Lec1 Local Area Networks

7/17/2019 Lec1 Local Area Networks

http://slidepdf.com/reader/full/lec1-local-area-networks 1/73

BROADBAND DIGITAL NETWORKS

By Aftab A. Memon

Mehran University of Engineering and Technology, Jamshoro.

07TL-BAT!

Today"s Lect#re$Local Area Networks Overview



LAN (Local Area Networks)

% A LA& consists of '(hared transmission medi#m

% no) so valid today d#e to s)itched LA&s

'set of hard)are and soft)are for the

interfacing devices

'reg#lations for orderly access to the medi#m



Why High Speed LANs?

% *+ce LA&s #sed to rovide asicconnectivity'onnecting s and terminals to mainframes and

midrange systems that ran cororate alications

' Tra+c atterns )ere light% Emhasis )as on /le transfer and electronic mail

% (eed and o)er of s has risen'rahics-intensive alications and U1s

% lient2server com#ting is no) dominantarchitect#re in #siness environment

% om#ting over net)or3

% 4re5#ent transfer of large vol#mes of data



LAN Protocol Architecture

% orresonds to lo)er t)o layers of *(1model

% 1EEE 08 reference model

'Logical lin3 control 9LL:'Media access control 9MA:

'hysical



I !"# Protocol Layers vs$

OSI %odel



I !"# Layers & Physical

% (ignal encoding2decoding% reamle generation2removal

'for synchroni;ation

% Bit transmission2recetion% (eci/cation for transmission medi#m and

toology



!"# Layers & %ediu' Access

otrol * Logical Lik otrol

% *(1 layer 8 9<ata Lin3: is divided into t)o in 08'Logical Lin3 ontrol 9LL: layer

'Medi#m Access ontrol 9MA: layer

% MA layer'Assemly of data into frame )ith address and error detection

/elds 9for transmission:

'<isassemly of frame 9on recetion:

'Address recognition

'Error detection

'overn access to transmission medi#m% &ot fo#nd in traditional layer 8 data lin3 control

% LL layer'1nterface to higher levels

'=o) control

'Based on classical <ata Lin3 ontrol rotocols



LAN Protocols i ote+t



,eeric %A * LL -or'at

% Act#al format di>ers from rotocol to rotocol% MA layer receives data from LL layer

% MA layer detects errors and discards frames% LL otionally retransmits #ns#ccessf#l frames



LAN .opologies

% B#s% ?ing

% (tar



/us .opology

% (tations attach to linear medi#m 9#s:' @ia a ta - allo)s for transmission and recetion

% Transmission roagates in medi#m in oth directions % ?eceived y all other stations

% Terminator asors frames at end of medi#m

% &eed to identify target station% Each station has #ni5#e address

% <estination address incl#ded in frame header

% &eed to reg#late transmission' To avoid collisions

% 1f t)o stations attemt to transmit at same time, signals )illoverla and ecome garled

' To avoid contin#o#s transmission from a single station. 1f onestation transmits contin#o#sly access loc3ed for others

% (ol#tion$ Transmit <ata in small loc3s frames



-ra'e .ras'issio & /us LAN



0ig .opology

% ?eeaters oined y oint-to-oint lin3s in closed loo'?eceive data on one lin3 and retransmit on another

'Lin3s #nidirectional

'(tations attach to reeaters% <ata transmitted in frames

'irc#late ast all stations

'<estination recogni;es address and coies frame

'4rame circ#lates ac3 to so#rce )here it is removed

% Medi#m access control determines )henstation can insert frame



-ra'e

.ras'issio0ig LAN



Star .opology

% Each station connecteddirectly to central node'#sing a f#ll-d#leC

9i-directional: lin3

% entral node can roadcast 9h#:'hysical star, logically #s

'*nly one station can transmit at a time

% entral node can act as frame s)itch'retransmits only to destination

'todayDs technology



%ediu' Access otrol (%A)

