Energy Efficient Design Strategies of Translucent and Transparent IP Over WDM Networks

Transcription

1 Energy Efficient Design Strategies of Translucent and Transparent IP Over WDM Networs F. Mousavi Madani Departent of coputer engineering Alzahra University Tehran, Iran, Received: Septeber 23, 2013-Accepted: Noveber 21, 2014 Abstract A surge of interest toward design and ipleentation of green networs are eerging in recent years. One obvious trend to reduce energy consuption of ajor active networ coponents is to craft bacbone networ architecture that taes into consideration traffic grooing of low-rate IP traffic as well as power-aware virtual topology design schees and RWA. Previous research efforts developed design strategies which assued digital processing of incoing traffic flows at every node structure in the optical layer (DXCs). This architecture provides full wavelength conversion capability by the use of optical transponders (OEO convertors) thus reduces coplicated RWA proble to a siple routing proble at the cost of sacrificing lightpath transparency. Moreover, introduction of transponders give rise to extra sources of power consuption which contrasts over goal. In this paper, energyiniized design of IP over WDM networs based on optical cross connects (OXCs) is investigated. Integer linear prograing forulation as well as heuristics for two design strategies viz. ulti-hop lightpath and direct bypass have been developed and their perforance with regard to power consuption and relative bandwidth utilization are copared. Siulation results indicate superior perforance of the proposed strategies with regard to previous studies. Keywords-coponent; Energy-iniized design, ulti-hop lightpath, direct lightpath. I. INTRODUCTION Growing energy consuption of bacbone optical networs has recently aroused global attention toward planning energy efficient networs. With rapid expansion and processing speed of underlying equipent to support next-generation high-speed Internet services and cloud coputing has further strengthened the iportance of power saving trends. Soe researchers proposed power-aware routing and wavelength assignent (PA-RWA) algoriths that taes power consuption of traffic load into routing considerations [1, 2]. For IP over WDM networs, soe authors have focused their intention on traffic grooing and optical bypass as green provisioning strategies [3]. Also, sleep ode option for the optical devices (e.g., aplifiers, optical switches) installed for protection purposes have been considered in [4]. These devices can be put in sleep ode to reduce the networ power consuption, but they can be proptly waen up (if necessary) upon a failure occurrence. In this paper, novel MILP forulations for optiization of power consuption in the networ design architecture based on optical cross-connect switches (OXCs) and IP core routers have been introduced. The ulti-hop translucent odel provides siultaneously optial virtual topology design and RWA to iniize the nuber of ports in core routers. It supports traffic grooing and full wavelength conversion at interediate cross-connecting nodes while aintaining optical transparency on each lightpath. The direct bypass odel investigates design of energy iniized single-hop all optical networ.

2 We further developed energy-iniized oriented heuristics for the fore entioned design scenarios to overcoe processing burden of pure atheatical odels. The rest of the paper is organized as follows: section 2 presents scheatic of the bacbone networ. Detail atheatical forulations for design strategies are introduced in section 3. Section 4 provides heuristics as near optial solution. Section 5 represents siulation results and perforance coparison aong design strategies for three test networs. Finally, section 5 concludes the paper. II. CORE NETWORK MODEL The architecture shown in Fig. 1 is used for odeling IP over WDM bacbone networ. Specifically, every node is coposed of a core router which collects user s traffic fro access routers at the IP layer and connects aggregated traffic streas to optical cross connect (OXC) via short-reach interface. OXCs at the optical layer are interconnected by optical fiber lins that carries at ost W wavelengths each with a carrying capacity of B Gb/s. For ultiplexing/de-ultiplexing of wavelength channels at output/input ports of OXC, a pair of optical passive ultiplexer/deultiplexer are used for each fiber lin. Clearly, the odel represents circuit-switched ultifiber optical networ that ipleents a virtual lin at the IP layer with a transparent lightpath at the optical layer. So wavelength conversion is not available in nodes and wavelength continuity should be conserved through whole networ. In order to enable optical signals to traverse long distances, EDFA aplifiers are introduced at regular distances. Also shown in Fig. 1, three ajor source of energy consuption are networ line card of core router (E r), transponder (E t) and EDFA (E e) so total power consuption can be coputed fro the nuber and types of router ports, total nuber of fibers and geographic span of the networ. Here, without losing generality, three types of router line cards are considered, naely one-port, two-ports and four-ports line cards. Such a distinction was ade based on the presuption that an N-port line card consues less energy than N one-port line cards. Fro the networ design perspective, two different strategies can be eployed to design IP over WDM networs, ulti-hop transparent lightpath bypass (naely translucent) and direct lightpath bypass strategies. Under ulti-hop bypass strategy, each virtual lin at IP layer is apped onto several concatenated lightpaths at optical layer. Over each lightpath, all IP traffic passing through an interediate router are directly bypassed at the corresponding OXC. At the destination node of a virtual lin, however, traffic carried by all wavelength channels are dropped and forwarded to core router for electronic processing. Low-end routers Low-end routers IP layer Er Core router j N : i j C Er Core router i id / B dn, di Et Optical layer W OXC Ee EDFA fn OXC L n Fig. 1. Architecture of IP over WDM networ This allows traffic grooing at interconnections between virtual lins to attain benefits of traffic grooing for iproved bandwidth utilization. Such iproveent, of course, can be obtained only at the cost of sacrificing full lightpath transparency. In contrast, direct lightpath strategy achieves full wavelength transparency by deploying direct lightpath between every source-destination pair at the cost of issing the benefits of traffic grooing. The perforance of these two scenarios in ters of energy consuption and relative BW utilization will be contrasted in the later section. We have also included ulti-hop opaque lightpath bypass scenario discussed in [5] where a cobination of O-E-O transponders and DXCs allow for ipleentation of full wavelength conversion at each node. It relieves wavelength continuity constraint and reduces the coplex RWA proble to a siple routing proble. For the sae of bencharing results with an ideal lower band and upper band liits, the LP-relaxed version of the odel and Non-bypass design schees are taen into consideration, respectively.

