabits per second can be achieved for a few kilometres in many cases. 
  • It is the least expensive media of Transmission for short distances. 
  • If portion of a twisted pair cable is damaged,  the entire network is not shut down as it may be the case of coaxial cable. 
  • Easily picks up noise signals which result in higher error rates when the line length exceeds 100 Meters.
  • Being thin in size, it is likely to break easily.
  • It can support 19200 BPS up to 50 feet on RS-232 port.On a 10BaseT, which supports 10 Mbps,twisted pair wires can be used up to 100 meters. 

Coaxial Cabling

Coaxial Cable

Coaxial Cable consists of a stiff copper wire as the core ,surrounded by an insulting material. The insulator is encased by a cylindrical conductor ,often as a closely woven braided mesh. the outer conductor is covered in a protective plastic sheath. A cut away view of a coaxial cable. The signal is transmitted by the inner copper wire and it is electrically shielded by the outer metal sleeve.

Two kinds of coaxial cable are widely used. One kind, 50-ohm cable, is commonly used for digital transmission. The other kind, 75-ohm cables, is commonly used for analog  transmission in cable TV transmission.

Installation of Coaxial Cable

Coaxial cable is typically installed in tow configuration: daisy – chain (from device to device- Ethernet) and star (ARCnet).The Daisy chain configuration. The Ethernet cabling is an example of Thinnet , which uses RG-58 type cable. Devices connect to the cable by means of T-connectors . Cables are used to provide connection between T-connectors .One characteristics of this type of cabling is that the ends of cable must be terminated by a special connecter, called a terminator .The  Terminator contains a resistor that is matched to the characteristics of the cable .The resistor prevent signal that reach the end of cable from bouncing back and causing interference.

Advantages of Coaxial Cable

  • It has better shielding against electromagnetic interference than twisted pair cable , so it can span longer distance at higher data bits per second (Bps).
  • It can be used for both analog and digital data transmission . For analog data transmission, 75-ohm broadband Coaxial is used and for Digital data transmission, 50-ohm Baseband cable is used.
  • It is inexpensive as compared to twisted pair wires and UTP cables but easy to handle.
  • Coaxial cable has higher bandwidth and excellent safeguard against electrical noise (noise immunity ) . RG 58 cable (10Base2) is a thin coaxial cable ( 50-ohm) in widespread use for Local Area Network (LAN) connection RG -11.(10Base5) cable is a coaxial cable that is much thicker and sturdier and can withstand more rugged surroundings and can be used with much longer segment length. RJ 59,a 75-ohm coaxial cable and RG-62(93-ohm )cable are used in ARCnet Local Area networks or the IBM 3270 applications.
  • Coaxial cable has a bandwidth in the range of 300-400 MHz .It is capable of carrying over 50 standard 6 MHz color TV channels or thousands of channels of voice-grade and/or low speed data over a single cable. CD-quality audio (1.4Mbps), or a digital bit stream at 3 Mbps can be mixed on coaxial cable for transmitting video signal. Broadband cable is inferior to baseband cable for sending digital data but has the advantage that a huge amount of broadband cable is already available in the Cable TV systems. Therefore, cable TV systems may begin operating as Metropolitan Area Network and offer telephone and internet service at low cost.

Optical Fiber

Optical Fiber Cable

Optical fiber is the newest from of bounded media. This media is superior in data handling and security characteristics.The fiber optic cable transmits light signals rather than electrical signals.It is far more efficient than the other network transmission media . Each fiber has an inner core of glass or plastic that conducts light. There are two types of light sources for which fiber cable are available. These sources of light are:

  • Light Emitting Diodes(LEDs)
  • Light Amplification by Stimulated Emission Radiation (Lasers)

The principle of operation of the fiber optic system. The system basically consists of fiber optic cables that are made of tiny threads of glass or plastic. In a single-mode fiber, the core is 8 to 10 microns (about the size of hair).In multimode fibers, the core is about of 50 microns in diameter.

Towards it’s source side is a converter that converts electrical signals into light waves.These light waves are transmitted over the fiber. Another converter placed near the sink converts the light waves back to electrical signals by photoelectric diodes.These electrical signals are amplified and sent to the receiver. Each fiber has an inner core of glass or plastic that conducts light. The inner core is surrounded by cladding.Cladding is a layer of glass that reflects the light back into the core . Each fiber is surrounded by a plastic sheath.