% 1n LA&s data is roadcast'there is a single medi#m shared y di>erent #sers

% e need MA s#layer for'orderly and e+cient #se of roadcast medi#m

% This is act#ally a Fchannel allocationGrolem

% (ynchrono#s 9static: sol#tions'everyone 3no)s )hen to transmit

% Asynchrono#s 9dynamic: sol#tion'in resonse to immediate needs

' T)o categories% ?o#nd roin

% ontention



Static hael Allocatio

% 4re5#ency <ivisionM#ltileCing 94<M:

% hannel is divided to carry

di>erent signals at di>erentfre5#encies

% E+cient if there is a constant9one for each slot: amo#nt of#sers )ith heavy tra+c

% rolematic is there are lessor more #sers

% Even if the amo#nt of #sersH I of channels, #tili;ation is

still lo) since tyical net)or3tra+c is not #niform andsome #sers may not havesomething to send all the

time



Static hael Allocatio

% Time <ivisionM#ltileCing

% Each #ser is staticallyallocated one time slot

' if a artic#lar #ser

does not haveanything to send, it)aits and )astes thechannel for thateriod

% 1ne+cient for thecases disc#ssed in4<M



1ya'ic hael Allocatio

ategories

% ?o#nd roin'each station has a t#rn to transmit

% declines or transmits 9to a certain limit:

% overhead of assing the t#rn in either case

'erforms )ell if many stations have data totransmit for most of the time

% other)ise assing the t#rn )o#ld ca#se ine+ciency



1ya'ic hael Allocatio

ategories

% ontention'All stations contend to transmit

'&o control to determine )hose t#rn is it

'(tations send data y ta3ing ris3 of collision

9)ith othersD ac3ets:% ho)ever they #nderstand collisions y listening to

the channel, so that they can retransmit

' There are several imlementation methods

'1n general, good for #rsty tra+c% )hich is the tyical tra+c tyes for most net)or3s

'E+cient #nder light or moderate load

'erformance is ad #nder heavy load



theret (S%A21)

% arriers (ense M#ltile Access )ithollision <etection

'is the #nderlying technology

% eroC Ethernet 9K7: y Metcalfe

% 1EEE 08.N standard 9KN:

% ontention techni5#e that has asis infamo#s AL*!A net)or3



ALOHA

% ac3et ?adio 9alicale to any shared medi#m:'initially roosed to interconnect !a)aiian 1slands

% y &orman Aramson of Univ. of !a)aii 9early 70s:

% hen station has frame, it sends

'collisions may occ#r% (tation listens for maC ro#nd tri time

% 1f no collision, /ne. 1f collision, retransmit after arandom )aiting time

% MaC channel #tili;ation is KO - very ad



Slotted ALOHA

% <ivide the time into discrete intervals 9slots:'e5#al to frame transmission time

'need central cloc3 9or other sync mechanism:

'transmission egins at slot o#ndary

% ollided frames )ill do so totally or )ill not collide

% Algorithm'1f a node has a ac3et to send, sends it at the eginning

of the neCt slot

'1f collision occ#rred, retransmit at the neCt slot )ith aroaility

% MaC channel #tili;ation is N7O'do#les &ormal AL*!A, #t still lo)



S%A (arrier Sese %ultiple

Access)

% 4irst listen for clear medi#m 9carrier sense:% 1f medi#m idle, transmit

% 1f #sy, contin#o#sly chec3 the channel #ntil it is idleand then transmit

% 1f collision occ#rs'ait random time and retransmit

% ollision roaility deend on the roagationdelay'Longer roagation delay, )orse the #tili;ation

% ollision occ#rs even if the roagation time is ;ero.'!PQ

% K-ersistent (MA

% Better #tili;ation than AL*!A



Nopersistet S%A

% atient (MA% 1f channel idle, send

% 1f not, do not contin#o#sly sei;e the

channel'instead )ait a random eriod of time

% Better #tili;ation, longer delay



p&Persistet S%A

% Alies to slotted channels% 1f channel is idle

'send )ith a roaility

'defer #ntil the neCt slot )ith roaility K

'reeat this algorithm #ntil it sends or channelecomes #sy y another station

% if channel ecomes #sy in this )ay, then )ait arandom eriod of time and reeat the same algorithm