3 III. ENERGY-MINIMIZED MATHEMATICAL MODELS In the so-called ulti-hop lightpath bypass and direct lightpath bypass strategies, the proble of designing an IP over WDM networ with iniu power consuption can be forulated as a ixed integer linear prograing (MILP) odel. Our objective is to find energy-iniized design subject to 1) serving all traffic deands, 2) a fixed axiu nuber of wavelengths per fiber. No liit on the nuber of fibers in each physical lin was set to accoodate required carrying capacity. Input paraeters: : A physical topology which consists of a set of nodes N and lins L. The node set corresponds to networ nodes, of which each consists of an IP router and an OXC. The lin set consists of physical fiber lins in underlying networ topology. G( N, E ) N : The set of neighboring nodes of node in the physical topology. T: set of router line card types. We assue three types of one-port, two-port and four-port types of line cards. : Traffic deand between each node pair (s, d). We further assue a syetric traffic deand atrix, i.e. =. E r ds : Power consuption of th type of router line card. E t: Power consuption of a transponder. E e: Power consuption of an EDFA. L n: Distance between node and node n in physical topology. A n: The nuber of EDFAs that should be placed in line on each physical lin (, n). Specifically, An L n / S 1 2, where S is the span distance between two adjacent EDFAs (the value of 80 is coon in practice and used in siulations). 2 counts for post- and preaplifiers at fiber ends. Δ i: The nuber of ports used to aggregate low-rate traffic fro low-end routers at node I (see figure. 1). P : The nuber of ports contained in the th type of router line card. W: Maxiu nuber of wavelengths per fiber. B: Bit rate per wavelength channel. Scenario I: ulti-hop lightpath bypass strategy Decision variables: : The aount of traffic deand between node pair (s, d) that traverses virtual lin (i, j). w n, w : The aount of traffic flow (nuber of wavelengths) between node pair (i, j) at wavelength w that traverses physical lin (, n). C w : Traffic flow (nuber of wavelengths) passing through virtual lin (i, j) at wavelength w. C : Total traffic flow passing through virtual lin (i, j). f n : Nuber of fibers on physical lin (, n). Y i : Nuber of th type of router line cards deployed at node i. Objective: Miniize Subject to: Er Yi Et C i N T i N j N : i j E A f e n n N nn (1) P Yi i C i N (2) T j N : i j j i j N : i j j N : i j if i s if i d s, d, i N : s d 0 otherwise sn dn : (3) C B, i j N : i j (4) nn w n, w wn, w nn Cw if i Cw if j, i j, N, w W : i j 0 otherwise i N j N : i j n, w n,, (5) w f N n N ww (6) Cw C, i j N : i j (7) ww

