QoS-aware energy-saving mechanism for hybrid optical-wireless broadband access networks

Transcription

1 DOI.07/s ORIGINAL PAPER QoS-aware energy-savng mechansm for hybrd optcal-wreless broadband access networks Ruyan Wang 1 Ale Lang 1 Chao Zhou 1 Dapeng Wu 1 Hong Zhang 1 Receved: 5 September 2016 / Accepted: 1 February 2017 Sprnger Scence+Busness Meda New York 2017 Abstract Hybrd optcal-wreless broadband access network (HOWBAN) takes full advantage of the hgh capacty and relablty of the passve optcal network and the flexblty, ubquty of the wreless network. Smlar to other access networks, the ssue of hgh energy consumpton s a great challenge for HOWBAN. In HOWBAN, optcal network unts (s) consume a great amount of energy. The sleep of s can greatly mprove the energy effcency of HOWBAN. However, the qualty of servce (QoS) wll be decreased whle the packets are watng n s and optcal lne termnal. In ths paper, we propose a QoS-aware energy-savng mechansm. A dynamc bandwdth allocaton mechansm s desgned to guarantee the QoS, where dfferent prortes are consdered. Meanwhle, we employ dfferent sleep strateges by takng dfferent prortes tolerant delays nto account to prolong the sleep tme of s. Then, based on the evaluaton of packet delay, the optmal sleep parameter s derved to maxmum the energy effcency. In addton, a load balancng and resource allocaton mechansm s adopted n the wreless doman to reduce the delay and congeston caused by s sleep. Results show that the proposed mechansm can effectvely mprove the energy effcency and meet the QoS requrements of packets. Keywords Passve optcal network QoS-aware Energysavng Wreless mesh network Resource allocaton B Dapeng Wu wudapengphd@gmal.com 1 Chongqng Unversty of Posts and Telecommuncatons, Chongqng , Chna 1 Introducton Passve optcal network (PON) has the advantages of hgh bandwdth, long dstance and hgh relablty, but t s not flexble and ts deployment cost s hgh [1]. On the contrary, wreless mesh network (WMN) has the advantages of promsng flexblty and low cost, but ts bandwdth capactyslow [2,3]. HOWBAN combnes the advantages of PON and WMN, thus becomes an mportant soluton to the nextgeneraton access networks. Fgure 1 presents a HOWBAN archtecture that ntegrates Ethernet PON (EPON) wth the WMN. Each PON has a unque optcal lne termnal (OLT), whch s located at the Central Offce (CO) and connected to multple optcal network unts (s). On the other hand, the WMN s composed of several Mesh Ponts (MPs) [4]. The MP drectly connected to the s called wreless gateway, whch completes the packet transmsson between the wreless network and the PON. In the upstream drecton, the users access the network through the MPs and users packets are forwarded to the s along wreless lnks. In the downstream drecton, the packets from the Internet are sent to the OLT, and then are broadcasted to the s. Consequently, the packets are routed to the users by MPs [5]. Statstcs show that the energy consumpton of nformaton and communcaton technology (ICT) accounts for about 8% of the world s total energy consumpton [6,7]. Meanwhle, as an mportant part of the entre network, the access network consumes about 70% of the ICT energy [8,9]. However, ts equpment s utlzaton rate s less than 15% []. Wth traffc s explosve growth, the huge energy consumpton wll restrct HOWBAN s large-scale applcaton. The sleep of s can effectvely mprove the energy effcency of HOWBAN, but t wll lead to the degradaton of QoS due to the ncrease of packets queung, and reroutng delay. There-

2 Gateway Internet OLT OLT spltter MP CO Fg. 1 Archtecture of HOWBAN fore, t s a great challenge to maxmum the energy effcency when dfferent QoS requrements are met. From the perspectve of traffc characterstc, the packets of HOWBAN manly consst of two types, namely hgh-prorty packets and low-prorty packets. Wheren the hgh-prorty packets delay requrements are hgher, thus the long sleep tme of wll lead to a sharp declne of QoS performance. On the contrary, low-prorty packets are not senstve to delay, so longer sleep tme of wll mprove the energy effcency and won t degrade the QoS performance. Obvously, the sleep of has dfferent effects on dfferent prortes because of ther dfferent delay tolerances. Therefore, t s necessary to desgn the optmal sleep tme to mprove the energy effcency based on dfferent prortes delay tolerances. In addton, the connecton status between the and the wreless gateway changes dynamcally