Networks Information SystemsS.K.Nuwan Buddika

Scope and CoverageThis topic will cover:Network media Network connectorsSelecting media and connectors

Physical Layer

MediaCabling (Guided media)Outline of mediaPlanningImplementation Management Wireless

Network MediaSupport the sending and receiving of signalsFor each media type, we require knowledge of:

Physical characteristicsLimitationsEach medium has a unique design and usage with implications for:

CostPerformanceInstallation

Physical MediaFactors to consider when choosing network media:

Bandwidth ratingMaximum segment lengthMaximum number of segments per internetworkMaximum number of devices per segmentInterference susceptibilityConnection hardwareCable gradeBend radiusCosts of materials and insulation

BandwidthIn analogue systems, this describes the band of frequencies that can carry information.In digital, the number of bits per secondCustomers demand more complex and powerful services and these require a much higher bandwidth.Bandwidth limits of existing technologies have been expanded:Older networking components can remain in useSupports higher bandwidth than originally rated

Physical Cable TypesCarry a physical signal that may be:

ElectricalLight pulsesThe primary cable types are:

Coaxial cableTwisted-pairFibre-optic cable

Coaxial CableWas the main original form of network cablingNow obsoleteContains shielding - protective layer(s) wrapped around cable to protect it from external interference

Twisted Pair CableUnshielded Twisted Pair (UTP)Most popular LAN cabling type10BaseT

Maximum length is 100 metersIncludes one or more pairs of insulated wiresSpecifications give the number of twists per foot (or per metre).

10BaseT10 for 10Mbps operationBase for basebandT for twisted pairMaximum length per segment 100 meters (330 ft)Maximum of 2 devices per segment

one is the station and the other is the hubUses a star topology

UTP Cabling CategoriesUTP cabling is rated according to a number of categories devised by the TIA and EIACat1: 0.4 MHzTelephone and modem Cat2: Unsuitable for modern systems Cat3: 16MHz10BASE-T and 100BASE-T4EthernetCat4: 20MHz16 Mbit/sToken Ring Cat5: 100MHz 100BASE-TX & 1000BASE-TEthernet Cat6: 250MHz 1000BASE-TEthernet Cat6a: 500MHz 10GBASE-T (under development)Cat5 and Cat6 are the most common

Fibre Optic CableThe core and cladding are made of ultra-pure glass.Light is guided down the centre of a fibre and reflects off the inner surface.Each fibre is protected by a plastic buffer coating.Further protection from the outer covering.

Fibre Optic Cable TypesTwo types:

Single-mode: costs more and generally works with laser-based emitters, but spans the longest distancesMultimode: costs less and works with light emitting diodes (LEDs), but spans shorter distancesInstallation is more difficult, time-consuming and costly than copper wire.

Fibre Optic AdvantagesImmune to electrical interferenceCan cover large distancesHigh transmission speedsNot easily tapped

The big disadvantage is cost.

Multimode Fibre OpticEarly fibre optic cablesLight signals from a laser are broken up into a number of paths.Each is reflected off the internal wall of the fibre.Signal quality is determined by the amount of reflection.

Monomode Fibre OpticSingle stream down each strandFurther developed to allow multiple frequencies to be sent down the same coreAllows for greater distances and transmission speeds

Wireless MediaMedia does not have to be physical.Wireless connections are also network media.Frequency is measured in Hertz

Affects the amount and speed of data transmissionLower-frequency transmissions carry less data more slowly over longer distancesRadio -10 KHz (kilohertz) to 1 GHz (gigahertz)Microwave -1 GHz to 500 GHzInfrared - 500 GHz to 1 THz (terahertz)

ConnectorsNetwork consists of:

NodesMediaAlso need to connect the media to the nodesRange of devices for doing thisChoice depends upon

Cable typeNetwork typeDevice

Coaxial Cable ConnectorMost common type of connector used with coaxial cables is the Bayonet Neill-Concelman (BNC) connectorE.g. 10Base2 thin Ethernet (now obsolete)Different adapters available for BNC connectors