% 1f channel is initially #sy, then chec3 theneCt slot

% larger means smaller channel #tili;ationand smaller )aiting time for the ac3ets



S%A21 (I !"#$3 4 theret)

% ith (MA, collision occ#ies medi#m ford#ration of transmission'it is ine+cient to comlete the transmission of

a collided ac3et

% As in K-ersistent (MA'1f medi#m idle, transmit

'1f #sy, listen for idle, then transmit

% (tations listen )hile transmitting

% 1f collision detected 9d#e to high voltageon #s:, cease transmission and )aitrandom time then start again' random )aiting time is determined #sing

binary exponential backo mechanism



S%A21

Operatio



/iary e+poetial 5ack o66

% random )aiting eriod #t consec#tive coll#sionsincrease the mean )aiting time'mean )aiting time do#les in the /rst K0 retransmission

attemts

'after /rst collision, )aits 0 or K slot time

'if collided again 9second time:, )aits 0, K, 8 or N slots'if collided for the ith time, )aits 0, K, R, or 8i-K slots

'the randomi;ation interval is /Ced to 0 R K08N after K0th collision

'station tries a total of K times and then gives # if

cannot transmit% lo) delay )ith small amo#nt of )aiting stations

% large delay )ith large amo#nt of )aiting stations

one slot time = max. round trip delay = 51.2 microsecs in 10 Mbps

Ethernet (see coming slides)



S%A21 & 1etails o6 otetio

% (ending station m#st ma3e s#re that' all other stations are a)are its transmission and

' there is no collision on the channel

% so the sending station has to contin#e

transmission for a d#ration of the )orstcase scenario in )hich #nderstanding acollision ta3es as long as the ro#nd tri time'this is closely related to the length of the cale

9#s: and the roagation seed'for 8S00 meters of coaC cale 9standard for K0Ms Ethernet:, ro#nd tri time is aroC S0microseconds



%ii'u' -ra'e Si7e

% revio#s disc#ssion also has minim#mframe si;e imlication

' at K0 Ms$ one it ta3es K00 ns to etransmitted

'1n order to occ#y the channel d#ring S0microsecs

% one frame at minim#m sho#ld e S00 its

% l#s some safety margins and ro#nding, minim#m

frame si;e is set to SK8 its 9 ytes: in 1EEE 08.N



I !"#$3 -ra'e -or'at

>= >=

Preamble is alternating 0’s and 1’s (for clock synchronization)

SFD is 10101011

FS e!cl"des Preamble and SFD

#ddresses are "ni$"ely assigned by %&&& to man"fact"rers'

hy "ni$"e



8"%5ps %ediu' Optios

% K0 Base8' Thic3 coaC - osolete

% K0BaseS' Thin coaC

'B#s toology

'S00meters maC segment length% maC S segments connected via reeaters maC. 8S00 meters

'K00 maC stations er segment

% K0BaseT'most commonly #sed one 9see neCt slide:

% K0Base4'*tical /er

'star toology or oint to oint

'too eCensive for K0 Ms



8"/AS&.

% Unshielded t)isted air 9UT: medi#m'reg#lar telehone )iring

% oint to oint #sing cross-cales

% (tar-shaed toology'(tations connected to central h# or s)itch 9m#ltiort

reeater:

' T)o t)isted airs 9transmit and receive:

'!# accets in#t on any one line and reeats it on all otherlines

% hysical star, logical #s

% collisions are ossile

% Lin3 limited to K00 m

% M#ltile levels of h#s can e cascaded



A +a'ple .wo&Level Star

.opology



Itercoectio le'ets i

LANs

% Bridges% !#s

% ()itches



/ridges

% &eed to eCand eyond single LA&% 1nterconnection to other LA&s and A&s

% Use Bridge or ?o#ter

% Bridge is simler'onnects similar LA&s

'1dentical rotocols for hysical and lin3 layers

'Minimal rocessing

% ?o#ter more general #rose

'1nterconnect vario#s LA&s and A&s



-uctios o6 a /ridge

% ?ead all frames transmitted on one LA&and accet those addressed to any stationon the other LA&

