COMP 1121COMP 1121

Computers and Computers and Computer NetworksComputer Networks

PM/RHPM/RH

Spring 2011Spring 2011

LANs: OSI levels 1&2 LANs: OSI levels 1&2 Topology, CablingTopology, Cabling, , HardwareHardware

Objectives:Objectives:» Show awareness of the various LAN

topologies, methods of data transmission, and IEEE 802 standards

» Explain the architecture of structured UTP cabling on a LAN

» Explain the roles of network adapter cards, repeaters, and hubs in a typical LAN

Classification by TopologyClassification by Topology

TopologyTopology of a network is of a network is concerned with the concerned with the layout of the computers that will become layout of the computers that will become networked – in particular:networked – in particular:» the pattern of the pattern of location of location of nodesnodes» the way those the way those nodesnodes are interconnected are interconnected

Topology can be used in association with Topology can be used in association with TTransmission ransmission MMediumedium (e.g. type of cabling) (e.g. type of cabling) toto determinedetermine::» the type of data that can be the type of data that can be sent across that sent across that

networknetwork» speed of transmissionspeed of transmission

Star Topology (revision)Star Topology (revision)

Central server(s)

Remote client

Remote client

Star Topology (revision)Star Topology (revision)

UUsed for mainframe computers/dumb sed for mainframe computers/dumb terminals since the very early days of terminals since the very early days of computer networkingcomputer networking

Went out of favour in the early days of Went out of favour in the early days of LANs, which generally used one of:LANs, which generally used one of:» Bus topology and coaxial cablingBus topology and coaxial cabling

» IEEE 802.3 base 2IEEE 802.3 base 2

» Token ring with twisted pairToken ring with twisted pair» IEEE 802.5IEEE 802.5

Bus TopologyBus Topology

Central Server

Remote client

Remote client

Bus TopologyBus Topology

T-pieces electrically connect computers T-pieces electrically connect computers to the backboneto the backbone

Bus carries all network dataBus carries all network data All nodes are connected to a single All nodes are connected to a single

common cable known as the common cable known as the backbonebackbone The backbone is end-to-end, and a The backbone is end-to-end, and a

terminator is needed at each end to terminator is needed at each end to prevent signal bounce and complete the prevent signal bounce and complete the circuitcircuit

Ring TopologyRing Topology

Central Server

Remote client

Remote client

Ring TopologyRing Topology

No central hubNo central hub data from one node:data from one node:

» passes into a “ring” of cablingpasses into a “ring” of cabling» taken round the ringtaken round the ring» off the ring to another nodeoff the ring to another node

Mechanism:Mechanism:» the node receives all network datathe node receives all network data» takes the data that is addressed to ittakes the data that is addressed to it» passes the rest back to the ringpasses the rest back to the ring

Return of the Star Topology…Return of the Star Topology… Breakthrough in LAN cabling technology Breakthrough in LAN cabling technology

(1984) (1984) First used by AT&T “StarLAN”First used by AT&T “StarLAN” Revolutionary at the time because it used Revolutionary at the time because it used

standard US analogue telephone wiringstandard US analogue telephone wiring» meant that telephone-type connectors (RJ45) could meant that telephone-type connectors (RJ45) could

be usedbe used» allowed TIA568 twisted pair cables to be used…allowed TIA568 twisted pair cables to be used…

IEEE base T standard soon followedIEEE base T standard soon followed» IEEE 802.3e (1987)IEEE 802.3e (1987)» Evolved to IEEE802.3i (1990) 10baseTEvolved to IEEE802.3i (1990) 10baseT» IEEE 802.3u (1995) 100baseTIEEE 802.3u (1995) 100baseT

Twisted Pair CableTwisted Pair Cable Four wire pairs distinguished by insulation colour Four wire pairs distinguished by insulation colour

codes:codes:» Two greenTwo green

» Pins 1 & 2 – “straight-through” connectionPins 1 & 2 – “straight-through” connection» Pins 3 & 6 – “crossover” connectionPins 3 & 6 – “crossover” connection

» Two orangeTwo orange» Pins 1 & 2 – “crossover” connectionPins 1 & 2 – “crossover” connection» Pins 3 & 6 –“straight-through” connectionPins 3 & 6 –“straight-through” connection

