ogy ABSTRACT 1. Introduction utiliza- PON system and who and ONU bandwidth de- flexible band- widely used in access net- a- network is found in [5].

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1 Communications and Network, 2013, 5, Published Online September 2013 ( Link and Cost Optimization o FTTH Network Implementation through GPON Technolo ogy Dheyaa Jasim Kadhim, Nahla Abdulrahman Hussain Electrical Engineering Department, University o Baghdad, Baghdad, Iraq dheyaak@gmail.com Received May 2013 ABSTRACT The motivation behind this work is the need or perormance analysis o Al-Gehad/Baghdad Fiber To The Home (FTTH) network which is one o the Iraq Telecommunication Post and Company (ITPC) FTTH proects in 2010 in Baghdad City. Based on the detailed study o this proect, the design, implementation, and analysis o this network has been putting under consideration through a mathematical model simulated and perormance evaluated. The link utiliza- was tion and number o OLT ports (PON) had been studied and evaluated as a unction o cycle time. Cost optimization done through evaluation the total cost o PON system and who it aected with the number o ONUs (i.e. splitting ratio), as well as cost ratio between EPON and GPON is evaluated. Then GPON system has been optimized to analyze and evaluate the eeder network cost, distribution network cost, and total network cost. Keywords: Gigabit Passive Optical Network (GPON); Fiber to the Home (FTTH) Network; OLT and ONU 1. Introduction With the development o many advanced multimedia ap- plications, there is a massive increase in bandwidth de- mand. PON technology, is eatured with lexible band- width, good management unction and high transmission eiciency, has already been widely used in access net- work [1. From 2003, the International Telecommunica a- tion Union-Telecommunication Standardization Sector (ITU-T) has published G.984.x standardd to deine the GPON system. GPON is a Passive Optical Network (PON) operating at Gbps downstream and Gbps upstream rates [2. FTTH (Fiber to the Home) is a viable solution to dep- loy access network, which allows serving multiple end users simultaneously at high speed. In the common ar- Line Terminal (OLT) usually placed in the center oice, to end user devices (ONT) by running a iber rom this center oice to the remote node in the middle o the way and then continuing by dierent ibers to dierent cus- tomers. For network access, it is always desired that iber optic network connectivity be the maor area o cost mi- chitecture, FTTH networks carry signal rom the Optical nimization, while keeping quality o service as high as possible. This is because overall cost o setting up a iber optic cable route is usually very high in relation to other components o the network. In [3 a modeling o the capital investments and opera- tions expenses incurred or some operator cases, and identiies the key parameters that impact FTTH economics covering these maor technologies. In [4 a comprehensivee cost modeling o FTTH was presented, which includes outside plan, head end, and premises equipment and labor with enhanced reach and split ratio. A linear programming in generating a model to solve the access network problem o connecting buildings across the university is ound in [5. In this work, we will introduce study, design, imple- then a mentation o Al-Gehad/Baghdad FTTH network, perormance analysiss o this network was done through evaluating link utilization and number o OLT ports (PON) as a unction o cycle time. Cost optimization was done throughh evaluation the total cost o PON system and who it aected with the number o ONUs (i.e splitting ratio), as welll as cost ratio between EPON and GPON is evaluated. Then GPON system has been optimized to analyze end evaluate the eeder network cost, distribution network cost, and total network cost. The rest o this paper is structured as ollows; Section 2 will illustrate the proect inormation, the network topology network willl be explained in Section 3 and its perormance analysiss is illustrated in Section 4, while its numerical results are shown in Section 5. Conclusion will be made in Section Optical Network Modeling Iraq Telecommunication and Post Company (ITPC), o-

