Thaere Eido

Packet Filling Optimization in Multiservice Slotted Optical Packet Switching MAN Networks

Many aspects about Optical Packet-Switching (OPS) networks have been studied in the last few years and it has been shown that their performance depends on several determinant factors, such as the transmission mode and the optical packet format A synchronous slotted mode is more adapted to MAN network specifications, since it produces higher throughput comparing to the asynchronous mode. In this paper, we propose an optimized mechanism for creation of fixed-size optical payloads filled with variable size electronic client packets. Our algorithm is called GPFO for graduated packet filling optimization. It avoids the need for complex segmentation methods. It also provides high network throughput and good performance results in terms of packet loss ratio and mean access delay. We investigated the performance of our algorithm throw simulation works. Using the ns simulator, our experiments are performed on an optical MAN network with a ring topology. Numerical results have shown that, compared to existing solutions, the GPFO enhances the network throughput and optimizes the global network performance in terms of queuing delay and bit loss ratio.

Impact of Fixed-Size Packet Creation Timer and Packet Format on the Performance of Slotted and Unslotted Bus-Based Optical MAN

In a typical slotted bus-based optical metropolitan network, the position of access node on the networkpsilas bus have a large impact on the network performance. We refer to this problem in data transmission as the unfairness property. In fact, the first nodes on the bus have priority over downstream nodes. Another factor which has a significant impact on the network performance is the choice of Timer value, which is used to create the fixed-size optical packet. An unsuitable choice of Timer values may lead to wasted network bandwidth. Indeed, small Timer values generate optical packets with very low filling ratios; while a very big Timer value leads to excessive packet creation delays (and therefore high access delays) when the arrival rate of electronic client packets becomes low. In this paper, we investigate the impact of Timer values on the network performance by simulating the slotted bus-based network that supports multi-service. In this context, we are interested in two study cases: with and without quality of service (QoS) Upgrade mechanism. Additionally, we will show that the slotted bus-based network with QoS Upgrade can improve the network performance, in terms of mean access delay and loss ratio of electronics packets clients, compared with unslotted bus-based network that supports variable-size optical packets.

An Enhanced QoS-enabled Dynamic Bandwidth Allocation Mechanism for Ethernet PON

The Ethernet Passive Optical Network (EPON) combines both inexpensive Ethernet equipments and the large bandwidth offered by the optical fiber. Therefore, EPON has been considered as an attractive solution for the next generation broadband access network. In this paper, we present an enhanced Dynamic Bandwidth Allocation (eDBA) algorithm for EPON network. Our mechanism allocates effectively and fairly the transmission bandwidth to ONUs. Some other algorithms, such as the Dynamic Bandwidth Allocation (DBA), introduce an idle period during the time that the Optical Line Terminal (OLT) is executing the bandwidth assignment procedure. During this idle time, no data are sent by any ONU node to OLT. In order to exploit this wasted bandwidth, the proposed algorithm calculates a vector of complementary bandwidth amounts to assign to the ONUs during the idle time. Finally, we simulate a multiservice-based EPON network configured with the eDBA mechanism. Obtained results are compared to the ones obtained with two other algorithms: Dynamic Bandwidth Allocation (DBA) and the Interleaved Polling with Adaptive Cycle Time (IPACT). We show that eDBA can significantly improve the network performance in term of packet access delay and packet loss rate as compared with other algorithms.

Modelling and Performance Evaluation of Improved Access Mechanisms in a Novel Multiservice OPS Architecture

Optical Packet Switching (OPS) technologies are among the most promising solutions for Next Generation Networks. In OPS networks, several mechanisms for Quality of Service (QoS) management have been developed. In this paper, we address QoS and fairness issues in a novel OPS ring architecture with a slotted synchronous transmission. The MAC protocol in the studied architecture is similar to CSMA/CA. Each node may use the available bandwidth in an opportunist manner. Therefore, the chances for each node to find available transmission resources are tightly correlated to the matrix of traffic at the other nodes. In order to remedy this problem, we elaborate two improved access mechanisms with preemptive approaches: Packet Erasing Mechanism (PEM) and Extraction and Reemission Mechanism (ERM). We evaluate the performance of the proposed mechanisms using a discrete-time analytical model. Finally, the results obtained by our model are validated and analyzed through several simulation scenarios.

DCUM: dynamic creation of fixed-size containers in multiservice synchronous OPS ring networks

Optical Packet Switched Metropolitan Area Networks (OPS MAN) are among the most promising solutions for Next Generation MAN architectures. As far as the network synchronization and the packet format are concerned, compared to an asynchronous MAN that supports packets of variable size, a synchronous network with large fixed-size packets offers a significant gain in the network throughput. It avoids bandwidth fragmentation and reduces the number of generated optical headers [1]. In such systems, client packets of variable size are aggregated and accommodated into optical fixed-size containers (fixed-size packets). In this paper, we show how delay constraints and the lack of segmentation mechanism may lead to the creation of optical fixed-size containers which are only partially filled with client packets. When optical containers pass intermediate without O/E/O conversion, the remaining unfilled space in such containers constitutes a wasted amount of bandwidth. Therefore, we propose a novel mechanism that improves the filling-ratio of optical containers. Our algorithm (so called DCUM for Dynamic CoS-Upgrade Mechanism) is based on the use of timers, which values change dynamically, in order to create containers with high filling ratio while limiting the time needed for their creation. We investigate the performance of our algorithm through simulation works. Our experiments are performed on an Optical MAN network with a ring topology. Numerical results show that, compared to existing solutions, DCUM provides optical containers with high filling ratios, and thus keeps the network performance (in terms of packet loss ratio and mean access delay) at safe-levels, regardless to the network load and the timeslot duration (transmission time of one optical container).

