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.