4 Objective (1) is defined to iniize the overall networ power consuption. The first ter coputes total power consuption by IP routers. The second ter sus up power consuption of all transponders connected to OXCs and the last ter calculates total power consuption of pre-, post- and inline optical aplifiers. Constraint (2) ensures that router line cards at each node have sufficient ports to accoodate IP traffic. Constraint (3) reflects traffic flow conservation at each node. Constraint (4) is included to dedicate enough virtual lin capacity to support all traffic deands that use the lin. Constraint (5) aintains flow conservation and wavelength continuity over a lightpath at optical layer. Constraint (6) prevents fro wavelength channel collision at every fiber lin. Finally, constraint (7) counts total aount of traffic flow over each virtual lin. Scenario II: direct lightpath bypass strategy Decision variables: C : Nuber of wavelength channels between node pair (s, d) that carry traffic deand. C w : Nuber of wavelength channels between node pair (s, d) on wavelength w. C n, w : Nuber of wavelength channels between node pair (s, d) on wavelength w that traverses physical lin (, n). f n Y i : Nuber of fibers on physical lin (, n). : Nuber of th type of router line cards deployed at node i. Objective: Miniize Subject to: nn Er Yi Et C i N T sn dn : E A f e n n N nn (8) P Yi i C i N (9) T j N : i j C B s, dn : s d (10) C n, w Cn, w nn Cw if s Cw if d s, d, N, w W : s d 0 otherwise sn dn : n, w n,, C f N n N w W (12) Cw C s, d N : s d (13) ww Constraint (9) is siilar to constrain (2). Constraint (10) is included to dedicate enough wavelength capacity at every node to support all traffic deands of that node. Constraint (11) aintains wavelength flow conservation and continuity over a lightpath between a pair of source-destination node. Constraint (12) prevents fro wavelength channel collision at every fiber lin. Finally, constraint (13) counts total nuber of wavelengths between an (s, d) pair. IV. HEURISTIC ALGORITHMS The preceding ILP forulation becoes coputationally intractable even for ediu-sized networs when fiber channel capacity grows beyond 4 ~ 8 wavelengths. Heuristic algoriths have been extensively studied to tacle VTD and RWA optiization probles. For the case in hand, two heuristics corresponding to the above design schees were developed toward iniizing energy consuing coponents. Flowchart of the ulti-hop bypass design schee is shown in Fig. 2. First, the sub-wavelength part of every traffic deand is extracted and stored for traffic grooing in the latter stage. Since wavelength granular part of every deand pair cannot be aggregated with other traffic deands, we try to carry it in a single-hop direct lightpath fashion in the first round. This proceeds as an attept to eliinate interediate optical regenerators thereby iniizing router line cards which are the ajor energy consuing coponents. The RWA heuristic was constructed based on -shortest path routing cobined with First-Fit wavelength assignent in an effort to iniize both nuber of inline aplifiers as well as required nuber of fibers per physical lin for a given W. The next round was crafted to exploit benefit of traffic grooing capability over ulti-hop virtual lins. For each reaining sub-wavelength traffic deand, it tries to find virtual path with iniu axial traffic load to enhance load balancing thus iproving resource utilization. As the new traffic pattern was developed after the copletion of VTD design stage, RWA heuristic is invoed again to decide optial physical resource allocation. The devised algorith wors for direct bypass strategy as well where whole traffic deand volue of every node pair is copletely processed in the first round without any concern to other deands. So every request was ipleented as ultiple direct lightpaths over a single virtual in. (11)

5 V. SIMULATION RESULTS To evaluate the perforance of the fore entioned design scenarios, three test networs were considered as shown in Fig. 3. The first one is conventionally chosen as a typical topology referred in any papers. The second one is a 15-node 21-lin NSFNET networ and the third one is 24-node 43-lin USA bacbone IP networ (USNET in short). The physical length of every lin is indicated just close to it in iloeters unit. Additionally, the following inputs were supplied to the odel: 1) The traffic deand between each pair of nodes was randoly generated with unifor distribution over the range [0, 2X] Gb/s where the average deand was taen fro preset values X {20, 40,...,140}. 2) The axiu nuber of wavelength channels in each fiber is taen fro the set W {2, 4,8,16} depending on the purpose of study and transission capacity of each wavelength channel is 40 Gb/s. 3) The energy consuption of each type of router line card is taen fro [6] to be: L_TYPE1 = 580 W, L_TYPE2 = 1000 W, and L_TYPE4 = 2000 W. Moreover, according to [7] each WDM transponder consues around 70 W, and each EDFA consues 10 W. Fig. 2. Flowchart of translucent design schee (a) n6s (b) NSFNET (c) USNET Fig. 3. Test networs

