3 Data Transmission Transmission of data depends on Quality of signalCharacteristics of mediumNeed to do signal processingNeed to measure quality of received signalAnalog: signal-to-noise ratioDigital: probability of symbol errorTo transmit bits (0’s or 1’s) we need to map them into electromagnetic waves. Modulation techniques.
4 Data Transmission Transmitted signals are AttenuatedDistortedCorrupted by noiseAttenuation and distortion depend onType of transmission mediumBit rateDistanceMedium determinesData rateBandwidth of channel
5 Data Transmission Medium: Direct link: point-to-point or guided Guided: twisted pair, coaxial cable, optical fiberUnguided: radio, satellite, infrared, microwaveDirect link: point-to-point or guidedTwo devices share the medium (intermediate repeaters, amplifiers)Indirect link: multipoint or broadcastMore than two devices share the mediumTransmission modes: simplex, half-duplex, full-duplexFrequency, spectrum, bandwidthTime-domain vs. frequency domain
6 Data TransmissionBandwidth: several criteria, choice depends on application (3dB or 50% power; fraction of signal power)Nyquist formulaMaximum data rate as a function of channel bandwidth (BW)if BW=B then max. data rate is 2B2 levels per signaling elementGeneralC = 2B log2 (M) [bps], M = levels per signaling element
7 Data TransmissionAttenuation: strength of signal falls off with distance; increases as a function of frequencyDelay distortion: propagation velocity varies with frequency; different frequency components arrive at different timesNoise: thermal, intermodulation, crosstalk, quantization, impulseData rate: C = B log2 (1 + S/N) [bps]
9 Transmission Medium Twisted pair (UTP, STP) two insulated copper wires arranged in a spiral fashionwire pair acts as a single communication linktwist length varies from 2-6 inchesthickness varies from to inchesused in telephone networksused within buildingsinexpensive compared to other mediaeasy to work withpoor noise and interference immunitytwisted to avoid crosstalk
10 Transmission Medium Twisted pair (UTP, STP) analog signal amplifiers required every 5 to 6 kmdigital signal repeaters required every 2 to 3 kminterference reduced by sheatingUTP: ordinary telephone wire, cheapest media for LANs, subject to interferenceSTP: less prone to interference, more expensive, harder to work withEIA-568-A standard recognizescategory 3 UTP capable of 16MHzcategory 4 UTP capable of 20 MHzcategory 5 UTP capable of 100MHz
11 Data Rate Capacity of UTP Cables Capacity Mb/s1000NEXT - DominatedEnvironment800Category 5600Category 4400Category 3200100mHorizontal Link (ft)100200300400500600700800
12 Transmission Medium Coaxial cable hollow outer cylindrical conductor surrounding a single inner wireregularly spaced insulating dielectric hold inner conductor in placejacket or shield covers the outer conductordiameter 0.4 to 1 inchtelevision distribution: CATVlong distance telephone transmissionshort run computer I/O channelsLANsbetter frequency characteristics, higher data rates, and more immune to interference than twisted pair
13 Transmission Medium Optical fiber 2 to 124 um flexible medium conducts and optical raycore: innermost section; cladding: middle section forms a plastic coating over the core; jacket: the outer most section covering the claddingdata rates of 2Gbps over tens of kmsignificantly low attenuationnot susceptible to interference or crosstalkused for: long haul, metropolitan, and rural trunks, subscriber loops and LANs
14 Transmission Medium Optical fiber Multimode transmission rays entering the core reflect and propagate along the fiberSingle mode transmissionradius of core reduced to one wavelengthonly a single angle of reflection is allowedprovides superior transmissionXMTR: light-emitting diode (LED) or injection laser diode (ILD)RCVR: photodiode or photo transistor
15 Transmission Medium Wireless terrestrial microwave satellite microwave broadcast radioinfraredlaser
16 Transmission Medium Terrestrial microwave requires line of sight requires fewer amplifiers or repeaterslong haul telecommunication servicesvoice and TV transmissionpoint-to-point links between buildings
17 Transmission Medium Satellite microwave relays used to link ground stationsfunctions as an amplifier or a repeatercan provide point-to-point to point-to-multipoint connectivitytelevision distributionlong distance telephone transmissionprivate business networks
18 Transmission Medium Broadcast radio omnidirectional does not require complex antennasantennas need not be precisely alignedFM radioVHF and UHF televisiondata networks
19 Transmission Medium Infrared XMTR/RCVR (transceivers) modulate non-coherent infrared lightline of sight is neededno frequency allocation is neededprovides point-to-point connectivity
20 Cabling Systems Evolution 1980’s View, Dedicated Application Proprietary Wiring, Central Processing, Voice and Data Separate1990’s View, Integrated Open Architecture Wiring System, Voice/Data/Image/VideoNeed for High-Speed Transmission, 100/155 Mbps and Higher, Require Significantly more Bandwidth
22 Cabling Systems Evolution Cable systems must be developed to address:Non CompatibleNon StandardConventional Type Wiring PlansDesigned to ease the introduction of new computer systems, LANs and PBXs
23 Cabling Systems Concerns Installing and Maintaining a Reliable Cable Plant is Essential to the Well-Being of Today’s Mission Critical LANsCategory 5 UTP is Today’s Preferred Choice for LAN CablingWhy is Category 5 UTP the Best Bet for Horizontal Wiring?How Does it Handle 100/155 Mbps + Data Rates?How Do You Maximize the Performance of Your UTP Installation?
