Data and Computer Data and Computer CommunicationsCommunications

Eighth EditionEighth Editionby William Stallingsby William Stallings

Lecture slides by Lawrie BrownLecture slides by Lawrie Brown

Chapter 16 – Chapter 16 – High Speed High Speed LANLANss

High Speed High Speed LANLANss

Congratulations. I knew the record would stand until it was broken.

Yogi BerraYogi Berra

IntroductionIntroduction range of technologiesrange of technologies

Fast and Gigabit EthernetFast and Gigabit Ethernet FibreFibre Channel Channel High Speed Wireless LANsHigh Speed Wireless LANs

Why High Speed LANs?Why High Speed LANs? speedspeed and power of and power of PCs PCs hashas risen risen

graphicsgraphics-intensive applications-intensive applications and GUIs and GUIs see LANsee LANss as essential to organizations as essential to organizations

forfor client/server computing client/server computing now have requirements fornow have requirements for

centralized server farmscentralized server farms power workgroupspower workgroups high-speed local backbonehigh-speed local backbone

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 with Carrier Sense Multiple Access with Collision Detection (CSMA/CD)Collision Detection (CSMA/CD) random / contention access to mediarandom / contention access to media

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 another frame 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%

Slotted ALOHASlotted ALOHA time on channel based on uniform slots equal to time 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 much less fail to use fact that propagation time is much less

than frame transmission timethan frame transmission time

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 time wait 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 time max utilization depends on propagation time (medium length) and frame length(medium length) and frame length

Nonpersistent CSMANonpersistent CSMA NonpersistentNonpersistent CSMA rules: CSMA rules:

1.1. if medium idle, transmitif medium idle, transmit2.2. if medium busy, wait amount of time drawn from if medium busy, wait amount of time drawn from

probability distribution (retransmission delay) & retryprobability distribution (retransmission delay) & retry randomrandom delays reduces probability of collisions delays reduces probability of collisions capacitycapacity is wasted because medium will remain is wasted because medium will remain

idle following end of transmissionidle following end of transmission nonpersistentnonpersistent stations are deferential stations are deferential

1-persistent CSMA1-persistent CSMA 1-persistent CSMA avoids idle channel time1-persistent CSMA avoids idle channel time 1-persistent CSMA 1-persistent CSMA rules:rules:  

1.1. if medium idle, transmit; if medium idle, transmit; 2.2. if medium busy, listen until idle; then transmit if 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 is collision is

guaranteedguaranteed

P-persistent CSMAP-persistent CSMA a compromisea compromise to try and reduce collisions to try and reduce collisions and and

idle timeidle time p-persistent CSMA p-persistent CSMA rules:rules:  

1.1. ifif medium idle, transmit with probability p, and delay medium 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 13.3. 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 p effective value of p to avoid to avoid instability under heavy loadinstability under heavy load

Value of p?Value of p? have n stations have n stations waitingwaiting to send to send at endat end of tx, expected no of stations of 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 repeated repeated txtx attempts mean attempts mean collisions likely collisions likely eventually when all stations trying to send have eventually when all stations trying to send have

ccontinuous ontinuous collisionscollisions hence zero hence zero throughput throughput thus want thus want npnp<1<1 for expected peaks of n for expected peaks of n

ifif heavy load expected heavy load expected,, p small p small but smaller p means stations wait longerbut smaller p means stations wait longer

CSMA/CD DescriptionCSMA/CD Description with CSMA, collision occupies medium with 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, transmit2.2. if busy, listen for idle, then transmitif busy, listen for idle, then transmit3.3. if collision detected, jam and then cease if collision detected, jam and then cease

transmissiontransmission4.4. after jam, wait random time then retryafter jam, wait random time then retry

CSMA/CDCSMA/CDOperationOperation

Which Persistence Which Persistence Algorithm?Algorithm?