T-connectorBarrel connectorTerminator

UTP ConnectorsUTP comes in 2 main forms:

Two-pair (four wire) for telephoneFour-pair (eight wire) for data networks

Each has a different connector:

RJ-11 for four-wire telephonyRJ-45 for eight wire data networks

RJ-11RJ stands for registered jackStrictly this is a combination of plug and wiring configurationUsed for a single telephone line

RJ-45The standard connector for UTP cabling in data networksLike a large telephone-style connector Made of plasticCan only be inserted one wayStandard designates which wire goes with each pin inside the connector

Wiring an RJ-45 ConnectorThe wiring configuration depends upon the standard being followed.Private Study Exercise 2 asks you to investigate the wiring configurations.

Fibre Optic ConnectorsTerminate the end of anoptical fibreEnable connection faster thansplicingAlign the cores of fibres so that light can passCommon connectors are:FCLCMT-RJSCST

FC ConnectorsFerrule ConnectorA popular connector for monomode fibre optic cableA screw on connection Must have the key aligned in the slot properly before tighteningIt is steadily being replaced by SCs and LCs.

LC ConnectorsLucent Connector (or Local Connector)A relatively recent connector that is smaller than many othersA standard ceramic ferrule connectorIt is easily terminated with adhesiveGood performanceUsed widely in monomode

MT-RJ ConnectorsMechanical Transfer Registered JackA duplex connectorBoth fibres in a single polymer ferruleUses pins for alignmentHas male and female versionsMultimode only

SC ConnectorsSubscriber Connector (or Square Connector or Standard Connector)A snap-in connector Widely used in monomode systemsHas excellent performanceConnects with a simple push-pull motionAlso available in a duplex configuration

ST ConnectorsStraight TipMost popular connector for multimode networksHas a bayonet mount and a long cylindrical ferrule to hold the fibreFerrules are usually ceramicFerrules are spring-loaded; you have to make sure they are seated properly.

USB ConnectorsUniversal Serial BusDeveloped as a means to connect a large number of devices to the PCThe standard for peripheralsAllows Plug and Play - no special user-knowledge required to install a new deviceAll devices distinguishable from other devicesthe correct driver software was always automatically used

USB 2.0The most common implementationVery easy to connectHalf-duplexUSB 3.0 has been developed:

Higher data speedsLess power consumptionFull duplex

NICNetwork Interface CardRequired for a computer to communicate on a network.Establishes and manages the computers network connectionTranslates incoming/outgoing messagesModern computers have a NIC built in

Cable ChoiceMost networks use some type of unshielded twisted-pair cabling.Some organisations use optic fibre directly to their desktop machines.Wireless is an optionIdeally use Cat5e UTP as a minimum, if using cable

Selection CriteriaFactors to be considered:

BandwidthBudgetCapacityPlacementExisting cablesEnvironmental considerationsGeographic areaSpecifics of organisation and location

Installation StandardsTwo standards bodies have recognised standards for the installation of data networks:The Telecommunications Industry Association (TIA) TIA-568-C.2, Balanced Twisted-Pair Telecommunications Cabling and Components Standard, 2009The International Organization for Standardization (ISO)ISO 11801, 2nd Ed., Information technology - Generic Cabling for Customer Premises, 2002

Structured CablingUses an extended star physical topologyCan be applied to any size networkCabling is organised into 6 components:

Work areaHorizontal wiringTelecommunications closetsEquipment roomsVertical wiringEntrance facilities

Work AreaRoom containing workstations and peripherals

Faceplates and wall jacks are installed.Patch cables connect computers and printers to wall jacks.Wall jacks connect to a telecommunications closet.Patch cables should be less than 6 meters long. Standard requires at least one voice and one data outlet on each faceplate in each work area.Connection between wall jack and telecomms closet (TC) is made via horizontal wiring.

