Performance Evaluation of Standard IPACT for Future Long Reach Passive Optical Networks (LR-PON).

Transcription

1 Performance Evaluation of Standard IPACT for Future Long Reach Passive Optical Networks (LR-PON) A M Ragheb 1, M Elnamaky 2, H Faallah 3, and H T Mouftah 4 1,3 Electrical Engineering Department, - King Saud University, Saudi Arabia 2 PSATRI - King Saud University, Saudi Arabia 4 School of Information Technology and Engineering, University of Ottawa Abstract Eernet Passive Optical Networks (EPONs) have been regarded as one of e best choices for next generation access networks Many algorims have been suggested to boost e efficiency of EPON Interleaved Polling wi Adaptive Cycle Time (IPACT) algorim was one of e first solutions to dynamically allocate bandwids In is paper, modeling and simulation of Eernet Passive Optical Networks (EPONs) have been developed using new Matlab Simulink tool SimEvents considering e IPACT algorim as e dynamic bandwid allocation (DBA) scheme Models for low span area wi moderate network load and long span area (Long-Reach PON) have been investigated Simulation results show a consistent performance of e IPACT scheme Results also show at e implementation of IPACT algorim is not preferable for long span area (LR-PON) Keywords : Eernet Passive Optical Networks, EPON, Interleaved Polling wi Adaptive Cycle Time, IPACT, SimEvents Introduction In recent years, e demand on bandwid capacity of telecommunication networks and e speed of local-area networks (LANs) have rapidly increased Wi e ever-increasing users demand for various broadband applications, e subscriber access networks covering e last mile areas are still considered as e bandwid bottleneck in today s telecommunication infrastructure (Zheng, 2009) To get rid of is bottleneck, passive optical networks (PONs) have been viewed as a smart solution to implement e subscriber access networks as fiber-to-e-home (FTTH), fiber-to-e-curb (FTTC), and fiber-to-e-building (FTTB) (Zhu, 2006) Eernet passive optical networks (EPONs) have received a great attention as one of e promising solutions because of its advantages over e traditional access networks Larger bandwid capacity, longer operating distance, lower equipment and maintenance cost, and easier update to higher bit rates were e main merits of e EPON networks (Zheng, 2009) & (Kramer, 2001) In an EPON system all Optical Network Units (ONUs) access e shared fiber channel to reach e Optical Line Terminal (OLT) rough 1: N passive splitter/combiner, as shown in Fig1 In e downstream direction (from OLT to ONUs), data frames are broadcasted to all ONUs Each ONU extracts its information based on MAC address basis In e upstream direction (from ONUs to OLT), data from ONUs are transmitted over e same fiber channel to reach e OLT in dedicated timeslots Thus, it is a point-to-multipoint system in e downstream direction and a multipoint-to-point system in e upstream direction (Zhu, 2006) & (Song, 2009) ONU 1 ONU 2 OLT 1: N splitter/combiner Fig1 EPON architecture ONU N In order to share e medium by different ONUs, many multiple access schemes based on dynamic bandwid allocation (DBA) algorims have been developed Interleaved Polling wi Adaptive Cycle Time (IPACT) scheme is widely regarded as a pioneer solution to dynamically allocate bandwid to different ONUs in EPONs networks

