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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sanjeev Ghai Irs Network Devices

15.1 Connecting Devices:

15.1 Connecting Devices Five connecting devices Repeaters Hubs Bridges Switches Routers Gateway

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Figure 15.1 Five categories of connecting devices


Repeaters A physical layer device the acts on bits not on frames or packets Can have two or more interfaces When a bit (0,1) arrives, the repeater receives it and regenerates it, the transmits it onto all other interfaces Used in LAN to connect cable segments and extend the maximum cable length  extending the geographical LAN range Ethernet 10base5 – Max. segment length 500m – 4 repeaters (5 segments) are used to extend the cable to 2500m ) Ethernet 10Base2- Max. segment length 185m - 4 repeaters (5 segments) are used to extend the cable to 925m Repeaters do not implement any access method If any two nodes on any two connected segments transmit at the same time collision will happen

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Figure 15.3 Function of a repeater

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Figure 15.2 A repeater connecting two segments of a LAN


Hubs Acts on the physical layer Operate on bits rather than frames Also called multiport repeater Used to connect stations adapters in a physical star topology but logically bus Connection to the hub consists of two pairs of twisted pair wire one for transmission and the other for receiving . Hub receives a bit from an adapter and sends it to all the other adapters without implementing any access method. does not do filtering (forward a frame into a specific destination or drop it) just it copy the received frame onto all other links The entire hub forms a single collision domain , and a single Broadcast domain Collision domain : is that part of the network (set of NICs ) when two or more nodes transmit at the same time collision will happen. Broadcast domain: is that part of the network (set of NIC) where each NIC can 'see' other NICs' traffic broadcast messages. Multiple Hubs can be used to extend the network length For 10BaseT and 100BaseT the maximum length of the connection between an adapter and the hub is 100 meters  the maximum length between any two nodes is 200 m = maximum network length

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Figure 16.4 Hubs

Interconnecting with hubs :

Interconnecting with hubs Backbone hub interconnects LAN segments Advantage : Extends max distance between nodes Disadvantages Individual segment collision domains become one large collision domain  ( reduce the performance ) Can’t interconnect different Ethernet technologies(like 10BaseT & 100BaseT) because no buffering at the hub Here we have a single collision domain and a single broadcast domain

Hubs Vs. Repeaters:

Hubs Vs. Repeaters Hub are different than repeaters in the following: The provide network management features by gathering information about the network and report them to a monitoring host connected to the hub so some statistics about the network (bandwidth usages, collision rates, average frame sizes) can be generated. If an adapter is not working the hub can disconnect it internally and the network will not be affected.

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