TransmissionMedia

Transmission MediaTransmission Media

two major classestwo major classes

Conducted or guided mediaConducted or guided media use a conductor such as a wire or a fiber optic cable to use a conductor such as a wire or a fiber optic cable to

move the signal from sender to receivermove the signal from sender to receiver

Wireless or unguided mediaWireless or unguided media use radio waves of different frequencies and do not use radio waves of different frequencies and do not

need a wire or cable conductor to transmit signalsneed a wire or cable conductor to transmit signals

Classes of transmission media

Guided MediaGuided Media

Twisted-Pair Cable

Coaxial Cable

Fiber-Optic Cable

Twisted Pair WiresTwisted Pair Wires

Consists of two insulated copper wires Consists of two insulated copper wires arranged in a regular spiral pattern to minimize arranged in a regular spiral pattern to minimize the electromagnetic interference between the electromagnetic interference between adjacent pairs.adjacent pairs.

Often used at customer facilities and also over Often used at customer facilities and also over distances to carry voice as well as data distances to carry voice as well as data communications.communications.

Low frequency transmission medium.Low frequency transmission medium.

Copper WiresCopper Wires Primary medium to connect computers becausePrimary medium to connect computers because

Inexpensive & easy to installInexpensive & easy to install Low resistance to electric currentLow resistance to electric current

When wires placed close together in parallel, When wires placed close together in parallel, interference takes placeinterference takes place

To minimize interference, networks use:To minimize interference, networks use: Twisted pairTwisted pair

AdvantagesAdvantages Limits electromagnetic energy emissionLimits electromagnetic energy emission Prevents signals from other wires from interferingPrevents signals from other wires from interfering

Plastic coated wires

Twisted PairTwisted Pair

Twisted-pair cable

Twisted Pair WiresTwisted Pair Wires Two varietiesTwo varieties UTP (unshielded twisted pair)UTP (unshielded twisted pair)

Each wire is insulated with plastic wrap.Each wire is insulated with plastic wrap. The plastic insulation is color-banded for identification.The plastic insulation is color-banded for identification. UTP is ordinary telephone wire.UTP is ordinary telephone wire. UTP can transfer data at 1 to 100Mbps over a distance of 100M.UTP can transfer data at 1 to 100Mbps over a distance of 100M.

STP (shielded twisted pair)STP (shielded twisted pair) The pair is wrapped with metallic foil or braid to insulate the The pair is wrapped with metallic foil or braid to insulate the

pair from electromagnetic interference.pair from electromagnetic interference. The metal covering prevents the penetration of electromagnetic The metal covering prevents the penetration of electromagnetic

noise.noise. It can eliminate the phenomena called crosstalk.It can eliminate the phenomena called crosstalk. Provide better performance at lower data rates.Provide better performance at lower data rates.

UTP & STPUTP & STP

Twisted Pair WiresTwisted Pair Wires

Category 3 UTPCategory 3 UTP data rates of up to 10mbps are achievabledata rates of up to 10mbps are achievable Standard cable for most telephone systemsStandard cable for most telephone systems

Category 5 UTPCategory 5 UTP data rates of up to 100mbps are achievabledata rates of up to 100mbps are achievable more tightly twisted than Category 3 cablesmore tightly twisted than Category 3 cables more expensive, but better performancemore expensive, but better performance Used in LAN.Used in LAN.

STPSTP More expensive, harder to work withMore expensive, harder to work with

Twisted PairTwisted Pair

(a)(a) Category 3 UTP. Category 3 UTP.(b)(b) Category 5 UTP. Category 5 UTP.

Twisted Pair - Twisted Pair - ApplicationsApplications

Most common mediumMost common medium Telephone networkTelephone network

Between house and local exchange (subscriber Between house and local exchange (subscriber loop)loop)

Within buildingsWithin buildings To private branch exchange (PBX)To private branch exchange (PBX)

For local area networks (LAN)For local area networks (LAN) 10Mbps or 100Mbps10Mbps or 100Mbps

Twisted Pair AdvantagesTwisted Pair Advantages

Twisted-pair cable is used in telephone lines Twisted-pair cable is used in telephone lines for voice and data communications. for voice and data communications.

Inexpensive and readily availableInexpensive and readily available Flexible and light weight Flexible and light weight Easy to work with and installEasy to work with and install

Twisted Pair DisadvantagesTwisted Pair Disadvantages

Susceptibility to interference and noiseSusceptibility to interference and noise Attenuation problemAttenuation problem

For analog, repeaters needed every 5-6kmFor analog, repeaters needed every 5-6km For digital, repeaters needed every 2-3kmFor digital, repeaters needed every 2-3km

Relatively low bandwidth (3000Hz)Relatively low bandwidth (3000Hz)

Coaxial Cable (or Coax)Coaxial Cable (or Coax) Carries the signal of high frequency ranges than Carries the signal of high frequency ranges than

twisted pair cable,twisted pair cable, Bandwidth of up to 400 MHz.Bandwidth of up to 400 MHz. Coaxial cable has the following layers (starting from Coaxial cable has the following layers (starting from

the center): the center): a metallic rod-shaped inner conductor, an a metallic rod-shaped inner conductor, an insulator covering the rod, a metallic outer conductor insulator covering the rod, a metallic outer conductor (shield), an insulator covering the shield, and a plastic (shield), an insulator covering the shield, and a plastic cover. cover.

