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Communicatio n http://dx.doi.or g Copyright © 2 0 L ABSTRA C The motivati o (FTTH) netw o Baghdad Cit y b een putting u tion and num b done through as well as co s evaluate the f e Keywords: G 1. Introdu c With the dev e p lications, th e mand. PON t width, good m efficiency, h a work [1]. Fro tion Union- T (ITU-T) has GPON syste m operating at 2 upstream rate s FTTH (Fib e loy access n e users simulta n chitecture, F T Line Termina to end user d e center office t and then con t tomers. For n e optic networ k nimization, w p ossible. Thi s optic cable r o components o In [3] a mo tions expens e n s and Networ k g /10.4236/cn.2 0 0 13 SciRes. L ink a n Imple m E C T o n behind thi s o rk which is o y . Based on th e u nder conside r b er of OLT po r evaluation th e s t ratio betwe e e eder network G igabit Passiv e c tion e lopment of m e re is a massi v t echnology, is m anagement f u a s already bee n m 2003, the I T elecommunic a published G. 9 m . GPON is a P 2 .488 Gbps d s [2]. e r to the Ho m e twork, which n eously at hi g T TH networks l (OLT) usual e vices (ONT) t o the remote n t inuing by di ff e twork access , k connectivity w hile keeping s is because o v o ute is usually o f the network. deling of the c e s incurred f o k , 2013, 5, 438- 4 0 13.53B2081 P u n d Cost m entat Dheyaa Ja s E lectrical Engin e s work is the n o ne of the Ir a e detailed stu d r ation through rts (PON) ha d e total cost of P e n EPON and cost, distribu t e Optical Net w m any advanced v e increase i n featured wit h u nction and hi n widely use d I nternational T a tion Standar d 9 84.x standar d P assive Optica l d ownstream a n m e) is a viable allows servi n g h speed. In t h carry signal fr ly placed in t h by running a n ode in the m i ff erent fibers t , it is always d be the major a quality of se r v erall cost of s e very high in r c apital invest m o r some oper a 4 43 u blished Online Opti m ion thr o s im Kadhim , e ering Departm e Email: d h Rece i n eed for perf o a q Telecomm u d y of this proj e a mathematic a d been studied a P ON system a n GPON is ev a t ion network c o w ork (GPON); F multimedia a p n bandwidth d h flexible ban d gh transmissi o d in access n e T elecommunic a d ization Sect o d to define t h l Networ k (PO n d 1.244 Gb p solution to de p n g multiple e n h e common a fr om the Optic h e center offi c fiber from t h i ddle of the w a o different c u d esired that fib a rea of cost m r vice as high a e tting up a fib r elation to oth m ents and oper a tor cases, a n September 201 3 m ization o ugh G , Nahla Abd u e nt, University o h eyaajk@gmail. c i ve d May 2013 o rmance anal y u nication Post e ct, the design , a l model sim u and evaluated n d who it affe c a luated. Then G o st, and total n F iber to the H o p - e- d - o n et - a- o r h e N) p s p - n d a r- al c e, h is a y u s- er m i- a s er er a- n d identif i ics co v hensiv e includ e and la b p rogra m networ k versity In t h mentat i p erfor m evaluat i as a fu n throug h it affec as wel l luated. lyze e n networ k The 2 will i p ology p erfor m numeri be ma d 2. Op t Iraq T e 3 (http://www.s c of FT T G PON T u lrahman H o f Baghdad, Ba g c o m y sis of Al-Ge h and Compan y , implementat i u lated and per f as a function o c ted with the n G PON syste m n etwork cost. o me (FTTH) N i es the key pa r v ering these m e cost modeli n e s outside pla n b or with enha n m ming in gen k problem of c is found in [5 ] h is work, we w i on of Al-Ge h m ance analysi s i ng link utiliz a n ction of cyc l h evaluation t h ted with the n l as cost ratio Then GPON n d evaluate t h k cost, and tot a res t of this p a i llustrate the p network wil l m ance analysi s cal results are d e in Section 6 t ical Netw o e lecommunica t c irp.org/journal / T H Net w T echnol o H ussain g hdad, Ira q h ad/Baghdad “ y (ITPC) FT T i on, an d analy s f ormance eval u o f cycle time. n umber of ON U m has been op t N etwor k ; OL T r ameters that i m m ajor technolo g n g of FTTH n , head end, a n n ced reach a n erating a mo d c onnecting b u ] . w ill introduce h ad/Baghdad F s of this netw o a tion and num b l e time. Cost o h e total cost o f n umber of ON U between EP O system has b h e feeder net w a l network co s a per is structu r p roject infor m l be explaine d s is illustrated shown in Sec t . o rk Modeli n t ion and Post / cn) w