This document discusses high speed local area networks (LANs). It begins with an introduction to different high speed LAN technologies such as Fast and Gigabit Ethernet, Fibre Channel, and wireless LANs. It then discusses why organizations need high speed LANs to support applications, server farms, workgroups, and backbones. The remainder of the document focuses on Ethernet technologies including the CSMA/CD protocol, various Ethernet standards up to 10Gbps, and their physical layer implementations.

1. Data and ComputerData and Computer
CommunicationsCommunications
Eighth EditionEighth Edition
by William Stallingsby William Stallings
Lecture slides by Lawrie BrownLecture slides by Lawrie Brown
Chapter 16 –Chapter 16 – High SpeedHigh Speed LANLANss

2. High SpeedHigh Speed LANLANss
Congratulations. I knew the record would stand
until it was broken.
Yogi BerraYogi Berra

3. IntroductionIntroduction
 range of technologiesrange of technologies

Fast and Gigabit EthernetFast and Gigabit Ethernet

FibreFibre ChannelChannel

High Speed Wireless LANsHigh Speed Wireless LANs

4. Why High Speed LANs?Why High Speed LANs?
 speedspeed and power ofand power of PCsPCs hashas risenrisen

graphicsgraphics-intensive applications-intensive applications and GUIsand GUIs
 see LANsee LANss as essential to organizationsas essential to organizations

forfor client/server computingclient/server computing
 now have requirements fornow have requirements for

centralized server farmscentralized server farms

power workgroupspower workgroups

high-speed local backbonehigh-speed local backbone

5. Ethernet (CSMEthernet (CSMAA/CD)/CD)
 most widely used LAN standardmost widely used LAN standard
 developed bydeveloped by

Xerox - original EthernetXerox - original Ethernet

IEEE 802.3IEEE 802.3
 Carrier Sense Multiple Access withCarrier Sense Multiple Access with
Collision Detection (CSMA/CD)Collision Detection (CSMA/CD)

random / contention access to mediarandom / contention access to media

6. ALOHAALOHA
 developed for packet radio netsdeveloped for packet radio nets
 when station has frame, it sendswhen station has frame, it sends
 then listens for a bit over max round trip timethen listens for a bit over max round trip time

if receive ACK then fineif receive ACK then fine

if not, retransmitif not, retransmit

if no ACK after repeated transmissions, give upif no ACK after repeated transmissions, give up
 uses a frame check sequence (as in HDLC)uses a frame check sequence (as in HDLC)
 frame may be damaged by noise or by anotherframe may be damaged by noise or by another
station transmitting at the same time (collision)station transmitting at the same time (collision)
 any overlap of frames causes collisionany overlap of frames causes collision
 max utilization 18%max utilization 18%

7. Slotted ALOHASlotted ALOHA
 time on channel based on uniform slots equal totime on channel based on uniform slots equal to
frame transmission timeframe transmission time

need central clock (or other sync mechanism)need central clock (or other sync mechanism)
 transmission begins at slot boundarytransmission begins at slot boundary
 frames either miss or overlap totallyframes either miss or overlap totally
 max utilization 37%max utilization 37%
 both have poor utilizationboth have poor utilization
 fail to use fact that propagation time is muchfail to use fact that propagation time is much
less than frame transmission timeless than frame transmission time

8. CSMACSMA
 stations soon know transmission has startedstations soon know transmission has started
 so first listen for clear medium (carrier sense)so first listen for clear medium (carrier sense)
 if medium idle, transmitif medium idle, transmit
 if two stations start at the same instant, collisionif two stations start at the same instant, collision

wait reasonable timewait reasonable time

if no ACK then retransmitif no ACK then retransmit

collisions occur occur at leading edge of framecollisions occur occur at leading edge of frame
 max utilization depends on propagation timemax utilization depends on propagation time
(medium length) and frame length(medium length) and frame length

9. Nonpersistent CSMANonpersistent CSMA
 NonpersistentNonpersistent CSMA rules:CSMA rules:
1.1. if medium idle, transmitif medium idle, transmit
2.2. if medium busy, wait amount of time drawn fromif medium busy, wait amount of time drawn from
probability distribution (retransmission delay) & retryprobability distribution (retransmission delay) & retry
 randomrandom delays reduces probability of collisionsdelays reduces probability of collisions
 capacitycapacity is wasted because medium will remainis wasted because medium will remain
idle following end of transmissionidle following end of transmission
 nonpersistentnonpersistent stations are deferentialstations are deferential