Faceplate & Patch Cable

Telecommunications ClosetAlso known as cable closet

Horizontal WiringRuns from the work area wall jack to the telecommunications closetTypes include four-pair UTP (Category 5e or 6) or two fibre-optic cablesHorizontal wiring from the wall jack to the patch panel should be no longer than 90 metres

Patch cables in the work area and in the telecommunications closet can total up to 100 meters

Structured Cabling Max Distances

Equipment RoomsContains servers, routers, switches, and other major network equipmentServes as a connection point for vertical cabling running between TCsIn installations covering several buildings, each building may have its own equipment room.

Vertical CablingInterconnects telecommunications closets and equipment roomsRuns between floors and between buildingsOften fibre optic (but can be UTP)

Multimode fibre optic, up to 2000 metersSingle-mode fibre optic, up to 3000 metersBetween equipment rooms and TCs, distance is limited to 500 metres for both fibre optic cable typesFrom the main cross-connect to equipment rooms, fibre optic cable can run up to 1500 meters

Entrance FacilitiesThe location of the cabling and equipment connecting corporate network to telecoms providerCan also serve as an equipment room and the main cross-connect for all vertical cabling

Where a connection to a WAN is madeWhere corporate LAN equipment ends and a third-party providers equipment and cabling begins

Wireless NetworksRemember that wireless networking is gaining in popularity

Acts like a wired network

Uses electromagnetic frequencies:

RadioMicrowaveInfraredLaser

Wired Networks (LANs)Still the most commonNecessary to business for survivalEach element of the network infrastructure is essentialUses include data transmission and IP telephony

Cabling Infrastructure Cabling infrastructure has the longest useable life of all network componentsCosts normally about 2% of network budgetAccounts for up to 50% of network failuresSecurity measures at this level are essentialManagement tools are also available to allow you to monitor the physical layer infrastructure

A modern wired networkUTPCat5Cat5eCat6Described as 10BaseTX to 1000BaseTXRelatively cheapFlood wiring a building provides flexibilityCan also be used for telephony, thus require only one network

Power over Ethernet (PoE)Describes any system to transmit electrical power, along with data, to remote devices over standard UTP cable in an Ethernet network (IEEE 803.2af)Can be used for IP telephones, requires switches that provide in-line power

A modern wired networkFibreUsed for LANs and long-haul transmissionMore complex connectionsMulti-mode fibreSingle-mode fibreRequires two fibres or two frequency bands on one fibre for full duplex transmissionFibre must be the same from end-to-end so patch leads must match the fibre runs

Fibre vs. CopperFibre has greater bandwidthFibre has low attenuation, therefore longer runs are possibleFibre is not affected by power surges, electromagnetic interference or power failureFibre is not affected by corrosive particles in the air (good for industry)Fibre is thin and lightweight Fibres are difficult to tap and do not leak their signal (i.e. light)

Copper vs. FibreCopper is more familiarCopper is more robust (e.g. to bending)Fibre interfaces cost more than copperCannot carry electrical power to operate terminal devices

Planning a wired networkWhat considerations need to be taken into account when planning a wired network?

Managing cable infrastructureWhat information do you require to manage a cable infrastructure effectively?

Cable management An essential part of the cabling infrastructureOrganises cablingPrevents problems such as: -Bend radius violationsCable pinchingCabinet capacity

Cable Management Ceiling Trays

Cable Management Ceiling Trays

Cable Management Ceiling Trays

Cable Management Patch Panel & Switch Cabinet

Cable Management Wall Port

Cable Management Floor Ports

Physical Layer SecurityPhysical layer security is vital to ensuring a network service.SLAs often refer to availability and loss of the physical link can have a significant impact.List the risks might you expect with cabling infrastructure

StandardsIEEE 802 ProjectFormed in early 80sInvolved with development of LAN/MAN technologiesUses a standards based approachManaged through committees

Some 802 Committees

802.1qVLAN802.3CSMA/CD802.3 Fast Ethernet802.3zGigabit Ethernet802.3ae10 Gigabit Ethernet