2 D. J. KADHIM, N. A. HUSSAIN 439 cuses on the users requirements and the technology trends, is constructing the national FTTH network to provide Voice over IP (VoIP) and High Speed Internet (HSI) services to the residential customers. FTTH network in Al- Gehad consists rom two OLTs placed in Al-Gehad exchange will be serving 6000 subscribers in total area o about 32 km. It has been planned to use 6000 ONTs, one ONT per subscriber. Each OLT will connect to the converged Layer 3 switches and then the routers to ITPC Passive Distribution Network (PDN) network. The length o eeder cables is 243 km, and the length o distribution cables is 5 km, so the total iber cables length will be 647 km. Ater studying the proect maps and summarized the varying building eatures and application scenarios o the detail site survey, and based on the requirement o IPTC, the design will be as ollow [6: For general network topology, a ring topology is used to deploy the FTTH passive network, oer the protection to Optical Distribution Network (ODN). There is 20% o spare capacity in the eeder cables, rom the Central Oice up to the Fiber Distribution Terminal (FDT), to meet the uture requirements. Feeder section rom CO to FDT, 144F optical cable will be proposed by ring topology and 2:4 irst level splitters will be proposed in FDT cabinet. Distribution section rom FDT to Fiber Access Terminal (FAT), 72F, 48F, 24F, and 12F optical cable will be proposed by star topology, 1:16 second level splitter will be proposed in FAT, which is closure to wall mounted FAT product to meet dierent requirement and scenarios. Two topologies are used as shown in Figure 1, ring topology or eeder cables that are connect the Fiber Distribution Terminals (FDTs) to the Central Oice (CO) by irst level splitting o 2:4, and star topology to connect several numbers o Fiber Allocation Terminal (FAT) to each FDT by second level splitting o 1:16. OLT will be deployed in each central oice and the quantity will be calculated to satisy the coverage capacity. Each OLT will connect to the converged Layer 3 switches and then the routers to ITPC PDN network. BRAS will be installed in the core central oices. BRAS are ull-loaded coniguration with the processing capability o not less than 115,000 lines. In the normal status, each BRAS ust take the service traic which belongs to the corresponding areas. When one is broken, the other BRAS will take the whole service. AAA is the same with BRAS. EMS remote redundancy is ensuring the reliability. For FTTH solution the access layer will provide OLT equipment in exchange; all subscribers will be connected through Optical Distribution Network (ODN). The proposed connection will be rom the OLT to access point Fiber Access Terminal distribution box (FAT). As it is obvious rom Figure 2 the FTTH system comprises the Optical Line Terminal (OLT) on the CO, the Optical Network Terminal (ONT) on the user side, and the Optical Distribution Network (ODN). The FTTH construction eatures the PON technology, which provides point to point and point to multi-point applications. ODN provides the physical channels rom OLT and ONT to communicate with each other. 3. Perormance Analysis o FTTH Network Use o passive optical networks is very advantageous in designing FTTH architectures [7. I a two main standards (EPON and GPON), named xpon, are considered, a series o important optimization problems or the design, plan, and deployment o FTTH networks and passive optical networks should be considered since they truly eect on the network eiciency and perormance. The target is to compare the network cost o an EPON and GPON system based on the utilization o the optical link s transport capacity. The utilization aects directly the segmentation need in an optical network and this eect on the total network cost [ Link Utilization Equation (11) calculates link utilization (υ Ed ) o an EPON downstream channel. Figure 1. Network Topology. Figure 2. General FTTH System.

