Chapter 11 Extending LANs

8/9/2019 Chapter 11 Extending LANs

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Chapter 11 Extending LANs:Chapter 11 Extending LANs:

Fiber Modems, Repeaters, Bridges, & SwithesFiber Modems, Repeaters, Bridges, & Swithes

Repeater

Hub

Bridge

Switch


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Each LAN technology is designed for a specific

combination of speed, distance, and cost.

A maimum length specification is a fundamental

part of LAN technology. LAN hardware is

engineered for a fied maimum length cable andthe hardware will not wor! correctly o"er wires

that eceed the bound

#iber $ptic Etensions %fig &&.&'

( a pair of fiber transcei"ers and optical fibers can be

used to pro"ide a connection between the A)* on a

hub and a remote A)* on a router on a remote LAN.
http://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_1CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_1CT.GIF


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Repeater (Hub)Repeater (Hub) a hardware de"ice used to etend a LAN.

+ro"ides connecti"ity between two cable segments amplifies and sends all electrical signals that occur

on one segment to the other segment %fig &&.'%AN*-/0&.-$1'

A hub is essentially a multiport repeaterSpeed of signals in copper cable 2 &3m4s

any two stations cannot be separated by morethan 5 repeaters %fig &&.6'

7rawbac! of repeaters( all signals are repeated, including those o"erlapping

signals that correspond to collisions and those due toelectrical noise. 8herefore repeaters cause the same

problem to occur on all other segments.
http://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_2CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_3CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_3CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_2CT.GIF


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BridgeBridge a hardware de"ice that etends a LAN by forwarding

complete, correct frames from one segment to another%fig &&.5'%AN*-/0.-$1'

Reads each frame in promiscuous mode and "erifies dataintegrity

bridge will not forward collisions or interference fromone segment to another

9omputers do not !now whether a bridge separates them

Bridges operate at data:lin! %layer ' layer.

A bridge filters, forwards, or floods an incoming framebased on the -A9 address of that frame

#rame filtering function of bridge; frames are notforwarded across bridge unless necessary.

)sing bridges and fiber modem%transcei"er' %fig &&.


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Adapti!e "#earning$ bridgeAdapti!e "#earning$ bridge

loo!s at the physical addresses in the header ofeach frame it recei"es.

source address used to determine location ofsender

destination address used to determine whether toforward a frame

Since bridge does not !now location of computers

at bootup, frames are forwarded until location ofcomputer can be determined %fig &&.5' %fig &&.='

Broadcast and multicast frames are alwaysforwarded

Broadcast storms can cripple networ!
http://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_4CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_5CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_5CT.GIFhttp://www.calstatela.edu/faculty/egean/cs447/lecture-notes/figures/F11_4CT.GIF


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Swith "La%er $Swith "La%er $-ultiport bridge

Segment

( a section of a networ! that is bounded by bridges,

switches, or routers

switching simulates a bridged LAN with onecomputer per segment while a hub simulates a

single shared medium %fig &&.&'

#looding

( forwarding pac!ets out all ports%segments' ecept

source segment

( $ccurs at power up and for un!nown destinations

( occurs for all broadcast pac!ets


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-aimum bandwidth of a switch 2 RN4

R is data transmission rate on a gi"en port

N is the total number of switch ports.


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Memor% b'((ering in swithesMemor% b'((ering in swithes

port:based %separate *4$ >ueues per port'

shared memory buffering


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Swithing methodsSwithing methods

store ? forward

cut:through switching

( fast forward @wait 3:bytes

( collision fragment:free @wait


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Co##ision domainCo##ision domain

the networ! area within which frames that ha"e

collided are propagated.

Repeaters and hubs propagate collisions.LAN bridges, switches, and routers do not.


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Broadcast domainBroadcast domain

the set of all de"ices that will broadcast

frames originating from any de"ice within

the setcrosses layer switches

bounded by layer 6 de"ices %router'


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Ad!antages o( bridged"swithed$Ad!antages o( bridged"swithed$

networ) o!er repeaters and h'bsnetwor) o!er repeaters and h'bsLarger aggregate bandwidth

( allows simultaneous communication between more than onepair of computers

8raffic isolation( +ac!ets forwarded only when needed

#ewer collisions

Bridging across longer distances(point:to:point and special bridge hardware at each end.

Both sites filters pac!ets due to bandwidth constraints.

Buffering is done on bridge to accommodate speeddifferences between bridge ports.

( leased serial line to connect sites

( leased satellite channel


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C%#e o( BridgesC%#e o( Bridges

$ccurs when multiple paths between twomachines eist

may cause infinite loops

8o pre"ent infinite loops in a bridgenetwor! that contains a cycle of bridge

segments, some bridges must agree not to

forward frames %fig &&./'


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Spanning-Tree protocolSpanning-Tree protocol

used to insure loop:free path between any twonodes on networ!.

protocol detects and brea!s loops by placing someconnections in standby mode

a bridge does not forward frames if the bridge findsthat each segment to which it attaches already

contains a bridge that has agreed to forward frames Spanning:tree protocol is used in fault:tolerant

networ!s


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*LAN*LANA 1LAN is a broadcast domain.

1LANS group users by logical association insteadof physical location.

broadcast domain of 1LAN A is separate fromthat of 1LAN B

1LAN is a logical grouping of networ!de"ices4users not restricted to a physical switchsegment

#rame tagging %3.&' in trun! connections8ypes of 1LAN

(port:based %layer&'

( mac:based %layer'

( *+:based 1LANS %layer6'

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Chapter 11 Extending LANs