due to the s swtchng between sleep state and actve state. In other words, the sleep of wll break the connecton. Then, the upstream packets cannot reach the and are buffered n the WMN, whch wll degrade the QoS performance of hgh-prorty packets sgnfcantly. Therefore, the connecton status and lnk qualty should be fully consdered to guarantee hgh-prorty packets delay requrements by selectng another actve to reroute the hgh-prorty packets. Currently, researchers have proposed several energysavng mechansms. Reference [11] proposes an energysavng mechansm based on dynamc bandwdth allocaton, where the OLT allocates uplnk slots to the and the sleeps n other tme slots. However, the mechansm does not consder packets dfferent prortes and the delay of hgh-prorty packets s large. Reference [12] proposes a loadaware sleep mechansm. Whenever the load s less than a threshold and the remanng load can be transferred to other s, the sleeps for a perod. However, the mechansm does not consder users QoS performance. In addton, the transton ncreases the packet delay. Reference [13]proposes a perodc sleep energy-savng mechansm. The OLT calculates an optmal wake-up tme and sends t to the. Then, the sends a confrmaton message to the OLT and sleeps. Nevertheless, the energy effcency s low. Reference [14] extends EEE packet coalescng by consderng QoS prortes and mproves the QoS support for vdeo delvery by proposng a green QoS dfferentated routng strategy. More specfcally, packets of all lnks wll be frstly assembled at the node and each tme when hgh-prorty packets arrve, the coalescng perod wll be nterrupted and all the watng packets wll be sent out n the next transmttng perod. To better guarantee QoS for vdeo traffc, the capacty and delay-aware routng (CaDAR) scheme s adopted to route hgh-prorty traffc flows, whereas a concentraton routng strategy s used to reroute low-prorty traffc flows. Reference [15] proposes a green mechansm wth dfferent classes of servce. The OLT assgns tme slots to the dependng on the class of servce and the sleeps n other tme slots. However, such mechansm cannot take full advantage of exstng connectons between other actve s and wreless gateways when the s sleepng. Therefore, the energy effcency s also low. To solve the above problems, a QoS-aware energy-savng mechansm (QESM) s desgned. A dynamc bandwdth allocaton mechansm s desgned by takng dfferent prortes nto account to guarantee the QoS. Then, consderng dfferent tolerant delays of dfferent prores, we desgn dfferent sleep strateges to prolong the sleep tme of s. In order to maxmum the energy effcency, the optmal sleep parameter s obtaned based on analyss of the packet delay. Meanwhle, a load balancng and resource allocaton mechansm

3 s desgned n the wreless doman to avod the degradaton of QoS performance due to the sleep of s. Eventually, the network not only meets the QoS of packets, but also acheves the hghest energy effcency. Our contrbutons are summarzed as follows: Frstly, we desgn a dynamc bandwdth allocaton mechansm to guarantee dfferent QoS requrements and mprove the bandwdth utlzaton where dfferent prortes are consdered. Secondly, based on tolerant delays and analyss of the packet delay, the optmal sleep tme s derved to prolong s sleep tme, further mprove the energy effcency. Lastly, we propose a load balancng and resource allocaton mechansm to reduce hgh-prorty packets delay and s congeston due to s sleep. The remander of the paper s structured as follows. The proposed mechansm s descrbed n greater detal n Sect. 2. We evaluate the performance of our proposed mechansm, and compare t wth some of prevous works n Sect. 3. Fnally, Sect. 4 concludes the paper. 2 QoS-aware energy-savng mechansm As known, there are dfferent servces n the network, such as vdeo on demand, voce over Internet protocol and e- mal. As a result, the packets n the network have dfferent prortes and QoS requrements. Although researches have proposed many mechansms to mprove the energy effcency of the HOWBAN, they seldom consder dfferent QoS requrements smultaneously. Therefore, the QoS-aware energy-savng mechansm s proposed to mprove the energy effcency when dfferent QoS requrements are met. The proposed energy-savng mechansm conssts of three parts: dynamc bandwdth allocaton, determnaton of the optmal energy effcency, load balancng and resource allocaton. 