» Two blueTwo blue» Pine 4 & 5 - only used in “Gigabit” EthernetPine 4 & 5 - only used in “Gigabit” Ethernet

» Two brownTwo brown» Pins 7 & 8 – Power (to 48v) over EthernetPins 7 & 8 – Power (to 48v) over Ethernet

Star Topology (RJ45 connectors)Star Topology (RJ45 connectors)

Pins 1 & 2Pins 1 & 2» TX_D1+ Transceive Data+TX_D1+ Transceive Data+» TX_D1- Transceive Data-TX_D1- Transceive Data-

Pin 3Pin 3» RX_D2+ Receive Data+RX_D2+ Receive Data+

Pins 4 & 5Pins 4 & 5» BI_D3+ Bi-directional Data+BI_D3+ Bi-directional Data+» BI_D3- Bi-directional Data-BI_D3- Bi-directional Data-

Pin 6Pin 6» RX_D2- Receive Data-RX_D2- Receive Data-

Pins 7 & 8 – Power over EthernetPins 7 & 8 – Power over Ethernet» BI_D4+ Bi-directional Data+BI_D4+ Bi-directional Data+» BI_D4- Bi-directional Data-BI_D4- Bi-directional Data-

Star TopologyStar Topology RJ45 connectors have 8 wire connections or RJ45 connectors have 8 wire connections or

“pins” “pins” » appropriate for 4 “twisted pairs”appropriate for 4 “twisted pairs”

Possible confusion: can be wired in two ways:Possible confusion: can be wired in two ways:» TIA568A connection – “straight-through”TIA568A connection – “straight-through”

» cables connect PCs through an intermediate device (hub cables connect PCs through an intermediate device (hub or switch)or switch)

» send on pins 1 & 2, receive on 3 & 6send on pins 1 & 2, receive on 3 & 6

» TIA568B connection – “crossover”TIA568B connection – “crossover”» cables connect PCs together directlycables connect PCs together directly» send on pins 3 & 6, receive on 1 & 2send on pins 3 & 6, receive on 1 & 2» wiring requirements: Pin 1-Pin 3 Pin 5-Pin 5 Pin 2-Pin 6 Pin wiring requirements: Pin 1-Pin 3 Pin 5-Pin 5 Pin 2-Pin 6 Pin

6-Pin 2 Pin 3-Pin 1 Pin 7-Pin 7 Pin 4-Pin 4 Pin 8-Pin 86-Pin 2 Pin 3-Pin 1 Pin 7-Pin 7 Pin 4-Pin 4 Pin 8-Pin 8

SStar tar TTopology (Hubs)opology (Hubs)

Client-Server network: all nodesClient-Server network: all nodes connectedconnected to hubs to hubs

Hubs can link to other hubs, creating a Hubs can link to other hubs, creating a hierarchyhierarchy

Ultimately join to a common central Ultimately join to a common central locationlocation» all packets of data transferred through the all packets of data transferred through the

network have to go through the network have to go through the main main hubhub» this must be able to support a VERY high this must be able to support a VERY high

bandwidthbandwidth

Simple SSimple Star tar TTopology with Hubopology with Hub

server

hub

client

Structured SStructured Star tar TTopologyopology

server

main hub

client

Sec. hub Sec. hubSec. hub

client client

IEEE Standards and Simplex, IEEE Standards and Simplex, Half Duplex, Full Duplex transn.Half Duplex, Full Duplex transn.

IEEE standards developed to accept the various transmission options:» 802.3e assumed simplex» 802.3u provides a choice of simplex, half-

duplex, duplex or autonegotiation using network adapter card software

» can cause problems with increased collisions if autonegotiation produces “duplex mismatch”

» 802.3ab provides for using duplex transmission on all four twisted pairs of wires

» overcomes the “duplex mismatch” problem» “unkind” to poor wiring

Fault Tolerance and Fault Tolerance and Structured CablingStructured Cabling

QuiteQuite fault tolerant system because fault tolerant system because::» if if one network link failsone network link fails……» only a single node loses connectiononly a single node loses connection

If the hub itself fails then thIf the hub itself fails then thatat whole whole subsubnetwork failsnetwork fails!!» break needs to be detected efficiently and break needs to be detected efficiently and

the hub replaced as quickly as possiblethe hub replaced as quickly as possible» Needs to be a spare readily availableNeeds to be a spare readily available

Mesh TopologyMesh Topology

Each computer on the network is Each computer on the network is attached to several other computersattached to several other computers

Only suitable for peer-peer networksOnly suitable for peer-peer networks Uses a lot of cableUses a lot of cable VVery good for fault toleranceery good for fault tolerance The Internet is a mesh networkThe Internet is a mesh network

The Internet is a large The Internet is a large Mesh NetworkMesh Network

275+ million Server computers!