Optical fibers may be of the type of multimode or single mode . Single mode fibers allow a single light path and are typically used with laser signaling.Single mode fiber can allow greater bandwidth than multimode but it is more expensive. Multimode fibers use multiple light paths .The physical characteristics of the multimode fiber make all parts of the signal (those from the various path)arrive at the same time, appearing to the receiver as though they were just one pulse.The single mode and multimode optical fibers and the transmission of light through them .

Following are the common types of fiber-optic cable:

  • 8.3-micron core /12.5-micron cladding, single-mode,
  • 62.5-micron core /125-micron cladding,multi mode 
  • 50-micron core / 125-micron cladding,multi mode and 100 – micron core /140-micron cladding, multimode

Micron is one millionth of a meter =1/25,000 inch (approximately).

Characteristics of Fiber Optic 

Cost Fiber – optic cable is more expensive than copper cable, but fibre cable cost are falling. Associated equipment costs can be much higher than for copper cable, making fiber-optic network much more expensive .

Installation Fiber optic cable is more difficult to install than copper cable. Every fiber connection and splice must be carefully made to avoid obstruction of light path.

Bandwidth Capacity Because it uses light, which has higher frequency than electrical signals, fiber  optic cabling provides data rates from 100 MBPS to 2 gigabytes per second. The data rate depends on the fiber composition, the mode, and the wavelength (frequency) of transmitter light.

Node Capacity In the case of Ethernet network,fiber optic cables have the useful upper limit of around 75 nodes on a single collision domain.

Attenuation Fiber optic cable has much lower attenuation that then copper wires, mainly because the light is not radiated out in the way electricity is radiated from copper cables it has a different problem, namely chromatic dispersion. Different wavelengths of light travel through glass differently, and the colours of a single pulse of light spread apart slightly as they travel down a Cable. At a distance of several miles, one bit may shift into the next bit, causing data to be corrupted or lost.

Electromagnetic interferences This type of cable is ideal for high-voltage served areas or installation wear  eavesdropping could be a problem. Fiber optic cable or particularly appropriate for campus and multi-building backbones and for high security applications such as financial transactions, military of operation, and public safety.

Mode of transmission of fiber optic cable Fibre optic transmission channel are half duplex that means that light signals can only move in one direction at a time of full duplex circuit would cost light wave interference without a special electronics and hands it is generally not economically viable.

Uses of Optical fiber media 

Fibre optic media can support high bandwid application search as video conference digital voice image graphics networking in lan fibre optic media are the basis of for several high bandwid networking standards such as fibre distributed data in interface (FDDI)and Synchronous Optical Network (SONET) fiber optics can be used for LAN as well as for long transmission.

Comparison of fiber optics and copper wire 
  • It can handle much higher band with can copper due to the low attenuation Repeaters are needed only about every 30 km on fibre lines versus about every 5 km for copper
  • Fibre is not affected by power surgers electromagnetic interference or power failures nor is affected by corrosive chemical in the air making it idol for factory environments where electrical interference is very high
  • Fibre is lighter than copper 1000 twisted pair copper cables of 1 km long with long weigh 8000 kg but fibre have more capacity and weigh only 100 kg which greatly reduces the need for expensive mechanical support system that must be maintain.
  • Fibre do not leak light and are quite difficult to tap this gives them excellent security against potential wires  tapers.
  • Fibre is an unfamiliar technology requiring which may not be easily available
  • Since optical transmission is inherently you need a rational to way communication required either to fibre cables or two frequency bands no one fibre.
  • Fiber interfaces cost more than electrical interfaces.

Unguided Media

Radio , Microwaves and Satellites channels are electromagnetic broadcast in open space .The advantages of these channels lie in their capabilities to cover large geographical areas .It is less expensive than the wire installation. The differential between radio, Microwave and satellites channels lie in the frequencies in which they operate .Frequency below 1000 MHZ radio frequencies and higher the Microwave frequencies .

Media in which the signals are not guided through a solid medium are known as Unguided Media air is the media through which electromagnetic energy can flow easily their four there are several methods which are in used to send electromagnetic energy through air.

These Methods Are : 

  • Radio wave communication including VHF and microwave links.
  • Satellite links.
  • VSATs ( Very Small Aperture Terminals ) 
  • Infrared and Millimetre Waves .

