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.