ICT - Chapter 2 (Notes)

Data Communication & Networking

Chapter - 2

BY:   MUHAMMAD MAHDI BILLAH

 

       Bandwidth or Data transmission speed

       Speed and capacity of computers and communication networks can be classified by bandwidth.

       Data transmission speed:

       3 basic categories

1. Narrow band/sub voice band – Range in speed from 45 to 300 band. Handling low data volumes. Ex-Telegraph lines and low speed terminal.
2. Voice band – Range speed from 9600 baud. (Bps – bit per second). Handling moderate data volumes. Ex- data transmission for slow I/O devices to CPU and telephone voice communication.
3. Broad band/wide band – Range speed 1 million baud or more. Handling large volume of data.

      Data transmission method:

      3 types of data transmission:

1.  Asynchronous Transmission
2. Synchronous transmission
3. Isochronous transmission

  

                    Transmission Medium:

•       Transmission medium is the way in which data is transmitted from one place to another.

•       It provide a pathway over which the message can travel from sender-to-receiver.

•       Each of the message can be sent in the form of data by converting them into binary digits.

•       These binary digits are then encoded into a signal that can be transmitted over the appropriate medium.

              Wired/Guided Media

•       Guided transmission media are the cables that are tangible or have physical existence.

•       Bounded transmission means having connectivity between a source and destination using cables or wires. The signals have to travel through this channel i.e. physical media 

             Twisted Pair Cable:

 

• A twisted pair cable is a pair of copper wires.
• Copper wires are the most common wires used for transmitting signals because of good performance at low costs.
•  A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together to form a single media.
• Out of these two wires, only one carries actual signal and another is used for ground reference.
• To identify every cable, these cables are color coated.
• The twists between wires are helpful in reducing noise (electro-magnetic interference) and cross-talk.
• This type of cable is used in telephone lines to provide voice and data channels.

The two types of twisted pairs are:

1. Unshielded twisted pair (UTP)

2. Shielded twisted pair (STP)

                1. Unshielded twisted pair (UTP):-

•       UTP is more common. 

•       UTP cost less than STP and easily available due to its many use.

•       Due to its low cost, UTP cabling is used extensively for local-area networks (LANs) and telephone connections.

•       UTP cables consist of 2 or 4 pairs of twisted cable.

•       Cable with 2 pair use RJ-11 connector and 4 pair cable use RJ-45 connector.

•       RJ-45 connectors is used with Ethernet cables in computer networking.

•       RJ-11 connectors is used in connecting telephone unit.

2.  Shielded twisted pair (STP):-

·         This type of cable has a metal foil covering which encases each pair of insulator conductors.

•       Electromagnetic noise penetration is prevented by metal casing. Shielding also eliminates crosstalk.

•       It is similar to UTP but has a mesh shielding that’s protects it from EMI which allows for higher transmission rate.

•       It is more expensive than coaxial and unshielded twisted pair.

                                            Coaxial Cables

•       Coaxial cables are copper cables with better shielding than twisted pair cables, so that transmitted signals may travel longer distances at higher speeds.

•       The shield minimizes electrical and radio frequency interference.

•       Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks, such as Ethernet.

•       Coaxial cable has two wires of copper.

•       The core/inner copper wire in centre and is made of solid conductor. It is enclosed in an insulating sheath.

•       The second/outer copper wire is wrapped around, and is used to protect from external electromagnetic interference (Noise).

•       This all is covered by plastic cover used to protect the inner layers from physical damage such as fire or water.

 

     
                     Fiber Optic Cable

•       A fibre optic cable is made of high quality of thin glass or plastic and is used to transfer digital data signals in the form of light up to distance of thousands of miles.

•       Fibre optic cables are not affected by electromagnetic interference, so noise and distortion is very less.

•       Fibre optic cables carry communication signals using pulses of light generated by small lasers or light-emitting diodes (LEDs).

•       The cable consists of one or more strands of glass, each only slightly thicker than a human hair. The centre of each strand is called the core, which provides the pathway for light to travel. The core is surrounded by a layer of glass called cladding that reflects light inward to avoid loss of signal and allow the light to pass through bends in the cable. No light escapes the glass core because of this reflective cladding.