6 Fig. 4(a) shows the variation of iniu power consuption of n6s8 networ versus average traffic intensity for different design strategies when the axiu nuber of wavelengths per fiber is set to 8. Fig. 4(b) and (c) depict the sae plot for the NSFNET and USNET networs respectively. In the first two cases we notice better energy perforance of the proposed ulti-hop translucent design copared to the reference opaque ulti-hop lightpath bypass odel. Energy saving is slightly higher for heavy loads and as expected ainly stes fro significant reduction in the nuber of transponders for passing by channels due to the replaceent of DXC with OXC. However, in considering bandwidth utilization of these two schees, it ay be postulated that higher resource requireents for aintaining transparency in the translucent design schee leads inevitably to sacrifice in BW utilization. Relative BW utilization of test networs for different average traffic loads are illustrated in Fig. 5 (a) to (c). For each case, the BW utilization of single-channel direct-bypass networ was taen as a reference and was calculated as ratio of overall networ throughput to total wavelength capacity. Apparently, in both n6s8 and NSFNET networs, relative BW utilization of the proposed ulti-hop translucent design shows alost the sae quantity or even better than the opaque design for all traffic loads. Higher energy consuptions and inferior BW utilization of the direct bypass design schee refers bac to the fact that it requires ore wavelength channels at each node for a given traffic deand owing to the lac of traffic grooing capability and wavelength continuity constraint. As a result higher nuber of IP router ports and inline aplifiers (due to the scarcity of available wavelengths to route a lightpath thus iposing an increase in fiber strands) translates into poor energy perforance. This is the price we should pay to aintain full transparency over whole networ. The above conclusions can be extended to the larger USNET networ since results fro heuristic analysis of the ulti-hop translucent design provide just an upper estiation to exact optial values. In addition, the total nuber of fiber segents which was calculated fro heuristics turned to be an upper approxiation to the optial one thereby values of relative BW utilization of the ulti-hop translucent design in Fig. 5 (c) should be lower than actual ones. Fig.4. Coparison of total power consuption of different design strategies Fig. 5. Coparison of relative BW utilization of different design strategies

7 As a conclusion, the proposed heuristic for the calculation of power consuption of the ulti-hop translucent design obtained satisfactory estiation within 5~7% accuracy and nearly exact results for the case of direct bypass design schee. Perforance of ulti-hop translucent design rendered superior than ulti-hop opaque design when considering both energy-consuption and BW utility factors. The variation of total power consuption with the growing scale of wavelength channel capacity per each fiber strand for an average traffic load of 120 erlangs is depicted in Fig. 6. Although none of ajor energy consuing coponents are directly affected by expanding transission capacity, slow decay of power consuption is attributed to noticeable saving in total nuber of EDFAs which is acquired by scaling down the required fiber strands. Fig. 6. Variation of total power consuption with wavelength capacity expansion for different design schees VI. CONCLUDING REMARKS Design of green optical networs have recently attracted enorous research attitude due to rapid expansion and exclusive role of these networ as the bacbone of next generation Internet. In this paper two design strategies to deploy IP over WDM optical networ based on optical cross-connect switches were introduced and atheatical odels to optiize their energy consuption perforance and proper heuristic algoriths were developed. Energy consuptions for different traffic loads were copared with those of a siilar odel where digital cross-connect switches were eployed instead. Siulation results showed that the proposed ulti-hop translucent lightpath bypass approach achieved better energy perforance than the opaque lightpath bypass design under the sae traffic loads. Direct bypass design approach could also achieve good energy perforance and acceptable BW utilization at higher traffic loads. REFERENCES [1] A. Coiro, M. Listanti, and A. Valenti, "Dynaic poweraware routing and wavelength assignent for green WDM optical networs," in Counications (ICC), 2011 IEEE International Conference on, 2011, pp [2] Y. Wu, L. Chiaraviglio, M. Mellia, and F. Neri, "Poweraware routing and wavelength assignent in optical networs," in Optical Counication, ECOC'09. 35th European Conference on, 2009, pp [3] M. Xia, M. Tornatore, Y. Zhang, P. Chowdhury, C. Martel, and B. Muherjee, "Greening the optical bacbone networ: A traffic engineering approach," in Counications (ICC), 2010 IEEE International Conference on, 2010, pp [4] A. Muhaad, P. Monti, I. Cerutti, L. Wosinsa, P. Castoldi, and A. Tzanaai, "Energy-efficient WDM networ planning with dedicated protection resources in sleep ode," in Global Telecounications Conference (GLOBECOM 2010), 2010 IEEE, 2010, pp [5] Y. Lui, G. Shen, and W. Shao, "Energy-Miniized Design for IP over WDM Networs under Modular Router Line Cards." [6] F. Musueci, M. Tornatore, and A. Pattavina, "A power consuption analysis for IP-over-WDM core networ

8 architectures," Journal of Optical Counications and Networing, vol. 4, pp , [7] G. Shen and R. S. Tucer, "Energy-iniized design for IP over WDM networs," Optical Counications and Networing, IEEE/OSA Journal of, vol. 1, pp , Fariborz Mousavi Madani was born in Shiraz, Iran, on August 23, He received his the B.Sc. degree in electrical engineering fro Shiraz University, Shiraz, Iran in 1987 and his the M.Sc. degree in telecounications fro Sharif University of Technology (SUT), Tehran, Iran in He received his Ph.D. degree in electrical engineering fro University of Toyo, Toyo, Japan in He is currently woring with Departent of Coputer Engineering as a full-tie Assistant Professor at Alzahra University. His research interests are in the areas of Optical Networ Virtualization, Design and Optiization of Elastic Optical Networs, Next-Generation Passive Optical Networs,and Fi-Wi networs as well.