Types of Wireless Media - Types of Wireless Media - MicrowavesMicrowaves

Frequency range:Frequency range:» 300 MHz to 300 GHz300 MHz to 300 GHz

Examples:Examples:» Cellular Mobile Phone networksCellular Mobile Phone networks

» Connecting mobile phones to the InternetConnecting mobile phones to the Internet

» Satellite microwaveSatellite microwave» Data to/from satellite in geocentric orbit (22300 miles up!)Data to/from satellite in geocentric orbit (22300 miles up!)

» Uplink at a different frequency to downlinkUplink at a different frequency to downlink

» Point-point microwavePoint-point microwave» Data transmitted either across roofs of adjacent campus Data transmitted either across roofs of adjacent campus

buildings, or “line of sight” point-point across open land (up to buildings, or “line of sight” point-point across open land (up to 30 miles away)30 miles away)

Types of Wireless Media – Types of Wireless Media – Radio WavesRadio Waves

Radio waveRadio wave» Either “spread-spectrum” or “narrow-band”Either “spread-spectrum” or “narrow-band”» Useful for connectingUseful for connecting mobile laptops to a LANmobile laptops to a LAN

Standards and Wireless Standards and Wireless Transmission MediaTransmission Media

Based on IEEE 802.11 standardBased on IEEE 802.11 standard» no commonly agreed and used stand until 1999 no commonly agreed and used stand until 1999

(IEEE802.11a – 5 GHz, 54 Mb/s)(IEEE802.11a – 5 GHz, 54 Mb/s)» Other popular standards:Other popular standards:

» IEEE802.11b – 2.4 GHz, 11 Mb/s (also 1999)IEEE802.11b – 2.4 GHz, 11 Mb/s (also 1999)» IEEE802.11g – 2.4 GHz, 54 Mb/s (2003)IEEE802.11g – 2.4 GHz, 54 Mb/s (2003)

Range:Range:» All roughly the same:All roughly the same:

» Av 35 m indoorsAv 35 m indoors» Av 120 m outdoorsAv 120 m outdoors

Mechanism of Wired Mechanism of Wired data transferdata transfer

Coaxial or twisted pair:Coaxial or twisted pair:» data is transmitted by electrical conductiondata is transmitted by electrical conduction» cabling system consist of twocabling system consist of two (or groups of two) (or groups of two)

conducting wiresconducting wires

Fibre opticFibre optic» Data transmitted by light internally reflected Data transmitted by light internally reflected

through a thin through a thin fibrefibre-glass tube-glass tube» Data can be safely transmitted separately in both Data can be safely transmitted separately in both

directionsdirections

Cabling and CrosstalkCabling and Crosstalk

Two parallel wires, as Two parallel wires, as used in used in domesticdomestic electricalelectrical cabling cabling, cannot be used for data, cannot be used for data

Reason -Reason - “crosstalk”: “crosstalk”:» electrical interferenceelectrical interference between signals in the two between signals in the two

wireswires» signals jumping from one wire to the othersignals jumping from one wire to the other

The longer the cable, the greater the chance The longer the cable, the greater the chance of crosstalkof crosstalk» Therefore there will always be a limit on cable run Therefore there will always be a limit on cable run

between data storage devices between data storage devices

Crosstalk and Crosstalk and Coaxial CablingCoaxial Cabling

Magnetic fields produced by electricity in the Magnetic fields produced by electricity in the two wires tends to cancel outtwo wires tends to cancel out

This greatly reducesThis greatly reduces, but does not eliminate, but does not eliminate cross talkcross talk

There is a There is a recommended maximum length for recommended maximum length for Ethernet cables for this reason:Ethernet cables for this reason:» thin Ethernet - 185 thin Ethernet - 185 metresmetres» thick Ethernet - 500 metresthick Ethernet - 500 metres