2.1 Dynamc bandwdth allocaton In EPON, the OLT allocates bandwdth (tme slots) to each by pollng them. Durng the granted tme slots, s transmt or receve packets, whereas outsde the granted slots, s sleep to save energy. However, as mentoned above, long sleep tme wll ncrease packet delay and short sleep tme wll ncrease the energy consumpton due to frequent wake-up. Thereby, to mprove energy effcency, a reasonable bandwdth allocaton mechansm s desgned to reduce the swtchng frequency and ncrease the sleep tme. When completes data transmsson wthn the granted tme slots, t sends a report message to the OLT, whch contans the queue statuses of hgh-prorty and lowprorty packets. After recevng all s report messages, the OLT derves the granted slots for all s n the next pollng cycle. The pollng cycle T cycle conssts of granted slots and guard slots, can be expressed as follows: T cycle = N (Tgrant + T g) (1) =1 where N s the number of s, Tgrant s s granted slots, and T g s the guard slot. Long sleep tme wll ncrease the watng delay and degrade QoS performance of hgh-prorty packets due to ther senstvty to delay. On the contrary, low-prorty packets can tolerate some delay, but short sleep tme wll lead to the frequent wake-up of and low energy effcency. For convenence, we call the that has hgh-prorty packets as H, and the that only has low-prorty packets as L. After recevng all s report messages, the OLT can judge whether t s a H or a L. To mprove the energy effcency and meet dfferent prortes QoS, we allow H to sleep wthn one pollng cycle and L to sleep for more than one pollng cycle. In tradtonal mechansms, the needs to exchange messages wth the OLT n each pollng cycle to determne ts sleep and wake-up tme n the next pollng cycle and montor whether there are downstream packets to be receved. In order to reduce the energy consumpton caused by the exchange of messages, the that sleeps contnuously doesn t need to exchange messages wth the OLT n each pollng cycle and the pollng cycle T cycle s set to be constant. In the proposed mechansm, to guarantee hgh-prorty packets QoS, the OLT allocates bandwdth to hgh-prorty packets frstly, then to low-prorty packets. However, when the L that has slept for more than one pollng cycle wakes, t should be allowed to transmt packets. Therefore, to ensure the QoS of the low-prorty packets n the L, bandwdth b k L s allocated to the k-th L. It should be noted that b k L can be known by the OLT from L s report messages. When allocatng bandwdth, f there s no L, the OLT wll not reserve bandwdth b k L. As a result, the average bandwdth allocated to a H s obtaned as Eq. (2). [ ] B avg = 1 N n (Tcycle N T g ) R n b k L (2) 8 k=1 where R s the upstream transmsson rate between OLT and, n s the number of L. Let B H and B L be the -th H s request bandwdth for hgh-prorty queue and low-prorty queue, respectvely. To ensure the farness of each H and avod that other Hs cannot get the bandwdth, the granted bandwdth for H s hgh-prorty queue s as follows: G HF avg B =, f B H B avg B H, f B H < B avg (3)

4 In general, some Hs bandwdth requests are hgher than B avg, whereas some Hs bandwdth requests are lower than B avg due to the uneven dstrbuton of users and traffc. Therefore, there may be remanng bandwdth B offset, can be calculated as: B offset = N =1 ( B avg B H ) ( B L δ B avg B H ) B L where δ ( B avg B H B L ) s a step functon. In order to mprove bandwdth utlzaton, the remanng bandwdth B offset s proportonally allocated to the hghprorty queues whch haven t got enough bandwdth as follows: G HS = N=1 ( B H R H B offset B avg ) ( δ B H (4) B avg ) (5) where R H s H s lackng bandwdth, t can be expressed as Eq. (6). R H = B H B avg (6) After the above bandwdth allocatons for hgh-prorty queues, H s granted bandwdth for hgh-prorty queue s expressed as Eq. (7). G H = G HF + G HS (7) Moreover, f there s stll remanng bandwdth, and there are bandwdth requests for low-prorty packets, we further allocate the remanng bandwdth to them smlarly to Eq. (5). Otherwse, the process of bandwdth allocaton ends. Let G L be the granted bandwdth for H s low-prorty queue, then s total granted bandwdth s shown n Eq. (8). Bgrant G = H + G L, f s a H b L, else. (8) At the begnnng of each pollng cycle, the OLT broadcasts grant messages to all s. Then, transmts packets wthn the granted slots and sleeps outsde the granted slots. The overhead tme spent swtchng an from sleep state to actve state s T oh. Therefore, the H s sleep tme T H s obtaned as Eq. (9). T H = T cycle T