Energy Efficient Ethernet Passive Optical Networks (EPONs) in Access Networks

Transcription

1 NEW ASPECTS of APPLIED INFORMATICS, BIOMEDICAL ELECTRONICS & INFORMATICS ad COMMUNICATIONS Eergy Efficiet Etheret Passive Optical Networks (EPONs) i Access Networks Yig Ya ad Lars Dittma Departmet of Photoics Egieerig Techical Uiversity of Demark Lygby, Demark yiya@fotoik.dtu.dk Abstract: As cocers about eergy cosumptio grow, the power cosumptio of the EPON becomes a matter of icreasig importace i the heterogeeous etworks. I respect of eergy efficiecy, the curret stadard has o maagemet protocols aimig to reduce power cosumptio i EPONs. To icrease eergy efficiecy while satisfyig diverse QoS requiremets, the sleep mode operatio is itroduced i a Optical Network Uit (ONU) ad a suitable sleep/wakeup time schedule is determied at the Optical Lie Termial (OLT). The schedulig algorithms are tightly coupled with the upstream badwidth allocatio ad dowstream trasmissio profile. Simulatio results show that a well desiged schedulig disciplie is essetial to achievig sigificat eergy savig while meetig the delay costrait. Key Words: EPON, schedulig algorithms Itroductio The future etwork architecture comprises of both fixed ad mobile etworks. Itegratio of optical ad wireless etworks combies their advatages i terms of high capacity, flexible structure, ad ubiquitous access. Etheret Passive Optical Network (EPON) is a cadidate i the optical access regime, which provides diverse commuicatio services to the frot-ed wireless etworks. Curret the issue of eergy efficiecy has raised attetios i the research of the future access etworks. Cosiderig the itegrated optical ad wireless etworks, the power cosumptio of the access etwork cotiues to rise i both domais, due to the expasio of etwork coectivity ad the icrease of data rate. The curret EPON stadard has o maagemet protocols aimig to reduce power cosumptio. I this paper, we ehace the existed EPON protocol with schedulig algorithms for eergy efficiecy. A typical EPON is a Poit-to-Multipoit (PMP) etwork with a tree based topology, where a OLT coects multiple ONUs via optical liks. The OLT plays a role of distributor, arbitrator ad aggregator of traffic. I the upstream directio (from ONUs to the OLT), multiple ONUs share a sigle lik ad traffic may collide. The OLT distributes the fiber capacity usig a upstream badwidth arbitratio mechaism to avoid collisios. I the dowstream directio (from the OLT to ONUs), data frames are broadcasted to all ONUs. ONUs filter ad accept data that are addressed to them. However, ONUs have to costatly liste ad examie dowstream traffic, which results i wastig sigificat eergy i the ONU. Show i Fig., i the traditioal EPON, ONUs cosume eergy to keep active whe there is either upstream or dowstream traffic. As a result, miimizig power cosumptio is a major factor drivig the desig of EPON devices ad of the protocols therei. A effective Eergy Maagemet Mechaism (EMM) that schedules the sleep mode period to ONUs is a key to coserve power. To reduce power cosumptio, ONUs are desiged to eter sleep mode whe they do ot eed to either receive or sed traffic. Durig a sleep period, ONUs tur off the trasceiver i order to save eergy. I case there is icomig data for a sleepig ONU, data is queued i buffers at the OLT. Obviously, it is better to keep a ONU to stay i sleep mode as much as possible to coserve its eergy. However, a power maagemet mechaism with efficiet schedulig for sleep ad wake-up periods amog multiple ONUs is a challegig task. The sleep period should be carefully scheduled, so target ONUs ca wake up ad complete trasmissio without violatig QoS requiremets. Several studies [,,, 4,?, 6] have bee proposed to aalyze the power cosumptio for EPON [][], while applyig the approach of allowig ONUs to sleep mode. However, there have bee few studies focusig o the protocol desig for supportig sleep mode ONUs i EPON. To implemet EMM i EPON, the legacy cotrol scheme requires modifica- ISSN: X 5 ISBN:

2 NEW ASPECTS of APPLIED INFORMATICS, BIOMEDICAL ELECTRONICS & INFORMATICS ad COMMUNICATIONS OLT uplik k k k dowlik :N splitter ONU ONU it costatly stays awake ad cosumes power, i.e., ever goes ito sleep mode. I EMM mode, ONUs receives the sleep ad awake period assigmets from the OLT, which is calculated usig either a Upstream Cetric Schedulig (UCS) algorithm or a Dowstream Cetric Schedulig (DCS) algorithm. Figure : EPON system. k k k ONU k tios ad extesios. Moreover, we discuss the tradeoff betwee eergy cosumptio ad etwork performaces. The remaider of this paper is orgaized as follows. We first give a detailed descriptio of the desig of EMM with two differet dowstream schedulers i Sectio. Simulatio eviromets ad results are outlied ad discussed i Sectio. Fially, coclusios is draw i Sectio 4. Eergy Maagemet Mechaism. System Model I this paper, we cosider a EPON system cosistig of a OLT, : K splitter ad multiple ONUs. TDMA is used i the physical layer where badwidth is divided i time slots. Each ONU maitais a upstream buffer ad seds upstream data to the OLT durig assiged time slots. I the dowstream directio, whe the arrival rate at the OLT exceeds the output data rate, data are queued i the OLT ad trasmitted whe dowstream badwidth is available.the power cosumptio value i the awake state icludes eergy cosumed i listeig to the OLT ad i receivig or trasmittig data. Assumig that the overall trasmissio period is divided ito N time slots, ONUs are either i awake mode or i sleep mode durig the time slot. The total eergy expediture model is formalized as follows: E = i= = T i [s i P awake + ( s i ) P sleep ] () The implemetatio of EMM is complied with EPON MAC protocol, Multipoit Cotrol Protocol (MPCP) [7, 9]. The OLT is i full cotrol of the badwidth allocatio i both dowstream ad upstream. A ONU ca associate with the OLT either i ormal mode, referred to as Power Igorig Scheme (PIS), or i EMM mode. Whe a ONU is i ormal mode,. Upstream Cetric Schedulig (UCS) The mai idea of UCS scheme is that the OLT assigs the awake period to ONUs accordig to their correspodig upstream allocatio. The OLT grats the upstream badwidth by pollig each ONU. Durig the grated upstream subframe period, the ONU is awake. Oce a ONU trasits ito the awake state, the OLT with UCS algorithm oly trasmits dowstream packets to the awake ONU, ad queues those packets destied for sleep ONUs ito a buffer. As a example, we cosider a system of a OLT ad three ONUs for two upstream trasmissio periods. For more ONUs ad trasmissio periods, the same logic ca be applied. Fig. shows the process of UCS protocol. I this work, the t deotes for the istat time ad T represets for a period. The OLT assigs ) the start trasmissio time (t starti ) ad grated badwidth (BWi ) for allocatig upstream badwidth; ) the sleep time (t sleepi ) ad the wakeup time (t wakei ) for assigig sleep period. As show i Fig., the ONU wakes up at t 0 ad receives sleep mode GATE message (G s ) at the time t. After learig the grated upstream subframe period (T sp ul ), ONU geerates REPORT message (R ) ad starts upstream trasmissio (d ul ) complyig with the assigmet. Durig T sp ul, the OLT derives dowstream data (d dl ) from the subqueue for the ONU ad trasmits them to the ONU. Notice that the data d dl represets either oe data packet or a series of itegrated data packets. The start time of sleep mode (t sleep ) for ONU is assiged so that the ONU eters ito sleep mode immediately whe the upstream subframe period is completed at t. The calculatios of upstream trasmissio period ad the time to tur ito sleep mode are listed i Equatio ad Equatio. Tsp ul,i = BW i () R o t sleep,i = t start,i + T sp ul,i () where BWi is the allocated upstream badwidth for the i th ONU durig the th cycle. R o is the trasmissio rate of the optical upstream ad T g is the guard time betwee two successive upstream trasmissios. The wakeup time (t wakeup ), which is same ISSN: X 54 ISBN:

3 NEW ASPECTS of APPLIED INFORMATICS, BIOMEDICAL ELECTRONICS & INFORMATICS ad COMMUNICATIONS ONU R d dl ONU R R 4 d dl d dl ONU T sp-dl R d dl ONU d dl R d dl ONU R d dl ONU R ddl t 0 t start t T sp-ul t (t sleep ) T cycle Tov t (t start ) t 4 t t t t 4 t 5 t 6 t 7 t 8 Figure : Sleep mode operatio with Dowstream Cetric Schedulig (DCS) scheme. Figure : Upstream Cetric Schedulig (UCS). as the legth of sleep period, is calculated based o the period before the ONU is polled agai (T cycle ). I the Fig., the ext wakeup time for the ONU is t. The value of wakeup time is computed at the OLT ad assiged to each ONU. The pollig cycle is computed usig Equatio 4. K Tcycle,i = (Tsp ul,i + T g) = i= ( BW i + T g ) R o i= (4) After a period of T cycle, the iterval betwee two adjacet pollig messages, a ONU is polled agai at t 4 (t + T cycle ). The calculatio of ONU wakeup time eeds to take the overhead period ito accout due to the time of recoverig the OLT clock ad retrievig the etwork sychroizatio. Durig the observatio period, the total awake time for each ONU is the sum of allocated upstream time slots ad a ONU eters the sleep mode otherwise. Durig the subframe period, the ONU i trasmits upstream data i ad receives dowstream data d dl i, withi the grated time slot. The total eergy cosumed by the ONU i is illustrated i Equatio 5: E UCS = + i= = i= = [Tsp ul,i + T ov] P awake [Tcycle,i T sp ul,i T ov] P sleep (5) The UCS based scheduler is simple because the sleep period is determied based o the upstream trasmissio. A OLT with the UCS based scheduler uses the awake ONU, which is assiged to the upstream trasmissio as destiatio to retrieve buffered data. However, the performace of dowstream data latecy ad badwidth utilizatio may ot be satisfied due to the depedecy o the upstream subframe period, the upstream pollig sequece, ad the total umber of active ONUs.. Dowstream Cetric Schedulig (DCS) The secod schedulig policy preseted i this paper is that the OLT stores dowstream traffic i a First- I First-Out (FIFO) buffer ad the ONU has to be awake ad receive dowstream traffic wheever the OLT seds oe. The awake periods are assiged to favor both upstream ad dowstream traffic. The DCS scheme is illustrated i Fig.. The sleep mode GATE message, i, is used for both upstream badwidth allocatio ad sleep period assigmet. The upstream trasmissio period is calculated usig the same equatios as i the UCS scheme. For example, the at time t idicates that the ext pollig time is at time t 8 ad the ONU eeds to wake up at time t 7. I the dowstream, the OLT serves data i a first-i first-out order. For istace, show i Fig., durig the upstream subframe,, the OLT seds packets to both ONU (data d dl ) ad ONU (data d dl ). As show i Fig., the admissio iformatio for both upstream ad dowstream trasmissio is otified by the sleep mode GATE message. The iforms ONU the allocated upstream trasmissio of ad assiged sleep period durig t to t 7. After trasmittig d dl to the ONU, the OLT gets data d dl from the head of its dowlik queue ad seds to the ONU together with. Sice there is data d dl i the buffer, the ONU is otified to wake up at t 4 istead of t 7. The sleep period is assiged if there is either upstream or dowstream trasmissio scheduled. If the OLT has queued data for the ONU, the wakeup time for the ext data ca be calculated. For example, the period betwee t ad t 4 is the idle period for ONU. Otherwise, the OLT seds a message to iform the ONU of remaiig i awake mode i ISSN: X 55 ISBN:

4 NEW ASPECTS of APPLIED INFORMATICS, BIOMEDICAL ELECTRONICS & INFORMATICS ad COMMUNICATIONS t sleep0 (t sleep ) t sleep t wakeup tsleep t wakeup t wakeup0 (t wakeup ) t sleep4 ONU i tx rx T ov T sp-ul i T sp-dl i T sp-dl i T ov T ov T ov G 4 s T sp-dl i T sp-dl i T sp-ul i t GATE0 GATE GATE GATE GATE4 Figure 4: Dowstream trasmissio i the sleep period model. order to avoid missig ay dowstream traffic. I the followig, the assigmet of sleep period is discussed i details. Uder the coditio that the dowstream traffic termiates the sleep mode ad the OLT assig the sleep period for the i th ONU, we distiguish four possibilities as show i Fig. 4. The sleep period is determied by favorig both the successful receptio of upstream ad dowstream data. Accordigly, we deote as the GATE cotrol message carryig the iformatio of sleep period, such as the start time of sleep period (t sleep ) ad the wakeup time (t wakeup ). Let T sp ul i ad T sp dl i be the th subframe period of uplik ad dowlik trasmissio, respectively. I additio, the T ov period represets a overhead time for clock recovery ad sychroizatio.. Case0: GATE0 is used to iform the allocated upstream badwidth for the ONU i. Because the OLT has full kowledge about the upstream badwidth allocatio, the sleep iterval is determied, icludig both the sleep time (t sleep0 ) ad the wakeup time (t wakeup0 ).. Case: The trasmissio of dowstream data (T sp dl i ) is completed withi the allocated upstream subframe period. If there is other queued data i the OLT, such as the payload with GATE, the sleep period is assiged as same as i Case0. If the ext received data is the payload with GATE, the time to wake up is reassiged as same as t wakeup. If there is o more queued data i the OLT for the ONU i, the origial assigmet, t sleep0, is removed, because ONU i should keep awake i order to avoid missig future arrival data.. Case: I this case, the dowstream data (T sp dli ) ca ot be fiished before the start time of the sleep period as assiged i Case0 ad Case. Therefore, the start time of sleep period is postpoed to t sleep. The OLT examies its dowstream queue ad schedules the trasmissio of the ext dowstream data (T sp dli ) for the i th ONU. Moreover, the wakeup time (t wakeup ) is calculated i order to esure a successful trasmissio. 4. Case: I this case, there is dowstream data received durig the sleep iterval. I GATE cotrol message, the ew time of eterig the sleep mode is updated, t sleep, which is calculated based o the dowstream subframe period (T sp dli ). 5. Case4: As showig i the last GATE4 i this figure, there is dowstream data arrived durig the sleep iterval ad lasted till the ext upstream subframe period. Upo the sleepig period is completed, the ONU trasits ito the awake mode ad will receive the GATE4 message with the iformatio of upstream badwidth allocatio, such as the start time ad legth of T 4 sp dli. Thus, the GATE4 message cotais badwidth assigmets for both upstream ad dowstream subframe period. Compared to the UCS algorithm, the OLT checks the available data i the buffer ad update the sleep period for the destiatio ONU with a sleep mode GATE message. The wakeup time is precisely calculated ad assiged, so that the ONU ca be active to carry out the ext upstream or dowstream trasmissio. Sice the operatios of the above schedulig mechaism requires the OLT to locate the ext packet i the buffer i order to calculate the wakeup time, ONUs which have o more queued packets caot eter the sleep mode. I this case, the OLT assigs the sleep period as zero. The awake period for upstream trasmissios (T awake ul ) ad dowstream trasmissios (T awake dl ) are defied to calculate the total eergy cosumptio i the DCS algorithm. First, we compute the awake period ad sleep period i the upstream directio (show i Equatio 6 ad Equatio 7), which is similar to Sectio.. T awake ul,i = T sp ul,i + T ov (6) T sleep ul,i = T cycle,i T sp ul,i T ov (7) ISSN: X 56 ISBN:

5 NEW ASPECTS of APPLIED INFORMATICS, BIOMEDICAL ELECTRONICS & INFORMATICS ad COMMUNICATIONS Next, assumig that there are M dowstream trasmissios to the i th ONU. For the dowstream, the awake period is calculated (i Equatio 8) differetly i each case metioed as Fig. 4. I Case, ONU i is i awake state, so that the awake period for receivig dowstream data is zero. From Case to Case4, if the time for wakig up ad sleepig is assiged, the period that the ONU has to wake up from its sleep mode is calculated as the iterval betwee t sleep ad t wakeup. Illustrated i Equatio 9, the sleep period is the upstream sleep period mius the awake period used for the dowstream trasmissio, which occurs durig the upstream sleep period. T awake dl,i = M = m= M m= T m awake dl,i 0, if Case t m sleep tm sleep, if Case t m sleep tm sleep, if Case t m sleep0 tm sleep, if Case4 (8) M Tsleep dl,i = T sp ul,i Tawake dl,i m (9) m= After aalyzig the active behavior of a ONU i both the upstream ad dowstream trasmissios, the total awake ad sleep periods are cocluded as Equatio 0 ad Equatio : T awake total,i = T awake ul,i + T awake dl,i (0) T sleep total,i = T sleep dl,i () The total eergy cosumed is calculated i Equatio. The DCS sleep mode scheduler trasmits dowstream traffic i a flexible way, ulike i the UCS that oly the active ONU scheduled with a upstream trasmissio period ca receive data from the OLT. The OLT tries to schedule the queued dowstream traffic i a way to miimize the delay. The UCS is simple where the sleep period ad wakeup time is determied oly by the upstream badwidth allocatio. O the other had, the DCS scheduler requires to keepig track of both dowstream ad upstream trasmissio widows. E DCS = + i= = i= = [Tsp ul,i P awake] [Tsleep total,i P sleep] () Simulatio Results I this sectio, we provide a performace aalysis as described i Sectio. The performace evaluatio is carried out by meas of OPNET simulator [8]. EPON system cosists of a OLT ad K ONUs (K=6 or ). The optical lik rate is Gbps for both upstream ad dowstream trasmissio. The guard time betwee two cosecutive trasmissio slots is 5 us. Traffic is geerated followig Poisso distributio ad the legth of packets is geerated idepedetly betwee 64 bytes to 00 bytes. Destiatios of dowstream traffic are uiformly distributed. A. Eergy cosumptio: The average awake time i ONUs is used as a merit for eergy efficiecy performaces, which is computed as the ratio of the awake time (Tawake i ) to the total observatio period (Tall i ). The less time a ONU is awake, the less eergy a ONU cosumes. T sp ul,i = K i= T i awake K i= T i all () Fig. 5 shows the eergy cosumptio, represeted by the ONU awake time. I the case of PIS, ONUs costatly cosumes eergy (00% of the observatio period). Whe the EMM is eabled i the EPON system, the awake time maitais at a low average percetage value if the UCS scheme is applied. The active period is decided by allocated upstream trasmissio periods i the UCS case. Whe each ONU is allocated with fixed amout of upstream badwidth, the awake time is also fixed. O the other had, the eergy cosumptio i the DCS case varies whe the traffic load chages. Uder the DCS case, ONUs wake up ad commuicate with the OLT for either upstream or dowstream traffic. Whe arrival traffic is low, the awake time of DCS is slightly icreased. Whe the