IEEE 802.3 IEEE 802.3 usesuses 1-persistent 1-persistent both both nonpersistent and p-persistent have nonpersistent and p-persistent have

performance problemsperformance problems 1-persistent seem1-persistent seemss more unstable than p- more unstable than p-

persistent persistent because of greedbecause of greed of the stations of the stations butbut wasted time due to collisions is short wasted time due to collisions is short withwith random backoff random backoff unlikely to collide on next unlikely to collide on next

attempt to sendattempt to send

Binary Exponential BackoffBinary Exponential Backoff for backoff stability, IEEE 802.3 and Ethernet for backoff stability, IEEE 802.3 and Ethernet

both use binary exponential backoffboth use binary exponential backoff stations stations repeatedly resend repeatedly resend whenwhen collide collide

on firston first 10 attempts, mean random delay doubled 10 attempts, mean random delay doubled valuevalue then remains same for 6 then remains same for 6 further further attemptsattempts after 16 unsuccessful attempts, station gives up and after 16 unsuccessful attempts, station gives up and

reports errorreports error 1-persistent algorithm with binary exponential 1-persistent algorithm with binary exponential

backoff efficient over wide range of loadsbackoff efficient over wide range of loads but backoffbut backoff algorithm algorithm hashas last-in, first-out effect last-in, first-out effect

Collision DetectionCollision Detection on baseband buson baseband bus

collision produces higher signal voltagecollision produces higher signal voltage collision detected if cable signal greater than collision 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

IEEE 802.3 Frame FormatIEEE 802.3 Frame Format

10Mbps Specification 10Mbps Specification (Ethernet)(Ethernet)

10BASE5 10BASE2 10BASE-T 10BASE-FP

Transmissionmedium

Coaxial cable (50ohm)

Coaxial cable (50ohm)

Unshielded twistedpair

850-nm optical fiberpair

Signalingtechnique

Baseband(Manchester)

Baseband(Manchester)

Baseband(Manchester)

Manchester/on-off

Topology Bus Bus Star Star

Maximum segmentlength (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

100Mbps Fast Ethernet100Mbps Fast Ethernet

100BASE-TX 100BASE-FX 100BASE-T4

Transmissionmedium

2 pair, STP 2 pair, Category5 UTP

2 optical fibers 4 pair, Category3, 4, or 5 UTP

Signalingtechnique

MLT-3 MLT-3 4B5B, NRZI 8B6T, NRZ

Data rate 100 Mbps 100 Mbps 100 Mbps 100 Mbps

Maximumsegment length

100 m 100 m 100 m 100 m

Network span 200 m 200 m 400 m 200 m

100BASE-X100BASE-X uses a unidirectionaluses a unidirectional data rate 100 Mbps over data rate 100 Mbps over

single twisted pair or optical fiber linksingle twisted pair or optical fiber link encodingencoding scheme scheme same assame as FDDI FDDI

4B/5B-NRZI4B/5B-NRZI twotwo physical medium specifications physical medium specifications

100BASE-TX 100BASE-TX • uses twouses two pairs of twisted-pair cable for tx & rx pairs 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 & rx optical fiber cables for tx & rx• convertconvert 4B/5B-NRZI code group into optical signals 4B/5B-NRZI code group into optical signals

100BASE-T4100BASE-T4 100-Mbps over lower-quality Cat 3 100-Mbps over lower-quality Cat 3 UTPUTP

takes takes advantage of large installed base advantage of large installed base doesdoes not transmit continuous signal between packets not transmit continuous signal between packets usefuluseful in battery-powered applications in battery-powered applications

can not get can not get 100 Mbps on single twisted pair100 Mbps on single twisted pair so dataso data stream split into three separate streams stream 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 two two pairs configured for bidirectional transmissionpairs configured for bidirectional transmission

use ternaryuse ternary signaling scheme signaling scheme ((8B6T8B6T))

100BASE-T Options100BASE-T Options

Full Duplex OperationFull Duplex Operation traditionaltraditional Ethernet half duplex Ethernet half duplex using full-duplexusing full-duplex, , station can transmit and station can transmit and

receive simultaneouslyreceive simultaneously 100-Mbps Ethernet in full-duplex mode, giving a 100-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 hub switching hub

eacheach station constitutes separate collision domain station 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

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-T attach to 10-Mbps hubs using 10BASE-T • hubshubs connected to switching hubs connected to switching hubs using using 100BASE-T 100BASE-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 links connected to 100-Mbps hubs use 100-Mbps links• 100-Mbps hubs provide building backbone100-Mbps hubs provide building backbone• connected connected toto router router providing providing connection to WANconnection to WAN

