ADTRAN Total Access 5000 - EFM Bonding Overhead Description

Total Access 5000 Business Services Deployment Guide
6-12 65K510DEP08-1A
EFM Bonding Overhead Description
Beforebeingtransportedoverthephysicallayer(DS3,T1,etc.),theEFMbondingenginefirst
encapsulatesEthernetframesintoEFMfragments.EFMFragmentpayloads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DS3,thiscomesoutto8overheadbytesperfragment.Inaddition,aspartofthe64/65
EFM
framing,therearecodewords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
DS3):
•Ethernetframes512bytesorsmaller:
%Utilization=(Frame
Size)/(FrameSize+8)x(64/65)
•Ethernetframesbetween513and1024bytes,inclusive:
%Utilization=(FrameSize)/(FrameSize+16)x(64/65)
•Ethernetframes1025bytesorlarger:
%Utilization=(FrameSize)/(FrameSize+24)x(64/65)
TheequationsaboveassumethattheNetVanta
isnotaddinganextratagtothecustomer
traffic(ie.whenthecustomertrafficistagged,andthecustomeredgetagisnotbeing
preserved).Inanycasewherethecustomertagispreserve d(themostlikelyscenario),andthe
NetVanta800issimplystackingtheprovisionedserviceprovidertag
(s‐tag)tothecustomer
tag(ifpresent),thecalculationmustaccountfortheadditional4bytesforthes‐tag,asfollows:
•ForEthernetframes512bytesorsmaller:
%Utilization=(FrameSize)/(FrameSize+12)x(64/65)
•ForEthernetframesbetween513and1024bytes,inclusive:
%
Utilization=(FrameSize)/(FrameSize+20)x(64/65)
•Ethernetframes1025bytesorlarger:
%Utilization=(FrameSize)/(FrameSize+28)x(64/65)
TodeterminetheEFMbondinggroupbandwidththatneedstobeprovisionedsothatthe
customerʹscommissionedrateisprovided,dividethe
customerratebythispercentage:
RequiredEFMGroupRate=(CustomerCommissionedRate)/(%Utilization.
Followingareexamplecalculationsforcustomerthroughputpercentage,givenafixedframe
size,assumingtheNetVanta800isaddingaVLANtag:
•For64byteEthernetframes(worstcasescenario):
%Utilization=(64)/(64
+12)x(64/65)=82.9%
•Foran8Mbpsbondinggroup,theactualthroughputwouldbe:
8Mbpsx.829=6.632Mbps
•Ifacustomerissolda4Mbpsservice,therequiredEFMgroupsizecalculationwouldbe:
(4Mbps)/(.829)=4.825Mbps