ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON)

Transcription

1 ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON) Amit Kumar Keshari 1, Partha Paul 2 1 Faculty of Science & Technology, ICFAI University Jharkhand, Ranchi India 2 Department of Computer Science and Engineering Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India ABSTRACT: In recent years, the energy crisis has become a great challenge in the whole world. It has been seen that Telecom networks also consume a largest amount of energy because as the network traffic increases, the energy consumed by network equipments is also goes on increasing. The main purpose of energy saving is for making environment green as well as it also provide many practical and financial advantages. Now the energy efficiency to access the networks is the major part of energy consumption in the internet. There are many components which consume energy in access networks, in our proposed work we have considered optical network units (ONUs) that consume about 60-70% of the energy in current fiber-to-the-home network. In this paper, we have used EPON(Ethernet Passive Optical Network), which is an important candidate of PONs(passive optical network).the main reason of power consumption by optical network units (ONU) is that it is also powered on during unused condition. In our proposed work, we have used a dynamic bandwidth allocation (DBA) algorithm that has a purpose to make a sleep mode functionality in which ONU is placed to sleep as per the situation of traffic load of the ONU. Keywords: Energy efficiency, EPON, Network Components, Dynamic Bandwidth allocation (DBA) [1] INTRODUCTION In recent years, the energy efficiency and environmental protection play an important role. The energy consumption also increases in the field of information and communication Technology (ICT) because more equipment added annually in networking and communications areas. According to the data comes on 2009, the energy consumed by ICT is near about 8% of the total world electricity [1]. Telecom networks are a part of the ICT. As there is rapid increase in broadband telecom networks and thus energy consumption also increasing. So we need to develop an energy efficient telecom network. This is done by designing new networking paradigms which consume less energy. We have considered optical network units (ONUs) that consume about 60-70% [2] of the energy in current fiber-to-the-home network (FTTH). Now a day s PONs are Amit Kumer Keshari and Partha Paul 1

2 ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON) considered as a optimistic technology that provides high data rates to users, and thus are generally more energy efficient than their previous counterparts (e.g., ADSL Asymmetric Digital Subscriber Line and VDSL very high bit rate Digital Subscriber Line) [3]. There are many ways through which minimization of power consumption of ONUs have been made.here we have considered the solution for power consumption is done through the implementation of low power modes where some functionalities are powered off if they are temporarily not in used[4]. One of the examples of low power mode is sleep mode [5, 6]. The sleep mode aware (SMA) dynamic bandwidth allocation (DBA) algorithm [7] provides the activity period slot for every ONU when ONU wake up and wants to transmit and receive packets. In our work, we have proposed DBA for next generation optical network units (NG- ONUs) which are based on latest technology. NG-ONUs uses the newest innovations in receiver and transmitter designs and thus they have minimal overheads (few microseconds). The challenges in designing DBA algorithm for NG-ONUs needs frame-by-frame (or cycle-by-cycle) sleep control. Thus, the proposed approach gives the solution to accomplish energy savings of about 70 80% depend on the network load. The rest of the paper is organized as follows: In section 2 we have discuss the overview and the requirements of sleep mode in EPON. In section 3, we introduce the energy efficient DBA algorithm. Section 4 gives results & discussion and Section 5 gives conclusion of the paper. [2] OVERVIEW OF LOW POWER MODE IN EPONS EPON An EPON is a point-to-multipoint fiber optical network which contains only passive elements in the optical distribution network (ODN), i.e. between an optical line terminal (OLT) at the central office (CO) and the ONU as shown in [Figure-1]. During the upstream direction, an EPON is a multipoint-to-point network, in which multiple ONUs transmits data to OLT through the 1: M passive combiner. In the upstream direction, the ONU sends REPORT messages requesting for bandwidth based on its queue size, and the OLT sends back a GATE message to the ONU informing the allocated bandwidth. During the downstream direction, an EPON is a point-to-multipoint network, in which the OLT broad casts data to each ONU on a first come first serve (FCFS) basis through the 1: M power splitter. 2