10. 1-persistent CSMA1-persistent CSMA
 1-persistent CSMA avoids idle channel time1-persistent CSMA avoids idle channel time
 1-persistent CSMA1-persistent CSMA rules:rules:
1.1. if medium idle, transmit;if medium idle, transmit;
2.2. if medium busy, listen until idle; then transmitif medium busy, listen until idle; then transmit
immediatelyimmediately
 1-persistent stations are selfish1-persistent stations are selfish
 if two or more stations waitingif two or more stations waiting, a, a collision iscollision is
guaranteedguaranteed

11. P-persistent CSMAP-persistent CSMA
 a compromisea compromise to try and reduce collisionsto try and reduce collisions andand
idle timeidle time
 p-persistent CSMAp-persistent CSMA rules:rules:
1.1. ifif medium idle, transmit with probability p, and delaymedium idle, transmit with probability p, and delay
one time unit with probability (1–p)one time unit with probability (1–p)
2.2. if medium busy, listen until idle and repeat step 1if medium busy, listen until idle and repeat step 1
3.3. if transmission is delayed one time unit, repeat step 1if transmission is delayed one time unit, repeat step 1
 issue of choosingissue of choosing effective value of peffective value of p to avoidto avoid
instability under heavy loadinstability under heavy load

12. Value of p?Value of p?
 have n stationshave n stations waitingwaiting to sendto send
 at endat end of tx, expected no of stationsof tx, expected no of stations is npis np

if npif np>1>1 on average there will be a collisionon average there will be a collision
 repeatedrepeated txtx attempts meanattempts mean collisions likelycollisions likely
 eventually when all stations trying to send haveeventually when all stations trying to send have
ccontinuousontinuous collisionscollisions hence zerohence zero throughputthroughput
 thus wantthus want npnp<1<1 for expected peaks of nfor expected peaks of n

ifif heavy load expectedheavy load expected,, p smallp small

but smaller p means stations wait longerbut smaller p means stations wait longer

13. CSMA/CD DescriptionCSMA/CD Description
 with CSMA, collision occupies mediumwith CSMA, collision occupies medium
for duration of transmissionfor duration of transmission
 better if stations listen whilst transmittingbetter if stations listen whilst transmitting
 CSMA/CD rules:CSMA/CD rules:
1.1. if medium idle, transmitif medium idle, transmit
2.2. if busy, listen for idle, then transmitif busy, listen for idle, then transmit
3.3. if collision detected, jam and then ceaseif collision detected, jam and then cease
transmissiontransmission
4.4. after jam, wait random time then retryafter jam, wait random time then retry

14. CSMA/CDCSMA/CD
OperationOperation

15. Which PersistenceWhich Persistence
Algorithm?Algorithm?
 IEEE 802.3IEEE 802.3 usesuses 1-persistent1-persistent
 bothboth nonpersistent and p-persistent havenonpersistent and p-persistent have
performance problemsperformance problems
 1-persistent seem1-persistent seemss more unstable than p-more unstable than p-
persistentpersistent

because of greedbecause of greed of the stationsof the stations

butbut wasted time due to collisions is shortwasted time due to collisions is short

withwith random backoffrandom backoff unlikely to collide on nextunlikely to collide on next
attempt to sendattempt to send

16. Binary Exponential BackoffBinary Exponential Backoff
 for backoff stability, IEEE 802.3 and Ethernetfor backoff stability, IEEE 802.3 and Ethernet
both use binary exponential backoffboth use binary exponential backoff
 stationsstations repeatedly resendrepeatedly resend whenwhen collidecollide

on firston first 10 attempts, mean random delay doubled10 attempts, mean random delay doubled

valuevalue then remains same for 6then remains same for 6 furtherfurther attemptsattempts

after 16 unsuccessful attempts, station gives up andafter 16 unsuccessful attempts, station gives up and
reports errorreports error
 1-persistent algorithm with binary exponential1-persistent algorithm with binary exponential
backoff efficient over wide range of loadsbackoff efficient over wide range of loads
 but backoffbut backoff algorithmalgorithm hashas last-in, first-out effectlast-in, first-out effect