24 Cabling Systems Concerns Voice: Wiring system placed by PBX vendor or telephony networks to all identified work locationsData: Wiring placed by data networks on an as needed basisProprietary Application Media (Coax, Dual Coax, Shielded)Data Processing Systems - Mainframe (IBM 3270, IBM System 36/38 AS 400, etc..)PC - Stand alone
25 Cabling Systems Concerns LAN electronics vendors estimate cabling problems account for 50% of all LAN failures and problemsLAN Technology stated that 70% of downtime is attributed to cable related problemsA Communications Week study in January 1992 Found network downtime cost small companies $3, per hourInfonectics Corporation study in October 1993 found network downtime cost Fortune 1000 companies an average of $62,500 per hour.
26 Network Costs 34% 5% 7% LAN Wiring Intelligent Workstation Wiring LAN Attachment5%LANAttachment7%Software &MainframeIntelligentWorkstation54%Software & Mainframe
27 Cabling Systems Trends 100 Mbps over Copper, solutions for UTP already exist100 Mbps over Fiber, Momentum has SlowedFast Ethernet* 100 Mbps, on both CAT3 and CAT5 CablesATM 155 Mbps do-ableTheoretical limits of some manufactures CAT5 cables is more than 950 Mbps at 100 Meters.
28 Cabling Systems Properties Open ArchitectureIntegrated Distribution PlanStandards CompliantCost EffectiveEnd-to-End OfferingFull Functionality and FlexibilityManageable GrowthInvestment Protection
29 Network cablingNetworking supports transmission and reception of data.Network cabling provides the physical path for transmission and reception of data.1
30 Overview Transmission media typically used Bounded media Electrical conductors (eg coaxial cable, twisted wire pairs).Optical conductors (eg Optical Fiber ).Waveguides (air is the transmission medium but the waveguide confines or “binds” the transmission).Unbounded mediaTransmission of electromagnetic waves or light through air or space.
31 Bounded media Also known as guided media. Bounded transmission media constrain and guide communication signals.Media using electrical signals areSingle conductorPaired cable andCoaxial cable
32 Bounded media ( Cont.) Media using light signals Optical fiberMedia using electromagnetic wavesWaveguides
33 Single conductorA single conductor is used to provide a path for an electric current.The earth provides the return path ( since a circuit needs to be complete for current to flow).Today, used for short distances, like on a circuit board or on a silicon chip.
34 Paired cableTwo Conductors are used, with second conductor providing the return path for the signal current.Two cables can beOpen wire pair (parallel to each other ).Unshielded twisted pair ( twisted ).Shielded twisted pair (seldom used today).Open wires are susceptible to to cross talk and electromagnetic interference and are seldom used.
35 Paired cable (Cont.)To avoid cross talk and interference the pairs of conductors are twisted.A twisted pair consists of 2 insulated copper wires twisted together.Usually number of these pairs are bundled together into a cable. Long distance cables may contain hundreds of pairs (eg telephone cables).
36 Paired cable (Cont.)Twisting decreases the cross talk interference between adjacent cables by confining the electromagnetic field.Twisted pair can be used for short distances ( usually less than 10 miles).Longer distances require repeaters to regenerate the signal.
37 Paired cable (Cont.)It has bandwidth limitations, when used over long distances.It is susceptible to noise since not all interference is eliminated.It is widely used for local telephone and data transmission.