Thin Coaxial CableThin Coaxial Cable

Also known asAlso known as::» Thin EthernetThin Ethernet» Base bandBase band

CCable consists ofable consists of::» single copper central wire covered with a layer of single copper central wire covered with a layer of

insulationinsulation» itself covered by wire braiding (a patchwork made itself covered by wire braiding (a patchwork made

of very thin copper wire)of very thin copper wire)» WWhole arrangement wrapped in a (usually black) hole arrangement wrapped in a (usually black)

plastic tubeplastic tube

Thin Coaxial CableThin Coaxial Cable

AAlso known as IEEE 10base2lso known as IEEE 10base2» IEEEIEEE - Institute of Electrical and Electronic - Institute of Electrical and Electronic

Engineers (more on this erudite body later)Engineers (more on this erudite body later) NotNot very flexible because of the nature of its very flexible because of the nature of its

constructionconstruction AAvailable in a range of different qualitiesvailable in a range of different qualities GGenerally used for networks using a bus enerally used for networks using a bus

topologytopology RRecommended maximum data transmission ecommended maximum data transmission

raterate - - 10Mbits/sec10Mbits/sec

Connecting Thin Coaxial CableConnecting Thin Coaxial Cable

ComputersComputers connected to aconnected to a thin coaxial thin coaxial bus bus network need a network card with a BNC network need a network card with a BNC socketsocket

Such network cards are becoming very rare…Such network cards are becoming very rare… The coaxial The coaxial bus bus connects to the network card connects to the network card

through a metal BNC “T connector”through a metal BNC “T connector” The The coaxial coaxial cable itself must be “terminated” at cable itself must be “terminated” at

each end with a BNC “terminator”each end with a BNC “terminator” that that completes the electrical circuitcompletes the electrical circuit

Thick Coaxial CableThick Coaxial Cable

Also known as Also known as Thick EthernetThick Ethernet or or broadbandbroadband cablecable

Includes two shielding layers between the Includes two shielding layers between the wires to allow for “harsh” environments (lots wires to allow for “harsh” environments (lots of electrical “noise” caused by nearby electric of electrical “noise” caused by nearby electric motors, etc.)motors, etc.)

Superior to thin Ethernet is two ways:Superior to thin Ethernet is two ways:» Higher data transmission rates (100Mbits/sec recd Higher data transmission rates (100Mbits/sec recd

maximum)maximum)» Larger cable lengths (500 metres recd. maximum)Larger cable lengths (500 metres recd. maximum)

Twisted Pair CableTwisted Pair Cable

The current standard in most LANsThe current standard in most LANs Compared to coaxial:Compared to coaxial:

» ccheaperheaper» much more flexiblemuch more flexible» easy to useeasy to use» doesn’t need BNC T connectors or terminatorsdoesn’t need BNC T connectors or terminators

Twisted Pair construction tends to cancel out Twisted Pair construction tends to cancel out magnetic fields - greatly reducing cross talk magnetic fields - greatly reducing cross talk (but not as effectively as coaxial)(but not as effectively as coaxial)

Twisted PairTwisted Pair v Thin Coaxialv Thin Coaxial - - Disadvantages Disadvantages

UUse of se of the the “twisted pairs” - wrapping the “twisted pairs” - wrapping the individual wires around one another - does individual wires around one another - does not reduce cross talk as effectively as coaxial not reduce cross talk as effectively as coaxial cablecable

More More susceptible to “ harsh” environmentssusceptible to “ harsh” environments (especially rapidly changing magnetic fields)(especially rapidly changing magnetic fields)» Extra insulation of twisted pair cable Extra insulation of twisted pair cable

recommended in such circumstancesrecommended in such circumstances» Cable therefore becomes more expensiveCable therefore becomes more expensive

EIA/TIA Cabling EIA/TIA Cabling StandardsStandards for for Twisted Pair cableTwisted Pair cable

EIAEIA - - Electronics Industries AssociationElectronics Industries Association TIA - Telecommunications Industries AssociationTIA - Telecommunications Industries Association EIA/TIA is a EIA/TIA is a Cabling standards Cabling standards bodybody