3 4 D. J. KADHIM, N. A. HUSSAIN E [ tc* BE NONU * cm Eo + E υed = (1) tc* BE Where is the EPON rame payload, E Eo the EPON rame overhead, it is taken to be 42 bytes, B E the bit rate o an EPON link, it is equal to 1.25 Gbps, N ONU the ONUs number in the network segment which is taken 10,000, cm the length o control message, it is equal to 88 bytes, and the cycle time. Utilization (υ EU ) o an EPON is given by Equation (2); E [ tc * BE NONU( cm + tpo* BE) Eo + E υeu = (2) tc * BE Where t po is the physical layer overhead (i.e. guard band), it is taken 1.44 µsec. Utilization (υ Gd ) o an GPON downstream is given by Equation (3); Ep NONU * td [ td * BG Go? ao GEMo + Ep tc υgd = (3) td * BG Where GEMo is the GEM raming overhead or Ethernet payload which is equal 30 bytes, Ep is Ethernet payload, t d is GPON duration o downstream rame, its equal 125 µsec, B G the GPON bit rate (1.25 Gbps), Go (27 bytes) is the GPON downstream rame overhead, and ao (27 bytes)is the upstream allocation overhead. Utilization (υ Gu ) o an GPON upstream is given by (4); Ep NONU * t [ * d td BG plou + dbru GEMo + Ep tc υgu = (4) td * BG Where plou is the length o physical layer overhead (include PLOAMu ield) it taken 15 bytes, and dbr is the average number o DBRu ields in an upstream GPON rame.since an ONU can send several GEM rames during its time slot and only the irst o them carries the PLOu ield and all rames carry the DBRu ield, dbr is approximated by: tc* B G plou NONU = (5) dbru Where GEM = GEMo + EP 3.2. Network Segmentation dbru+ GEM At building a passive optical network, segmentation is the way to guarantee air transport capacity per subscriber as shown in Figure 3. A number o needed network segments are determined Figure 3. Segmented PON layout [10. according to the total transport capacity and number o subscribers. For both EPON and GPON systems, assume that the total transport capacity o segment Seg k is C k, line coding eiciency is σ and utilization o the transport channel capacity is υ, so B k the total bit rate available or user in segment Seg k is: B k = σ υ C k (6) The total available bit rate or the segment Seg k is the sum o the traic o all ONUs connected to it as below: B k Mk = b (7) i= 0 Where M k represents the number o ONUs connected to the ith port o the OLT. Thus, the number o required segments (OLT ports) will be [10: Ω β Nr K = o (8) συc Where Ω is a broadband access (take rate) as (0 Ω 1), β is the percentage o active subscribers that operate during a busy hour, N is ONUs number, r o is the average bandwidth required to support all requested services on one or all OLT ports, σ is line coding eiciency, υ is the utilization o the transport channel capacity, and C is transport capacity. The number o PONs determines the number o OLTs required serving a whole region. This enables network planners to know the cost required or installing, coniguring and upgrading GPON resources. Each PON can serve up to ΩN/K subscribers, which can be expressed as ollows [10: ΩN Number o subscribers = = σ υ C (9) K βr o This ormula indicates that the number o subscribers supported on a single OLT port (PON) depends mainly on r o and β. Each OLT o Al-Gehad FTTH network has 18 ports, 14 are used and the other our ports are let or the possibility o traic growth Relative Network Cost k,i The number o network segments is the most important

4 D. J. KADHIM, N. A. HUSSAIN 441 actor when calculating the cost o EPON and GPON networks. The number o segments indicates the dierence between an EPON and GPON networks in the amount o installing iber and the number o the needed transceivers in the network. The relative network cost o an EPON and GPON is given by [8: φ σ GυGCG = (10) σ υ E ECE Where φ = K E /K G, and Setting the parameters (β, Ω, N, and r o ) equal in both approaches, (i.e. EPON and GPON). 4. GPON Capacity and Cost Optimization Optimization approach aims to optimally allocate the capacity on GPON access network links on Al-Gehad FTTH network, which can support current and uture traic demands, while guaranteeing a minimum throughput required min or all class traic, ρ. This approach is expressed in an optimization problem as ollows: Cost minimization o the capacity o the links in the GPON access network. Where α cost per bit with each link l in the GPON access network, and C l is the link capacity. min α l C l Capacity constraints o these links, where the total traic load generated by all lows sharing a link should be less than its capacity, l = H l C l. Subect to H < C l, l L Throughput perormance constraint in a GPON access network, where l the throughput o each class traic should be greater than the minimum required throughput o this class. Where H l denotes the set o lows that share link l. 1 1, = 1,2,., Z min ρ ρ The throughput constraint can be expressed with respect to the average delay o generated traic lows as ES [ ollows: ollows ρ = ET [, where S represent the volume o traic lows. Thus, the throughput perormance can be written as ollows: ES [ E[T min, = 1, 2,., N (11) ρ min Where ρ ρ. Ater some algebraic manipulations, the optimal capacities o both GPON eeder link and distribution links can be given by [9: C eeder = N + ρ min [1+ d N α α (12) C distribution = + ρ min [1+ 1 α N α d (13) Where N is the number o ONUs, C eeder is the eeder link capacity and C distribution is the distribution links capacity. I we consider that the cost o transmitting traic on eeder link is the same as that on a GPON distribution links, then α = αd, and or simplicity take α = αd = 1. Then, as N, the optimal capacity o the GPON eeder link and distribution links respectively will be: C eeder = N + ρ min (14) C distribution = + ρ min (15) So, the optimal total cost will be C eeder + N C distribution = 2N + (N+1) ρ min (16) 5. Nnumerical Results The results and discussions included link utilization o xpon, number o PONs and network cost analysis. Figure 4 illustrates the utilization as a unction o the cycle time in two cases when the payload size is 46 bytes and 1500 bytes or single and multi-olt EPON and single OLT GPON systems. This Figure shows that utilization is proportional with cycle time (i.e. short cycle time means less link utilization), with short access. Downstream direction achieves better utilization than the upstream does, but when cycle time increases the dierence will be very little. Lower utilization obtained with multi-olt EPON network, this is because the increasing number o ONUs since the total bandwidth must be divided among larger number o ONUs [10. For this reason, the second level splitting ratio in Al-Gehad FTTH network is 1:16 only. Utilization o transport channel link Utilization 0.4 GPON down/upstream(1500b) GPON down/upstream(64b) EPON(One OLT) down/up (1500) 0.3 EPON(One OLT) down/up(46) EPON(Tow OLTs) cycle time (ms) Figure 4. EPON and GPON Link Utilization vs. Cycle Time.

5 442 D. J. KADHIM, N. A. HUSSAIN Figure 5 shows that the number o PONs grows linearly with take rate. For the same type o traic, GPON needs ewer segments than EPON. Multi-OLT EPON network requires larger number o segments (PONs) than single OLT xpon to assure services required to the larger number o subscribers. Figure 6 illustrates the relationship between cycle time and cost ratio (φ) or 46 and 1500 bytes payload. For small payload size and short cycle time, cast ratio is higher, this reers to that GPON its better or low volume and small delay traic or example voice over IP (VoIP) and PSTN. For this type o traic and in upstream direction, φ is about 1.7. Figure 7 shows the relationship between the capacity o the GPON link, C Feeder /N, and the number o ONUs (N) or dierent amount o minimum throughput, ρ min. Subscribers are allocated less bandwidth as number o ONU increases. This is due that the capacity o GPON link is dimensioned such that C eeder equals the worst-case load (MF). The optimum value o C eeder converges around the total capacity required or accommodating general traic load in addition to ρ min. Figure 8 shows the optimal distribution link capacity required to guarantee dierent requirements o throughput, ρ min. Each ONU can support dierent applications, thereore distribution links should have suicient bandwidth such that the remaining capacity on distribution links, can guarantee the minimum throughput. Figure 9 illustrates the optimal total cost o GPON access network or dierent throughput requirements. The total costs converge in a slower manner or high minimum requirements, than when ρ min is taken to be smaller value. 6. Conclusions A study o ITPC access network proect 2010 in Baghdad by taking Al-Gehad FTTH network as a study case has been done. A study o link utilization o channel capacity Number o segments GPON Up(46B) GPON Up(1500B) EPON(One OLT)Up(46) EPON (One OLT)Up(1500) EPON (Two OLTs)Up(1500) Cost Ratio Distribution Cost (Mbps) Figure 6. EPON-to-GPON Cost Ratio. Figure 7. GPON Feeder Link Capacity vs. Number o ONUs. Distribution Cost (Mbps) Cycle time (ms) Up (payload 1500B) Down (payload 1500B) Up (payload 46B) Down (payload 46B) Number o ONUs Distribution Cost Distribution Cost R=20Mbps,?min=32Mbps R=20Mbps,?min=10Mbps R=20Mbps,?min=0.5Mbps R=20Mbps,?min=32Mbps R=20Mbps,?min=10Mbps R=20Mbps,?min=0.5Mbps Take rate Figure 5. Number o PONs vs. Take rate Number o ONUs Figure 8. GPON Distribution Link Capacity vs. Number o ONUs.