3 Figure: 1. Downstream and Upstream operation in EPON Requirements: The energy efficient algorithm must fulfill certain requirements which are as follows: i) There is no degradation of high-priority traffic performance: There are some High-priority traffic such as voice and interactive video which are very sensible to delay and thus the energy-efficient DBA algorithm must persist the good quality of service (QoS) requirements [8] and also gives minimum waiting time for an ONU. ii) Consistent with MPCP framework: According to the MPCP framework, if an ONU unable to reply within 50 ms, the ONU becomes deregistered. The ONU reregister itself after a time of 10s or more. Thus, the energy efficient algorithms should provides a maximum sleep period of 50ms for an ONU to overcome the problem of deregistration of ONU within a network. Low power modes The energy consumption of ONUs is minimize by different low power states such as power shedding, deep sleep,fast sleep, doze and dynamic power save state [9,10 ]. Such methods are used according to the different parts of the ONU that are switched off [6]. In our work, we concentrate on the sleep modes. Sleep mode is based on the cyclic movement between sleep and active state. In sleep state, unessential functional blocks as well as both the ONU receiver and transmitter are turned off. In active state, all the components are power on and consume full power. Amit Kumer Keshari and Partha Paul 3

4 ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON) The main challenges for energy efficient DBA algorithm NG-ONU is based n the small sleep overheads. When sleep overheads are small, sleep mode can be enabled on a per cycle basis. The per cycle sleep mode is also called as cyclic sleep which enables ONUs to transmit and receive packets in every cycle. For making energy efficient DBA algorithm, cyclic sleep is implemented for downstream transmission because the transmission in the upstream direction is already energy efficient as the ONU transmits only on its turn comes. When sleep modes are enabled, the downstream traffic of an ONU has to be transmitted within a time slot which is already known to an ONU. This arises two scheduling problems: (i) Determining the length of the slot and (ii) determining and letting an ONU to know in advance the time period of the next slot transmission. Currently, these problems have been handled by a scheduling mechanism known as a fixed bandwidth allocation (FBA)[11] scheme. In FBA, the downstream transmission is divided into fixed cycles, during which the OLT transmits a fixed number of time slots to each ONU. FBA is significantly energy-efficient as bandwidth is allocated in regular intervals, known to the ONUs. The next ONU can turn their Rx on only when it is required. The main demerit of FBA is that it cannot be applicable for a bursty traffic because it provides excessive bandwidth wastage as well as delay also. [3] DYNAMIC BANDWIDTH ALLOCATION (DBA) ALGORITHM We have proposed a new DBA algorithm, which is applicable for NG-ONUs. In new DBA, the OLT buffers the downstream traffic for each ONU and transmits it only during a known activity slot of an ONU. This provides the facility to ONU to not awake at all the times and thus provides a golden chance for an ONU to sleep. DBA polls ONUs in a round-robin fashion and introduce a GATE messages to every ONU in each cycle. The GATE message contains two important information for an ONU: (i) it contains the information about the activity slot for an ONU during which it is remain active, and (ii) it contains the sleep period. An ONU can receive and transmit message in the given activity slot and sleep only when it s sleep time expired. To determine these two messages, energy-efficient DBA scheduling has suffered from the two main problems: (i) To predict the sleep period and (ii) Determination of the activity slot (grant sizing). (i) Prediction of the sleep period: Here prediction to find sleep time for an ONU is occurred. The OLT place the sleep time S ST and transmission slot T R in the GATE message and an ONU sleeps for S ST time after transmitting and receiving its bandwidth for T R time. 4

5 To calculate the sleep time of ONU p, the OLT requires the following information using [Figure-2]: Figure: 2. GATE prediction for DBA algorithm. Time period of present GATE G (j, p) (let us assume cycle j), time period of next GATE G(j+1,p), time for transmission slot T R (j, p) and sleep overheads time T SO of ONU: The three components of sleep time are known for OLT but when the time of issuing the present GATE message, the time of issuing the GATE message for the next cycle of an ONU i.e. G (j+1, p) will be unknown. [Figure-3] describe this problem it more accurately. Figure: 3. An EPON contains one OLT and two ONUs. Amit Kumer Keshari and Partha Paul 5

