JOURNAL OF TELECOMMUNICATIONS, VOLUME 31, ISSUE 1, JULY 2015 19
Optimization of Passive FTTH Network Design Using Vertical Micro
Ducting Mousaab M. Nahas Abstract This paper presents a simple,
cost-effective fiber network design suitable for building FTTH
technology in brownfield
areaswherebuildings,roads,infrastructureetc.havealreadybeenconstructed.Thedesignemploysverticalmicroducting
system that is developed to eliminate damages in the existing
infrastructure thus minimizing restoration costs. The design also
ensuresminimaldeploymenttimehencepublicdisturbance.WebelievethatthemajorcostsavinginFTTHtechnologyis
achieved through optimizing the outside plant network design as
demonstrated in this research.
IndexTermsFibertothehome(FTTH),outsideplant(OSP),passiveopticalnetworks(PON),telecommunications
infrastructure. !
1INTRODUCTIONIBERopticcableshaveevolvedtobecomeverysmall
indiameterandnolongerrequirelargeducts[1]-[3]. While traditional
ducts have diameters in the range of 50 to 100 mm to hold cables
with diameters as large as 25 mm, today's duct diameters can be in
the range of 3 to 10 mm[4]-[6].Thesesmallductscanhavemultiplemicro
channelsortubestoholdmicrocableswithtypicalouter
diametersof6mmfor72-corescable,4mmfor24-cores cable, and 1.6 mm for
2-, 4- and 12-cores
cables.Howev-er,suchsmallmicrochannelsortubesnowdothejobof
largesub-ductedconduitswherelargecountscablecan be achieved by
using multiple micro cables.The number of micro channels or micro
tubes in these systems is
typi-callyinthe1to30range.Basedonthis,severalmicro
ductingsystemshavebeendeveloped[7]-[10]andthe most attractive one
is known as vertical inlaid fiber (VIF)
[10].TheideaofVIFistoinstallamicroductwithina vertical micro trench
made on existing roadways or
side-walks.Fibermicrocablesaredeployedbyeitherbeing
pulleddirectlyintothemicroductorblowninmicro
tubeswhereinbothcasestheductislaidverticallyinto the vertical micro
trench.In traditional deployment, once a cable is pulled into a
duct, it is considered full and addi-tional cables are not allowed
to be pulled into the duct as
theymaydamagethefirstcable.Thisisnotthecasein VIF where
installation of additional cables is still allowed thus the system
is expandable. Such principle is to be
ex-ploitedhereforoptimizingtheFTTHnetworkdesign
wheretheductsizeisproposedtobefurtherreduced. The micro system
presented in this paper is referred to as
verticalmicroductingsystem(VMDS)andisbasedon both micro
technologies presented in [9] and [10].2VMDS CHARACTERISTICS
VMDSissmallbydesigninordertominimizethe
amountofexcavationrequired.Unliketraditionalsys-temsthathavelargetrenches(>100mmwideand>200
mm deep), VMDS is typically installed by creating a nar-row trench
of 11 mm wide ! 200 mm deep in the ground
whereaverticalductcanlayalmostimperceptiblyinto
existingsurface.Asaresult,constructionactivityismin-imized hence
deployment time. In addition, fiber network
isinstalledabovetheutilitynetworkwhichisusually deeper than 25 cm.
Finally, fiber deployment can be
com-pletedwithsmallercrews,lessequipmentandminimal
disruptionanddisturbancetothesurroundingenviron-ment.Mostimportantly,thesurfacelooksintactafterin-stallation.VMDS
is specially designed to be efficiently installed
inbothhardsurfaces,suchasconcreteorasphalt,andin
softterrains.Themicrotrenchiscreatedwithoutaneed
forbackhoes,excavators,andlargesaws,butbyusinga
roadsawwhichcutswithathindiamondblade[9],[10].Afterdeployment,themicrotrenchisrestoredbyback-fillingwithcoldasphaltthatiscompactedtothemaxi-mum.Theoverallresultisthatsurfacedamagesarevir-tuallyinvisible.Thiscanincreasethesurfacelifesignifi-cantly.