38 Paired cable (Cont.)It provides the “local loop” for telephone but the bandwidth is limited.It can support 155Mbps transmission over short (less than 30ft) distances.It is therefore widely used for network cabling within buildings (intrabuilding cabling).
39 Coaxial cable Coaxial cable consists of two conductors. An inner conductor is completely sorrounded by an outer conductor.The two conductors are separated by high quality insulation.The outer conductor is sorrounded by a protective sheath.
40 Coaxial cable (Cont.)Coaxial cables can be used for transmission of high frequency signals.Using frequency or time division multiplexing (FDM or TDM) many channels can be supported by single cable.It is widely used for cable TV.
41 Coaxial cable (Cont.)It was widely used for (thick and thin cable) ethernets but it is being rapidly displaced by unshielded twisted pairs for this purpose.
42 WaveguidesA waveguide is a rectangular or circular pipe, usually made of some conductor such as copper.It confines and guides very high frequency radio waves between two locations.Waveguides are used for signals in the range of gigahertz (GHz) frequencies where twisted pair or even coaxial cables are not effective.
43 Optical fibersOptical fiber is a thin, flexible glass or plastic fiber through which light energy is transmitted.An optical fiber is actually a waveguide that guides the propogation of optical frequency waves through total internal reflection.
44 Optical fibers (Cont.)Since most of the data that need to be transmitted are in the form of electrical signals, these signals must be converted to light signals before they can be transmitted by optical fibers.
45 Optical fiber communication system TransmitterOpticalFiberOpticalReceiverInformationInformationMultiplexerOpticalReceiverOpticalRepeaterOpticalTransmitterMultiplexerFIG. 1. Typical optical fiber communication system.
46 Optical fibers (Cont.)Fiber optic transmission systems have transmitters which useLED (Light emitting diode) used primarily for short distances (< 2km) transmission orLASER diodes used primarily for longer distance transmissionto convert electrical signals to light signals.
47 Optical fibers (Cont.)The receiver uses a photo diode to convert the light signals back to electrical signals.It offers large bandwidth.Signal loss is very low.Fibers are immune to electromagnetic interference.
48 Optical fibers (Cont.)A basic optical fiber consists of two concentric layers, the inner core and the outer cladding which has a specific refractive index lower than the core.There are 2 types of refractive index profiles, step and gradedFor a step profile fiber, the inner core’s refractive index is uniform, for a graded fiber, the profile inner core’s refractive index is not uniform.
50 Optical fibers (Cont.) There are 3 basic types of fibers In multimode Single mode.Multimode graded index.In multimodeInner core diameter is relatively large (50 to 62.5 microns).Light travels in different modes.
51 Optical fibers (Cont.) In single mode fibers Used for short or medium distances ( < 2km).Cheap compared to other types.Supports medium to high bandwidths.In single mode fibersInner diameter is very small, typically 0.8 to 1 micron.Light travels in single mode.Used for medium and long distances (> 2km).More costly than multimode fiber.Can support very high bandwidths (6 Gbps).
52 Optical fibers (Cont.) In multimode graded index fibers Core is relatively large but difficult to manufacture.Properties are intermediate between single and multimode fibers.Because of difficulty in manufacture, such fibers are seldom used in data networking.
53 Unbounded media No physical connection is required. Space or air is the transmission medium for electromagnetic waves.Source and destination can be static or mobile.Broad spectrum from low to high bandwidth is available.Can be quickly implemented.
54 Unbounded media (Cont.) It is prone to interference.Transmission spectrum has to be shared and must be controlled to prevent interference in any given location.Different unbounded communication systemsBroadcast radio and television.Terrestrial microwave.Satellite.Infra red.
55 Network cabling Transmission media of interest for network cabling Twisted pairCoaxialFiberWireless
56 Twisted pair Least expensive. Flexible Easy to install Widely used. There are two varietiesUTP ( Unshielded twisted pair ).STP ( Shielded twisted pair ).
57 UTP Least expensive and popular. It is light and flexible. Easy to install.It is not shielded by external conductors.It is subject to electromagnetic interference and external noise.Twisting minimizes electromagnetic interference.
58 UTP (Cont.)For data transmission 3 categories of UTP cabling can be usedCategory 3 (cat 3 is for data rates upto 16 Mbps)Category 4 (cat 4 is for data rates upto 20 Mbps)Category 5 (cat 5 is for data rates upto 100 Mbps and even 155Mbps for limited distances)
59 UTP (Cont.) Cat 3 and Cat5 are used extensively Cat3 is voice grade cable and widely used for telephone.It has 3 to 4 twists per foot.Cat 5 is data grade cable and widely used for data networking.