6 ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON) [Figure-3] shows an EPON which contains one OLT and two ONUs. Here there are two REPORT messages R 1 for ONU 1 and R 2 for ONU 2 and two GATE messages G 1 for ONU 1 and G 2 for ONU 2 are used for transmission. Let us consider at time T, the OLT knows the buffer statistics of both the ONUs and their round-trip time (denoted by Δ). Thus, during the transmission time of the first GATE message G 1 to ONU 1, the OLT can easily find out the grant time of the next GATE message for ONU 1. But, at the time of issuing the second GATE message for ONU1, the REPORT message from ONU 2 has still not arrived, and thus the OLT unable to find out the time period of the next GATE message for ONU 1. Thus, the OLT requires prediction for the time of next GATE transmission. In the DBA algorithm, the OLT uses the existing REPORT statistics to predict the time of next GATE transmission. For an EPON containing n ONUs, the time of issuing the next GATE message G(j+1,p) to the ONU p actually depends upon (j-1+ mod(1,p) th REPORT message of the [n mod((n - p+1,n)] th ONU, where mod(a, b) gives the remainder of (a/b). Let us consider an example, the 3 rd GATE message of the 4 th ONU will depend on the 2 nd REPORT of the 3 rd ONU. Whenever the REPORT messages from an ONU comes, then we calculate the grant time of the next ONU. Thus,by using the current determined grant time of ONU k, then we have to calculate the time period G(j+1,p) when the (j+1) th GATE message to ONU p is transmitted and we formulate as Here Δ(p) denote the round trip time of ONU p and α gives the transmissions lot of the other remaining ONUs (the ONUs for which REPORTs messages do not come) as shown in [Figure-2]. We assume that the predicted transmission slot of the other remainder ONUs is (α-β), where β will be the error in prediction. Thus it will decrease the ideal value of S ST (j, p) to S ST (j, p) β. From [Figure-2], we can find out the sleep percentage (S PT) for an ONU as (ii) Determination of the grant sizing There are many approaches through which an OLT can determine the grant size for an active ONU. In our work we have considered the Minimum sleep time (MST) approach. 6

7 DBA polls an ONU according to the load. When the load is low, the ONU polls with a very shorter time and this needs an ONU to wake up more regularly, and thus decreasing the sleeping time for an ONU. In DBA-MST, each ONU is given a minimum T R due to which the polling time for an ONU must not be very short, and although when the load is low, an ONU has a minimum sleeping time. Hence, this approach provides a minimum sleep time for an ONU. [4] RESULT AND DISCUSSION Here, we have discussed the performance of the proposed DBA approach by using a simulation of an EPON access network with 8 ONUs within the OPNET simulation environment. In our simulation study, we have taken a maximum ONU load of 200Mbps and upstream & downstream bandwidth of the EPON as 1 Gbps, the maximum distance between OLT to ONU is 15km, the maximum cycle time of 2 ms, the buffer capacity of OLT and ONU is 2 MB, and the guard time between adjacent slots is 1ms.We have created traffic according to [8]. Every ONUs is considered to be symmetrically loaded. The packets which have higher priority constitute 20% of the overall network load, and the packets which have lower priority is displace if buffer has not adequate space to store the packet. the use of a burst mode receiver make the power consumption of 0.2W for both active and sleep state for an NG-ONUs. For NG-ONUs we have chosen 5 µs for the sleep over heads. For the DBA-MST approach, we have assumed a minimum sleep period of an ONU as 1.25ms. We discuss the result for NG-ONUs. For NG-ONUs, we measure the sleep time efficiency and average delay of upstream & downstream traffic. We compare the results of the proposed schemes with FBA and DBA-MST. The FBA scheme makes use of a fixed timeslot per ONU, which permit the ONUs to sleep for the maximum time. The DBA-MST approach applies the delay bound at a low load. The main benefit of the DBA-MST approach is that it provides a minimum sleeping period to an ONU which minimizes harmful effects of frequent mode switching [12]. [Figure-4] explains the performance of FBA and DBA-MST schemes on the sleep efficiency. The DBA-MST approach has a high sleep percentage even at a low load because it maintains longer polling cycles. The FBA approach achieves a load-independent and a high sleep percentage as the ONUs can sleep for a fixed time. Amit Kumer Keshari and Partha Paul 7