grant T oh = T cycle B grant 8 T oh (9) R The L can tolerate some delay, so the sleep tme of L s set to be more than one pollng cycle as follows: T L = m T cycle () The sleep tme TL has a great effect on the energy effcency. The longer tme the sleeps, the hgher energy effcency can be acheved, but the delay of packets ncreases. On the contrary, the shorter sleep tme sgnfes a shorter packet delay, but the energy effcency decreases. Obvously, the tradeoff between the energy effcency and packet delay s crucal to allow s to sleep as long as possble and meanwhle meet the delay requrements of packets. Accordng to the analyss of delay performance n Sect. 2.2, the optmal sleep parameter m can be obtaned. 2.2 Determnaton of the optmal energy effcency As mentoned earler, the sleep tme s dynamcally derved based on dfferent prortes and ther tolerant delays to acheve the optmal energy effcency and satsfy users QoS. However, the sleep parameter m determnes the sleep tme TL, further affects packets delay and the energy effcency. In ths paper, the optmal sleep parameter m s derved accordng to analyss of packets delay under specfc arrval rate λ. Wthout loss of generalty, low-prorty packets are assumed to arrve at a Posson process wth rate λ and the servce tmes have a general dstrbuton. Therefore, the M/G/1 queung model s adopted to analyze the packet delay. In the WMN, the propagaton delay s neglgble because the dstance between two adjacent MPs s relatvely short. Then, the delay for lnk u v d uv conssts of transmsson delay, slot synchronzaton delay and queung delay, t can be obtaned as follows [16]: d uv = λ uv + μc uv 2μC uv μc uv (μc uv λ uv ) (11) where 1/μ s the average packet length, C uv s the capacty of lnk u v and λ uv s the arrval rate at lnk u v. Based on the delay for a sngle-hop lnk, the delay for a wreless path can be derved as follows: D(W ) = o P k d o (12) where P k s the k-th path and o s a sngle-hop lnk on P k. The upstream packets whch arrve at durng the sleep perod have to wat untl s sleep perod ends. Besdes, after the sleep tme expres, the needs to synchronze and recover clock. Therefore, the average watng delay durng sleep and synchronzaton perods s obtaned as Eq. (13). D[I ]= T L + T oh 2 (13)

5 After the wakes, t transmts packets durng the grant slots. The expected watng tme n queue s calculated as Eq. (14) [17]. D[A] = λe X 2} 2(1 ρ) (14) where X s the servce tme, ρ = λ/μ = λ X and E X 2} s the second moment of servce tme, whch can be expressed as Eq. (15). E X 2} = X 2 + σ 2 (15) where σ 2 denotes the varance of servce tme and can be obtaned as follows: σ 2 = α (x T avg ) 2 + β (mt cycle T avg ) 2 (16) In Eq. (16), T avg denotes the average value of the servce tme for all types of traffc and s calculated as Eq. (17). T avg = mt cycle + T grant 2 (17) In Eq. (16), α s the rato of sleep slots to total slots and β s the rato of granted slots to total slots, can be obtaned as follows: T grant α = mt cycle + T grant (18) mt cycle β = mt cycle + T grant (19) Based on the above analyss, the total delay of a packet s derved as Eq. (20). D = D[W ]+D[I ]+D[A] (20) In EPON, sleep tme s lmted to 50 ms due to the mult-pont control protocol. Therefore, we can obtan the constrant as follows: mt cycle 50 (21) Let D r be the delay requrement of the low-prorty packet, then we can obtan constrant (22). D D r (22) Based on the above two constrants (21) (22), the maxmum m can be derved. Then, the optmal energy effcency can be acheved. Therefore, the maxmum m s the optmal sleep parameter we want. 2.3 Load balancng and resource allocaton In ths secton, a load balancng and resource allocaton mechansm s proposed to reduce hgh-prorty packets delay and s congeston. The path qualty has a great effect on the end-to-end delay of wreless path. Good path qualty sgnfes low path delay. In addton, the load affects the arrved packets watng delay. As known, hgh load wll result n hgh watng delay. Therefore, both path qualty and load should be consdered to mprove packets delay performances. We use the artme metrc defned n the hybrd wreless mesh protocol (HWMP) to evaluate the path qualty, where channel access overhead O ca, protocol overhead O p, and frame error rate e f are fully consdered [18]. The artme metrc of lnk o s calculated as follows: C o = [ O ca + O p + B ] t 1 (23) r 1 e f where B t s the number of bts n a test frame and r s the bt rate. In HWMP, the artme metrc s the default