3PASSIVE FTTH NETWORK DESIGN
TheentirepassiveFTTHnetworkdesigncanbedivided
intotwoparts:componentsdesign,andnetworkdesign.
Carefuldesignofthesetwowillconsiderablyreducethe overall cost of
the FTTH technology. 3.1 FTTH Components Design
ThispartbasicallyconsiderstheVMDScomponentsde-signincludingmicrocables,microducts,microjunctions
and fiber access terminals.
3.1.1 Micro Cables Design
VMDSemploysfibercablesthatareveryflexibleand small as mentioned
before. For main network feeders, the
systemusescablesof4mmwith24counts(cores)or6 mm with 72 counts based
on the network size. For distri- M.M. Nahas is with the Electrical
and Computer Engineering Department, Faculty of Engineering,
University of Jeddah, Jeddah, Saudi Arabia.F 20 bution from fiber
distribution points to homes, the system uses smaller cables of 1.6
mm which can carry between 2
to12fibercores.Each1.6mmmicrocableistypically
dedicatedforsinglepremisesinourpresentedFTTHde-sign,using2-or4-corescableforindividualhomeand
morecores(e.g.12)forcommercialbuildingsormulti-dwelling units. Fig.
1 shows the 4- and 12-cores cables. In case of 2- or 4-cores cable,
one core is used for connectivi-ty, enabling single user to have a
capacity of ~100 Mbit/s, while the other core(s) is reserved for
future expansion or backup. (a)(b) Fig. 1. 1.6 mm fiber cable with
(a) 4 cores, (b) 12 cores. 3.1.2 Micro Ducts Design In practice,
the above cables can be pulled or blown using
verticalPVCmicroduct.Thisductistwosliminter-lockableparts[10]andisrigidenoughtoprotectfiber
cablesfromanypossibledamageasitisintendedtobe
installedclosetothesurface.Therearetwodifferentsize
proposalsforthemicroductsdependingonthenumber
ofchannels(tracks)intheduct.Thesetwosizeoptions are shown in Fig.
2. In (a), the duct has dimensions of 10 !
20mmandisdesignedtoholdsinglechannelthrough
whichthemainfeedercablescanbepulledorasingle tube can be installed
in order to allow for future blowing
ofdrop-to-homemicrocables.In(b),theductis10!50
mmandisdesignedtoholdfourchannels(tracks)and can be used to
accommodate four feeder cables or to pull
multipledrop-to-homemicrocables.Typically,each
channelintheabovetwotypesaccommodatesupto7
microcables.However,theductsizesproposedhereare considerably
smaller than those of the VIF [10]. (a)(b)
Fig.2.Crosssectionof(a)singlechannelmicroduct,(b)multiple channel
micro duct. 3.1.3 Micro Junctions Design
Atthebranchingpoint,whereadedicatedcableisex-tractedtobedroppedtosinglepremises(home),avery
simple T-junction is used [10] instead of a splice enclosure
thatiscommonlyusedwithconventionalsystems.How-ever,theT-junctionsizemustbereducedtobecompati-ble
with the micro ducts presented in the previous section so that it
fits perfectly. This micro junction is an attractive
componentinVMDSasitconsiderablysimplifiesthede-sign and reduces the
field work, cost and disturbance. 3.1.4 Access Terminals Design
TheVMDS-basedFTTHdesignusessmallfiberaccess
terminals(FATs)aslocaldistributionpointsforsmall number of homes.
Each FAT is ideally fed by a main duct
thatisconnectedtothemainfiberdistributionterminal
(FDT)intheregion.Infact,theFATprovidesdirectac-cesstoslackcablesforrepairsornetworkextensions.
However,theproposedFATcanhaveacylindricalor rectangular prism
structure with dimensions of 500 mm !