Gigabit Ethernet Gigabit Ethernet ConfigurationConfiguration

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 to not needed if using a switched hub to

provide dedicated media accessprovide dedicated media access

Gigabit Ethernet – PhysicalGigabit Ethernet – Physical

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 other alternative to ATM and other WANWAN technologies technologies uniform technology for LAN, MAN, or WANuniform technology for LAN, MAN, or WAN advantages of 10Gbps Ethernetadvantages of 10Gbps Ethernet

no expensive, bandwidth-consuming conversion no expensive, bandwidth-consuming conversion between Ethernet packets and ATM cells between Ethernet packets and ATM cells

IP and Ethernet IP and Ethernet together together offers offers QoSQoS and traffic and traffic policing approach ATMpolicing approach ATM

have a varietyhave a variety of standard optical interfaces of standard optical interfaces

10Gbps Ethernet 10Gbps Ethernet ConfigurationsConfigurations

10Gbps Ethernet Options10Gbps Ethernet Options

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 short hardware 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

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/O protocol 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

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 line 100 Mbps to 800 Mbps on single line support distances up support distances up to 10 kmto 10 km small connectorssmall connectors high-capacity utilizationhigh-capacity utilization,, distance insensitivity distance insensitivity greater connectivity than existing multidrop channelsgreater connectivity than existing multidrop channels broad availabilitybroad availability multiplemultiple cost/performance levels cost/performance levels carry carry multiple existing interface command sets for multiple existing interface command sets for

existing channel and network protocols existing channel and network protocols 

Fibre Channel NetworkFibre Channel Network

Fibre Channel Protocol Fibre 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

Fibre Channel Physical MediaFibre Channel Physical Media

800 Mbps 400 Mbps 200 Mbps 100 Mbps

Single modefiber

10 km 10 km 10 km —

50-µmmultimode fiber

0.5 km 1 km 2 km —

62.5-µmmultimode fiber

175 m 1 km 1 km —

Video coaxialcable

50 m 71 m 100 m 100 m

Miniaturecoaxial cable

14 m 19 m 28 m 42 m

Shielded twistedpair

28 m 46 m 57 m 80 m

Fibre Channel FabricFibre Channel Fabric most generalmost general supported topology supported topology is is fabric or fabric or

switched topologyswitched topology arbitraryarbitrary topology with at least one switch to topology with at least one switch to

interconnect number of end systemsinterconnect number of end systems may may also consist of switched networkalso consist of switched network

routing transparent to nodesrouting transparent to nodes when data transmitted into fabric, edge switch uses when 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 switch deliver frame to node attached to same switch

or transfers frame to adjacent switchor transfers frame to adjacent switch

Fabric AdvantagesFabric Advantages scalabilityscalability of capacity of capacity protocolprotocol independent independent distance distance insensitiveinsensitive switch switch and transmission linkand transmission link technologies technologies

may change without affecting overall may change without affecting overall configurationconfiguration

burdenburden on nodes minimized on nodes minimized

Alternative TopologiesAlternative Topologies PointPoint-to-point topology-to-point topology

onlyonly two ports two ports directlydirectly connected, so no routing needed connected, so no routing needed

ArbitratedArbitrated loop topology loop topology simplesimple, low-cost topology, low-cost topology upup to 126 nodes in loop to 126 nodes in loop operatesoperates roughly equivalent to token ring roughly equivalent to token ring

topologies, transmission media, and data topologies, transmission media, and data rates may be combinedrates may be combined

Fibre Channel ApplicationsFibre Channel Applications

Fibre Channel ProspectsFibre Channel Prospects backedbacked by Fibre Channel Association by Fibre Channel Association various interfacevarious interface cards available cards available widely accepted as peripheral device widely accepted as peripheral device

interconnectinterconnect technicallytechnically attractive to general high-speed LAN attractive to general high-speed LAN

requirementsrequirements mustmust compete with Ethernet and ATM LANs compete with Ethernet and ATM LANs cost and performance issues will dominate cost and performance issues will dominate

consideration of competing technologies consideration of competing technologies

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