parameter for path selecton. When node A wants to fnd a path to node B, t wll broadcast a Path Request (PREQ) message. Then, the nodes that receve the PREQ message wll forward t to other nodes. When a node s forwardng a PREQ message, t wll add the artme metrc between t and ts predecessor to the Metrc feld of the PREQ message and forward the PREQ message to ts successor. In ths way, a node can know the artme metrcs of other lnks. The destnaton node wll receve some PREQ messages whch come from dfferent paths and then select the optmal path based on the artme metrcs recorded n the Metrc feld of the PREQ message. Eventually, the destnaton node sends a Path Reply (PREP) message to the source node to establsh the forwardng path. Based on the artme metrc, the path qualty s obtaned as Eq. (24). P k = o P k C o (24) where P k s the k-th path and o s a sngle-hop lnk on P k. In the HOWBAN, s perodcally broadcast state nformaton to MPs. The MPs drectly connected to the s receve the broadcast nformaton frstly, and then forward the nformaton to other MPs whch haven t receved the nformaton yet. Fnally, the MPs can receve the broadcast of an that locate far away. Then, each MP derves the wreless path wth the optmal path qualty to s based on Eq. (24). In addton, the state nformaton broadcasted by s also ncludes s load nformaton. To accurately assess an s load state, the average load of can

6 be calculated as Eq. (25). X (0) (k) = NP k AP (25) M where NP k s s total receved packets durng the k-th slot, AP s packet sze, and M s slot length, as well as s broadcast cycle. can record the sequence of the prevous n slots average loads as follows: X (0) = } x (0) (1), x (0) (2),...,x (0) (n) (26) When selectng the destnaton s, MPs need to determne s load states n the next slot accordng to the prevous load records to keep away from the hgh-load s. Obvously, s need to predct ther average loads n the next slot and broadcast them to MPs. The accuracy of the predcted results wll drectly affect the selecton of destnaton s and then affect transmsson delay of upstream packets. Dscrete gray predcton model (DGM) develops a mathematcal model based on small and ncomplete dscrete nformaton. Moreover, t has the advantages of requrng less sample data, hgh predcton accuracy and low computatonal complexty. Currently, DGM (1, 1) s the most wdely used model, whch s a sequence-orented DGM wth one varable and the frst-order dfferental equatons. Besdes, when raw data approxmately follows exponental dstrbuton, the predcton accuracy s much hgher. We use the DGM (1, 1) to predct s loads n the next slot to determne whether there s congeston because s receved upstream packets approxmately follow the exponental dstrbuton [19]. Based on the DGM (1, 1) establshed n Appendx, s average load n the next slot x (0) (n + 1) can be obtaned. After recevng the broadcast messages from s, whch contan s current average loads and the predcted average loads, MPs calculate the average load of all s n current slot and next slot as follows: that s on the path wth optmal path qualty s chosen as the transferred. The load transfer rato can be obtaned by Eq. (29). p = x(0) (n + 1) X (n + 1) x (0) (n + 1) (29) where p s the rato of the traffc to be transferred to the total traffc n. To transmt the delay-senstve hgh-prorty packets, the wreless path wth the optmal path qualty s chosen and the on the path s called prmary. When the load of the prmary s hgh, we reroute the low-prorty packets to other s to reduce the prmary s load and packets watng delay. When the prmary sleeps, the wreless path wth the suboptmal path qualty s chosen and the on the path s called secondary. Then, hgh-prorty packets wll be transmtted through the secondary and low-prorty packets wll be transmtted through the prmary after t wakes to avod the congeston of the secondary. To make t clear, we summarze the man procedures of the QoS-aware energy-savng mechansm and show the pseudo-code n Algorthm 1. X (n) = 1 N X (n + 1) = 1 N N =1 N =1 x (0) (n) (27) x (0) (n + 1) (28) To accurately determne whether s congested, we consder s loads of two consecutve slots. If x (0) (n) > (n + 1) > (1 + γ ) X (n + 1), s congested. On the contrary, f x (0) (n) < (1 γ ) X (n) and x (0) (n + 1) < (1 γ ) X (n + 1), s at low load. Otherwse, s steady. In order to releve hgh-load s congeston, we need to transfer part of hgh-load s traffc to other low-load s. Among the low-load s, the (1 + γ ) X (n) and x (0)