17. Collision DetectionCollision Detection
 on baseband buson baseband bus

collision produces higher signal voltagecollision produces higher signal voltage

collision detected if cable signal greater thancollision detected if cable signal greater than
single station signalsingle station signal

signal is attenuated over distancesignal is attenuated over distance

limit to 500m (10Base5) or 200m (10Base2)limit to 500m (10Base5) or 200m (10Base2)
 on twisted pair (star-topology)on twisted pair (star-topology)

activity on more than one port is collisionactivity on more than one port is collision

use special collision presence signaluse special collision presence signal

18. IEEE 802.3 Frame FormatIEEE 802.3 Frame Format

19. 10Mbps Specification10Mbps Specification
(Ethernet)(Ethernet)
10BASE5 10BASE2 10BASE-T 10BASE-FP
Transmission
medium
Coaxial cable (50
ohm)
Coaxial cable (50
ohm)
Unshielded twisted
pair
850-nm optical fiber
pair
Signaling
technique
Baseband
(Manchester)
Baseband
(Manchester)
Baseband
(Manchester)
Manchester/on-off
Topology Bus Bus Star Star
Maximum segment
length (m)
500 185 100 500
Nodes per segment 100 30 — 33
Cable diameter
(mm)
10 5 0.4 to 0.6 62.5/125 µm

20. 100Mbps Fast Ethernet100Mbps Fast Ethernet
100BASE-TX 100BASE-FX 100BASE-T4
Transmission
medium
2 pair, STP 2 pair, Category
5 UTP
2 optical fibers 4 pair, Category
3, 4, or 5 UTP
Signaling
technique
MLT-3 MLT-3 4B5B, NRZI 8B6T, NRZ
Data rate 100 Mbps 100 Mbps 100 Mbps 100 Mbps
Maximum
segment length
100 m 100 m 100 m 100 m
Network span 200 m 200 m 400 m 200 m

21. 100BASE-X100BASE-X
 uses a unidirectionaluses a unidirectional data rate 100 Mbps overdata rate 100 Mbps over
single twisted pair or optical fiber linksingle twisted pair or optical fiber link
 encodingencoding schemescheme same assame as FDDIFDDI

4B/5B-NRZI4B/5B-NRZI
 twotwo physical medium specificationsphysical medium specifications

100BASE-TX100BASE-TX
• uses twouses two pairs of twisted-pair cable for tx & rxpairs of twisted-pair cable for tx & rx
• STP and Category 5 UTP allowedSTP and Category 5 UTP allowed
• MTL-3 signaling scheme is usedMTL-3 signaling scheme is used

100BASE-FX100BASE-FX
• uses twouses two optical fiber cables for tx & rxoptical fiber cables for tx & rx
• convertconvert 4B/5B-NRZI code group into optical signals4B/5B-NRZI code group into optical signals

22. 100BASE-T4100BASE-T4
 100-Mbps over lower-quality Cat 3100-Mbps over lower-quality Cat 3 UTPUTP

takestakes advantage of large installed baseadvantage of large installed base

doesdoes not transmit continuous signal between packetsnot transmit continuous signal between packets

usefuluseful in battery-powered applicationsin battery-powered applications
 can not getcan not get 100 Mbps on single twisted pair100 Mbps on single twisted pair

so dataso data stream split into three separate streamsstream split into three separate streams

four twisted pairs usedfour twisted pairs used

data transmitted and received using three pairsdata transmitted and received using three pairs

twotwo pairs configured for bidirectional transmissionpairs configured for bidirectional transmission
 use ternaryuse ternary signaling schemesignaling scheme ((8B6T8B6T))

23. 100BASE-T Options100BASE-T Options

24. Full Duplex OperationFull Duplex Operation
 traditionaltraditional Ethernet half duplexEthernet half duplex
 using full-duplexusing full-duplex,, station can transmit andstation can transmit and
receive simultaneouslyreceive simultaneously
 100-Mbps Ethernet in full-duplex mode, giving a100-Mbps Ethernet in full-duplex mode, giving a
theoretical transfer rate of 200 Mbpstheoretical transfer rate of 200 Mbps
 stations must have full-duplex adapter cardsstations must have full-duplex adapter cards
 and must useand must use switching hubswitching hub

eacheach station constitutes separate collision domainstation constitutes separate collision domain

