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I.S. 4123Introduction to

Telecommunication in Business

Chapter 6 Network Hardware Components

Dr. Jan ClarkFALL, 2002

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Repeaters

Provide both physical and electrical connectionsFunction - regenerate and propagate a signalExtend distance coveredReceives signal from one cable segment, regenerates and transmits signal to one or more cable segmentsSource of propagation delay in a network

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Types of Hubs

Repeater hub - simplest connectionSwitching hub - does not broadcast to all nodesBridging hub - can connect dissimilar networksStackable Repeater Hub - two or more LANS daisy chained together

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Multislot Repeater Hub

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Stackable Hubs

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Repeater or Switch Hub?

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Which is Better?

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Bridge

Interconnects two or more LANs or LAN segmentsOperate at Data Link LayerPhysical Layer transparentUsually connect like networks, but can bridge unlike (e.g. Ethernet to Token Ring) - MAC Layer bridgeRely upon Data Link Layer address - monitor messages and forward when appropriate

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The LAN user is often unaware that a bridge exists. They do not experience performance degradation and are allowed access to any station on either network (within security reasons)

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Broadcast Storms

Bridges pass broadcast frames from one network to another.Broadcast storm occurs when several broadcasts are transmitted at the same time - can cause a network to crash or shut down.

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Bridges are Store-and-Forward

They capture an entire frame before deciding whether to filter or forward the frameCRC computed by bridge - if invalid, frame is dropped

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A user on one LAN can address another LAN as

though it were another node in their network. This is

done without signing onto a communication device,

dialing through a modem, or learning any new software

commands or menus

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"NEW" Bridge Definition

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Bridge Standards

Transparent - Broadcast, multicast frames always forwarded. If not broadcast or multicast, creates "learned" address table when frames sent.Source Routing (Token Ring only) - source address must know if destination address is on a different network. If so, provides routing info with message

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When Does a Bridge Forward Data?

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Source Routing Bridge

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Which Would You Select for

Interconnecting Networks - Bridge or

Repeater?

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Switches

Operate at the Data Link, Network, or Transport Layers (depending upon type of switch)Connect two or more computers or network segments. Ethernet switch - Layer 2 (Data Link)Designed for shared media LANsPermits multiple, simultaneous data transmission between different pathsStatic switching

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Switch TypesStore-and-forward switches copy the incoming packet into memory before processing the destination address - may hold for longer periods if destination is busy - performs CRCCut-through switches examine the destination of the incoming packet and immediately connect the port with the incoming message to the correct outgoing port (hardware based). No waiting, no error checking (great if not busy or error free, BUT…)Hybrid - works either way. When error rates fall below a certain range, switch act as cut-through. If above the range, switch acts as store-and-forward.

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Store-and-Forward Switch

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Cut-Through Switch

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Cut-Through Backplane Switch

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How Can Collisions Occur on a Switched Ethernet

Network?

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Latency

Amount of time a frame spends inside a network device such as a bridge or a switchThe lower the latency, the faster a device processes a data frameNetwork can time out with high latencyWhich has higher latency - store-and-forward, or switch-through?