7 OLT OLT MP Wreless Gataway Fg. 2 Smulaton topology 3 Performance evaluaton In ths secton, we present the performance evaluaton of our proposed mechansm by Network Smulator 2. The network topology s shown n Fg. 2 [], whch s composed of 20 MPs, 5 s and 2 OLTs. Then, we compare the proposed mechansm (QESM) wth DQAE mechansm [13] and SLAB mechansm [15]. To verfy the effectveness of the proposed mechansm, we compare and analyze the above three mechansms at dfferent network loads. Performance ndcators are as follows: a. s total energy consumpton (TE) The value of TE s the sum of total energy consumed by all s under both actve and sleep states, can be expressed as: TE = P actve onu ( N n=1 T n actve ) + P sleep onu ( N n=1 T n sl ) (30) where Ponu actve and Ponu sleep are the power of each wth the actve state and sleep state, respectvely, Tsl n and T actve n are the sleep duraton and actve duraton of n, respectvely. b. Energy consumpton per Erlang (EPE) EPE s the rato of total energy consumpton to the network load (measured n Erlang). c. Average path delay from the access MP to the OLT (APD) APD s the rato of all packets path delays to the number of packets, can be calculated as follows: APD = num q=1 ( tq,receve t q,arrve ) num (31) where t q,arrve represents the tme when the q-th packet arrves at the access MP, t q,receve represents the tme when the OLT receves the q-th packet, and num s the number of all packets. d. Sleep duraton rato (SDR) SDR s the rato of total sleep duraton for each to the total smulaton tme for all s, can be expressed as: SDR = N n=1 T n sl N T sm (32) where T sm s the smulaton tme for each. The smulaton parameters are gven n Table 1. The total energy consumpton of s drectly reflects the energy effcency of the energy-savng mechansms. Fgure 3 llustrates the total energy consumptons of the three mechansms at dfferent network loads. Clearly, wth the ncrease of the network load, the total energy consumptons rse gradually. Ths s because that the needs to forward more and more packets and the sleep tme of s relatvely shorter. Moreover, the QESM mechansm chooses dfferent ways of sleep accordng to dfferent prortes. That s, the that has hgh-prorty packets sleeps wthn one pollng cycle, whereas the that only has low-prorty packets sleeps for more than one pollng cycle. Therefore,

8 Table 1 Smulaton parameters Parameter Smulaton tme Scenaro sze Maxmum capacty of a wreless lnk Total capacty of each power consumpton n actve state, sleep state Length of a pollng cycle overhead tme OLT- lnk capacty tal energy consumpton (%) SLAB DQAE QESM Value 00 s 1600 m 1600 m 54 Mbps 0 Mbps 5.052, 0.75 W 2 ms ms 1 Gbps Fg. 3 Total energy consumpton of s QESM s energy effcency s hgher than those of the other two mechansms due to the ncrease of s sleep tme. Fgure 4 shows the energy consumptons per Erlang of the three mechansms. The results show that the energy consumptons per Erlang are hgher when the network load s low. Ths s because that the needs to wake-up even the number of packets s small when the network load s low. In addton, the performance of QESM s better compared wth the other two due to QESM s dfferent responses to dfferent prortes. The average path delay for hgh-prorty packets s an mportant ndcator of users QoS performance. Fgure 5 shows that the average path delay for hgh-prorty packets rses wth the growng network load. The man reason s that the ncreasng number of packets leads to the congeston n nodes and over lnks. Then, the queung delay rses and the sleep of some s further ncreases the queung delay. However, a load balancng and resources allocaton mechansm s adopted n the QESM, where hgh-prorty packets are forwarded on the path wth the optmal path qualty and lowload. Therefore, hgh-prorty packets average path delay n QESM s lower than those n the SLAB and DQAE. Energy consumpton per Erlang (J) SLAB DQAE QESM Fg. 4 Energy consumpton per unt of Erlang Average path delay (ms) SLAB DQAE QESM Fg. 5 Average path delay for hgh-prorty packets Fgure 6 shows the average path delays for low-prorty packets at dfferent network loads. As can be seen, the average path delays for low-prorty packets rse wth the ncreasng network load due to the ncrease of queung delay and transmsson delay. The QESM mechansm takes full advantage of low-prorty packets tolerant delay to ncrease s sleep tme and further mprove the energy effcency. Therefore, when the network load s low, the average path delay for low-prorty packets n QESM s a lttle hgher than those n the other two. However, when the network load ncreases to a certan extent, the average path delay for lowprorty packets n QESM s lower than those n the other two due to the load balancng and resources allocaton mechansm s adopton. Fgure 7 shows the SDRs of QESM, DQAE and SLAB mechansms, respectvely. As can be seen, the SDRs decrease gradually wth the ncrease of network load due to the decrease of sleep tme. The QESM mechansm allows the