» joint venturejoint venture between the EIAbetween the EIA & TIA & TIA

The EIA/TIA 568 standard covers five types of The EIA/TIA 568 standard covers five types of unshielded twisted pair cable known as (in unshielded twisted pair cable known as (in increasing quality) CAT1 through to CAT6increasing quality) CAT1 through to CAT6

Existing EIA/TIA 568 standardsExisting EIA/TIA 568 standards CAT1CAT1: voice communications, not digital data: voice communications, not digital data CAT2: CAT2: digital data, transfer rates of up to 4 Mbits/secdigital data, transfer rates of up to 4 Mbits/sec CAT3: CAT3: digital data transfer rates of up to 10 Mbits/sec digital data transfer rates of up to 10 Mbits/sec

(lowest standard for IEEE 802.3 10BaseT Ethernet (lowest standard for IEEE 802.3 10BaseT Ethernet networksnetworks - future - future session) session)

CAT4: CAT4: digital data transfer rates of up to 16 Mbits/secdigital data transfer rates of up to 16 Mbits/sec CAT5CAT5 can officially handle up to 100 Mbits/sec, can officially handle up to 100 Mbits/sec,

although in “e” and “f” standards it although in “e” and “f” standards it isis be beinging used on used on faster networks (faster networks (e.g. “e” for e.g. “e” for FDDI, 155Mbit/sec & “f” FDDI, 155Mbit/sec & “f” for Gigabit) for Gigabit)

CAT6 can handle very fast rates, up to and beyond 1 CAT6 can handle very fast rates, up to and beyond 1 GigabitGigabit

Features of Twisted Pair CableFeatures of Twisted Pair Cable

MMost popular type currently ost popular type currently used:used:» CAT 5e still widely used - cCAT 5e still widely used - can carry data at an carry data at

reasonably reasonably high high transmission rates transmission rates ((up to up to 200200 Mbits/secMbits/sec))

» CAT 5f, 6CAT 5f, 6 currentcurrent preferred standards for fast preferred standards for fast networksnetworks

BBecause of the greater susceptibilityecause of the greater susceptibility of twisted of twisted pair pair to cross talk, the maximum recommended to cross talk, the maximum recommended cable length for CAT5 is 100 metrescable length for CAT5 is 100 metres

Optical Fibre Cable - Optical Fibre Cable - constructionconstruction

The cable itself consists ofThe cable itself consists of::» a glass or plastic central light conductora glass or plastic central light conductor» surrounded by a further layer of glass or plastic surrounded by a further layer of glass or plastic

claddingcladding» and a protective outer casingand a protective outer casing

Light source

Light detector

Optical Fibre – Data TransferOptical Fibre – Data Transfer

The fibre cable must be The fibre cable must be connected directly to:connected directly to:» light emitter (one end)light emitter (one end)» light detector (other end)light detector (other end)

Data Transfer through Data Transfer through Optical Fibre - summaryOptical Fibre - summary

1.1. The electrical signal is converted into light pulses:The electrical signal is converted into light pulses:

a)a) either by an LED (light emitting diode) either by an LED (light emitting diode)

b)b) or by a Laser or by a Laser

2.2. The light pulses are then directed into the central The light pulses are then directed into the central tubetube

3.3. The light is repeatedly totally internally reflected as The light is repeatedly totally internally reflected as it passes along the inside of the tube - as if it were it passes along the inside of the tube - as if it were on the inside of a mirroron the inside of a mirror

4.4. On emerging from the cable, the pulse is converted On emerging from the cable, the pulse is converted back into an electrical signal by a photodiodeback into an electrical signal by a photodiode

SimulationSimulation

Source: http://www.datacottage.com/nch/anigifs/lightdispani.gif

Optical Fibre Cable - Optical Fibre Cable - advantagesadvantages

speed of transmission (up to Gbits/sec)speed of transmission (up to Gbits/sec) ability to support voice and digital data along ability to support voice and digital data along

the same cablethe same cable security (very difficult to tap) and reliability of security (very difficult to tap) and reliability of

transmission (almost immune to electrical transmission (almost immune to electrical interference)interference)

WithWith copper cable copper cabless, signals , signals in adjacent cablesin adjacent cables ccould interfere with each otherould interfere with each other» a a pair of optical fibres can simultaneously pair of optical fibres can simultaneously carry carry

light/data in each direction (full duplex)light/data in each direction (full duplex) with no with no danger of signal attenuationdanger of signal attenuation