Radio Waves

Radio Wave

Radio waves have frequencies between 10 kilohertz (kHz) and 1 gigahertz (GHz). Radio waves include the following types:

  • Short – Waves 
  • Very – High – Frequency ( VHF) television and FM radio.
  • Ultra – High – Frequency (UHF) radio and television.

The range of frequency and type of medium used for the transfer of radio waves . Radio waves can be broadcast omnidirectional or unidirectionally . Various kinda of antennae can be used to broadcast radio signals .The power of th Radio Frequency (RF) signal is determined by the antenna and trans – receiver ( a device that TRANSmits and reCEIVEs a signal over a medium such aa copper , radio waves or fiber – optic cables ) . 

Radio Transmission

Radio Transmission

Some of the characteristics of radio waves are as follows:

  • Radio waves are easy to generate.
  • They can travel long distance.
  • They can penetrate buildings easily , thus they are widely used for communications both indoors and outdoors.
  • Radio waves are Omni directional , meaning that they travel in all direction from the sources, so that the transmitter and the receiver do not have to be carefully aligned physically.

In Very Low Frequency (VLF),Low Frequency (LF) and Medium Frequency (MF) bands, radio waves follow the ground. Amplitude modulated radio broadcasting uses the MF band . This brand of frequencies cannot be used for data transfer because they offer relatively low bandwidth.

The amount of information that an electromagnetic wave can carry is related to its bandwidth. With current technology, it is possible to encode a few bits per Hertz at low frequencies , but often as many as 40 under certain conditions at high frequency.So a cable with a 500 MHz bandwidth can carry several gigabytes / second.

Microwave Transmission

Above 100 MHz , the Waves travel in a straight lines and can therefore be narrowly focused. Concentrating all the energy into a small beam using a parabolic antenna (like the satellite TV dish) gives a much higher signal to noise ratio, but the transmitting and receiving antennas must be accurately aligned with each other. Before the advent of fibre optics, these microwaves formed the heart of the long distance telephone transmission system. In order to overcome the problems of line – of – sight and power amplification of weak signal, microwave system used repeaters at interval of about 25 to 30 km in between the transmitting and receiving station.

Types of Microwave Communication System:

There are two types of Microwave data communication system. These are :

  • Terrestrial
  • Satellite

Terrestrial Microwave System

Terrestrial Microwave System

Terrestrial microwave system typically use directional parabolic antennas to send and receive signals in the lower gigahertz range. The signal are highly focused and the physical path must be line – of – sight . Relay towers and repeaters are used to extend signals . Terrestrial microwave system are used when ever cabling is cost – prohibitive such as in hilly areas or crossing river, etc Because terrestrial microwave system does not use cables , microwave links often connect separate buildings were cabling would be to expensive , difficult to install or prohibited For Examples, if two buildings are separated by a public road you may not be able to get permission to install cable over or under the road . Microwave links would be a good choice in this type of situation .

Satellite Microwave System

Satellite Microwave System

Satellite Microwave system transmit signals between directional parabolic antennas . Like terrestrial microwave system, they use low gigahertz frequencies and must be in line – of –  sight . The main difference with satellite system is that one antenna is on the satellite in geo – synchronous orbit about 36000 km (22300 Miles) above the equator . Because of this, satellite microwave system can reach the most remote places on earth and communicate with mobile device.

In satellite communication microwave signals at 6GHz (read as gigahertz is =109 Hz ) are transmitted from a transmitter on a to a satellite positioned in space . By the time this signals reaches the satellite it becomes weak as it travel or distance of 36000 km the transponder in a satellite amplifies the week signals and send them back to the at a frequency of 4 GHz.These  signal are received at a receiving station on the earth . It may be noted that the transmitting frequency is different from the receiving frequency of the satellite . This is done to avoid interference of the powerful re – transmitted signal with the week incoming signal .

Difference between Guided and Unguided Media 

Guided Media Unguided Media
It is known as wired and bounded transmission .It is known as wireless and unbounded transmission .
It cover limited area with using wire .It cover large geographical area .
It is secure ,small and limited network transmission speed is faster .It is not more secure as compare to guided and part of large network transmission speed is slow.
It is cheaper than unguided media and no side effect on human healthIt is expensive and more effect on human health .
Example of guided media is Twisted pair cabel ,Coaxial cable and Fiber optic cable .Example of unguided media are Radio wave , microwave sattelite and infrared .
Difference between Guided & Unguided Media

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Pooja Rastogi

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