% Using MA rotocol for second LA&,retransmit each frame

% <o the same the other )ay ro#nd



/ridge Operatio +a'ple



/ridge 1esig Aspects

% &o modi/cation to content or format of frame% &o additional header

% ECact it)ise coy of frame from one LA& to another'that is )hy t)o LA&s m#st e identical

% Eno#gh #>ering to meet ea3 demand

% ?o#ting and addressing intelligence'M#st 3no) the addresses on each LA& to e ale to tell

)hich frames to ass

'May e more than one ridge to reach the destination

% May connect more than t)o LA&s

% Bridging is transarent to stations'Aears to all stations on m#ltile LA&s as if they are on one

single LA&



/ridge Protocol Architecture

% 1EEE 08.K<% oerates at MA level

'(tation address is at this level

'Bridge does not need LL layer



Shared %ediu' Hu5

% entral h#% !# retransmits incoming signal to all

o#tgoing lines

%*nly one station can transmit at a time% ith a K0Ms LA&, total caacity isK0Ms



Layer # Switches

% entral reeater acts as s)itch% 1ncoming frame s)itches to aroriate

o#tgoing line'Un#sed lines can e #sed to s)itch other tra+c

'More than one station transmitting at a time'Each device has dedicated caacity e5#al to theLA& caacity, if the s)itch has s#+cient caacity forall



Layer # Switch /ee6its

% &o change to soft)are or hard)are ofdevices

% Attachment is not logically di>erent fromthe attached device oint of vie)



.ypes o6 Layer # Switch

% (tore and for)ard s)itch'Accet in#t, #>er it rie=y, then o#t#t

% #t thro#gh s)itch

' Ta3e advantage of the destination addresseing at the start of the frame

'Begin reeating incoming frame onto o#t#tline as soon as address recogni;ed

'May roagate some ad frames% !PQ



Layer # Switch vs$ /ridge

% A layer 8 s)itch may f#nction as a m#ltiortridge'i.e. a ridge f#nctionality also eCists in layer 8 s)itches

% (ome di>erences

'Bridge only analy;es and for)ards one frame at a time'()itch has m#ltile arallel data aths

% an handle m#ltile frames at a time

'Bridge #ses store-and-for)ard oeration

'()itch also has c#t-thro#gh oeration

% Bridges are not common no)adays'&e) installations tyically incl#de layer 8 s)itches )ith

ridge f#nctionality rather than ridges

P 5l ith L #



Pro5le's with Layer #

Switches (8)

% As n#mer of devices in LA&s gro)s, layer 8s)itches sho) some limitations'Broadcast overload

% 1n LA&s some rotocols 9e.g. A?: )or3 in roadcastmanner

'Lac3 of m#ltile lin3s

% (et of devices and LA&s connected y layer 8s)itches share common MA roadcast address'1f any device iss#es roadcast frame, that frame is

delivered to all devices attached to net)or3 connectedy layer 8 s)itches and2or ridges

'1n large net)or3, roadcast frames can create asigni/cant overhead

P 5l ith L #



Pro5le's with Layer #

Switches (#) ad Solutio

% #rrent standards for ridge rotocols dictateno closed loos'*nly one ath is allo)ed et)een any t)o devices

% Limits oth erformance and reliaility.

%(ol#tion$ rea3 # net)or3 into s#net)or3sconnected y ro#ters 9that oerate at 1layer:'MA roadcast frame limited to devices and

s)itches contained in single s#net)or3

'1-ased ro#ters emloy sohisticated ro#tingalgorithms

% Allo) #se of m#ltile aths et)een s#net)or3s goingthro#gh di>erent ro#ters

P 5l ith 0 t d



Pro5le's with 0outers ad

Layer 3 Switches

% ?o#ters are designed to e imlemented at thegate)ay and only rocess ac3ets to2from o#ternet)or3s'o#tside tra+c is less than the internal tra+c

% !igh-seed LA&s and high-erformance layer 8 s)itches #m

millions of ac3ets er second'the same ro#ter may create a erformance ottlenec3 in

the heart of a LA&

% (ol#tion$ layer N s)itches'1mlement ac3et-for)arding logic of ro#ter in hard)are