CSMA/CD algorithm no longer neededCSMA/CD algorithm no longer needed

802.3 MAC frame format used802.3 MAC frame format used

25. Mixed ConfigurationsMixed Configurations
 Fast Ethernet supports mixture of existing 10-Fast Ethernet supports mixture of existing 10-
Mbps LANs and newer 100-Mbps LANsMbps LANs and newer 100-Mbps LANs
 supporting older and newer technologiessupporting older and newer technologies

e.g.e.g. 100-Mbps backbone LAN supports 10-Mbps hubs100-Mbps backbone LAN supports 10-Mbps hubs
• stationsstations attach to 10-Mbps hubs using 10BASE-Tattach to 10-Mbps hubs using 10BASE-T
• hubshubs connected to switching hubsconnected to switching hubs usingusing 100BASE-T100BASE-T
• highhigh-capacity workstations and servers attach directly to-capacity workstations and servers attach directly to
10/100 switches10/100 switches
• switchesswitches connected to 100-Mbps hubs use 100-Mbps linksconnected to 100-Mbps hubs use 100-Mbps links
• 100-Mbps hubs provide building backbone100-Mbps hubs provide building backbone
• connectedconnected toto routerrouter providingproviding connection to WANconnection to WAN

26. Gigabit EthernetGigabit Ethernet
ConfigurationConfiguration

27. Gigabit Ethernet - DifferencesGigabit Ethernet - Differences
 carrier extensioncarrier extension

at least 4096 bit-times long (512 for 10/100)at least 4096 bit-times long (512 for 10/100)
 frame burstingframe bursting
 not needed if using a switched hub tonot needed if using a switched hub to
provide dedicated media accessprovide dedicated media access

28. Gigabit Ethernet – PhysicalGigabit Ethernet – Physical

29. 10Gbps Ethernet10Gbps Ethernet
 growing interest in 10Gbps Ethernetgrowing interest in 10Gbps Ethernet

for high-speed backbone usefor high-speed backbone use

with future wider deploymentwith future wider deployment
 alternative to ATM and otheralternative to ATM and other WANWAN technologiestechnologies
 uniform technology for LAN, MAN, or WANuniform technology for LAN, MAN, or WAN
 advantages of 10Gbps Ethernetadvantages of 10Gbps Ethernet

no expensive, bandwidth-consuming conversionno expensive, bandwidth-consuming conversion
between Ethernet packets and ATM cellsbetween Ethernet packets and ATM cells

IP and EthernetIP and Ethernet togethertogether offersoffers QoSQoS and trafficand traffic
policing approach ATMpolicing approach ATM

have a varietyhave a variety of standard optical interfacesof standard optical interfaces

30. 10Gbps Ethernet10Gbps Ethernet
ConfigurationsConfigurations

31. 10Gbps Ethernet Options10Gbps Ethernet Options

32. Fibre Channel - BackgroundFibre Channel - Background
 I/O channelI/O channel

direct point to point or multipoint comms linkdirect point to point or multipoint comms link

hardware based, high speed, very shorthardware based, high speed, very short
distancesdistances
 network connectionnetwork connection

based on interconnected access pointsbased on interconnected access points

software based protocol with flow control,software based protocol with flow control,
error detection & recoveryerror detection & recovery

for end systems connectionsfor end systems connections

33. Fibre ChannelFibre Channel
 combines best of both technologiescombines best of both technologies
 channel orientedchannel oriented

data type qualifiers for routing frame payloaddata type qualifiers for routing frame payload

link level constructs associated with I/O opslink level constructs associated with I/O ops

protocol interface specifications to support existing I/Oprotocol interface specifications to support existing I/O
architecturesarchitectures
 network orientednetwork oriented

full multiplexing between multiple destinationsfull multiplexing between multiple destinations

peer to peer connectivitypeer to peer connectivity

internetworking to other connection technologiesinternetworking to other connection technologies

