Dynamic Bandwidth Allocation Schemes in Hybrid TDM/WDM Passive Optical Networks Ahmad R. Dhaini * , Chadi M. Assi * , and Abdallah Shami † * Concordia Institue for Information Systems Engineering Concordia University, Montreal, Quebec, Canada Email: {a dhaini, assi}@ciise.concordia.ca † Electrical and Computer Engineering Department Universtiy of Western Ontario, Ontario, Canada Email: ashami@eng.uwo.ca Abstract— Ethernet Passive Optical Networks (EPONs) are considered the most promising solutions for upgrading the cur- rent congested access networks to enable the delivery of broad- band integrated services. Although current EPON architectures are economically feasible, they are however bandwidth limited. In this paper, we discuss a simple upgrade architecture from EPON to WDM-PON. We present various Dynamic Wavelength and Bandwidth Allocation algorithms (DWBAs) that exploit both inter-channel and intra-channel statistical multiplexing in order to achieve good performance. We use extensive simulation experiments to validate our reasoning. I. I NTRODUCTION Ethernet Passive Optical Network (EPON) represents the convergence of inexpensive and ubiquitous Ethernet equipment with low-cost fiber infrastructure. It is viewed by many as an attractive solution for the broadband access network bottleneck and has been under intense research activities recently. EPON is a point-to-multipoint access network with no active elements in the signal’s path from source to destination [1]. It has been standardized by the IEEE 802.3ah working group [4] and it comprises one Optical Line Terminal (OLT) connected to mul- tiple Optical Network Units (ONUs). EPON systems deploy only one channel for downstream traffic and another channel for upstream traffic. In the downstream, Ethernet frames are broadcast by the OLT and are selectively received by each ONU. Alternatively, in the upstream, multiple ONUs share the same transmission channel to transmit data and control packets to the OLT. Since ONUs are unable to detect collision and due to the difficulty to implement a carrier sense multiple access with collision detection (CSMA/CD), it is necessary to design a mechanism that arbitrates the access of ONUs to the shared medium. This is achieved by designing a Medium Access Control (MAC) protocol to prevent collision between packets of different ONUs transmitting simultaneously. Current MAC supports Time Division Multiplexing (TDM) [1], where each ONU is allocated a fixed or dynamic time slot to transmit data to the OLT and each ONU buffers packets received from different subscribers until they are transmitted in the assigned window. Current EPONs efficiently support up to 32 ONUs, where beyond that the performance degrades. Given the widespread popularity of broadband services, the continuous increase of the number of subscribers, and the emergence of new bandwidth intensive applications, the need to deploy more ONUs ( ≈ 64) becomes indispensable. Therefore, upgrading the existing EPON architecture becomes necessary. There have been recently some discussions pertaining to this upgrade; the authors of [3] presented a new wavelength division multiplex- ing (WDM) PON architecture where multiple channels are simultaneously used by the ONUs to transmit their traffic. The authors of [6], [9] presented a new Hybrid TDM/WDM- PON architecture named SUCCESS ”Standford University aCCESS”. In this paper, we introduce a new WDM-PON architecture and we present a possible simple migration from TDM-PON to TDM/WDM-PON. We present new bandwidth allocation schemes for the hybrid WDM/TDM PON and we study their differences. These new schemes enable different ONUs to efficiently share (both in time and wavelength) the access network bandwidth to achieve better utilization. The rest of the paper is organized as follows. Section 2 presents the proposed WDM-PON architecture. In section 3, we present our bandwidth allocation schemes and section 4 presents analysis and comparative study of the proposed algorithms. Finally section 5 concludes our work. II. WDM-PON ARCHITECTURE In our proposed architecture, we keep the same EPON tree topology; however we increase the number of supported wavelengths [3]. In that context, two different architectures (A 1 , A 2 ) are possible. In A 1 , the set of all ONUs is divided into multiple subsets each allocated a fixed wavelength channel for upstream transmission. Hence, every ONU maintains a fixed transceiver, whereas the OLT maintains a bank of fixed transceivers. Within each subset, the transmission of different ONUs is arbitrated by the OLT through either a fixed or dynamic time slot assignment. Clearly, this architecture limits the sharability of different wavelengths among ONUs. An alternative A 2 (shown in Fig. 1) allows for simultaneous time/wavelength-sharing of WDM-PON resources among all ONUs. Here, every ONU will maintain a fast tunable laser, with a tuning speed in the range of micrometers and a tuning range of more than 60nm [6], [9], that enables it to tune its upstream transmission from one wavelength to another depending on the dynamic wavelength and bandwidth allo-