60 UTP (Cont.) It has 6 to 12 twists per inch. Tighter twisting provides better performance but is more expensive.Characteristic impedance of both cat 3 and cat 5 is 100 Ohms.Cat5 is recommended, for data since it can support higher bandwidths.
61 STPTwisted pairs of copper wire are sorrounded with metallic braid or sheathing.Interference is reduced due to sheathing.Characteristic impedance is 150 Ohms.At lower data rates STP provides better performance than UTP.It creates less electrical noise.It is more expensive.
62 STP (Cont.) It is bulky. Less flexible. Installation is more expensive.Difficult to work with compared to UTP.
63 Coaxial cableIt consists of single copper conductor at its center surrounded by a hollow cylindrical outer conductor, with the 2 conductors separated by a dielectric medium.Outer conductor provides a shield.Coaxial cable is highly resistant to signal interference because the electromagnetic field is confined between the inner and outer conductors.
64 Coaxial cable (Cont.)Less susceptible to cross talk than twisted pair cable.It can support greater cable lengths between network devices than twisted pair cables.It can support much larger bandwidths than twisted cable pairs.It is bulky.
65 Coaxial cable (Cont.)More difficult to install and work with than twisted pair cables.It is more expensive than twisted pairs.Coaxial cable was used in thin ethernet (10Base-2) and thick ethernet (10Base-5), but is now largely being replaced by cat5 UTP.
66 Fiber optic cableAn optical fiber is a thin (0.8 to 125 µm), flexible medium capable of conducting light.It has the ability to transmit signals over much longer distances than coaxial and twisted pair cables.Very high data rates (gigabits per second ) can be achieved over optical fiber.
67 Fiber optic cable (Cont.) Theoretically 50Gbps are possible over fiber optic.Data rates of 4.8 Gbps over tens of kilometers have been demonstrated.Current dat rates are limited by the electronics and the optical transmitter/receivers.Optical fiber has the advantage of being thinner and lighter over coax or a bundle of twisted pair cables.
68 Fiber optic cable (Cont.) It has lower attenuation than coax and twisted pair cables.Since it transmits light, the problem of electrical interference is eliminated.It is also immune to the environmental (eg. moisture, lightening) disturbances.
69 Fiber optic cable (Cont.) The advantage of optical fiber over coax and twisted pair will be more compelling as the demand for greater bandwidth increases.It is highly secure medium, because it is difficult for any break to go undetected.The main disadvantage is it is very expensiveInstallation is expensive.
70 Fiber optic cable (Cont.) Cannot tolerate small bending radius.Difficult to work with because it is delicate.
71 WirelessWireless media has the benefit of relatively inexpensive installation in an environment where users are mobile.It can also be beneficial in extending the network without rewiring the existing network.The 3 ways in use as of now areMicrowaveSpread spectrumInfrared
72 Microwave signalsUses a highly directional antenna to minimize interference.Frequencies used for transfer of information are dedicated.Usually suports point to point transmission.FCC regulates the bandwidth allocation.
73 Microwave signals (Cont.) Has the disadvantage of using only part of the total available bandwidth.Microwave signals can cross through walls and physical barriers.Prone to interference from other sources of microwave signals.
74 Microwave signals (Cont.) In general, it is relatively expensive but it may be the cheapest form of transmission over rough and mountainous terrain.Requires high power.Data rates upto 500 Mbps are possible.Exposure to microwave radiation may be risky (health wise).
75 Spread spectrum It doesn’t require FCC license. In this method each node has a radio transceiver.Each node uses an antenna to send and receive information.The signal to be transmitted is spread over a broad range of frequencies, so that signals look like noise.
76 Spread spectrum (Cont.) The receiving station extracts its message, thus allowing a greater number of users to share the bandwidth.There are 2 ways to do thisFrequency hopping.Direct Sequence.
77 Spread spectrum (Cont.) In frequency hoping the transmission frequency is made to hop (change) rapidly. The receiver also hops in synchronism with transmitter and picks up the message.In direct sequence method, each bit is chipped into multiple bits using a bit pattern (thus spreading the signal over wider frequencies), with the help of same bit pattern receiver detects the bits.Data rates of upto 1-2Mbps are achievable.