8 ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON) 100 FBA 95 DBA-MST 90 Sleep Time(%) Symmetric Network Load Figure: 4 The time (in % ) for an ONU remains in sleep state 40 FBA 35 DBA-MST 30 Power Consumption(%) Symmetric Network Load Figure: 5 Power consumption (in % ) of the ONUs in FBA and DBA-MST 8

9 [Figure-5] provides the power consumption of DBA-MST and FBA schemes. Power consumption (P CM) can be deduced from the time an ONU remains in sleep, P AC and P SC : From the above results, it is found that DBA-MST should be more advantageous because it saves maximum energy while keeping the performance within QoS bounds. [5] CONCLUSIONS In our work, we have proposed a DBA algorithm for the NG-ONUs. NG-ONUs is assumed as small sleep overheads. NG-ONUs can wake-up in each frame, and thus have QoS performance that is more powerful. For NG-ONUs, we have proposed a novel sleepperiod prediction scheme and grant-sizing possibilities,according to the buffer back log of the up-and the downstream traffic, i.e. the minimum sleep time(mst). The MST approach is found to be most useful for maintaining the delay bound and for simultaneously reducing frequent mode switching. In the proposed approaches, an ONU remains in sleep state for about 70 93%, power savings of about70 80% depending on the network load. Amit Kumer Keshari and Partha Paul 9

10 ENERGY SAVING FOR THE ETHERNET PASSIVE OPTICAL NETWORKS (EPON) REFERENCES [1] Leisching P., et al. Energy footprint of ICT: forecasts and network solutions, in: OFC/NFOEC 09, Workshop on Energy Footprint of ICT: Forecast and Network Solutions, San Diego, CA, Mar [2] A. Dixit, B. Lannoo, D. Colle, M. Pickavet, P. Demeester, Energy efficient dynamic bandwidth allocation for Ethernet passive optical networks: Overview, challenges, and solutions, [3] J. Baliga, R. Ayre, W.V. Sorin, K. Hinton, R.S. Tucker, Energy consumption in access networks, in: Proceedings of OFC, L. Barbosa, J. Freire: Siphoning hidden-web data through keyword-based interfaces. In: SBBD, 2004, Brasilia, Brazil, pp [4] R. Dhaini, P.H.Ho, G.Shen, Toward green next-generation passive optical networks, IEEE Commun. Mag.49 (11)94 101(2011). [5] A.Dixit,B.Lannoo,S.Lambert,D.Colle,M.Pickavet,P.Demeester, Evaluation of ONU power saving modes in next generation optical access networks, in : Proceedings of ECOC,Amsterdam, Netherlands, September [6] A.Dixit, B.Lannoo, D.Colle, M. Pickavet, P.Demeester, O.N.U. Power, Saving mode s in next generation optical access networks: progress, efficiency andchallenges, Opt.Express20 (26)(2012)B52 B63. [7] A. Dixit, B. Lannoo, D. Colle, M. Pickavet, P. Demeester, Energy Efficient dynamic bandwidth allocation for Ethernet passive optical networks, in: Proceedings of IEEE ANTS 2012, Bangalore, India, December [8] A.Dixit, B.Lannoo, G.Das, D.Colle, M.Pickavet, P.Demeester, Dynamic bandwidth allocation with SLA awareness for QoS in Ethernet Passive Optical Networks, J.Opt. Commun. Netw. 5(3) (2013) [9] E. Igawa, M. Nogami, J. Nakagawa, Symmetric 10G-EPON ONU burst- mode transceiver employing dynamic power save control circuit, in: Proceedings of OFC, [10] ITU-T Rec. G.Sup45, GPON Power Conservation, [11] S. Lee, A. Chen, Design and analysis of a novel energy efficient ethernet passive optical network, in: Proceedings of ICN, [12] L. Shi, B.Mukherjee, S.S.Lee, Efficient PON with sleep-mode ONU: Progress, challenges, and solutions, IEEE Netw.Mag.26 (2) (2012)

11 Author[s] brief Introduction Amit Kumar Keshari I have received the M.Tech. degree in Computer Science & Engineering from Birla Institute of Technology, Mesra, Ranchi. Presently I am working as a faculty in ICFAI University Jharkhand, Ranchi Partha Paul Assistant Professor, Department of Computer Science and Engineering. Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India, Amit Kumer Keshari and Partha Paul 11