2 (Zhu, 2008) In is scheme, e OLT polls each ONU for e number of bytes each ONU has to transmit After receiving e requests from all ONUs, e OLT uses e DBA algorim to grant e appropriate bandwid (timeslot) to each ONU Since e polling of each ONU is interleaved, where e next ONU is polled before e transmission from previous one has arrived at e OLT, is scheme provides a statistical multiplexing for ONUs and results in efficient upstream channel utilization (Song, 2009) Based on is scheme, many dynamic bandwid allocation (DBA) schemes have been developed to improve e performance of e EPON network In (Byun, 2003), Byun et al proposed an estimation-based dynamic bandwid allocation algorim to keep e queue leng of each ONU low and to improve e packet delay on e EPON network In addition, (Zhu, 2008) proposed e IPACT wi Grant Estimation (IPACT-GE) scheme, which can achieve shorter average packet delay by estimating e amount of new packets arriving between two consecutive polls and grant ONUs wi additional bandwid Moreover, (Song, 2009) proposed a multi-read polling algorim for Long-Reach PON (LR-PON), which can extend up to 100 km or higher Song based his algorim on having multiple polling processes running simultaneously in order to reduce e average packet delay In is study, e EPON network has been modeled and successfully simulated using new Matlab simulink tool SimEvents Then, e performance of IPACT algorim has been analyzed in bo traditional EPON and Long-Reach PON (LR-PON) networks This paper is organized as follows Section II reviews e Multi-Point Control Protocol (MPCP) Interleaved Polling wi Adaptive Cycle Algorim (IPACT) is explained in section III System modeling using Matlab SimEvents and simulation results are described in section IV Section V concludes e study Multi-Point Control Protocol Multi-Point Control Protocol (MPCP), developed and standardized by e IEEE 8023ah Task Force, is a signaling protocol at facilitates e transmission of multiple ONUs (IEEE 8023ah, 2009) & (Zheng, 2006) MPCP has been used as a bandwid negotiation tool in EPON networks to exchange information between OLT and ONUs Each ONU reports its bandwid demand to e OLT, which in return sends bandwid allocations to each ONU (Zheng, 2009) There are two operation modes of e MPCP; auto-discovery mode and normal mode Auto-discovery mode is responsible of discover newly connected ONUs, calculate associated round trip time (RTT), and get e MAC address of at ONU (Kramer, 2005) In is mode of operation, e MPCP relies on ree Eernet control messages, REGISTER, REGISTER_REQUEST, and REGISTER_ACK In normal mode, e MPCP depends on two 64-bytes Eernet control messages; REPORT and GATE The REPORT message is generated by each ONU and piggybacked at e end of data timeslot to inform e OLT about ONU s queue status Upon receiving e REPORT message, e OLT starts allocating bandwids and sends its bandwid allocations back to each ONU in e form of GATE messages, as shown in Fig2 Fig2 REPORT & GATE messages flow Interleaved Packet wi Adaptive Cycle Time In is section we will give an overview on e Interleaved Packet wi adaptive Cycle Time (IPACT) algorim and how e scheduling of e control messages is achieved A IPACT Algorim For simplicity of illustration, we assume at we have an EPON network wi ree ONUs as shown in Fig3 (Kramer, 2002):

3 1 Assume at at time t 0 OLT knows exactly how many bytes buffered at each ONU and e round trip time (RTT) to each ONU OLT stores is information on its polling table and starts sending a GATE message to The GATE message should contain e ID of as well as e size of e granted window 2 Once receives its GATE message, it starts sending its buffered data up to e granted window size - bytes in is example At e end of e transmission window, will generate and send its REPORT control message, which allows e OLT to know exactly e newly requested window size for e next cycle - bytes in is example 3 Since e OLT knows exactly e round trip time (RTT) of and how many bytes is OUN will send, it can schedule e control GATE message of so at ere will be no data collision 4 Upon receiving data and REPORT message from, e OLT updates its polling table for e next polling cycle 5 Similarly, e OLT can schedule e transmission of GATE message as it knows e RTT of and how many bytes will send Polling Table ONU Bytes RTT OLT OLT 2000 bytes bytes 800 bytes (a) bytes bytes (c) 800 OLT OLT 2000 bytes bytes 800 bytes (b) bytes bytes (d) B Fig3 Steps of e IPACT algorim B GATE Messages Scheduling GATE messages for different ONUs are being scheduled using e following formula (Kramer, 2002): [ i] W [ i] [ i] [ i+ 1] G [ + 1] r r B i G = max RU (1) [ i+ 1] [ i+ 1] G 1 + r

4 where: G is e time when grant to r is e round trip time for e W is e window size for R U B i ONU is transmitted i ONU i ONU is e transmission speed (bit rate) is e guard time between data received from ONUs (in µs) The top line in Eq (1) states at e GATE message scheduled to ONU i+1 such at its request arrives after a guard band starts at e end of e transmission window from ONU i, as shown in Fig4 The bottom line states at e GATE message cannot be sent before e previous request from e same ONU is received, ie, e interval between two successive GATE messages to e same ONU is at least e round-trip time to at ONU This is because e GATE message needs information contained in e previous request (Kramer, 2002) OLT G G [ i+1] r [ i+1] r i W [ ] R U B Transmission from ONU i Grant to ONU i Transmission from ONU i+1 ONU i ONU i+1 Grant to ONU i+1 Fig4 GATE messages Scheduling Time System Modeling & Simulation Results SimEvents software extends Matlab Simulink software wi a discrete-event simulation (DES) model of computation Wi SimEvents software you can develop activity-based models of systems to evaluate system parameters such as congestion, resource contention, and processing delays (Maworks, 2009) Discrete-event simulations typically involve discrete items of interest These items are called entities in SimEvents software Entities can pass rough a network of queues, servers, gates, and switches during a simulation Entities can carry data, known in SimEvents software as attributes One can configure entities wi user-defined attributes, and en aggregate entities and attributes to model data hierarchy and transport in different applications such as; packet-based networks, mission planning, supervisory control, real-time operating systems, and computer architecture Using is powerful Simulink tool, SimEvents, an experimental model has been developed for e EPON network to evaluate e performance of e IPACT algorim As shown in Fig5, e model is consisting of a single OLT and 16 ONUs Bo OLT and ONUs are consisting of two parts, transmitter and receiver Each ONU is assigned a downstream and an upstream propagation delays The upstream and downstream propagation delays have been selected randomly wi a uniform distribution over e interval of [50 µs, 100 µs] These values correspond to a coverage distances ranging from 10 to 20 km between OLT and ONUs The transmission data rate in e downstream direction and upstream direction is set to be 1000 Mbps The maximum transmission window size from a single ONU is set to bytes, which is equivalent to a maximum cycle time of 2 ms wi a guard band of 5 µs ONUs packet sizes are uniformly selected between 64 bytes and 1518 bytes according to IEEE 8023 standards