ork o gy “ Fiber To Th e T H projects in s is of this net w u ated. The lin k Cost optimiz a U s (i.e. splitti n t imized to ana T and ONU m pact FTTH e g ies. In [4] a was presente d n d premises e q n d split ratio. d el to solve t h u ildings across study, desig n F TTH networ k o rk was done b er of OLT po r o ptimization w f PON system U s (i.e splitti n O N and GPO N een optimize d w ork cost, dis s t. r ed as follows ; m ation, the net w d in Section 3 in Section 4, w t ion 5. Conclu ng Company (I T CN e Home” 2010 in w or k has k utiliza- a tion was n g ratio), lyze and e cono m - compre- d , which q uipment A linear h e access the uni- n , imple- k , then a through r ts (PON) w as done and who n g ratio), N is eva- d to ana- tribution ; Section w ork t o- 3 and its w hile its sion will T PC), fo- D. J. KADHIM, N. A. HUSSAIN Copyright © 2013 SciRes. CN 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) ser- vices to the residential customers. FTTH network in Al- Gehad consists from two OLTs placed in Al-Gehad ex- change will be serving 6000 subscribers in total area of about 32 km. It has been planned to use 6000 ONTs, one ONT per subscriber. Each OLT will connect to the con- verged Layer 3 switches and then the routers to ITPC Passive Distribution Network (PDN) network. The length of feeder cables is 243 km, and the length of distribution cables is 405 km, so the total fiber cables length will be 647 km. After studying the project maps and summarized the varying building features and application scenarios of the detail site survey, and based on the requirement of IPTC, the design will be as follow [6]: For general network topology, a ring topology is used to deploy the FTTH passive network, offer the pro- tection to Optical Distribution Network (ODN). There is 20% of spare capacity in the feeder cables, from the Central Office up to the Fiber Distribution Terminal (FDT), to meet the future requirements. Feeder section from CO to FDT, 144F optical cable will be proposed by ring topology and 2:4 first level splitters will be proposed in FDT cabinet. Distribution section from FDT to Fiber Access Ter- minal (FAT), 72F, 48F, 24F, and 12F optical cable will be proposed by star topology, 1:16 second level split- ter will be proposed in FAT, which is closure to wall mounted FAT product to meet different requirement and scenarios. Two topologies are used as shown in Figure 1, ring topology for feeder cables that are connect the Fiber Dis- tribution Terminals (FDTs) to the Central Office (CO) by first level splitting of 2:4, and star topology to connect several numbers of Fiber Allocation Terminal (FAT) to each FDT by second level splitting of 1:16. Figure 1. Network Topology. OLT will be deployed in each central office and the quantity will be calculated to satisfy the coverage capac- ity. 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 offices. BRAS are full-loaded configuration with the processing capabil- ity of not less than 115,000 lines. In the normal status, each BRAS just take the service traffic 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 reliabil- ity. For FTTH solution the access layer will provide OLT equipment in exchange; all subscribers will be connected through Optical Distribution Network (ODN). The pro- posed connection will be from the OLT to access point Fiber Access Terminal distribution box (FAT). As it is obvious from Figure 2 the FTTH system com- prises 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 con- struction features the PON technology, which provides point to point and point to multi-point applications. ODN provides the physical channels from OLT and ONT to communicate with each other. 3. Performance Analysis of FTTH Network Use of passive optical networks is very advantageous in designing FTTH architectures [7]. If a two main stan- dards (EPON and GPON), named xPON, are considered, a series of important optimization problems for the de- sign, plan, and deployment of FTTH networks and pas- sive optical networks should be considered since they truly effect on the network efficiency and performance. The target is to compare the network cost of an EPON and GPON system based on the utilization of the optical link’s transport capacity. The utilization affects directly the segmentation need in an optical network and this ef- fect on the total network cost [8]. 