78 Infrared In this method infrared light is modulated by transmitter. Transceivers must be in line of sight either directly or via reflection from a light colored surface such as a ceiling of a room.Data rates of upto 20Mbps are possible.No security or interference problems, as infrared transmission does not penetrate the walls.
79 Infrared (Cont.) License is not required. Short range, point to point and potential eye damage if exposed to IR rays are the main disadvantages of infrared transmission.
80 Standards based cabling Unstructured cablingNo single standard is followed for interconnectionLow initial cost, more expenses later.Difficulties in the long run with developing technologies.Difficulty in maintenance and scalabilityStructured cabling increases initial cost but can avoid the problems and future expenses.
81 Standards based cabling (Cont.) Telecommunications industry and the users realized the need for cost effective, efficient cabling systems.
82 Standards based cabling (Cont.) Electronic Industries Association (EIA), Telecommunications Industry Association (TIA) and other leading telecommunication companies worked cooperatively to create ANSI/TIA/EIA-568-A standard for commercial buildings.This standard defines structured cabling, a telecommunication cabling system that can support virtually any voice, imaging or data applications that an end user chooses.
83 TIA/EIA 568-A standard EIA/TIA 568-A specifications address Recognized media.Topology.Cabling distances.User interfaces.Cabling and Connecting hardware performance.Installation practices.Link performances.
84 Cabling elements Horizontal Cabling. Backbone Cabling. Work Area (WA). Telecommunications closet (TC).Equipment Room (ER).Entrance Facility (EF).
85 Horizontal cablingIt extends from the telecommunications outlet in the work area to the horizontal cross connect in the telecommunications closet.TerminalWork AreaTelecommunicationsCloset
86 Horizontal cabling (Cont.) It includesThe outlet.Horizontal cables.Mechanical terminations and Patch cords (or jumpers) that comprise the horizontal cross connect (each outlet in work area is connected to a horizontal cross connect in the telecommunications closet) .
87 Horizontal cabling (Cont.) Specifications here are aboutProximity to EMI.No. of outlets for each individual workarea.UTP, STP and Fiber are recognized.Coax is recognized but not recommended for new cabling installations.Horizontal cabling shall be configured in star topology.Other such issues.
88 Backbone cablingThe backbone cabling system provides interconnections betweenTelecommunication closets.Equipment rooms.Entrance facilities.It also includes the vertical wiring between floors, hence also known as vertical wiring.Backbone also extends between buildings in a campus environment.
89 Backbone cabling (Cont.) The specifications includeBackbone cables.Intermediate and main cross connects including mechanical terminations.Patch cords or jumpers used for backbone to backbone cross connections.Recognized cables here are UTP, STP, Multimode and single mode fiber.
90 Work area Work area specifications consist of Cable connecting user station to wall plate.Devices connecting the user station to the wall plate.Work area wiring is typically UTP or STP.
91 Telecommunication closet Also known as wiring closet.One on each floor (typically, depending on the floor space and special requirements number may vary).Standards complaint connecting hardware should be used.Specifications about short cables (patch chords) are made.
92 Equipment roomIn large office buildings, there will be centralized equipment rooms to house servers, hubs, modems etc.It is the central interconnection point for network cabling.Main cross connections are specified here.
93 Entrance facility It is the network entry point of the building. Within the network entrance facility, a cross connect device provides a termination point for all the cables.Interfaces are specified.Interconnection for cross connect devices and network devices are specified.
94 Other specificationsIn addition to the cabling elements in TIA-568-A, there are specifications (connectors, cables, color coding etc) forUTP cabling.Fiber Optic cabling.STP cabling.
95 Design considerations Structured wiring is the way to go.Highest quality connectors should be used.While connecting twisted pair cables to punch down blocks, care must be taken not exceed the bend radius of the cable (otherwise there can be signal leaks, leading to interference).Copper cables should not be run very close to power lines or parallel to them, otherwise there can be interference.
96 Design considerations(Cont.) The end of the cable should not be untwisted more than needed, as this may result in excessive cross talk.Plenum grade cable must be used where there is a possibility of fire (like area above the suspended ceilings).NEC specifications for fire safety of cable installation should be followed .
97 Design considerations(Cont.) While splicing fiber optic cable care must be raken to splice it perfectly at right angles.The connection of fiber to the optical connector must be perfect.Fiber should not be bent beyond its bending radius (several inches).Have patch cables as short as possible.
98 Design considerations(Cont.) Label all the cables and connectors.Maintain an accurate wiring plan.Avoid using already installed telephone cable (since it is not a data grade cable).