6 D. J. KADHIM, N. A. HUSSAIN 443 Total Cost (Mbps) Total Cost R=20Mbps, =32Mbps R=20Mbps, =10Mbps R=20Mbps, =0.5Mbps Number o ONUs Figure 9. Total Cost o GPON Resources Vs. Number o ONUs. in both EPON and GPON has been done and uses that inormation to compare the cost o these two systems. From the numerical results we can say that the GPON system uses the link capacity more eiciently than EPON system does. The cost to build an EPON or GPON system is almost the same, the relative cost is aected widely by the cost o transceivers. For example, or VoIP service, the GPON transceiver is about 70% more expensive than EPON transceivers. In this work we can ind that GPON network planners should take into their considerations the number o demanding and basic services that will be supported on each PON (OLT port) to achieve traic balancing among all PONs. Link utilization can be used to calculate the number o subscribers that can be supported on a single PON and then can determine the size o population and services that can be supported on OLT ports. An optimization problem has been ormulated to ind the optimal capacity and cost o GPON access network links guarantee that a minimum throughput can be ensured or supported traic classes. REFERENCES [1 I. Cale, A. Salihovic, M. Ivekovic and T-HTd. D. Split, Gigabit Passive Optical Network GPON, 29th International Conerence ITI [2 S. Lallukka and P. Raatikainen, Link Utilization and Comparison o EPON and GPON Access Network Cost, Proceeding o IEEE Globecome, [3 S. Kulkarni, M. El-Sayed, P. Gagen and B. Polonsky, FTTH Network Economics: Key Parameters Impacting Technllogy Decisions, Network Planning-Bell Labs, Alcatel-Lucent Technologies, [4 M. Vaughn, D. Kozischek, D. Meis, A. Boskovic and R. Wagner, Value o Reach and Split Ratio Increase in FTTH Access Network, Journal o Lightwaves Technology, Vol. 22, No. 11, [5 C. Bolu, A. Talulade and A. Adeshina, University Optical Fiber Network Access Optimization: A Case Study, International Journal o Mechanical & Mechatronics Engineering, Vol. 12, No. 6, [6 ITPC Documents, Reports, and Maps. [7 D. Nowak, Dynamic Bandwidth Allocation Algorithms or Dierentiated Services enabled Ethernet Passive Optical Networks with Centralized Admission Control, Ph.D. Thesis, [8 H. Alshaer and J. J. Elmirghani, Enabling Novel Premium Service Classes in DiServover MPLS-Enabled Network, International Journal o Network Management, Vol. 18, 2008, pp [9 M. D. Vaughn, D. Kozischek, D. Meis, A. Boskovic and R. E. Wanger, Value o Reach-and-Split Ratio Increase in FTTH Access Networks, Journal o Lightwave Technology, Vol. 22, No. 11, 2004, pp [10 S.ami Lallukka and P. Raatikainen, Link Utilization and Comparison o EPON and GPON Access Network Cost, Proceedings o IEEE Conerence on Global Telecommunications, [11 H. Alshaer, R. Shubair and M. Alyaei, A Framework or Resource Dimensioning in GPON Access Network, International Journal o Network Management, Vol. 22, No. 3, 2011, pp