3.1. Link Utilization Equation (11) calculates link utilization (υEd) of an EPON downstream channel. Figure 2. General F TTH System. D. J. KADHIM, N. A. HUSSAIN Copyright © 2013 SciRes. CN 440 Ed [** ] * E cE ONUcm Eo E cE ftB Nf ff tB υ − + = (1) Where E f is the EPON frame payload, E o f the EPON frame overhead, it is taken to be 42 bytes, E B the bit rate of an EPON link, it is equal to 1.25 Gbps, ONU N the ONUs number in the network segment which is taken 10,000, cm f the length of control message, it is equal to 88 bytes, and the cycle time. Utilization (υEU) of an EPON is given by Equation (2); Eu [*(* )] * E cE ONUcmpoE Eo E cE ftB NftB ff tB υ −+ =+ (2) Where po t is the physical layer overhead (i.e. guard band), it is taken 1.44 µsec. Utilization (υGd) of an GPON downstream is given by Equation (3); * Gd [* ?] * ONU td Ep dGGoao GEMo Epc dG N ftB ff ff t tB υ − + = (3) Where GEMo f is the GEM framing overhead for Ether- net payload which is equal 30 bytes, E p f is Ethernet payload, d t is GPON duration of downstream frame, its equal 125 µsec, G B the GPON bit rate (1.25 Gbps), Go f (27 bytes) is the GPON downstream frame over- head, and ao f (27 bytes)is the upstream allocation over- head. Utilization (υGu) of an GPON upstream is given by (4); * Gu [* ] * d ONU t Ep d Gploudbru GEMo Epc dG N ftBf f ff t tB υ −+ + = (4) Where plou f is the length of physical layer overhead (include PLOAMu field) it taken 15 bytes, and dbr f is the average number of DBRu fields in an upstream GPON frame.Since an ONU can send several GEM frames dur- ing its time slot and only the first of them carries the PLOu field and all frames carry the DBRu field, dbr f is approximated by: *G GEM cB plou ONU dbru dbru f t f N ff+ − = (5) Where GEMGEMo EP f ff=+ 3.2. Network Segmentation At building a passive optical network, segmentation is the way to guarantee fair transport capacity per subscrib- er as shown in Figure 3. A number of needed network segments are determined Figure 3. Segmented PON layout [10]. according to the total transport capacity and number of subscribers. For both EPON and GPON systems, assume that the total transport capacity of segment Segk is Ck, line coding efficiency is σ and utilization of the transport channel capacity is υ, so Bk the total bit rate available for user in segment Segk is: Bk = σ υ Ck (6) The total available bit rate for the segment Segk is the sum of the traffic of all ONUs connected to it as below: kk,I 0 Bb Mk i= = (7) Where Mk represents the number of ONUs connected to the ith port of the OLT. Thus, the number of required segments (OLT ports) will be [10]: Ω β σC K N o r υ = (8) Where Ω is a broadband access (take rate) as (0 ˂ Ω ˂ 1), β is the percentage of active subscribers that operate during a busy hour, N is ONUs number, o r is the aver- age bandwidth required to support all requested services on one or all OLT ports, σ is line coding efficiency, υ is the utilization of the transport channel capacity, and C is transport capacity. The number of PONs determines the number of OLTs required serving a whole region. This enables network planners to know the cost required for installing, confi- guring and upgrading GPON resources. Each PON can serve up to ΩN/K subscribers, which can be expressed as follows [10]: Number of subscribers = N K Ω = σC βo r υ (9) This formula indicates that the number of subscribers supported on a single OLT port (PON) depends mainly on ro and β. Each OLT of Al-Gehad FTTH network has 18 ports, 14 are used and the other four ports are left for the possi- bility of traffic growth. 3.3. Relative Network Cost The number of network segments is the most important D. J. KADHIM, N. A. HUSSAIN Copyright © 2013 SciRes. CN 441 factor when calculating the cost of EPON and GPON net- works. The number of segments indicates the difference between an EPON and GPON networks in the amount of installing fiber and the number of the needed transceivers in the network. The relative network cost of an EPON and GPON is given by [8]: φσ σ G E GGC EEC υ υ = (10) Where φ = KE/KG, and Setting the parameters (β, Ω, N, and o r) equal in both approaches, (i.e. EPON and GPON). 