Protection of WDM PON Systems based on Modified 2-OLT Architecture Fahmida Rawshan and Youngil Park Department of Electronics Engineering, Kookmin University, Seoul, South Korea E-mail: fahmida_rawshan@yahoo.co.in, ypark@kookmin.ac.kr Abstract—In this paper, we propose a novel protection architecture of passive optical network (PON) system. Two optical line terminals (OLTs) are connected to each other as well as to the access area. This network can sustain services to access area and restores normal operation in faulty conditions. Subscribers are divided into two groups to reflect priority based bandwidth allocation. WDM access increases the efficiency of the system by operating both OLTs using different wavelengths in normal condition. During fault, a Shared-bandwidth allocation scheme is employed in operating the survived OLT. Performance analysis shows the improvement of the proposed scheme over an existing scheme. Keywords—Passive optical network, multi-OLT, WDM, Self- similar traffic. I. INTRODUCTION A multi-OLT PON is a good solution to meet recent demands of telecommunication industry as it provides large capacity, user freedom and protection facilities [1-2]. Protection is very important issue since the business and home services demand intact access. Protection mechanism via dual- homed PON is already proposed by some research groups [3]. This operation in revertive mode keeps a standby OLT idle in normal condition. To improve the bandwidth utilization by using all OLTs in normal operation, we propose a WDM based architecture of 2-OLT PON system in our previous study [4]. In this paper, we propose a modified architecture to improve the performance further. In normal status, two OLTs transmit data to different ONU groups using different wavelengths. In failure status, the survived OLT transmits in two wavelengths in turn, thereby replacing the failed OLT. Direct connectivity between two OLTs is the improved feature of this modified structure which decreases protection time. A modified version of control protocol is suggested to operate the proposed 2-OLT PON system. Users are divided into two groups to distinguish home and enterprise services. Besides, we suggest a Shared-bandwidth DBA (SBA) scheme for downstream transmission to further improve the performance of the 2-OLT PON in faulty situation [4]. The rest of this paper is organized as follows. Section II introduces system architecture and operation algorithm of the WDM based 2-OLT PON system. DBA schemes for both normal operation and faulty condition are also described here. Section III provides simulation results to demonstrate network , 1 2 λ λ 3 λ , 1 2 λ λ 3 λ 1 λ 2 λ 3 λ 1 λ 3 λ 3 λ 2 λ 3 λ Figure 1. Proposed network architecture. performance using the suggested DBA schemes. Finally, Section IV concludes our work. II. OPERATION OF THE MODIFIED TWO-OLT WDM NETWORK In the proposed two-OLT PON, two OLTs are connected to the access area via a passive optical distribution network. The ONUs are divided into two groups ‘Premium’ and ‘Home’. Premium group has lower number of ONUs and receives higher bandwidth facilities than the other group. Each OLT works as a backup OLT for the other one. In normal situation, each OLT is responsible for data transmission of its corresponding ONU group. In the modified structure, OLTs are connected to the other ONU group and works for it during failure condition. Figure 1 shows the architecture of the proposed network for two OLTs and sixteen ONUs. OLT x manages data transmission to Premium Group (ONU 1 to ONU 6 ) in wavelength Ȝ 1 , while OLT y manages it for ONUs in Home Group (ONU 7 to ONU 16 ) in wavelength Ȝ 2 . As two OLTs are connected directly, the exchange of control packets to measure RTT for ranging between OLT x and Home ONU Group, and between OLT y and Premium Group is unnecessary. Each OLT measures RTT of the corresponding group and shares it with the other OLT which results in short protection time. During failure of one OLT the other OLT is capable of transmitting data to both groups. Each OLT can transmit in one of two wavelengths, Ȝ 1 or Ȝ 2 at a time while receives in Ȝ 3 . 2013 International Conference on Electrical Information and Communication Technology (EICT) 978-1-4799-2299-4/13/$31.00 ©2013 IEEE