% faster

% T)o categories'ac3et y ac3et

'4lo) ased



Layer 3 Switch ategories

% ac3et y ac3et'*erates in same )ay as traditional ro#ter

'#t m#ch faster

% 4lo)-ased layer N s)itch tries to enhance

erformance y identifying =o)s of 1ac3ets that have same so#rce anddestination

'<one y oserving ongoing tra+c or #sing a

secial =o) lael in ac3et header 91v:

'*nce =o) is identi/ed, rede/ned ro#te can eestalished to seed-# the for)arding rocess



.ypical Large LAN Orgai7atio

% Tho#sands to tens of tho#sands of devices% <es3to systems lin3s K0 Ms to K00 Ms

'1nto layer 8 s)itch

% ireless LA& connectivity availale for moile #sers

% Layer N s)itches at local net)or3"s core'4orm local ac3one

'1nterconnected at K s

'onnect to layer 8 s)itches at K s

% (ervers connect directly to layer 8 or layer Ns)itches at K s

% Lo)er-cost ro#ter rovides A& connection

% ircles in diagram identify searate LA& s#net)or3s'MA roadcast frame limited to a single s#net)or3

.ypical Local Network



.ypical Local Network

o6iguratio



8""%5ps (-ast theret)% K00BaseT

' to #se voice grade cat N cales

' N airs in each direction )ith NN.N Ms on each #sing a ternarysignalling scheme 9BT H its ma to trits:

% total airs 98 of them idirectional:

' an e #sed )ith cat S cales 9#t )aste of reso#rces:

% K00Base-' Unidirectional data rate of K00 Ms

' Uses t)o lin3s 9one for transmit, one for receive:

' T)o tyes$ K00Base-T and K00Base-4

% K00Base-T' (T or cat S UT only 9one air in each direction:

'at K8S Mh; )ith secial encoding that has 80O overhead% its are encoded #sing S-it time

% K00Base-4' *tical /er 9one at each direction:

' (imilar encoding



-ast theret & 1etails

% (ame message format as K0 Ms Ethernet% (tar-)ire toology

're5#ires s)itches for f#ll-d#leC comm#nicationto achieve 800 Ms e>ective transmission rate

'1n fact, shared medi#m no longer eCists% no collisions, th#s (MA2< algorithm no longer

needed

% #t stations can contin#e (MA2< and same

message format is #sed for ac3)ard comatiilityreasons



,iga5it theret

% (trategy same as 4ast Ethernet'&e) medi#m and transmission seci/cation

'?etains (MA2< rotocol and frame format

'omatile )ith K00BA(E-T and K0BA(E-T

% hy gigait EthernetQ

' K02K00 Ms load from end #sers createsincreased tra+c on ac3ones

% so gigait Ethernet is meaningf#l for ac3ones

+a'ple ,iga5it theret



+a'ple ,iga5it theret

o6iguratio



,iga5it theret 4 Physical

% K000Base-('(hort )avelength, m#ltimode /er

% K000Base-L

'Long )avelength, M#lti or single mode /er

% K000Base-

'A secial (T 98Sm:% one for each direction

% K000Base-T' airs, cat S UT 9idirectional:

,iga5it theret %ediu'



,iga5it theret %ediu'

Optios (Log Scale)



8",5ps theret

% hyQ'same reasons$ increase in tra+c, m#ltimedia

comm#nications. etc.

% rimarily for high-seed, local ac3oneinterconnection et)een large-caacity s)itches

% Allo)s constr#ction of 9MA&s: and A&s'onnect geograhically disersed LA&s

% @ariety of standard otical interfaces9)avelengths and lin3 distances: seci/ed for K0 Ethernet'N00 m to 0 3ms

'f#ll d#leC

8" ,



8"&,5ps theret 1ata 0ate ad

1istace Optios (Log Scale)