4. GPON Capacity and Cost Optimization Optimization approach aims to optimally allocate the ca- pacity on GPON access network links on Al-Gehad FTTH network, which can support current and future traffic de- mands, while guaranteeing a minimum throughput required for all class j traffic, min j ρ. This approach is expressed in an optimization problem as follows: Cost minimization of the capacity of the links in the GPON access network. Where j α cost per bit with each link l in the GPON access network, and Cl is the link capacity. min j jl α ∈ C l Capacity constraints of these links, where the total traffic load generated by all flows sharing a link should be less than its capacity, l H llj jC ∈ =≤ . Subject to llj jH C ∈< , lL∀∈ Throughput per- formance constraint in a GPON access network, where the throughput of each class j traffic should be greater than the minimum required throughput of this class. Where l H denotes the set of flows that share link l. min ,2,., Z 11j1 jj = ρρ ≤∀…， The throughput constraint can be expressed with re- spect to the average delay of generated traffic flows as follows: follows ρj = [] [] j j ES ET , where Sj represent the vo- lume of traffic flows. Thus, the throughput performance can be written as follows: E[Tj] ≤ min [] ,1, 2,., j j N ES j ρ ∀…= (11) Where m j in ρ j ρ ≥. After some algebraic manipulations, the optimal ca- pacities of both GPON feeder link and distribution links can be given by [9]: Cfeeder = N + ρmin[1+ d f N α α ] (12) Cdistribution = + ρmin[1+ 1 f d N α α ] (13) Where N is the number of ONUs, Cfeeder is the feeder link capacity and Cdistribution is the distribution links ca- pacity. If we consider that the cost of transmitting traffic on feeder link is the same as that on a GPON distribution links, then f d αα =, and for simplicity take 1 fd αα == . Then, as N →∞, the optimal capacity of the GPON feeder link and distribution links respectively will be: Cfeeder = N + ρmin (14) Cdistribution = + ρmin (15) So, the optimal total cost will be Cfeeder + N Cdistribution = 2N + (N+1) ρmin (16) 5. Nnumerical Results The results and discussions included link utilization of xPON, number of PONs and network cost analysis. Fig- ure 4 illustrates the utilization as a function of the cycle time in two cases when the payload size is 46 bytes and 1500 bytes for 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 di- rection achieves better utilization than the upstream does, but when cycle time increases the difference will be very little. Lower utilization obtained with multi-OLT EPON network, this is because the increasing number of ONUs since the total bandwidth must be divided among larger number of ONUs [10]. For this reason, the second level splitting ratio in Al-Gehad FTTH network is 1:16 only. Figure 4. EPON and GPON Link Utilization vs. Cycle Time. 00.5 11.5 22.5 33.5 4 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1 cycle time (ms) Uti l izat ion of t ransport channel link Utilization GP ON down/upstream(1500B ) GP ON down/upstream(64B ) E P O N(One OLT) down/ up (1500) E P ON(One OLT) down/up(46) EPON(Tow OLTs) D. J. KADHIM, N. A. HUSSAIN Copyright © 2013 SciRes. CN 442 Figure 5 shows that the number of PONs grows li- nearly with take rate. For the same type of traffic, GPON needs fewer segments than EPON. Multi-OLT EPON network requires larger number of segments (PONs) than single OLT xPON to assure services required to the larg- er number of subscribers. Figure 6 illustrates the relationship between cycle time and cost ratio (φ) for 46 and 1500 bytes payload. For small payload size and short cycle time, cast ratio is higher, this refers to that GPON fits better for low volume and small delay traffic for example voice over IP (VoIP) and PSTN. For this type of traffic and in upstream direction, φ is about 1.7. Figure 7 shows the relationship between the capacity of the GPON link, CFeeder/N, and the number of ONUs (N) for different amount of minimum through- put, ρmin. Subscribers are allocated less bandwidth as num- ber of ONU increases. This is due that the capacity of GPON link is dimensioned such that Cfeeder equals the worst-case load (Mℱ). The optimum value of Cfeeder con- verges around the total capacity required for accommo- dating general traffic load in addition to ρmin. Figure 8 shows the optimal distribution link capacity required to guarantee different requirements of throughput, ρmin. Each ONU can support different applications, therefore distri- bution links should have sufficient bandwidth such that the remaining capacity on distribution links, can guaran- tee the minimum throughput. Figure 9 illustrates the op- timal total cost of GPON access network for different throughput requirements. The total costs converge in a slower manner for high minimum requirements, than when ρmin is taken to be smaller value. 6. Conclusions A study of ITPC access network project 2010 in Baghdad by taking Al-Gehad FTTH network as a study case has been done. A study of link utilization of channel capacity Figure 5. Number of PONs vs. Take rate. Figure 6. EPON-to-GPON Cost Ratio. Figure 7. GPON Feeder Link Capacity vs. Number of ONUs. Figure 8. GPON Distribution Link Capacity vs. Number of ONUs. 00.1 0.2 0.3 0.4 0.5 0.6 0.70.8 0.91 0 5 10 15 20 25 30 35 40 Take rate Number of segm ent s GPON Up(46B) GP O N Up(1500B ) E P ON(One OLT)Up(46) E P ON (One OLT)Up(1500) E P ON (Two OLTs )Up(1500) 0.5 11.5 22.5 33.5 4 1.2 1.3 1.4 1.5 1.6 1.7 Cycl e ti m e (ms) Cos t Rat i o Up (pay load 1500B) Down (pay l oad 1500B) Up (pay load 46B) Down (pay l oad 46B) 020 40 60 80100120140 20 30 40 50 60 70 80 Number of ONUs Dis t ri but ion Cos t (M bps ) Di st ri b uti on Co st R=20M bps, ?m i n=32M bps R=20M bps, ?m i n=10M bps R=20M bps, ?m i n=0.5M bps 020 40 60 80100120140 20 30 40 50 60 70 80 Number of ONUs Distribution Cost (Mbps) Di st ri b uti on Co st R=20M bps, ?m i n=32M bps R=20M bps, ?m i n=10M bps R=20M bps, ?m i n=0.5M bps D. J. KADHIM, N. A. HUSSAIN Copyright © 2013 SciRes. CN 443 Figure 9. Total Cost of GPON Resources Vs. Number of ONUs. in both EPON and GPON has been done and uses that information to compare the cost of these two systems. From the numerical results we can say that the GPON system uses the link capacity more efficiently than EPON system does. The cost to build an EPON or GPON system is almost the same, the relative cost is affected widely by the cost of transceivers. For example, for VoIP service, the GPON transceiver is about 70% more expen- sive than EPON transceivers. In this work we can find that GPON network planners should take into their considerations the number of de- manding and basic services that will be supported on each PON (OLT port) to achieve traffic balancing among all PONs. Link utilization can be used to calculate the number of subscribers that can be supported on a single PON and then can determine the size of population and services that can be supported on OLT ports. An optimization problem has been formulated to find the optimal capacity and cost of GPON access network links guarantee that a minimum throughput can be en- sured for supported traffic classes. REFERENCES [1] I. Cale, A. Salihovic, M. Ivekovic and T-HTd. D. Split, “Gigabit Passive Optical Network—GPON,” 29th Inter- national Conference ITI 2007. [2] S. Lallukka and P. Raatikainen, “Link Utilization and Comparison of EPON and GPON Access Network Cost,” Proceeding of IEEE Globecome, 2005. [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, 2010. [4] M. Vaughn, D. Kozischek, D. Meis, A. Boskovic and R. Wagner, “Value of Reach and Split Ratio Increase in FTTH Access Network,” Journal of Lightwaves Tech- nology, Vol. 22, No. 11, 2004. [5] C. Bolu, A. Talulade and A. Adeshina, “University Opti- cal Fiber Network Access Optimization: A Case Study,” International Journal of Mechanical & Mechatronics En- gineering, Vol. 12, No. 6, 2012. [6] ITPC Documents, Reports, and Maps. [7] D. Nowak, “Dynamic Bandwidth Allocation Algorithms for Differentiated Services enabled Ethernet Passive Opt- ical Networks with Centralized Admission Control,” Ph.D. Thesis, 2005. [8] H. Alshaer and J. J. Elmirghani, “Enabling Novel Pre- mium Service Classes in DiffServover MPLS-Enabled Network,” International Journal of Network Management, Vol. 18, 2008, pp. 447-464. http://dx.doi.org/10.1002/nem.693 [9] M. D. Vaughn, D. Kozischek, D. Meis, A. Boskovic and R. E. Wanger, “Value of Reach-and-Split Ratio Increase in FTTH Access Networks,” Journal of Lightwave Tech- nology, Vol. 22, No. 11, 2004, pp. 2617-2622. http://dx.doi.org/10.1109/JLT.2004.836741 [10] S.ami Lallukka and P. Raatikainen, “Link Utilization and Comparison of EPON and GPON Access Network Cost,” Proceedings of IEEE Conference on Global Telecommu- nications, 2005. [11] H. Alshaer, R. Shubair and M. Alyafei, “A Framework for Resource Dimensioning in GPON Access Network,” International Journal of Network Management, Vol. 22, No. 3, 2011, pp. 199-215. 020 40 6080 100 120 140 40 45 50 55 60 65 70 75 80 85 90 Number of ONUs Total Cost (Mbps) To tal C ost R= 20M bps, =32M b ps R= 20M bps, =10M bps R= 20M bps, =0.5 Mb ps |