INTRODUCTION TO INTERNET PART :- 2

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         COMMUNICATION CHANNEL
A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.
Communicating data from one location to another requires some form of pathway or medium. These pathways, called communication channels, use two types of media: cable (twisted-pair wire, cable, and fiber-optic cable) and broadcast (microwave, satellite, radio, and infrared). Cable or wire line media use physical wires of cables to transmit data and information. Twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass.

Networking cables are networking hardware used to connect one network device to other network devices or to connect two or more computers to share printers, scanners etc. Different types of network cables, such as coaxial cable, optical fiber cable, and twisted pair cables, are used depending on the network's physical layer, topology, and size. The devices can be separated by a few meters (e.g. via Ethernet) or nearly unlimited distances (e.g. via the interconnections of the Internet).
There are several technologies used for network connections. Patch cables are used for short distances in offices and wiring closets. Electrical connections using twisted pair or coaxial cable are used within a building. Optical fiber cable is used for long distances or for applications requiring high bandwidth or electrical isolation. Many installations use structured cabling practices to improve reliability and maintainability. In some home and industrial applications power lines are used as network cabling.
Twisted pair cabling, with the ubiquitous "RJ-45" 8P8C modular connector, is a form of wiring in which pairs of wires (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from other wire pairs and from external sources. This type of cable is used for home and corporate Ethernet networks. Twisted pair cabling is used in short patch cables and in the longer runs in structured cabling.
An Ethernet crossover cable is a type of twisted pair Ethernet cable used to connect computing devices together directly that would normally be connected via a network switch, Ethernet hub or router, such as directly connecting two personal computers via their network adapters. Most current Ethernet devices support Auto MDI-X, so it doesn't matter whether you use crossover or straight cables.[1]
Coaxial cables form a transmission line and confine the electromagnetic wave inside the cable between the center conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.
Early Ethernet, 10BASE5 and 10BASE2, used baseband signaling over coaxial cables. In the 20th century the L-carrier system used coaxial cable for long-distance calling.
Coaxial cables are commonly used for television and other broadband signals. Although in most homes coaxial cables have been installed for transmission of TV signals, new technologies (such as the ITU-T G.hn standard) open the possibility of using home coaxial cable for high-speed home networking applications (Ethernet over coax).
An optical fiber cable consists of a center glass core surrounded by several layers of protective material. Optical fiber deployment is more expensive than copper but offers higher bandwidth and can cover longer distances.[2] There are two major types of optical fiber cables: shorter-range multi-mode fiber and long-range single-mode fiber.

                            Differences Between Guided and Unguided Media
1.    The key difference between guided and unguided media is that guided media uses a physical path or conductor to transmit the signals whereas, the unguided media broadcast the signal through the air.
2.    The guided media is also called wired communication or bounded transmission media. However, the unguided media is also called wireless communication or unbounded transmission media.


3.    The guided media provide direction to the signal whereas, the unguided media does not direct the signal.
4.    Categories of guided media are twisted pair cable, coaxial cable and optical fibre. On the other hands, the categories of unguided media are radio wave, microwave, and infrared signal.

                                                                              Microwaves

Microwaves are of two types:
  • Terrestrial microwave
  • Satellite microwave communication


Terrestrial Microwave Transmission

  • Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio signal from one ground-based microwave transmission antenna to another.
  • Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000 GHz.
  • Microwaves are unidirectional as the sending and receiving antenna is to be aligned, i.e., the waves sent by the sending antenna are narrowly focussed.
  • In this case, antennas are mounted on the towers to send a beam to another antenna which is km away.
  • It works on the line of sight transmission, i.e., the antennas mounted on the towers are the direct sight of each other.
Characteristics of Microwave:
  • Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz to 21-23 GHz.
  • Bandwidth: It supports the bandwidth from 1 to 10 Mbps.
  • Short distance: It is inexpensive for short distance.
  • Long distance: It is expensive as it requires a higher tower for a longer distance.
  • Attenuation: Attenuation means loss of signal. It is affected by environmental conditions and antenna size.
Advantages Of Microwave:
  • Microwave transmission is cheaper than using cables.
  • It is free from land acquisition as it does not require any land for the installation of cables.
  • Microwave transmission provides an easy communication in terrains as the installation of cable in terrain is quite a difficult task.
  • Communication over oceans can be achieved by using microwave transmission.
Disadvantages of Microwave transmission:
  • Eavesdropping: An eavesdropping creates insecure communication. Any malicious user can catch the signal in the air by using its own antenna.
  • Out of phase signal: A signal can be moved out of phase by using microwave transmission.
  • Susceptible to weather condition: A microwave transmission is susceptible to weather condition. This means that any environmental change such as rain, wind can distort the signal.
  • Bandwidth limited: Allocation of bandwidth is limited in the case of microwave transmission.

               


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