» however, there is some energy loss over distancehowever, there is some energy loss over distance

Optical Fibre Cable - Optical Fibre Cable - disadvantagesdisadvantages

EExpensivexpensive Not as flexible as twisted pairNot as flexible as twisted pair ExpensiveExpensive to install & maintain to install & maintain Needs expensive hardware to reliably Needs expensive hardware to reliably

convert light into electricity and vice versaconvert light into electricity and vice versa

Choosing Transmission Media Choosing Transmission Media for a LANfor a LAN

The following general characteristics must be The following general characteristics must be carefully considered:carefully considered:» Agreed TopologyAgreed Topology» Geographic area covered by networkGeographic area covered by network» Bandwidth requirementsBandwidth requirements» Amount of electrical interferenceAmount of electrical interference

TopologyTopology & Transmission & Transmission MediaMedia

The planned layout of the nodes will affect The planned layout of the nodes will affect the route of the cablingthe route of the cabling

SSome nodes may be quite far apart ome nodes may be quite far apart Use of long cables could well result in signal Use of long cables could well result in signal

strength degradationstrength degradation This This will result in some communication delay will result in some communication delay

on account of data having to be on account of data having to be (automatically) retransmitted(automatically) retransmitted

Appropriate cabling choice will minimise Appropriate cabling choice will minimise such problemssuch problems

BandwidthBandwidth, Interference, & , Interference, & Transmission MediaTransmission Media

BandwidthBandwidth - the maximum amount of data - the maximum amount of data that can be transmitted during a specified time that can be transmitted during a specified time period (usually one second)period (usually one second)

Use of higher bandwidth cable allows more Use of higher bandwidth cable allows more data to be transmitted in a given time perioddata to be transmitted in a given time period

InterferenceInterference – – as well as crosstalkas well as crosstalk,, there are there are many different types of many different types of electrical electrical noisenoise

In particular, electrical “spikes”, caused by In particular, electrical “spikes”, caused by sudden power changes, can cause problemssudden power changes, can cause problems if the cables are not sufficiently well shieldedif the cables are not sufficiently well shielded

HealtHealth, h, SafetySafety & & Transmission MediaTransmission Media

Asthetic objections to cables being visibleAsthetic objections to cables being visible» also a potential H &S hazardalso a potential H &S hazard

DDifferent types of twisted pair cable ifferent types of twisted pair cable availableavailable forfor different environments (e.g. under different environments (e.g. under carpets; in the plenum space above a carpets; in the plenum space above a “lowered” ceiling“lowered” ceiling))

UUsually increases the likelihood of crosstalk, sually increases the likelihood of crosstalk, and effectively reduces the recommended and effectively reduces the recommended minimum cable lengthminimum cable length

Standards for variations laid down by IBM in Standards for variations laid down by IBM in the 1980s - Token Ring becoming popular…the 1980s - Token Ring becoming popular…

The IBM Cabling ModelThe IBM Cabling Model – – Twisted Pair CablesTwisted Pair Cables

Covers different types of twisted cabling Covers different types of twisted cabling to cover all types of commercial to cover all types of commercial networking environmentsnetworking environments

With the subsequent growth of With the subsequent growth of networks, networks, IBM cabling categories IBM cabling categories have have become “industry standard”become “industry standard”

Nine categories in allNine categories in all Most are concerned with carrying digital Most are concerned with carrying digital

data, but some also handle voice datadata, but some also handle voice data

IBM Cabling IBM Cabling CategorCategoriesiesCategory Contents Purposes Type 1 Shielded Twisted Pair x2

with casing Data

Type 2 as above, with further 4 pairs added outside the shield for voice

Data & Voice

Type 3 4 twisted pairs unshielded (as above)

Voice

Type 5 2 x 62.5/125 micron Optical Fibre

Data

Type 6 as 1, with foil-braid shield Data (2/3 distance limits of category 1)

Type 8 as 1 - flattened Data (under carpets - 1/2 distance limits of category 1)

Type 9 as 1 - fire-resistant case (e.g. PVC)

Data (in plenum space above ceiling)

Break time…Break time…