200mm.Suchsmalldesignalsosavesconsiderablesize and disruption. 3.2
FTTH Network Design 3.2.1 Design Requirements
IndesigninganFTTHnetworkusingVMDS,acoupleof
issuesaretakenintoconsiderationtoensurethebestde-sign.Theseissuesare:avoidingcrossesovermainand
highlyusedroadwaysthusminimizingdisruption,and
usingtheexistinginfrastructure(e.g.manholes,hand-holes,ducts,coppernetworketc.)thusminimizingthe
overall number of fiber cabinets and ducts. In addition, a
dedicatedfibercableisproposedtobeusedforsingle
premises(asmentionedearlier)which,ingeneral,makes
theentiredesignmuchsimplerthantraditional.Inthis
case,eachcableisindependentthusabreakinonecable will never affect
the other cables hence users. 3.2.2 Design Solution To design such
system, first of all, a connectivity is
initial-lyestablishedbetweentheexisting(backbone)fibernet-work
andthe main FDT unit(s) in the FTTH project area.
Thisconnectionispracticallydonebypullingconven-tionalhigh-countcable(withnumberofcorespropor-tionaltothenumberofpremisesinthearea)fromthe
nearest existing manhole to the FDT that is typically used
toservelargenumberofhomes(typically>150homes).
Thisingeneralsimplifiesthedesignandminimizesthe
initialcost.However,todistributefibercablesfromFDT
tohomes,weproposetwoVMDS-baseddesignap-proaches:thefirstisreferredtoasdirectFDT-homeap-proachwhilethesecondoneisreferredtoasFDT-FAT
approach as explained below. 3.2.3 Direct FDT-Home Design
Inthisapproach,thecoresofthehigh-countcableenter-ing the FDT are
split into the number of homes in the
dis-tributionareawhereadedicated1.6mmcableisrunall 21
thewayfromtheFDTtoeachhome.Thisapproachcan
beshowninFig.3.ThereareMspokes;eachhasN homes, where the distance
between the FDT and the first drop is a. By and large, this can be
a good option as it has
onlyonemaindistributionpointforlargenumberof
homes.Also,aseparatededicated1.6mmmicrocableis used to connect each
individual home directly to the FDT,
resultinginhighuserindependency.However,thisde-signisexpensivebecauselargequantityofthemicroca-blesisrequired.Inaddition,itisquitedifficulttomain-tain
a system with such long micro cable distances. These drawbacks are
avoided in the next approach. Fig. 3. FTTH network design using
direct FDT-home approach. 3.2.4 FDT-FAT Design
Inthisapproach,thesystemhasFDTandFATunitsas
showninFig.4.SingleFDTisconnectedtomanyFAT
unitsthroughmulti-countscables(typically6mmcable
with72cores)wherethecoresaresplicedattheFATto
servehomesatshorterdistancesthroughdedicated1.6
mmfibercables.Thisindeedsavesalotofmicrocable
quantitywhileusingsinglecableinsteadbetweenthe FDT and FAT. For
example, assume the distance between the FDT and the first drop
(distance a in Fig. 3, 4) is 300 m
andthesystemhas3spokes;eachhas15homeswith20
mspacingbetweenthetwosuccessivehomes(cinthe pictures). Using the
FDT-FAT approach, we save 300 m of
the1.6mmcableforeachhome,whichmeansatotalof 13,500 m (300 ! 45).
This is huge saving in the quantity of
fibermicrocables.Inaddition,thesystemismuchfaster
todeployandhasalocalizedtestingreference(atthe FAT) hence easier to
test and maintain. Typically,ourVMDS-basedFTTHnetworkdesignis
proposedtohave4spokesfromeachFATwhereeach
spokehasnomorethan18homes.Thisisassignedfor
bothpulledandblowncablesandhasbeenchosenac-cording to the maximum
possible capacity of blown
verti-calmicroductsusingthesmallestavailabletubediame-ters. In
addition, the ideal number of FATs in this system can be up to 20
for single FDT. Nevertheless, this number
canbereducedbyusingmoreFATspokesifnecessary.
Moreover,thenumbercanalsobedecreasedifthemain feeder cable (of 72
counts) passes by number of homes on
thewayfromFDTtoFATwherefewfiberscanbe dropped off the main feeder
directly to homes. This basi-cally reduces the number of homes that
will be connected toFATthussomeFATunitsmaybesaved.Anyhow,
carefuldesignofthenetworkcanreducetheoverallcost considerably. Fig.