-i5re hael & /ackgroud

% 12* channel'<irect oint to oint or m#ltioint comms lin3

'!ard)are ased

'!igh (eed

'@ery short distance

'User data moved from so#rce #>er to destiation #>er

% &et)or3 connection'1nterconnected access oints

'(oft)are ased rotocol

'4lo) control, error detection Vrecovery

'End systems connections



-i5re hael

% Best of oth technologies% hannel oriented

'<ata tye 5#ali/ers for ro#ting frame ayload

'Lin3 level constr#cts associated )ith 12* os

'rotocol interface seci/cations to s#orteCisting 12* architect#res% e.g. ((1

% &et)or3 oriented'4#ll m#ltileCing et)een m#ltile destinations

'eer to eer connectivity

'1nternet)or3ing to other connection technologies



-i5re hael 0e9uire'ets% 4#ll d#leC lin3s )ith t)o /ers er lin3

% K00 Ms to 00 Ms on single line' 4#ll d#leC 800 Ms to K00 Ms er lin3

% U to K0 3m

% (mall connectors

% !igh-caacity #tili;ation, distance insensitivity

%reater connectivity than eCisting m#ltidro channels% Broad availaility' i.e. standard comonents

% M#ltile cost2erformance levels' (mall systems to s#ercom#ters

% arry m#ltile eCisting interface command sets for eCisting channel andnet)or3 rotocols

% Uses generic transort mechanism ased on oint-to-oint lin3s and as)itching net)or3

% (#orts simle encoding and framing scheme

% 1n t#rn s#orts a variety of channel and net)or3 rotocols



-i5re hael le'ets

% End systems - &odes% ()itched elements - the net)or3 or faric

% omm#nication across oint to oint lin3s



-i5re hael Network

-i5re hael Protocol



-i5re hael Protocol

Architecture (8)

% 4-0 hysical Media'*tical /er for long distance

'coaCial cale for high seed short distance

'(T for lo)er seed short distance

%4-K Transmission rotocol'B2K0B signal encoding

% 4-8 4raming rotocol' Toologies

'4raming formats

'4lo) and error control

'(e5#ences and eCchanges 9logical gro#ing of frames:

-i5re hael Protocol



% 4-N ommon (ervices'1ncl#ding m#lticasting

% 4- Maing

'Maing of channel and net)or3 services onto

/re channel% e.g. 1EEE 08, ATM, 1, ((1

-i5re hael Protocol

Architecture (#)



-i5re hael Physical %edia

% rovides range of otions for hysicalmedi#m, the data rate on medi#m, andtoology of net)or3

% (hielded t)isted air, video coaCial cale,

and otical /er

% <ata rates K00 Ms to N.8 s

% oint-to-oint from NN m to K0 3m



-i5re hael -a5ric

% eneral toology called faric or s)itched toology% Aritrary toology incl#des at least one s)itch to

interconnect n#mer of end systems

% May also consist of s)itched net)or3'(ome of these s)itches s#orting end nodes

% ?o#ting transarent to nodes'Each ort has #ni5#e address

'hen data transmitted into faric, edge s)itch to )hichnode attached #ses destination ort address to determine

location'Either deliver frame to node attached to same s)itch or

transfers frame to adacent s)itch to egin ro#ting toremote destination



-a5ric Advatages

% (calaility of caacity'As additional orts added, aggregate caacity ofnet)or3 increases

'Minimi;es congestion and contention

'1ncreases thro#gh#t

% rotocol indeendent% <istance insensitive

% ()itch and transmission lin3 technologies maychange )itho#t a>ecting overall con/g#ration

% B#rden on nodes minimi;ed'4ire hannel node resonsile for managing oint-to-

oint connection et)een itself and faric

'4aric resonsile for ro#ting and error detection



-ive Applicatios o6 -i5re



-ive Applicatios o6 -i5re

hael



-i5re hael Prospects

% Bac3ed y 4ire hannel Association% 1nterface cards for di>erent alications availale

% Most )idely acceted as eriheral deviceinterconnect

' To relace s#ch schemes as ((1% Technically attractive to general high-seed LA&

re5#irements

% M#st comete )ith Ethernet and ATM LA&s

% ost and erformance iss#es sho#ld dominatethe consideration of these cometingtechnologies

Lec1 Local Area Networks

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