34. Fibre Channel RequirementsFibre Channel Requirements
 full duplex links with two fibers per linkfull duplex links with two fibers per link
 100 Mbps to 800 Mbps on single line100 Mbps to 800 Mbps on single line
 support distances upsupport distances up to 10 kmto 10 km
 small connectorssmall connectors
 high-capacity utilizationhigh-capacity utilization,, distance insensitivitydistance insensitivity
 greater connectivity than existing multidrop channelsgreater connectivity than existing multidrop channels
 broad availabilitybroad availability
 multiplemultiple cost/performance levelscost/performance levels
 carrycarry multiple existing interface command sets formultiple existing interface command sets for
existing channel and network protocolsexisting channel and network protocols

35. Fibre Channel NetworkFibre Channel Network

36. Fibre Channel ProtocolFibre Channel Protocol
ArchitectureArchitecture
 FC-0 Physical MediaFC-0 Physical Media
 FC-1 Transmission ProtocolFC-1 Transmission Protocol
 FC-2 Framing ProtocolFC-2 Framing Protocol
 FC-3 Common ServicesFC-3 Common Services
 FC-4 MappingFC-4 Mapping

37. Fibre Channel Physical MediaFibre Channel Physical Media
800 Mbps 400 Mbps 200 Mbps 100 Mbps
Single mode
fiber
10 km 10 km 10 km —
50-µm
multimode fiber
0.5 km 1 km 2 km —
62.5-µm
multimode fiber
175 m 1 km 1 km —
Video coaxial
cable
50 m 71 m 100 m 100 m
Miniature
coaxial cable
14 m 19 m 28 m 42 m
Shielded twisted
pair
28 m 46 m 57 m 80 m

38. Fibre Channel FabricFibre Channel Fabric
 most generalmost general supported topologysupported topology isis fabric orfabric or
switched topologyswitched topology

arbitraryarbitrary topology with at least one switch totopology with at least one switch to
interconnect number of end systemsinterconnect number of end systems

maymay also consist of switched networkalso consist of switched network
 routing transparent to nodesrouting transparent to nodes

when data transmitted into fabric, edge switch useswhen data transmitted into fabric, edge switch uses
destination port address to determine locationdestination port address to determine location

eithereither deliver frame to node attached to same switchdeliver frame to node attached to same switch
or transfers frame to adjacent switchor transfers frame to adjacent switch

39. Fabric AdvantagesFabric Advantages
 scalabilityscalability of capacityof capacity
 protocolprotocol independentindependent
 distancedistance insensitiveinsensitive
 switchswitch and transmission linkand transmission link technologiestechnologies
may change without affecting overallmay change without affecting overall
configurationconfiguration
 burdenburden on nodes minimizedon nodes minimized

40. Alternative TopologiesAlternative Topologies
 PointPoint-to-point topology-to-point topology

onlyonly two portstwo ports

directlydirectly connected, so no routing neededconnected, so no routing needed
 ArbitratedArbitrated loop topologyloop topology

simplesimple, low-cost topology, low-cost topology

upup to 126 nodes in loopto 126 nodes in loop

operatesoperates roughly equivalent to token ringroughly equivalent to token ring
 topologies, transmission media, and datatopologies, transmission media, and data
rates may be combinedrates may be combined

41. Fibre Channel ApplicationsFibre Channel Applications

42. Fibre Channel ProspectsFibre Channel Prospects
 backedbacked by Fibre Channel Associationby Fibre Channel Association
 various interfacevarious interface cards availablecards available
 widely accepted as peripheral devicewidely accepted as peripheral device
interconnectinterconnect
 technicallytechnically attractive to general high-speed LANattractive to general high-speed LAN
requirementsrequirements
 mustmust compete with Ethernet and ATM LANscompete with Ethernet and ATM LANs
 cost and performance issues will dominatecost and performance issues will dominate
consideration of competing technologiesconsideration of competing technologies

43. SummarySummary
 High speed LANs emergenceHigh speed LANs emergence
 Ethernet technologiesEthernet technologies

CSMA & CSMA/CD media accessCSMA & CSMA/CD media access

10Mbps ethernet10Mbps ethernet

100Mbps ethernet100Mbps ethernet

1Gbps ethernet1Gbps ethernet

10Gbps ethernet10Gbps ethernet
 Fibre ChannelFibre Channel