Both conductors share a common center axial, hence Both conductors share a common center axial, hence the term “co-axial”.the term “co-axial”.

Coaxial cable

Classification:Classification:

Coaxial cable is classified by size (RG) and by Coaxial cable is classified by size (RG) and by the cable resistance to electric currents.the cable resistance to electric currents.

Following are some coaxial cable commonly Following are some coaxial cable commonly used in networking.used in networking.

50 ohm , RG-8 and RG-11 for Ethernet.50 ohm , RG-8 and RG-11 for Ethernet. 75 ohm , RG-59 used for cable TV. 75 ohm , RG-59 used for cable TV.

Transmission rate is 10 mbps.Transmission rate is 10 mbps.

Coax AdvantagesCoax Advantages Easy to installEasy to install Coaxial cable is used in cable TV networks and traditional Coaxial cable is used in cable TV networks and traditional

Ethernet LANs. Ethernet LANs. Higher bandwidthHigher bandwidth

400 to 600Mhz400 to 600Mhz Easy to handle and relatively inexpensive as compared to fiber Easy to handle and relatively inexpensive as compared to fiber

optic cables.optic cables. Since it is shielded can span a longer distances at higher data Since it is shielded can span a longer distances at higher data

rates.rates. Excellent noise immunity.Excellent noise immunity. Much less susceptible to interference than twisted pair.Much less susceptible to interference than twisted pair.

Coax DisadvantagesCoax Disadvantages

High attenuation rate makes it expensive over High attenuation rate makes it expensive over long distancelong distance

Distance is limited.Distance is limited. Bulky Bulky Higher cost compared to twisted pairHigher cost compared to twisted pair Harder to work with & cable easily get Harder to work with & cable easily get

damageddamaged

Fiber Optic CableFiber Optic Cable Fiber-optic cables are composed of a glass or plastic inner core Fiber-optic cables are composed of a glass or plastic inner core

surrounded by cladding, all encased in an outside jacket. surrounded by cladding, all encased in an outside jacket.

Fiber-optic cables carry data signals in the form of light. The Fiber-optic cables carry data signals in the form of light. The signal is propagated along the inner core by reflection.signal is propagated along the inner core by reflection.

Relatively new transmission medium used by telephone Relatively new transmission medium used by telephone companies in place of long-distance trunk lines.companies in place of long-distance trunk lines.

Also used by private companies in implementing local data Also used by private companies in implementing local data communications networks.communications networks.

Require a light source with injection laser diode (ILD) or Require a light source with injection laser diode (ILD) or light-emitting diodes (LED).light-emitting diodes (LED).

plastic jacket glass or plasticcladding

fiber core

Fiber Optic LayersFiber Optic Layers

consists of three concentric sectionsconsists of three concentric sections

Refraction

Critical Angle

Reflection

Refraction & ReflectionRefraction & Reflection

Fiber Optic TypesFiber Optic Types Signal propagation in optical fibers can be multimode Signal propagation in optical fibers can be multimode

(multiple beams from a light source moves through different (multiple beams from a light source moves through different path) or single-mode (essentially one beam from a light path) or single-mode (essentially one beam from a light source). source).

Multimode step-index fiberMultimode step-index fiber In multimode step-index propagation, the core density is In multimode step-index propagation, the core density is

constant and the light beam changes direction suddenly at constant and the light beam changes direction suddenly at the interface between the core and the cladding.the interface between the core and the cladding.

Multimode graded-index fiberMultimode graded-index fiber In multimode graded-index propagation, the core density In multimode graded-index propagation, the core density

decreases with distance from the center. This causes a decreases with distance from the center. This causes a curving of the light beams.curving of the light beams.

Single mode fiberSingle mode fiber•This uses step-index fiber and a highly focused source of light This uses step-index fiber and a highly focused source of light •Has very low density,which make c=90,so beam becomes almost Has very low density,which make c=90,so beam becomes almost horizontal.horizontal.

fiber optic multimodestep-index

fiber optic multimodegraded-index

fiber optic single mode

Fiber Optic SignalsFiber Optic Signals

Fiber Optic AdvantagesFiber Optic Advantages Higher transmission rate of 100Mbps.Higher transmission rate of 100Mbps. It supports voice,video and data.It supports voice,video and data. Greater capacity (bandwidth of up to 2 Gbps).Greater capacity (bandwidth of up to 2 Gbps). Smaller size and lighter weightSmaller size and lighter weight Lower attenuationLower attenuation Immunity to environmental interferenceImmunity to environmental interference Highly secure , it is almost impossible to tap into a Highly secure , it is almost impossible to tap into a

fiber cable.fiber cable. Safe and easy installation.Safe and easy installation. More compact & lighter than copper wireMore compact & lighter than copper wire

Fiber Optic DisadvantagesFiber Optic Disadvantages

expensive over short distanceexpensive over short distance UnidirectionalUnidirectional requires highly skilled installersrequires highly skilled installers adding additional nodes is difficultadding additional nodes is difficult Maintenance and repairing cost is high.Maintenance and repairing cost is high.