Some 802 Committees

802.5Token passing ring802.7Broadband advisory group802.8 Fibre optic advisory group802.10Security802.11WLAN

CablingHow not to do it: -

Cabling StandardsTIA/EIA 568Structured cabling standardsAmendments occur as technologies improveE.g. higher signalling rates, great bandwidth requirementsDefines the standards for Cat 1 to Cat 6 cablingDefines cable characteristics such as performance

Cabling StandardsISO/IEC 11801Specifies general-purpose telecommunications structured cabling systems. Standards include both copper wire and optical fiber inside cabling systems.Specifies classes of twisted pair copper performance: Class A: 100 kHz Class B: 1 MHz Class C: 16 MHz Class D: 100 MHz Class E: 250 MHz Class F: 600 MHz

Factors affecting transmissionAttenuationCrosstalkAttenuation to crosstalk ration (ACR)Propagation DelayDelay Skew

EIA/TIA UTP Cable Categories

Category 5Supports transmission up to 100MHz10/100MbpsCategory 5eSupports transmission up to 100MHz10/100/1000MbpsCategory 6Supports transmission up to 250MHz10/100/1000Mbps

Category 6Improved performance through greater bandwidth1 Gigabit/sImproved reliability through improvements regarding: -Signal-to-noise ratioCross-talkCan support 10GBaseTBut distance limitations apply

Category 6aAugmented Cat 6Offers up to 500 MHzCan support 10GbaseTUp to 100m

Cat 6a/Cat 7From: http://www.universal-cables.co.uk/uploads/pdfs/Cat6%20SFTP12-Cat6a%20SFTP%20Patch%20Cables.pdf

Category 7Designed to run 10G EthernetAdheres to 100m distance of UTP EthernetImproved performance due to strict regulations for cross talkUses shielding for wire pairsAlso shielding on cableNot an EIA/TIA standard but available and in use

Mechanical Characteristics

Bending radius>=20 mmrepeated bending>=1000 cyclesTensile strength #>=56 NTemperature range:-During installation0C to +50CIn operation-20C to +60C

Scope and CoverageThis topic will cover:Network topology conceptsCommon network topologies and their applicationTopologies and protocols

Learning OutcomesBy the end of this topic, students will be able to:Explain the concept of network topology and its designDiscuss various common network topologies and their application(s)Propose a simple network topology in response to detailed requirements

TopologyTo install a network, you need to know how to connect all the elements together.A network topology is the layout of computers, cables and peripherals and also the paths that data travels along on the network.There are two forms of network topology:Physical topologyLogical topologyPhysical and logical topology may differ.

Network ElementsThere are two main components of a network:NodesLinksA network node is an intersection between links that will contain some equipment:To aid signal transmission (hub, switch, bridge, etc)For data processing (computer, printer, etc)A link is the media through which the signals are transmitted (fibre-optic, coaxial cable, RF, etc)

Physical TopologyExplains how the computers and peripherals are physically connected together

It is a map showing how each piece of hardware is connected to the other hardware on a network.

This may be via physical cables or could be wireless.

Logical TopologyExplains how data passes between network devices

It is a map showing the logical path of data around the network.

The logical topology of a network may be different to its physical topology.

Topology CategoriesThere are many different topologies.There are many different technologies for physical connections.There are many different protocols for logical connections.We can broadly categorise networks as:

Point-to-point networksBroadcast networks

Point-to-Point NetworksMany connections between individual pairs of machinesPackets of information may have to pass through intermediate machines.Multiple routes of different length are possible, so routing algorithms are used.Generally used in larger networks (e.g. Internet)

Broadcast NetworksSingle communication channel that is shared by all the machines on the networkPackets sent by a machine are received by all the others.Address field specifies the recipientGenerally used for smaller networks (LANs)

RedundancyRedundancy involves having more links and/or nodes in a network than are strictly necessary for network operation.Redundancy is built into a network as a back-up feature to allow the network to function if one part fails.High levels of redundancy are required where network operation is vital.