4. FTTH network design using FDT-FAT approach. However, what is
demonstrated here is a generalized
VMDS-baseddesignconceptthatfitscomfortablyinany
areabutneedspropercustomizationforeveryspecific project. So it is
the engineers role to implement the above
proposalsuchthattheminimalcostisattained.Thistask literally
involves right selection of the FDT and FAT
loca-tionsaswellasthetrenchlayout,dependingonthedis-trictdetailssuchasroadmap,utilitynetworklayout,
manholes/handholeslocations,blocksdimensionsetc.
Thesedetailsareusuallyobtainedduringtheinitialsur-vey of the
project. 4CONCLUSION
WepresentedapassiveFTTHnetworkdesignusingver-ticalmicroductingsystem(VMDS).Thesystemdemon-strated
hereis suitable for establishing an FTTH network
inwell-constructedurbanareas,whereiteliminatesthe
damagesintheexistingcivilinfrastructure.Webelieve
thattheproposedVMDS-basednetworkdesignisthe most suitable solution
for all FTTx applications (including
FTTH,FTTB,etc.)whereitenablesfulldeploymentof
fiberopticsinshortertime,minimaldisruptionandrea-sonablecostcomparedtoconventionaldeployment
methodologies.Suchquickdeploymentmeansthatcus-tomerswillnolongerwaitinordertogetconnectedto
existing backbone telecom infrastructure. ACKNOWLEDGMENT
TheauthorthanksTeraSpanandLiteAccesscompanies for some information
about their micro ducting technolo-gies. 22 REFERENCES [1]K.
Nothofer, A. Weiss and P. Lausch, Optical Fiber Cable
Suit-edforBlownInstallationorPushingInstallationinMicroducts of
Small Diameter, US Patent, US7570852B2, 2009.[2]K. Konstadinidis,
J. Turnipseed and P. Weimann, Optical Fiber
CablesforMicroductInstallations,USPatentUS7431963B2, 2008.
[3]W.StckleinandH.Knoch,DevelopmentofaMicroCable Family with
Stranded Micromodules for Blown Cable
Applica-tions,Proc.InternationalWire&CableSymposium,pp.293-296,
2009. [4]P.Curzio,L.Jawerth,3mmMicroductSystemforFTTHNet-works in
MDUs, Proc. The International Cable Connectivity Sym-posium, pp.
527-533, 2012. [5]HDPE Conduit, Dura-Line, http://www.duraline.com,
2012. [6]Micronet Micro Cable System, Hexatronic Cables &
Interconnect Systems, http://www.hexatronic.com. 2014.
[7]S.Purcell,MicroTrenchDuctPlacement,USPatent US20050191133A1,
2005.
[8]D.Comteq,MicroductCabling:FibertotheHome,Proc.In-ternational
Wire & Cable Symposium, pp. 431-437, 2003.
[9]AirBlownFibre&MicroductSolutions,LiteAccessTechnolo-gies,
http://www.liteaccess.com. 2015.
[10]VerticalInlaidFiber(VIF),TeraSpanNetworks,
http://www.teraspan.com. 2015.
MousaabM.NahasreceivedaBScdegreefromtheUniversityof
Jordanin1999andanMScdegreefromAstonUniversityin2002. His
specialization is communications engineering. In 2003, he joined
thePhotonicsResearchGroupatAstonUniversityandreceiveda
PhDdegreeinopticalfibercommunicationsin2007.Heworkedin
telecommunicationsindustryfrom2007to2009.In2009,hejoined King
Abdulaziz University in KSA and worked as Assistant Professor
inElectricalEngineeringuntil2014.Since2015,hehasbeenwork-ingintheElectricalandComputerEngineeringdepartmentatthe
UniversityofJeddahinKSA.Dr.Nahassmainresearchinterests
areupgradinglegacyWDMcommunicationsystemsandmonitoring long-haul
fiber links. He is also interested in the optimization of fiber
optic networks including FTTx systems.