5 (a) (b) (c) Fig5 EPON model using Matlab SimEvents; (a) System model (b) OLT transmitter and receiver (c) ONU transmitter and receiver Fig 6 shows e change in polling cycle time (adaptive cycle) wi different ONU loads ranging from about 02 ms for minimum network load up to 2 ms for maximum network load That figure shows e adaptation of cycle time according to network load; illustrating e main advantage of e IPACT algorim, at makes it preferable for Eernet Passive Optical Networks (EPON) over e traditional time-division multiple access (TDMA) algorims wi fixed cycle time Fig 6 Change in cycle time wi ONU load Fig 7 Average packet delay wi 20 km and 120 km span

6 Fig 7 shows e average packet delay when ONUs are located in km range (traditional PON) and km range (LR-PON) from e OLT For 20 km span, e polling algorim has a good performance in terms of average packet delay Simulation results show at e average packet delay is less an 2 ms when network load is not very high (0-05) wi a small RTT, approximately 02 ms On e oer hand, for 120 km span, e performance of polling algorim is not preferable even in light network load, since e average packet delay can reach up to 30 ms wi RTT of 12 ms Conclusion In is paper we have proposed e use of new available Matlab Simulink tool SimEvents in order to model EPON systems The IPACT algorim has been tested under small coverage area and large coverage area Simulation results show a consistence performance of our Matlab SimEvents based model Results also show at e implementation of e IPACT algorim for Long-Reach PON is not preferable In e next stage of our work, we will propose and investigate a new polling protocol for LR-PON to simulate e multi-read polling exiting algorims References - Byun, HJ, Nho, JM, and Lim, JT, (2003), Dynamic bandwid allocation algorim in Eernet passive optical networks, Electron Lett, vol 39, no 13, pp IEEE 8023ah Eernet in e First Mile Task Force, 2009, viewed 18 Augest, 2009, < - Kramer, G, Mukheree, B, and Pesavento, G, (2001), "Eernet PON (epon): Design and Analysis of an Optical Access Network", Photonics Network Communications,, pp Kramer, G, Mukheree, B, and Pesavento, G, (2002), "IPACT: A Dynamic Protocol for an Eernet PON (EPON)", IEEE Communications Magazine, Vol 40, Issue 2, pp Kramer, G,(2005), Eerenet Passive Opitcal Networks McGraw-Hill Professional,USA - Maworks, 2009, Viewed 15 April, 2009, < - Song, H, Kim, BW, and Mukheree, B, (2009)," Multi-Thread Polling: A Dynamic Bandwid Distribution Scheme in Long-Reach PON", IEEE Journal on Selected Areas in Communication, Vol 27, No 2, pp Zheng, J, (2006) Efficient bandwid allocation algorim for Eernet passive optical networks, IEE proceeding, Vol 153, pp Zheng, J & Mouftah, HT, (2009), A survey of dynamic bandwid allocation algorims for Eernet Passive Optical Networks,Optical Switching and Networking 6, pp Zhu, Y, Ma, M, and Cheng, TH, (2006), "IPACT wi Grant Estimation for EPON", 10 IEEE Singapore International Conference, Singapore - Zhu, Y & Ma, M,(2008)," IPACT Wi Grant Estimation (IPACT-GE) Scheme for Eernet Passive Optical Networks", Journal of Lightwave Technology, Vol 26, No 14, pp