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BROADBAND DIGITAL NETWORKS
By Aftab A. Memon
Mehran University of Engineering and Technology, Jamshoro.
07TL-BAT!
Today"s Lect#re$Local Area Networks Overview
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LAN (Local Area Networks)
% A LA& consists of '(hared transmission medi#m
% no) so valid today d#e to s)itched LA&s
'set of hard)are and soft)are for the
interfacing devices
'reg#lations for orderly access to the medi#m
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Why High Speed LANs?
% *+ce LA&s #sed to rovide asicconnectivity'onnecting s and terminals to mainframes and
midrange systems that ran cororate alications
' Tra+c atterns )ere light% Emhasis )as on /le transfer and electronic mail
% (eed and o)er of s has risen'rahics-intensive alications and U1s
% lient2server com#ting is no) dominantarchitect#re in #siness environment
% om#ting over net)or3
% 4re5#ent transfer of large vol#mes of data
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LAN Protocol Architecture
% orresonds to lo)er t)o layers of *(1model
% 1EEE 08 reference model
'Logical lin3 control 9LL:'Media access control 9MA:
'hysical
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I !"# Protocol Layers vs$
OSI %odel
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I !"# Layers & Physical
% (ignal encoding2decoding% reamle generation2removal
'for synchroni;ation
% Bit transmission2recetion% (eci/cation for transmission medi#m and
toology
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!"# 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
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LAN Protocols i ote+t
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,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
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LAN .opologies
% B#s% ?ing
% (tar
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/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
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-ra'e .ras'issio & /us LAN
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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
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-ra'e
.ras'issio0ig LAN
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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
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%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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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S%A21 (I !"#$3 4 theret)
% ith (MA, collision occ#ies medi#m ford#ration of transmission'it is ine+cient to comlete the transmission of
a collided ac3et
% As in K-ersistent (MA'1f medi#m idle, transmit
'1f #sy, listen for idle, then transmit
% (tations listen )hile transmitting
% 1f collision detected 9d#e to high voltageon #s:, cease transmission and )aitrandom time then start again' random )aiting time is determined #sing
binary exponential backo mechanism
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S%A21
Operatio
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/iary e+poetial 5ack o66
% random )aiting eriod #t consec#tive coll#sionsincrease the mean )aiting time'mean )aiting time do#les in the /rst K0 retransmission
attemts
'after /rst collision, )aits 0 or K slot time
'if collided again 9second time:, )aits 0, K, 8 or N slots'if collided for the ith time, )aits 0, K, R, or 8i-K slots
'the randomi;ation interval is /Ced to 0 R K08N after K0th collision
'station tries a total of K times and then gives # if
cannot transmit% lo) delay )ith small amo#nt of )aiting stations
% large delay )ith large amo#nt of )aiting stations
one slot time = max. round trip delay = 51.2 microsecs in 10 Mbps
Ethernet (see coming slides)
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S%A21 & 1etails o6 otetio
% (ending station m#st ma3e s#re that' all other stations are a)are its transmission and
' there is no collision on the channel
% so the sending station has to contin#e
transmission for a d#ration of the )orstcase scenario in )hich #nderstanding acollision ta3es as long as the ro#nd tri time'this is closely related to the length of the cale
9#s: and the roagation seed'for 8S00 meters of coaC cale 9standard for K0Ms Ethernet:, ro#nd tri time is aroC S0microseconds
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%ii'u' -ra'e Si7e
% revio#s disc#ssion also has minim#mframe si;e imlication
' at K0 Ms$ 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
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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
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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
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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
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A +a'ple .wo&Level Star
.opology
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Itercoectio le'ets i
LANs
% Bridges% !#s
% ()itches
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/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
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-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
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/ridge Operatio +a'ple
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/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&
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/ridge Protocol Architecture
% 1EEE 08.K<% oerates at MA level
'(tation address is at this level
'Bridge does not need LL layer
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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
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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
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Layer # Switch /ee6its
% &o change to soft)are or hard)are ofdevices
% Attachment is not logically di>erent fromthe attached device oint of vie)
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.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
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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 #
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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 #
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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
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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
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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
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.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
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.ypical Local Network
o6iguratio
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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
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-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
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,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
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+a'ple ,iga5it theret
o6iguratio
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,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'
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,iga5it theret %ediu'
Optios (Log Scale)
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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" ,
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8"&,5ps theret 1ata 0ate ad
1istace Optios (Log Scale)
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-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
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-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
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-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
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-i5re hael le'ets
% End systems - &odes% ()itched elements - the net)or3 or faric
% omm#nication across oint to oint lin3s
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-i5re hael Network
-i5re hael Protocol
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-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
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% 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 (#)
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-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
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-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
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-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
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-ive Applicatios o6 -i5re
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-ive Applicatios o6 -i5re
hael
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-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