    Ø  Advantages of Optical Fiber:-

•       Fiber optic cables have a much High bandwidth than metal cables. This means that they can carry more data.

•       Smaller Size and Lighter weight.

•       low attenuation

•       Not affected electromagnetic interference (No EMI interference)

•       Signals carrying data can travel long distances without weakening

•       Suitable for industrial and noisy areas

    Ø  Disadvantages of Optical Fiber:-

•       Optical fiber cables are expensive

•       Difficult to install

•       Maintenance is expensive and difficult


Wireless (Unguided/Unbound) Transmission Media

•      A wave can be described as a disturbance that travels through a medium from one location to another location. 

•       A wave is a transfer of energy, usually through a form of matter called a medium.

•       There are a special type of wave that can travel without a medium, called electromagnetic waves (also called EM waves), which are waves like radio waves and microwaves.

•       Unlike sound waves and water waves, electromagnetic waves don't need a fluid, or a solid, or even air to help them travel from one place to another. EM waves can travel across the great vacuum of space, which is why we see light from distant stars and planets.

•       Electromagnetic waves are formed when an electric field comes in contact with a magnetic field. They are hence known as 'electromagnetic' waves. 

•     Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma rays.

•       Sunlight is also a form of EM energy. Electromagnetic energy from the sun comes to Earth in the form of radiation. 

• A little part of electromagnetic spectrum can be used for wireless transmission.

 •       The Electromagnetic Spectrum describes a wide range of different electromagnetic waves.

        Radio Waves Transmission

• Radio waves are EM (Electromagnetic) waves that have wavelengths between 1 millimetre and 100 kilometres (or 300 GHz and 3 kHz in frequency).
• Radio frequency is easy to generate because it has large wavelength and can travel long distance.
• Radio waves are generated by radio transmitters and received by radio receivers.
• Radio stations transmit radio waves using transmitters, which are received by the receiver installed in our devices. Both transmitters and receivers use antennas to radiate or capture radio signals.
• It can penetrate walls easily, so these waves are widely used for communication both indoors and outdoors.
• Radio waves are omnidirectional means they travel in all the directions from the source.
• When an antenna transmits radio waves, they are propagated in all directions.
• A sending antenna send waves that can be received by any receiving antenna. The omnidirectional property has disadvantage, too. The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signal using the same frequency or band.
• It is Used Mobile, AM/FM radio, television

      Micro Waves Transmission

•       Microwaves are a type of radio waves with high frequencies. It can be classified as a subclass of radio waves. The frequency of microwaves lies in the 300 MHz to 300 GHz. 

•       Unlike radio waves, microwaves are unidirectional, in which the sending and receiving antennas need to be aligned.

•       Microwaves are widely used for point-to-point communications because their small wavelength, which means that the signal is focused into a narrow beam. Additionally, each antenna must be within line of sight of the next antenna.

•       Microwaves are a type of radio waves with high frequencies. It can be classified as a subclass of radio waves. The frequency of microwaves lies in the 300 MHz to 300 GHz. 

•       Unlike radio waves, microwaves are unidirectional, in which the sending and receiving antennas need to be aligned.

•       Microwaves are widely used for point-to-point communications because their small wavelength, which means that the signal is focused into a narrow beam. Additionally, each antenna must be within line of sight of the next antenna.

•       Electromagnetic waves above 100 MHz tend to travel in a straight line and signals over them can be sent by beaming those waves towards one particular station. Because Microwaves travels in straight lines, both sender and receiver must be aligned to be strictly in line-of-sight.

     
              Infrared Waves Transmission

•       Infrared signals have frequencies between 300 GHz to 400 THz. They are used for short-range communication.

•       Infrared waves are used for very short distance communication like TV remote, wireless speakers, automatic doors, hand held devices etc. 

•       Infrared waves having high frequencies prevents interference b/w one system to another.

•       Infrared signals have high frequencies and cannot penetrate walls. Due to its short-range communication system, the use of an infrared communication system in one room will not be affected by the use of another system in the next room. This is why using an infrared TV remote control in our home will not interfere with the use of our neighbors infrared TV remote control.   

       Ø  THE DISADVANTAGES OF USING INFRARED

•       Infrared signals cannot be used for long distance communication. In addition, we cannot use infrared waves outside a building because sun's rays contain infrared waves that can interfere with communication.

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