Performance of a Virtual Synchronization Mechanism in an Asynchronous Optical Network

Optical Packet Switched (OPS) ring Metropolitan Area Networks (MAN) are among the most promising solutions for Next Generation MAN architectures. However, a particular phenomenon is observed in optical ring networks with random access to the transmission medium, such as in asynchronous Optical Unslotted Carrier Sense Multiple Access with Collision Avoidance (OU-CSMA/CA). Due to the random moments of packet transmissions, the amount of bandwidth which is available for use, on each wavelength, becomes divided into many small pieces. This problem, also called bandwidth fragmentation, causes a waste of some transmission resources. In fact, free spaces which are smaller then the optical packet size are out of use for traffic insertion. The bandwidth fragmentation is reduced in synchronous networks, thanks to the better use of the transmission resources provided by these networks [6]. This paper describes an access scheme that is proposed to improve the performance of the original OU-CSMA/CA applied to an asynchronous optical ring network. We propose a “virtual synchronization” mechanism (VSC), which improves significantly the bandwidth utilization while being very simple to implement. We provide simulation works in order to validate the efficiency of the proposed mechanism. Numerical results show the improvement of performance provided by the VSC mechanism, compared to the original CSMA/CA protocol.

Dynamic resource allocation algorithm for metropolitan optical packet-switched ring networks

The problem studied in this paper is a wavelength allocation algorithm applied to a metropolitan optical packet-switched ring network. Existing algorithms that provide optimal wavelength allocation generally require excessive computational time even with a small network of 8 to 16 nodes. Therefore, those approaches seem to be inappropriate for providing a dynamic real time wavelength allocation, which reacts as rapidly as possible to the growth of data traffic. In this work we present an approach for real time resource allocation (the so-called R2A) algorithm applied to optical packet-switched ring networks. This is based on equivalent bandwidth methods and heuristic iterative algorithm that can be executed in real-time. We also use simulations to evaluate the performance of the network configured according to the wavelength allocation map provided by R2A.

Performance Analysis of an Enhanced Distributed Access Mechanism in a Novel Multiservice OPS Architecture

Optical Packet Switching (OPS) technologies are among the most promising solutions for Next Generation Internet. In this paper, we address Quality of Service (QoS) and fairness issues in a novel OPS ring architecture with a slotted synchronous transmission mode. The basic MAC protocol in the studied architecture is similar to the CSMA/CA mechanism. Using this mechanism, each node in the network may use the available bandwidth in an opportunist manner. Moreover, in the considered network, optical packets bypass intermediate nodes without being delayed or converted to the electronic domain. Therefore, the chances for a ring node to find available transmission resources are tightly correlated to the matrix of traffic of the other nodes. This leads to unfair sharing of the transmission medium. In order to remedy this problem, we elaborate a distributed Tag-based Enhanced Access Mechanism (TEAM). The proposed solution evolves from two preemptive access mechanisms that we have proposed recently (namely the Packet Erasing Mechanism PEM and the Extraction and Reemission Mechanism ERM). In order to resolve the unfairness issue, which characterizes ring OPS architectures with transparent transit at intermediate nodes, we use an advanced distributed approach where all ring nodes cooperate together. Finally, we evaluate the performance of the TEAM mechanism through several simulation scenarios.

Aggregation issues in time slotted packet ring networks

This paper analyses the aggregation process in time slotted packet ring networks. The paper demonstrates that Timer-based upgrade mechanisms can be used to optimise the filling ratio of optical packets.

Multiservice Optical Packet Switched Networks: Modeling, Performance Evaluation and QoS Mechanisms in a Mesh Slotted Architecture

Optical Packet Switching (OPS) technologies are among the most promising solutions for Next Generation Network architectures. Resource contention resolution and Quality of Service (QoS) management mechanisms have been developed in order to remedy the lack of optical buffering and implement multi-service support in OPS networks. In this paper we propose an analytical model for the access and core nodes of a multiservice mesh network architecture which operates in a synchronous slotted transmission mode. The proposed model captures the effect of the client traffic matrix and considers a priority-based multi-service support. Moreover, we elaborate two resource management mechanisms: Cumulative Credits Mechanism (CCM) and Distributed Deflection Routing (DDR). The former solves inter-class fairness issues at the access nodes and the latter optimizes the resource contention resolution in the core of the network. We use our analytical model to show the interest of the developed mechanisms. The results obtained by the proposed model are validated and analyzed through several simulation scenarios.