ADTRAN Total Access 5000 - Auto-Provision the SHDSL Pairs Using EZ-EFM; EFM Bonding Overhead Description

Total Access 5000 Business Services Deployment Guide
4-12 65K510DEP08-1A
Auto-Provision the SHDSL Pairs Using EZ-EFM
TheEZ‐EFMfeatureautomatically provisionsthemaximumandminimumratesofeach
SHDSLpairinthebondinggroup,asfollow s:
•SHDSLmaximumrate=(upstream_rate)/(mimimum_links)
•SHDSLminimumrate=((upstream_rate)/(minimum_links))/4
NOTE
Forfixedratemode,theminimumrateissetequaltothemaximumrate.
TheSHDSLTrainingMode(fixed,worst‐caserateadaptive,orcurrent‐caserateadaptive)
mustbemodifieddirectly(perSHDSLpairintheCLI,and perEFMGroupintheEMS).
TheSHDSLWorstCaseMarginmustalso
bemodifieddirectly(perSHDSLpairintheCLIor
EMS).
Oftheitemslistedabove,onlytheSHDSLTrainingModeandWorstCaseMarginarepassed
downtotheN etVanta838.TheminimumandmaximumratespusheddownfromtheEZEFM
totheSHDSLTotalAccess5000pairsare
notpusheddowntotheNetVanta.Thisresultsinthe
NetVantarangesremainingattheminimumandmaximumvalues(3and89),ratherthan
matchingthoseoftheTotalAccess5000.Thetrainingattemptsucceedsdespitethisdifference
inprovisioning.TheSHDSLrateadaptivetrainingalgorithmrequiresthateachSHDSL
trans‐
ceiverdeterminesatwhichrateitcantrain,andthenpassesthatinformationtotheother
transceiver.TheNetVanta838SHDSLinterfacedeterminesthemaximumrateatwhichitcan
train,andthennotifiestheTotalAccess5000interfacethatitcantrainuptothatrate. Aslong
as
theNetVantacantrainattheminimumrateprovisionedattheTotalAccess5000(group
ratedividedbyactive‐links‐minimum,thendividedagainby4),thetrainsucceeds.Ifthe
NetVantacannotachievethattrainingrate,thetrainfails,andtrainingattemptswillcontinue.
EFM Bonding Overhead Description
Beforebeingtransportedoverthephysicallayer(SHDSL,T1,etc.),theEFMbondingengine
firstencapsulatesEthernetframesintoEFMfragments.EFMFragmentpayloadcanvaryfrom
64to512bytesdependingontheEthernetpacketsize.IfanEthernetFrameis512bytesor
smaller,itisplacedintoone
EFMfragment.Iftheframeisbetween513and1024bytes,itis
splitbetweentwoEFMfragments.Iftheframeis1025bytes orgreater,itissplitbetweenthree
EFMfragments.
EachEFMfragmenthasthefollowingoverhead:
•Thereare2bytesofoverheadperfragmentthatarethe
sameforallfragments: astartbyte 
andCkbyte(anEOFdesignator)
•Theframechecksequence(FCS):thesizeofthisdependsontechnology
•Thereare2additionaloverheadbondingheaderbytes
ForSHDSL,thiscomesoutto8overheadbytesperfragment.Inaddition,aspartofthe64/65
EFM
framing,therearecodewordsthatare64payloadbytesand1syncbyte.
Usingthisinformation,thefo llowingequationscanbeusedtodeterminetheeffective
percentageoftheEFMbondinggroupthatisavailableforcustomerEthernettransport(for
SHDSL):
•Ethernetframes512bytesorsmaller:
%Utilization=
(FrameSize)/(FrameSize+8)x(64/65)