Dynamic Hybrid Slot Size Bandwidth Allocation Algorithm for Reducing Packet Delay of Real Time Traffic in EPON Md. Selim Morshed, Monir Hossen, Mohammad Mahbubur Rahman Department of Electronics and Communication Engineering Khulna University of Engineering & Technology Khulna, Bangladesh Masanori Hanawa Interdisciplinary Graduate School of Medicine and Engineering University of Yamanashi Kofu-shi, Japan Abstract— In the modern data networks, users are communicating via real time traffic very often, i.e., high priority (HP) traffic. The demand is increasing for that interruption free, high speed, high efficiency, best quality of services to perform successful communications. This paper emphasizes on the HP traffic like Video Conferencing, Video Chat, Telemedicine, Teleconferencing, and Interactive games for the real time communication. In contrast, the low priority data is considered as the best effort (BE) traffic because the BE traffic do not require delay sensitive applications. To achieve the best quality data communication for the HP traffic, in this paper, we propose a new dynamic bandwidth allocation (DBA) algorithm called dynamic hybrid slot size bandwidth allocation (DHSSBA) algorithm that is the modified version of the existing hybrid slot- size/rate (HSSR) algorithm. The performance of the proposed scheme has been analyzed by using numerical simulation in terms of the end to end packet delay for both the HP and BE traffic. We also have compared the simulation results of the proposed scheme with the existing HSSR scheme. From the comparison of the simulation results it is clear that the proposed scheme provides less end to end delay for the HP traffic than the HSSR scheme. However, the proposed scheme provides marginally higher delay than the HSSR scheme for the BE traffic at the higher offered loads. Keyword: DBA Algorithm, DHSSBA, HSSR, High Priority traffic, Best Effort traffic. I. INTRODUCTION With the advancement of communication technology, currently, the optical communication and networking is using for high capacity, high speed and high efficient data transfer. However, the end user optical access network is still in a developing stage. Passive optical network (PON) is a highly capable access network providing numerous advantages to the several service providers without any bandwidth problem [1]. The PON is considered as a promising next-generation access technology to fulfill the high bandwidth demand by the real time data traffic [2]. It is an efficient access network that provides lower operation and maintenance costs and allows larger distance between the central office (CO) and end users [3]. Ethernet PON (EPON) is a most effective standard of the PON technology. The EPON is deployed with bus or tree topology and connects the multiple optical network units (ONUs) with a single optical line terminal (OLT) which eventually connects to the metro and wide area networks (WANs) [4]. A feeder fiber is used to connect the OLT to multiple ONUs and a passive coupler, i.e., splitter/combiner, splits the optical signal into different ONUs in the downstream direction [5]. The EPON does not require any active element between the CO and the end users that only comprises with the passive optical components such as optical fiber, couplers, splices, and splitters [6]. The EPON is a topology based on IEEE 802.3ah standard has 8B/10B encoding with 1.25 Gbps nominal or 1 Gbps data rate effective for both the upstream and downstream directions [6]. The EPON structure with hybrid slot size bandwidth distribution principle is shown in Fig.1. Here, N is the number of ONUs those are connected to the OLT through an optical combiner / splitter. A cycle time is divided into two equal parts, i.e., part 1 is for the high priority (HP) data traffic and part 2 is for the best effort (BE) data traffic. The HP and BE data traffic of each ONU are sent to the OLT by using priority management in the ONU. One of the main problems of the EPON is to share a common upstream channel by the multiple ONUs. For better Fig.1. EPON Architecture in proposed method