arrival traffic rate is high, the awake time icreases ad close to the level as i the PIS case. B. Queueig delay: Show i Fig. 6, the queuig delay is measured i the dowstream data buffer at the OLT. Packets are queued whe the dowstream badwidth is ot available. The average delay of the EMM DC scheme is better tha that of the UCS scheme. With UCS scheme, dowstream packets have to wait for their awake period i the OLT buffer. Additioal message overhead: I the UCS case, the sleep mode GATE message is used to poll ONUs, grat upstream badwidth, ad iform assiged sleep period. The Gs is geerated ad set to ONUs i the same meas as the origial MPCP case. However, i the DCS case, message is trasmitted together with each dowstream packet, which results i amout of cotrol message overhead. Therefore, i ISSN: X 57 ISBN:

6 NEW ASPECTS of APPLIED INFORMATICS, BIOMEDICAL ELECTRONICS & INFORMATICS ad COMMUNICATIONS Averagy percetage of ONU awake time (%) ONU: EMM-UC (TDM) 6 ONU: EMM-DC (TDM) ONU: EMM-UC (TDM) ONU: EMM-DC (TDM) PIS 0 0,0 0, 0, 0, 0,4 0,5 0,6 0,7 0,8 0,9,0 ONU Dowstream Trasmissio Rate (Gbps) Total umber of trasmitted sleep mode GATE messages bits 400 bits 400 bits 400 bits 4400 bits 5400 bits 6400 bits 7400 bits 8400 bits 9400 bits 0 0,0 0, 0,4 0,6 0,8,0, ONU Dowstream Trasmissio Rate (Gbps) Avg Queue Delay i ONU.mea (ms) Figure 5: Awake time aalysis. 6 ONU: EMM-UC (TDM) 6 ONU: EMM-DC (TDM) ONU: EMM-UC (TDM) ONU: EMM-DC (TDM) PIS 0 0,0 0, 0, 0, 0,4 0,5 0,6 0,7 0,8 0,9,0 ONU Dowstream Trasmissio Rate (Gbps) Figure 6: Queueig delay aalysis. this test case, we simulate a etwork sceario with 6 ONUs ad focus o EMM DCS scheme. Fig. 7 shows the umber of trasmitted as a fuctio of icomig packet sizes. Uder a certai iput data rate, the larger the data size, the less trasmitted cotrol message. With respect to badwidth utilizatio, icreased umber of message itroduces high value of cotrol overhead, therefore, results i low badwidth utilizatio. 4 Coclusio The proposed EMM aims to reduce power cosumptio ad maitai the etwork capacity. For this purpose, we assess the system performace accordig to the power cosumptio, the average queuig delay, ad the additioal message overhead. As show from the simulatio, the eergy cosumptio of EPON system is reduced by EMM ad the trade-off betwee power savig ad etwork performaces is aalyzed. Ackowledgemets: This work is supported by the Daish Natioal Advaced Techology foudatio project Stadards Agoostic Itelliget Radio Systems for the High Capacity Wireless Iteret. Refereces: Figure 7: Additioal overhead aalysis. [] J. Baliga, R. Ayre, K. Hito, W.V. Sori ad R. S. Tucker, Eergy Cosumptio i Optical IP Networks, Joural of Lightwave Techology (JLT) vol.7, 009, pp [] T. Smith, R. S. Tucker, K. Hito ad A. V. Tra, Implicatios of Sleep Mode o Activatio ad Ragig Protocols i PONs, st Aual Meetig of the IEEE Lasers ad Electro-Optics Society (LEOS) 008, pp [] S. Wog, L. Valcareghi, S. Ye, D. Campelo, S. Yamashita ad L. Kazovsky, Sleep Mode for Eergy Savig PONs: Advatages ad Drawbacks, Globlecom 09 Secod Iteratioal workshop o Gree Commuicatio 009. [4] R. Kubo, J. Kai, Y. Fujimoto, N. Yoshimoto ad K. Kumozaki, Proposal ad Performace Aalysis of a Power-Savig Mechaism for 0 Gigabit Class Passive Optical Network Systems, Mobile Networks ad Applicatios vol. 009, pp [5] EPON Powersavig via Sleep Mode, IEEE 80.az Meetig 008. [6] I. Cerutti, L. Valcareghi ad P. Castoldi, Power Savig Architectures for Uidirectioal WDM Rigs, Mobile Networks ad Applicatios vol. 009, pp.. [7] K. Gle, M. Biswaath ad P. Gerry, IPACT: a dyamic protocol for a Etheret PON (EPON), IEEE Commuicatio Magazie vol.40 00, pp [8] OPNET Modeler 4.5, [9] IEEE 80.ah Etheret i the First Mile Task Force, ISSN: X 58 ISBN: