Communication Media, Servers and Clients

FUNDAMENTALS OF NETWORKINGCHAPTER 3TRANSMISSION MEDIA ; SIGNAL POWERIntroduction

Communications network cannot exist without a medium to connect the source and the receiver to provide a path over which messages can be sent.Medium : 1) Physical wire or cable 2) Wireless transmission medium

Guided MediaTwisted Pair WireCoaxial CableFiber Optic Cable

Twisted Pair Wire:1) Unshielded Twisted Pair (UTP)The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices.The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging).

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connectorA slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connectorShielded Twisted Pair (STP)Each pair of wires is placed into a metallic shieldWhich is a wrapping made of thin wires to absorb any interference.The wires then are put into a plastic outer shell.STP typically is used when many wires need to be packed together in a small space or in an environment with considerable electrical equipment.STP wires are reliable for transmitting data in high-interference area.

Coaxial CableCoaxial cabling has a single copper conductor at its centre. A plastic layer provides insulation between the centre conductor and a braided metal shieldAlthough coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable.

Fiber Optic Cable

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials .It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference

Fibre optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services.There are three common types of fibre cablesMultimode step index is an early form of fiber optic cable that uses a plastic coating or a mirror-like cladding around the core to reflect the light from the laser and LED.As the light is reflected off the sides of the cables, it moves down the cable to its destination.Multimode graded index- the core of the varies in density, which bends the light.Single mode can provide more distance, but it is more expensive.

Unguided Media

Type of unguided Media :Air,Vacuum of space

Forms of transmission that use unguided media : broadcast radio, terrestrial and satellite microwave transmission, cellular radio, spread spectrum radio, and infrared transmission.Wireless (Unguided Media) Transmissiontransmission and reception are achieved by means of an antennadirectionaltransmitting antenna puts out focused beamtransmitter and receiver must be alignedomnidirectionalsignal spreads out in all directionscan be received by many antennasWireless Examplesterrestrial microwavesatellite microwavebroadcast radioinfraredTerrestrial MicrowaveAsystem,method,technology, orservice, such asMultichannel Multipoint Distribution Service, which utilizesmicrowaveline of sightcommunicationsbetween sending and receiving units located on thegroundor on towers, as opposed to asenderand/orreceiverantennabeing located on a communications satellite. Used, for instance, fortelephone,TV, and/ordataservices. Also called Terrestrial Microwaveradio.uses radio frequency spectrum, from 2 to 40 Ghzparabolic dish transmitter, mounted highused by common carriers as well as private networksrequires unobstructed line of sight between source and receivercurvature of the earth requires stations (repeaters) ~30 miles apart

20Satellite Microwave TransmissionMicrowave transmissionrefers to the technology oftransmittinginformation or energy by the use ofradio waveswhosewavelengthsare conveniently measured in small numbers of centimeter; these are calledmicrowaves.a microwave relay station in spacecan relay signals over long distancesgeostationary satellites remain above the equator at a height of 22,300 miles (geosynchronous orbit)travel around the earth in exactly the time the earth takes to rotate21Satellite MicrowaveApplicationsTelevision distributionLong-distance telephone transmissionPrivate business networks

Microwave Transmission Disadvantagesline of sight requirementexpensive towers and repeaterssubject to interference such as passing airplanes and rainSatellite Transmission LinksInsatellite communication, signal transferring between the sender and receiver is done with the help ofsatellite. In thisprocess,the signal which is basically a beam of modulated microwaves is sent towards thesatellite. Then thesatelliteamplifiesthe signaland sent it back to the receivers antenna present on the earths surface. So, allthe signaltransferring is happening in space. Thus this type of communication is known as space communication.24

dishdishuplink stationdownlink stationsatellitetransponder22,300 milesSatellite Transmission Process25Satellite Transmission Applicationstelevision distributiona network provides programming from a central locationdirect broadcast satellite (DBS)long-distance telephone transmissionhigh-usage international trunksprivate business networksPrincipal Satellite Transmission BandsC band: 4(downlink) - 6(uplink) GHzthe first to be designated Ku band: 12(downlink) -14(uplink) GHzrain interference is the major problemKa band: 19(downlink) - 29(uplink) GHzequipment needed to use the band is still very expensiveFiber vs Satellite

28Radioradio is omnidirectional and microwave is directionalRadio is a general term often used to encompass frequencies in the range 3 kHz to 300 GHz. Mobile telephony occupies several frequency bands just under 1 GHz.InfraredInfrared(IR) light iselectromagnetic radiationwith longerwavelengthsthan those ofvisible light, extending from the nominalrededge of thevisible spectrumat 0.74micrometers(m) to 0.3mm.Uses transmitters/receivers (transceivers) that modulate noncoherent infrared light. Transceivers must be within line of sight of each other (directly or via reflection ). Unlike microwaves, infrared does not penetrate walls.AttenuationIt is the gradual loss in intensity of any kind offluxthrough a medium. For instance, sunlight is attenuated by dark glasses,X-raysare attenuated by lead, andlightandsoundare attenuated by waterInelectrical engineeringandtelecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, as well as in air (radio waves)Attenuation (Cont.)Reduction of signal strength during transmission. Attenuation is the opposite ofamplification,and is normal when a signal is sent from one point to another. If the signal attenuates too much, it becomes unintelligible, which is why mostnetworksrequirerepeatersat regular intervals. Attenuation is measured indecibels