LAN Physical TopologyMain factors that determine the choice of physical topology of a LAN are:

Office layoutNeed for redundancyCost

Office LayoutSeveral issues that determine physical topologyA single room provides more options.Multiple rooms may mean cables through walls/ceilings or reduced signal strength for wireless.Large building with several floors enhances the problem

Need for RedundancyDependent upon how important guaranteeing network integrity isSome topologies isolate breaks in the network so that the rest of the network functions normally.Other topologies have built in redundancy so that:

If a link breaks, alternative paths are availableIf a device breaks, there are back up devices available

CostCost is a function of:

The network topologyThe size of the networkThe office layoutNot all topologies have equal cost.A bigger network requires more cable, etc.The office layout may make laying cables difficult.

Real World NetworksThere is no one size fits all solution.Must determine topology based upon the specifics of the organisation the network is forOne private study exercise will involve deciding on a topology for a specific network.

Standard TopologiesThere are three main network topologies in common use:Bus is a series of computers connected along a single cable segment.Star is a group of computers connected through a central point (hub).Ring has computers connected to form a loop.There are variations:Extended starMeshStar combined with bus

Bus Topology - 1

Bus Topology - 2E.g. EthernetDevices connected along a single cableElectrical pulses (signals) travel along the length of the cable in all directions.The signals continue to travel until they weaken enough so as not to be detectable or until they encounter a device that absorbs them.At the end of a cable, the signal bounces back unless there is a terminator.

Logical BusLogical topologies describe the path that data travels from computer to computer.A physical bus topology is usually also implemented as a logical bus.The physical bus has fallen out of use due to technological advances.Logical bus topology is used on some physical topologies, in particular a star topology.

Passive TopologyThe bus topology is a passive topology.Workstations on the bus are not responsible for regenerating the signal as it passes them.The workstations are not required for the bus to function.If a workstation fails, the bus does not fail.

Physical Bus AdvantagesCostLess cable required than star or meshNo additional devices such as hubsEase of installationSimply connect device to cable segmentResistant to workstation failureNetwork functions if device failsNOTE: problems if cable breaks

Physical Bus DisadvantagesDifficult to troubleshoot

Faults are usually a break in the main cable and this is difficult to isolate on a large network

Scalability

Increasing network size and layout can be important for productivityBus topology is not easily scaled up.

Ring Topology

Physical Ring TopologyAll computers are connected in a ring.The ring has no start and no end.

Does not need a terminator as there are no reflected signalsSignals travel in one direction.Signals are regenerated by each computer in turn

Active topology.

Logical Ring TopologyData travels from one node to the next device until it reaches its destination.Modern ring topologies use smart hubs that recognise a computer failure and remove that computer from the ring automatically.Shares network resources fairly

Physical Ring AdvantagesLow signal degeneration

Each workstation is responsible for boosting the signalIn passive systems, the signal is not boosted and weakens, which limits the size of the networkStrong signal means signal seldom needs retransmittingFair allocation of network access to nodes

Physical Ring DisadvantagesNot resistant to workstation failure

Failure of workstation or cable causes network to failNote: modern systems and logical rings can isolate failed workstation and maintain network uptimeNetwork maintenance

Changes to cabling or moving a workstation can cause network downtime.

Star Topology

Physical Star TopologyAll devices connected through a central hub or switch

Each workstation is connected directly to the hub.

Very popular topology for modern networks

Star Topology AdvantagesEasy to add new devices just connect to hubCable break only affects one single node.Ease of administration

Centralised management and monitoring of network traffic simplifies job of network administratorEase of changing configuration

Star Topology DisadvantagesHub Failure

If the hub fails, the whole system fails.However, this is easy to troubleshoot.

Cost

Cost is higher as extra cabling and devices (hubs) are required.However, this cost is no longer great and therefore not a real barrier to implementing a star topology.

Star as Logical Bus

Star as Logical Ring

Switching as Star TopologySwitched networks are neither bus nor ring logically, but are implemented as a physical star.

A switch takes a signal coming from a network device and builds a link to the intended destination computer on the fly.

Superior to other logical topologies, because multiple computers can communicate simultaneously without affecting each other

Main method used in most LAN designs

WLAN as Physical Star TopologyUses a central device (access point) to control communications

Star physical topology because all the signals travel through one central device

Mesh TopologyEvery workstation is connected to every other workstation.Not very common

Mesh Topology AdvantagesResilience

Multiple pathways for sending dataCable fault is not a problem as data can go via another pathAlmost impossible for network to fail due to cable failure as there are so many routes available

Mesh Topology DisadvantagesCost

Additional cablingAdditional interfaces

Difficult to administer

Due to the number of connections

Extended StarSeveral stars connected in a star from a switch

Combination of Star & BusSeveral stars connected along a bus

Star TopologyThe most common physical topology in modern LANsRequires a device at the centre of the network that controls trafficBoth hubs and switches can act as the centre of a star topology.

HubsActive hubs are the most common type of hub. Regenerate or repeat the signals

Needs electrical powerHas many portsAlso called multiport repeaters or repeating hubsSignal comes in on one portCleans the signal (filters out noise)Strengthens the signalSends the regenerated signal out to all other ports

SwitchesCentral connecting point in a star topology networkDoes more than regenerate signalsHas several ports for connecting workstations in a star topologyDetermines which port the destination device connects to and forwards the message to that portHandles several conversations at a timeProvides the full network bandwidth to each device rather than requiring bandwidth sharing

Network AccessIn any network, providing access for nodes to transmit messages is a key element.It must be assumed that any node may require access at any time.Controlling access to networks becomes more difficult for larger networks and faster data speeds.Access is controlled by a combination of topology, wiring and protocols that combine into network standards.

Non-contention TechniquesDesigned to prevent conflict between nodes wishing to transmitDoes not allow two nodes to transmit at the same timeEach node is given exclusive access to the network.This right to access is passed throughout the network.Token passing is a common form.

Contention TechniquesAllow conflicts and collisions to occurDealing with collisions is part of the designNo order of access to transmitAny node can transmit at any time.

Common Contention TechniqueCSMA/CDAs used in EthernetWhen a collision occurs, each node waits a random time before retransmitting, why?

Designing a NetworkThe main steps are as follows:

Determine what the network will be used for this will be a major factor in deciding the topology you use.Choose the types of devices that will be used for interconnecting computers and sites.Consider the type of devices the network will employ and the usage of network resources this will determine how many servers are required and where servers should be placed.

Selecting a TopologyModern networks have one key factor in this choice - how fast should the network be?Physical topology will almost certainly be a starLogical topology is usually a switched networkEthernet switches are used on most LANsOther logical topologies can be the result of:Use of legacy equipmentNetwork sizeCost restrictionsDifficulty of running cables

Planning a Logical Topology - 1Can either start from scratch or upgrade an existing network?You should have sufficient information about:

Networking componentsHardwareProtocolsPhysical topologies

Planning a Logical Topology - 2Analyse the following:

Security needsTraffic patternsNeed for future expansionServer capabilitiesInternet access requirementsYou should also make a plan for disaster recovery, data recovery and troubleshooting techniques.

Creating a Network Layout - 1A network layout must be documented in a diagram.Factors to considerNumber of client computersNumber of serversWill there be an Internet connection?The architecture of the buildingThe best topology or topologiesAny diagram must be updated if the layout changesVersion control.

Creating a Network Layout - 2

*NCC Education - Slide Master*CablingConcentrate on UTP 10BaseTX, 100BaseTX and 1000Base TX, Cat 5 and 6Cat 5 up to 100BaseTX (fast ethernet)Cat 5e up to 1000BaseTX and telephonyCat6 up to 10Gig.

FibreMultimode and single mode fibreMultimode often used for LANsSingle mode includes telephony and CCTVProvides 10BaseFX, 100BaseFX and Gigabit ethernet

WirelessMicrowave, satellite and radioWLANGPRS always on perception***Remember telephony requires power and this often comes from the switch, though a small amount of power can be achieved over UTPCat 6 offers 10Gb*Without POE telephones require and electrical socket.**Weight 1000 UTP cables 1km long = 8000kg2 fibres have more capacity and weigh 100kg

**GeneralTransmission requirements now and in the futureIs it a new building? so wiring can be embedded into the buildingIs it an existing building?How long are the runs?Where will wiring cabinets be placed? Budget?What already exists, can it be reused?

DetailLocation of outletsNumber of outlets requiredRisk areas e.g. cabling/outlets in public areas

Long termFuture proofing Physical capacityTransmission capacity*Detailed plans of cable runs within the buildingsLocation of cablesType of cablesLength of cablesSource and destination devicesBuilding plans marked up

Information on every network deviceConnection details, source and destination ports, room numbers, device connected, user details possiblyPort configuration e.g. 100mb/s full duplex (policies)**Disconnection of a link, maliciously or accidentallyCould be in patch panel, at wall port, at network device or a break anywhereTapping on a linkInterference from electromagnetic sourcesConnection to a live port by an intruderLoss of power, maliciously or accidentallyPoor cable infrastructure administration, poor records, inexperienced staff etc.

*Attenuation is the loss of signal over the length of a network link due to the resistance of the wire plus other electrical factors that cause additional resistance (impedance and capacitance for example). A longer cable length, poor connections, bad insulation, a high level of crosstalk, or EMI can all increase attenuation. For each category of cable, the TIA-568B standard specifies the maximum amount of attenuation that is acceptable in a network link.

Attenuation to Crosstalk Ratio (ACR) ACR is probably the most important result when testing a link. ACR is the difference between the signal attenuation and the near-end crosstalk, representing the strength of the attenuated signal in the presence of crosstalk. If ACR is not high enough, errors will occur or the data signal can be lost. Power Sum ACR (PSACR) is calculated in the same way as ACR, but uses the PSNEXT results rather than NEXT.

Crosstalk is the "bleeding" of signals from one pair in a cable onto another pair through induction (wires need not make contact because signals are transferred magnetically). Crosstalk is an unwanted effect that can cause slow data transfer, or completely inhibit the transfer of data signals. Crosstalk is minimized by the twisting of the pairs in the cable. Fiber Optic cable is the only cable medium that is 100% immune to the effects of crosstalk or EMI.

Return Loss Return Loss is the difference between the power of a transmitted signal and the power of the signal reflections caused by variations in link and channel impedance.

Propagation Delay Propagation Delay tests for the time it takes for the signal to be sent from one end of a link and received by the other end.

Delay Skew Only a critical parameter in high-speed networks that transmit data using multiple pairs, Delay Skew is the difference in time between the fastest arrival of a data signal on a pair and the slowest. Signals divided over multiple pairs need to reach the other end within a certain amount of time to be re-combined correctly.*Cat 5 can do 1000 but does not perform well under loading

Bandwidth vs data rates: -Bandwidth precedes data rates just as highways come prior to traffic. Doubling the bandwidth is like adding two times the number of lanes on a highway

The general difference between category 5e and category 6 is in the transmission performance, and extension of the allowed bandwidth from 100 MHz for category 5e to 200 MHz for category 6.

In addition to performance improvements Cat 6 provides better reliability due to reduced cross talk*Because of its greater transmission performance and better immunity from external noise, systems operating over 6 cabling will have fewer errors vs. category 5e for current applications. This means fewer re-transmissions of lost or corrupted data packets under certain conditions, which translates

into higher reliability for category 6 networks compared to category 5e networks

term crosstalk (XT) refers to any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another. This an be heard on telecommunications channels *A shielded cable to provide greater reliability and performance due to reduction in noise/cross-talk*NCC Education - Slide Master*