9 15 0 Average path delay (ms) SLAB DQAE QESM Percentage % Total energy savng Extra energy consumpton Fg. 6 Average path delay for low-prorty packets Fg. 8 Extra energy consumpton 0 4 Conclusons SDR % SLAB DQAE QESM In ths paper, a novel QoS-aware energy-savng mechansm s proposed to reduce the energy consumpton of HOWBAN. Based on consderaton of dfferent prortes, a dynamc bandwdth allocaton mechansm s proposed to guarantee the QoS; at the same tme, dfferent sleep strateges are desgned for dfferent prortes to prolong the sleep tme of s. In order to further maxmum the energy savng, the optmal sleep parameter s derved based on analyss of the packet delay. In addton, a load balancng and resource allocaton mechansm s desgned n the wreless doman to avod the degradaton of QoS performance due to the sleep of s. Results show that the energy effcency can be dramatcally mproved by our ntroduced mechansms. Fg. 7 SDR at dfferent network loads that only has low-prorty packets to sleep for more than one consecutve pollng cycle. Therefore, the sleep tme ncreases due to the decrease of s overhead tme. From the results, we can see that the SDR performance of the QESM mechansm s hgher than those of DQAE and SLAB mechansms by 22.5 and 38.3%, respectvely. In our proposed mechansm, the hgh-prorty packets arrvng durng s sleep perods wll be transferred to other actve s. However, the process of transfer wll consume extra energy. As can be seen from Fg. 8, theextra energy consumpton decreases wth network load s ncreasng. Ths s because that the hgher s the network load, the smaller s the number of sleepng s. As a result, the smaller s the number of packets that should be transferred. On the whole, the lttle extra energy consumpton doesn t affect the hgh energy effcency of our proposed mechansm. Acknowledgements Ths work s supported n part by the Natural Scence Foundaton of Chna (613797, ), Youth Talents Tranng Project of Chongqng Scence and Technology Commsson (CSTC2014KJRC-QNRC40001), Program for Innovaton Team Buldng at Insttutons of Hgher Educaton n Chongqng (CXTDX ). Appendx The detaled process of the DGM (1, 1) s as follows: Step 1 Accumulated generatng operaton The sequence of the prevous n slots average loads for s expressed as follows: X (0) = } x (0) (1), x (0) (2),...,x (0) (n) (33) Makng one accumulated generatng operaton (1-AGO) X (1) = } x (1) (1), x (1) (2),...,x (1) (n) (34)

10 where x (1) (k) = k =1 x (0) (), k = 1, 2,...,n. 1-AGO makes any nonnegatve, fluctuant and nonfluctuant column translate to nondecreasng and ncreasng column, whch weakens the randomness and strengthens the regularty. Step 2 Establshment of DGM (1, 1) The DGM (1, 1) mode s establshed as follows: x (1) (k + 1) = β 1 x (1) (k) + β 2 (35) Step 3 Solutons of parameters Let ˆβ = [β 1,β 2 ] T be the parameter column, and x (1) (2) x (1) (1) 1 x (1) (3) Y =., B = x (1) (2) 1.. x (1) (n) x (1) (n 1) 1 Then, we can get ˆβ = β 1 = ( B T B) 1 B T Y = [ β1 β 2 ] Substtutng Y and B nto Eq. (37), β 1,β 2 are gven by n 1 k=1 x(1) (k + 1) x (1) (k) n 1 1 n 1 n 1 k=1 [ x (1) (k) ] 2 1 n 1 [ β 2 = 1 n 1 ] n 1 n 1 x (1) (k + 1) β 1 x (1) (k) k=1 k=1 (36) (37) k=1 x(1) (k + 1) n 1 k=1 x(1) (k) [ n 1 ] 2 k=1 x(1) (k) (38) (39) Step 4 Acqurement of predcton equaton Substtutng β 1,β 2 nto Eq. (35), then the recurrence functon of DGM (1, 1) s obtaned as follows ˆx (1) (k + 1) = β k 1 x(0) (1)+ ( ) 1 β k 1 β2, k = 1, 2,...,n 1 1 β 1 (40) The predcton equaton s obtaned by nverse 1-AGO as ˆx (0) (k + 1) =ˆx (1) (k + 1) ˆx (1) (k), k = 1, 2,...,n 1 (41) where ˆx (0) (k + 1) s the predcted value of s average load n the next slot. References [1] Zhou, H., Mao, S., Agrawal, P.: Optcal power allocaton for adaptve transmssons n wavelength-dvson multplexng free space optcal networks. Dgtal Commun. Netw. 1(3), (2015) [2] Peng, M., L, Y., Jang, J., L, J., Wang, C.: Heterogeneous cloud rado access networks: a new perspectve for enhancng spectral and energy effcences. IEEE Wrel. Commun. 