TechnicallySpeaking
C
omparedwithtraditional
routersandbridges,Ethernet
switchesofferdistinct
advantagesinperformance,ease
ofuse,andcost.
Inparticular,anIntel®Express
410StandaloneSwitchcanhelp
alleviatebottlenecksinyour
client/serverenvironment.A
workgroup-basedswitchsuch
astheExpress410takesalogical
approachtoeasingcongestion:
Itboostsperformanceona
portionofthenetworkanddivides
thelocalnetworksofewerusers
occupyasegment.
Theswitchalsoprovideseach
high-performancedevice(sucha
serveroraswitchuplink)withits
owndedicated segment, onethat
canrun at thesamespeedasthe
otherswitched ports orathigher
speeds.
Tofurther ease theflowof
traffic,the Express 410Temploys
flowcontrol, which temporarily
suspendsa transfer ofdatafroma
sendingworkstation until its
destinationport is readytoreceive
it.Flow control appliedduring
Ethernettraffic bursts—when
switchbuffer memory isfull—
helpsprevent information from
beingdropped and, inturn,saves
youfrom costly delays.
Manyconventional bridges,
routers,and switches relyon
large,expensive buffers tohold
packetsthat can’t betransmitted.
However,if the destination
segmentbecomes overloaded,
incomingdata can overrunthe
buffer,forcing the devicetodrop
excesspackets. And, althoughthe
sendingnodes’ NIC software
detectsdropped packets, the
solutiontypically involves avery
inefficienttime-out mechanism.
Flowcontrol goes tothe
source—beforethe segment is
flooded.When a port’sinternal
buffersnear capacity, flowcontrol
enablesthe switch totransmita
mockcollision (also knownasa
jampattern) back tothesource
node.The sending nodeseesthe
interruptionas a collisionand
backsoff. When theswitchhas
emptiedits internal buffers,it
directsthe sender’s NICto
retransmitthe packet fromits
hardwarebuffers.
Youcan enable anddisable
flowcontrol for eachportonthe
Express410T. By default,flow
controlis enabled. Themethodof
flowcontrol depends onwhether
theports are settofullorhalf
duplex.For instance, iftheportis
operatingat full duplex,theswitch
sendsout an 802.3xPAUSEframe,
insteadof a collision,todelay
traffic.
And,as a store-and-forward
switch,the 410T storesthe
incomingframe in aninternal
bufferand delays transmission
untilthe switch successfully
completespacket error-checking.