Chapter 10Chapter 10ExpendingExpendingNetworkingNetworking

Network ConnectivityNetwork Connectivity

To expend the single network without breaking To expend the single network without breaking into new parts or connecting it to other networks, into new parts or connecting it to other networks, you can usually use one of the following:you can usually use one of the following: Passive hubsPassive hubs Active hubsActive hubs Intelligent hubsIntelligent hubs RepeatersRepeaters BridgesBridges Multiplexers Multiplexers

RepeatersRepeaters

Connectivity devices that regenerate and Connectivity devices that regenerate and amplify an analog or digital signalamplify an analog or digital signal

Figure 6-16: Repeaters

HubsHubs

Multiport repeater containing multiple ports Multiport repeater containing multiple ports to interconnect multiple devicesto interconnect multiple devices

Figure 6-17: Detailed diagram of a hub

HubsHubs

Elements shared by most hubs:Elements shared by most hubs: PortsPorts Uplink portUplink port Port for management consolePort for management console Backbone portBackbone port Link LEDLink LED

HubsHubs

Elements shared by most hubs (cont.):Elements shared by most hubs (cont.): Traffic (transmit or receive) LEDTraffic (transmit or receive) LED Collision LED (Ethernet hubs only)Collision LED (Ethernet hubs only) Power supplyPower supply Ventilation fanVentilation fan

HubsHubs

Figure 6-18: Hubs in a network design

HubsHubs

Passive hubsPassive hubs Only repeats signalOnly repeats signal

Active hubsActive hubs They have electronic components that regenerate or They have electronic components that regenerate or

amplify signals.amplify signals.

Intelligent hubsIntelligent hubs In addition signal regeneration, Intelligent hubs In addition signal regeneration, Intelligent hubs

perform some network management and intelligent perform some network management and intelligent path selection. A switching hub chooses only the port path selection. A switching hub chooses only the port of the device where the signal needs to go.of the device where the signal needs to go.

Stackable HubsStackable HubsPhysically designed to be linked with other hubs in a single Physically designed to be linked with other hubs in a single telecommunications closettelecommunications closet

Figure 6-20: Stackable hubs

Figure 6-21: Rack-mounted stackable hubs

Installing a HubInstalling a Hub

As with network As with network adapters, the adapters, the best way to best way to ensure a hub is ensure a hub is properly installed properly installed is to follow the is to follow the manufacturer’s manufacturer’s guidelinesguidelines

Figure 6-22: Connecting a workstation to a hub

Choosing the Right HubChoosing the Right Hub

Factors to consider when selecting the Factors to consider when selecting the right hub for your network:right hub for your network: PerformancePerformance CostCost Size and growthSize and growth SecuritySecurity Management benefitsManagement benefits ReliabilityReliability

BridgesBridges

Like a repeater, Like a repeater, a bridge has a a bridge has a single input and single input and single output portsingle output portUnlike a Unlike a repeater, it can repeater, it can interpret the data interpret the data it retransmitsit retransmits

Figure 6-23: A bridge

BridgesBridges

Spanning tree algorithmSpanning tree algorithm Routine that can detect circular traffic patterns and Routine that can detect circular traffic patterns and

modify the way multiple bridges work together, in order modify the way multiple bridges work together, in order to avoid such patternsto avoid such patterns

Transparent bridgingTransparent bridging Method used on many Ethernet networksMethod used on many Ethernet networks

Source-route bridgingSource-route bridging Method used on most Token Ring networksMethod used on most Token Ring networks

Translation bridgingTranslation bridging Method that can use different logical topologiesMethod that can use different logical topologies

MultiplexersMultiplexersMultiplexingMultiplexing technologies allow multiple signals to be technologies allow multiple signals to be transmitted over a single communication link; transmitted over a single communication link; multiplexersmultiplexers (muxes) allow several devices to share a common circuit(muxes) allow several devices to share a common circuitMultiplexers combine data from all incoming lines and Multiplexers combine data from all incoming lines and transmits them via one line to another multiplexer which transmits them via one line to another multiplexer which separates the data and distributes it among outgoing terminal separates the data and distributes it among outgoing terminal lineslinesFigure 10-8 illustrates a generic multiplexer configurationFigure 10-8 illustrates a generic multiplexer configurationTo terminal users, the multiplexer appears to function as To terminal users, the multiplexer appears to function as though there were several physical lines to the host instead of though there were several physical lines to the host instead of just onejust oneMultiplexers avoid the need to have multiple connections Multiplexers avoid the need to have multiple connections between two locationsbetween two locations

Figure 10-8

Kinds of MultiplexersKinds of Multiplexers

A communication link is divided among several A communication link is divided among several users in two basic ways:users in two basic ways: Frequency division multiplexingFrequency division multiplexing (FDM)(FDM) which which

separates the link’s available bandwidth into sub-separates the link’s available bandwidth into sub-channels, one for each incoming line (see Figure 10-channels, one for each incoming line (see Figure 10-9)9)

Time division multiplexing (TDM)Time division multiplexing (TDM) which separates link which separates link into time slots. Each incoming line is given a time slot into time slots. Each incoming line is given a time slot for transmitting a byte (or bit) – see Figure 10-10(a)for transmitting a byte (or bit) – see Figure 10-10(a)

Figure 10-9

Figure 10-10(a)

Statistical TDMStatistical TDM

A major shortcoming of TDM is revealed when attached A major shortcoming of TDM is revealed when attached lines do not have data to transmitlines do not have data to transmit

Times slots allocated to idle lines go unused (see Figure 10-10b Times slots allocated to idle lines go unused (see Figure 10-10b and Figure 10-11)and Figure 10-11)

Communication circuit is not used to its fullest extent in this Communication circuit is not used to its fullest extent in this circumstancecircumstance

A statistical time division multiplexor (STDM) improves A statistical time division multiplexor (STDM) improves on TDM efficiency by transmitting data only for lines with on TDM efficiency by transmitting data only for lines with data to send by reallocating time slots so that idle lines data to send by reallocating time slots so that idle lines take up none of the carrying capacity of the take up none of the carrying capacity of the communication circuit (see Figure 10-10c and Figure 10-communication circuit (see Figure 10-10c and Figure 10-12)12)

Figure 10-10(b)

Figure 10-10(c)

Internetwork ConnectivityInternetwork Connectivity

The hardware devices can be The hardware devices can be computers or special purpose devices computers or special purpose devices used for interconnecting networks used for interconnecting networks including:including: bridges, bridges, routers routers BroutersBrouters GatewaysGateways CSUs/DSUsCSUs/DSUs

SwitchesSwitches

Subdivide a Subdivide a network into network into smaller smaller logical pieceslogical pieces

Figure 6-25: Examples of LAN switches

Cut-Through Mode andCut-Through Mode andStore and Forward ModeStore and Forward Mode

Cut-through modeCut-through mode Switching mode in which switch reads a frame’s Switching mode in which switch reads a frame’s

header and decides where to forward the data header and decides where to forward the data before it receives the entire packetbefore it receives the entire packet

Cut-through switches can detect Cut-through switches can detect runtsrunts, or , or packet fragmentspacket fragments

Store and forward modeStore and forward mode Switching mode in which switch reads the entire Switching mode in which switch reads the entire

data frame into its memory and checks it for data frame into its memory and checks it for accuracy before transmitting the informationaccuracy before transmitting the information

RoutersRouters

Multiport connectivity deviceMultiport connectivity deviceCan integrate LANs and WANs running at Can integrate LANs and WANs running at different transmission speeds and using a different transmission speeds and using a variety of protocolsvariety of protocolsRouters operate at the Network layer Routers operate at the Network layer (Layer 3) of the OSI Model(Layer 3) of the OSI Model

Router Features and FunctionsRouter Features and Functions

Modular routerModular router Router with Router with

multiple slots multiple slots that can hold that can hold different different interface cards interface cards or other or other devicesdevices

Figure 6-27: Routers

Router Features and FunctionsRouter Features and Functions

Filter out broadcast transmission to alleviate Filter out broadcast transmission to alleviate network congestionnetwork congestionPrevent certain types of traffic from getting to a Prevent certain types of traffic from getting to a networknetworkSupport simultaneous local and remote activitySupport simultaneous local and remote activityProvide high network fault tolerance through Provide high network fault tolerance through redundant componentsredundant componentsMonitor network traffic and report statistics to a MIBMonitor network traffic and report statistics to a MIBDiagnose internal or other connectivity problems Diagnose internal or other connectivity problems and trigger alarmsand trigger alarms

Router Features and FunctionsRouter Features and Functions

Static routingStatic routing Technique in which a network administrator programs Technique in which a network administrator programs

a router to use a specified paths between nodesa router to use a specified paths between nodes

Dynamic routingDynamic routing Automatically calculates best path between nodes Automatically calculates best path between nodes

and accumulates this information in a routing tableand accumulates this information in a routing table

HopHop Term used in networking to describe each trip data Term used in networking to describe each trip data

take from one connectivity device to anothertake from one connectivity device to another

Router Features and FunctionsRouter Features and Functions

Figure 6-28: The placement of routers on a LAN

Routing ProtocolsRouting Protocols

The four most common routing protocols:The four most common routing protocols: RIP (Routing Information Protocol) for IP and RIP (Routing Information Protocol) for IP and

IPXIPX OSPF (Open Shortest Path First) for IPOSPF (Open Shortest Path First) for IP EIGRP (Enhanced Interior Gateway Routing EIGRP (Enhanced Interior Gateway Routing

Protocol) for IP, IPX, and AppleTalkProtocol) for IP, IPX, and AppleTalk BGP (Border Gateway Protocol) for IPBGP (Border Gateway Protocol) for IP

Brouters and Routing SwitchesBrouters and Routing Switches

Bridge routerBridge router Also called a Also called a brouterbrouter Industry term used to describe routers that Industry term used to describe routers that

take on some characteristics of bridgestake on some characteristics of bridges

Routing switchRouting switch Router hybrid that combines a router and a Router hybrid that combines a router and a

switchswitch

GatewaysGateways

Combination of networking hardware and Combination of networking hardware and software that connects two dissimilar kinds of software that connects two dissimilar kinds of networksnetworksPopular types of gateways include:Popular types of gateways include: E-mail gatewaysE-mail gateways IBM host gatewaysIBM host gateways Internet gatewaysInternet gateways LAN gatewaysLAN gateways

CSUs/DSUsCSUs/DSUs

Channel Service Units/Digital Service Channel Service Units/Digital Service Units (CSUs/DSUs): Network Units (CSUs/DSUs): Network interconnectivity devices that connect a interconnectivity devices that connect a network to the public telephone network. network to the public telephone network. CSUs/DSUs translate signals and shield CSUs/DSUs translate signals and shield networks from noise and high voltage on networks from noise and high voltage on the public netwrok.the public netwrok.