21(6), (2014) [3] Luo, C., Guo, S., Guo, S., Yang, L., Mn, G., Xe, X.: Green communcaton n energy renewable wreless mesh networks: routng, rate control, and power allocaton. IEEE Trans. Parallel Dstrb. Syst. 25(12), (2014) [4] Shaddad, R.Q., Mohammad, A.B., Al-Galan, S.A., Al-Hetar, A.M., Elmagzoub, M.A.: A survey on access technologes for broadband optcal and wreless networks. J. Netw. Comput. Appl. 41(5), (2014) [5] Sargannds, A.G., Ilordou, M., Ncopoltds, P., Papadmtrou, G., Pavldou, F.N., Sargannds, P.G., Louta, M.D., Vtsas, V.: Archtectures and bandwdth allocaton schemes for hybrd wreless-optcal networks. IEEE Commun. Surv. Tutor. 17(1), (2015) [6] Zhang, Z., Y, Y., Yang, J., Jng, X.: Energy effcency based on jont moble node groupng and data packet fragmentaton n shortrange communcaton system. Int. J. Commun. Syst. 27(4), (2014) [7] Wu, D.P., He, J., Wang, H.G., Wang, C.G., Wang, R.Y.: A herarchcal packet forwardng mechansm for energy harvestng wreless sensor networks. IEEE Commun. Mag. 53(8), (2015) [8] Valcarengh, L., Van, D.P., Rapon, P.G., Castold, P., Campelo, D.R., Wong, S., Yen, S., Kazovsky, L.G., Yamashta, S.: Energy effcency n passve optcal networks: where, when, and how. IEEE Netw. 26(6), (2012) [9] L, Y., Lao, C., Wang, Y., Wang, C.: Energy-effcent optmal relay selecton n cooperatve cellular networks based on double aucton. IEEE Trans. Wrel. Commun. 14(8), (2015) [] Chowdhury, P., Tornatore, M., Sarkar, S., Mukherjee, B.: Buldng a green wreless-optcal broadband access network (WOBAN). J. Lghtw. Technol. 28(16), (20) [11] Dhan, A.R., Ho, P.H., Shen, G.: Toward green next-generaton passve optcal networks. IEEE Commun. Mag. 49(11), 94 1 (2011) [12] Kantarc, B., Mouftah, H.T.: Towards energy-effcent hybrd fber-wreless access networks. In: Proceedngs of ICTON, pp. 1 4 (2011) [13] Schütz, G., Correa, N.: Desgn of QoS-aware energy-effcent fber wreless access networks. J. Opt. Commun. Netw. 4(8), (2012) [14] Lu, X., Ghazsad, N., Ivanescu, L., Kang, R.: On the tradeoff between energy savng and QoS support for vdeo delvery n EEEbased FW networks usng real-world traffc traces. J. Lghtw. Technol. 29(18), (2011) [15] Sh, L., Mukherjee, B., Lee, S.S.: Energy-effcent PON wth sleep-mode : progress, challenges, and solutons. IEEE Netw. 26(2), (2012) [16] Sarkar, S., Yen, H.H., Dxt, S., Mukherjee, B.: A novel delayaware routng algorthm (DARA) for a hybrd wreless-optcal broadband access network (WOBAN). IEEE Netw. 22(3), (2008) [17] Bertsekas, D.P., Gallager, R.G., Humblet, P.: Data Networks. Prentce-Hall, Upper Saddle Rver (1992) [18] Hertz, G.R., Max, S., Zhao, R., Denteneer, D., Berlemann, L.: Prncples of IEEE s. In: Proceedngs of Internatonal Conference on Computer Communcatons and Networks, pp (2007) [19] Hertz, G.R., Denteneer, D., Max, S., Taor, R., Cardona, J., Berlemann, L., Walke, B.: IEEE s: the WLAN mesh standard. IEEE Wrel. Commun. 17(1), (20)

11 Ruyan Wang receved hs Ph.D. degree n 2007 from the Unversty of Electronc and Scence Technology of Chna (UESTC) and the M.S. degree from Chongqng Unversty of Posts and Telecommuncatons (CQUPT), Chna, n From Dec. 2002, he s a professor n Specal Research Centre for Optcal Internet and Wreless Informaton Networks at CQUPT. Hs research nterests nclude: optcal burst swtchng networks, network performance analyss, and multmeda nformaton processng. Ale Lang s workng for hs M.S. degree n Chongqng Unversty of Posts and Telecommuncatons. Hs research nterest ncludes hybrd optcal-wreless broadband access networks and green computng technologes. Dapeng Wu receved hs M.S. degree of communcaton and nformaton system n June 2006, Chongqng Unversty of Posts and Telecommuncatons, the Ph.D. degree from Bejng Unversty of Posts and Telecommuncatons n Hs research nterests nclude next generaton network, IP QoS archtecture, network relablty, performance evaluaton n communcaton systems. Hong Zhang s a Ph.D. student n Chongqng Unversty of Posts and Telecommuncatons. He receved the M.S. degree n Chongqng Unversty of Posts and Telecommuncatons n Hs research ncludes optcal communcaton, survvablty technology and next generaton passve optcal network. Chao Zhou receved hs M.S. degree n 2016, from Chongqng Unversty of Posts and Telecommuncatons (CQUPT), Chna. He has several years of research experence n QoS control of hgh speed networks and network performance analyss.