Incremental scheduling algorithms for WDM/TDM networks with arbitrary tuning latencies

We focus on all-optical broadcast and select slotted WDM networks. Each network user is equipped with one tunable transmitter and one fixed receiver; full connectivity is achieved by tuning transmitters to all different wavelengths available in the optical spectrum. Tuning latencies are considered to be not negligible with respect to the slot time. A network controller allocates fixed size slots in a TDM/WDM frame according to requests issued by users via signalling procedures. User requests are accommodated in the frame incrementally, as soon as they are received by the network controller. Since we aim at an incremental solution, we impose a transparency constraint in the scheduling algorithm: new user requests may be accepted only without affecting existing allocations, otherwise they are refused. We propose a novel scheduling algorithm that may route some flows from source to destination through some intermediate nodes, following a multi-hop approach. A formal definition of an optimal transparent incremental scheduling algorithm is provided as an integer linear programming problem. The optimal incremental scheduling algorithm is NP-hard. Thus, a heuristic quasi-optimal scheduling algorithm is proposed, and its complexity is evaluated. Performance results show that significant benefits can be achieved with respect to traditional single-hop approaches and to other multi-hop approaches.     

Packet scheduling in broadcast WDM networks with arbitrarytransceiver tuning latencies

We consider the problem of scheduling packet transmissions in a broadcast, single-hop wavelength-division multiplexing (WDM) network, with tunability provided only at one end. Our objective is to design schedules of minimum length to satisfy a set of traffic requirements given in the form of a demand matrix. We address a fairly general version of the problem as we allow arbitrary traffic demands and arbitrary transmitter tuning latencies. The contribution of our work is twofold, First we define a special class of schedules which permit an intuitive formulation of the scheduling problem. Based on this formulation we present algorithms which construct schedules of length equal to the lower bound provided that the traffic requirements satisfy certain optimality conditions. We also develop heuristics which, in the general case, give schedules of length equal or very close to the lower bound. Secondly, we identify two distinct regions of network operation. The first region is such that the schedule length is determined by the tuning requirements of transmitters; when the network operates within the second region however, the length of the schedule is determined by the traffic demands, not the tuning latency. The point at which the network switches between the two regions is identified in terms of system parameters such as the number of nodes and channels and the tuning latency. Accordingly, we show that it is possible to appropriately dimension the network to minimize the effects of even large values of the tuning latency     

Message scheduling in WDM optical networks with reduced transmitter tuning overhead

Relatively large transceiver tuning overhead is one major difficulty when designing a medium access control scheme for a single-hop passive-star coupled WDM optical network. To overcome this difficulty, we propose two algorithms, namely continuous channel scheduling (CCS) and continuous channel-minimum scheduling latency (CC-MSL), to reduce the negative impact of tuning overhead as much as possible. Extensive simulations have been conducted. And the simulation results show that significant improvement in average delay can be achieved by our new algorithms.     

Multicast traffic scheduling in single-hop WDM networks with arbitrary tuning latencies

To accommodate the demands of quality of service (QoS) and multicast applications, a multicast QoS traffic-scheduling algorithm with tuning latency consideration in wavelength-division multiplexing star-coupled networks is provided in this paper. To furnish different levels of QoS, two classes of traffic are considered: constant bit rate and available bit rate (ABR). An effective bandwidth-normalization scheme for ABR traffic is also derived. We define the slot scanning problem in the connection-setup process as the maximum assignable slots (MAS) problem. We prove that the optimal solution of the MAS problem can be obtained in polynomial time. Owing to its high-order time complexity, we also propose two heuristics for the MAS problem. The performance of these strategies are evaluated and compared by simulations under different system parameters, such as number of wavelengths, traffic load, and tuning latency.     

Mini-slot TDM WDM optical networks

In recent years, optical transport networks have evolved from interconnected SONET/WDM ring networks to mesh-based optical WDM networks. Time-slot wavelength switching is to aggregate the lower rate traffic at the time-slot level into a wavelength in order to improve bandwidth utilization. With the advancement of fiber-optics technologies, continual increase of fiber bandwidth and number of wavelengths in each fiber, it is possible to divide a wavelength in a fiber into time-slots, and further divide a time-slot into mini-slots so that the fiber bandwidth can be more efficiently utilized. This article proposes a router architecture with an electronic system controller to support optical data transfer at the mini-slot(s) of a time-slot in a wavelength for each hop of a route. The proposed router architecture performs optical circuit switching and does not use any wavelength converter. Each node in the mini-slot TDM WDM optical network consists of the proposed router architecture. Three different network topologies are used to demonstrate the effectiveness and behavior of this type of network in terms of blocking probability and throughput.     

Efficient scheduling of nonuniform packet traffic in a WDM/TDMlocal lightwave network with arbitrary transceiver tuning latencies

A passive-star-based, broadcast-and-select, local lightwave network which can support a limited number of wavelength-division multiplexed (WDM) channels, but serve a much larger number of nodes, is considered. Each node is equipped with one tunable transmitter and one fixed receiver, and each WDM channel is operated in a time-division multiplexed (TDM) fashion for carrying packet traffic. Bandwidth is allocated to the node pairs when traffic flow between them is nonuniform, while also accommodating transceiver tuning latency. Our approach exploits well-known results from scheduling theory to create efficient transmission schedules. Multiprocessor task scheduling heuristics that can be applied to load balancing in a multichannel network is also examined     

Efficient multi-hop scheduling algorithms for packet transmissions in WDM optical star networks

This paper proposes multi-hop scheduling algorithms for the All-to-All Broadcast (AAB) problem in Wavelength Division Multiplexed (WDM) optical star networks. The multi-hop AAB problem can be split into two subproblems: Logical Topologies Construction (LTC) problem, and Transmission Scheduling (TS) problem. For improving the efficiency of multi-hop scheduling, we focus on a new multi-hop transmission model and transfer the LTC problem to a special case of the Round Robin Tournament (RRT) problem. In the proposed logical topologies, our multi-hop scheduling algorithms can easily overlap the tuning latency and reduce the number of tuning operations on each node. We compare our results with previous research in terms of schedule length. Overall results indicate that our multi-hop scheduling algorithms have better performance than previous algorithms.     

TDM policies in multistation packet radio networks

A multistation packet radio network with m stations and a finite number of nodes n that uses a conflict-free protocol to access the backbone network of stations through a shared channel is discussed. The goal is to derive an allocation of the channel time slots (time-division multiplexing cycle), so that all transmissions will be conflict-free and some measure of performance (e.g., the expected total weighted throughput, the expected weighted holding cost) will be optimized. The methodology that is used is to bound the performance and to allocate the slots according to the golden ratio policy     

Analysis of call blocking probability in TDM/WDM networks withtransparency constraint

In this letter we devise and validate by simulation an analytical model to study the performance of TDM/WDM networks using a three-stage switching architecture as an abstract model. We consider the transparency property as a constraint: a new incoming call can be accepted only without modifying the routing of previously accepted calls. We concentrate on the analysis of the call blocking probability by varying the traffic pattern and the configuration of the switching architecture. We show that a very good agreement is obtained between simulation and analytical results     

RSOA在光接入网TDM/WDM混合PON中的应用

介绍了RSOA的工作原理、技术指标以及它在TDM-/WDM混合PON网络中的应用.实际应用表明,RSOA在50mA下,小信号光增益可达28dB、输出光功率6dBm,噪声指数6.5dB;讨论、分析了RSOA的温度稳定性、噪声指数和激射等问题.     

Fair scheduling in wireless packet networks

Fair scheduling of delay and rate-sensitive packet flows over a wireless channel is not addressed effectively by most contemporary wireline fair-scheduling algorithms because of two unique characteristics of wireless media: (1) bursty channel errors and (2) location-dependent channel capacity and errors. Besides, in packet cellular networks, the base station typically performs the task of packet scheduling for both downlink and uplink flows in a cell; however, a base station has only a limited knowledge of the arrival processes of uplink flows. We propose a new model for wireless fair-scheduling based on an adaptation of fluid fair queueing (FFQ) to handle location-dependent error bursts. We describe an ideal wireless fair-scheduling algorithm which provides a packetized implementation of the fluid mode, while assuming full knowledge of the current channel conditions. For this algorithm, we derive the worst-case throughput and delay bounds. Finally, we describe a practical wireless scheduling algorithm which approximates the ideal algorithm. Through simulations, we show that the algorithm achieves the desirable properties identified in the wireless FFQ model     

QoS-guaranteed packet scheduling in wireless networks

To guarantee the quality of service (QoS) of a wireless network, a new packet scheduling algorithm using cross-layer design technique is proposed in this article. First, the demand of packet scheduling for multimedia transmission in wireless networks and the deficiency of the existing packet scheduling algorithms are analyzed. Then the model of the QoS-guaranteed packet scheduling (QPS) algorithm of high speed downlink packet access (HSDPA) and the cost function of packet transmission are designed. The calculation method of packet delay time for wireless channels is expounded in detail, and complete steps to realize the QPS algorithm are also given. The simulation results show that the QPS algorithm that provides the scheduling sequence of packets with calculated values can effectively improve the performance of delay and throughput.     

WDM packet routing for high-capacity data networks

We present experimental and numerical studies of a novel packet-switch architecture, the data vortex, designed for large-scale photonic interconnections. The selfrouting multihop packet switch efficiently scales to large port counts (>10 k) while maintaining low latencies, a narrow latency distribution, and high throughput. To facilitate optical implementation, the data-vortex architecture employs a novel hierarchical topology, traffic control, and synchronous timing that act to reduce the necessary routing logic operations and buffering. As a result of this architecture, all routing decisions for the data packets are based on a single logic operation at each node. The routing is further simplified by the employment of wavelength division multiplexing (WDM)-encoded header bits, which enable packet-header processing by simple wavelength filtering. The packet payload remains in the optical domain as it propagates through the data-vortex switch fabric, exploiting the transparency and high bandwidths achievable in fiber optic transmission. In this paper, we discuss numerical simulations of the data-vortex performance and report results from an experimental investigation of multihop WDM packet routing in a recirculating test bed     

Design and evaluation of scheduling algorithms for TDM/WDM PON based on RSOA

This paper presents a scalable and costeffective hybrid time division multiplexing (TDM)/wavelength division multiplexing (WDM) passive optical network (PON), in which reflective semiconductor optical amplifiers (RSOAs) are used as optical network units (ONUs) and a shared tunable laser and photoreceiver stack locate at the optical line terminal (OLT). Especially,tunable transmitters are not only shared by all ONUs, but also used for both upstream and downstream transmissions. To solve resource contention problem and provide and the ONUs, two novel algorithms are proposed to manipulate the wavelength accessibility and the burst scheduling. The performance of both algorithms in terms of the average packet end-to-end delay and throughput were simulated and evaluated.     

Routing, wavelength and time-slot-assignment algorithms for wavelength-routed optical WDM/TDM networks

This paper studies the connection-assignment problem for a time-division-multiplexed (TDM) wavelength-routed (WR) optical wavelength-division-multiplexing (WDM) network. In a conventional WR network, an entire wavelength is assigned to a given connection (or session). This can lead to lower channel utilization when individual sessions do not need the entire channel bandwidth. This paper considers a TDM-based approach to reduce this inefficiency, where multiple connections are multiplexed onto each wavelength channel. The resultant network is a TDM-based WR network (TWRN), where the wavelength bandwidth is partitioned into fixed-length time slots organized as a fixed-length frame. Provisioning a connection in such a network involves determining a time-slot assignment, in addition to the route and wavelength. This problem is defined as the routing, wavelength, and time-slot-assignment (RWTA) problem. In this paper, we present a family of RWTA algorithms and study the resulting blocking performance. For routing, we use the existing shortest path routing algorithm with a new link cost function called least resistance weight (LRW) function, which incorporates wavelength-utilization information. For wavelength assignment, we employ the existing least loaded (LL) wavelength selection; and for time-slot allocation, we present the LL time-slot (LLT) algorithm with different variations. Simulation-based analyses are used to compare the proposed TDM architecture to traditional WR networks, both with and without wavelength conversion. The objective is to compare the benefits of TDM and wavelength conversion, relative to WR networks, towards improving performance. The results show that the use of TDM provides substantial gains, especially for multifiber networks.     

Novel hybrid WDM/TDM PON architectures to manage flexibility in optical access networks

Different hybrid WDM/TDM PON architectures are compared in terms of flexibility, simplicity (affecting the cost), insertion loss (affecting the reach) and security. Special attention is given to the flexibility aspect in next generation optical access networks by designing different architectures with a different degree of flexibility, which are able to cope with different ranges of dynamic bandwidth allocation (DBA) possibilities. This paper assesses the degree of architectural flexibility needed to deal with some important flexibility advantages. It is shown that mostly a partially flexible architecture fulfils the needs. The architectures are then further evaluated from a cost and reach perspective. In this way, we provide a complete comparison considering all the key aspects of access network design. It is shown that a hybrid WDM/TDM PON with a partially flexible architecture in the first remote node can be an interesting candidate for next-generation optical access networks.     

Optimal Transceiver Scheduling in WDM/TDM Networks

In this paper, we study the benefits of using tunable transceivers for reducing the required number of electronic ports in wavelength-division-multiplexing/time-division multiplexing optical networks. We show that such transceivers can be used to efficiently “groom” subwavelength traffic in the optical domain and so can significantly reduce the amount of terminal equipment needed compared with the fixed-tuned case. Formulations for this “tunable grooming” problem are provided, where the objective is to schedule transceivers so as to minimize the required number of ports needed for a given traffic demand. We establish a relationship between this problem and edge colorings of graphs which are determined by the offered traffic. Using this relationship, we show that, in general, this problem is NP-complete, but we are able to efficiently solve it for many cases of interest. When the number of wavelengths in the network is not limited, each node is shown to only require the minimum number of transceivers (i.e., no more transceivers than the amount of traffic that it generates). This holds regardless of the network topology or traffic pattern. When the number of wavelengths is limited, an analogous result is shown for both uniform and hub traffic in a ring. We then develop a heuristic algorithm for general traffic that uses nearly the minimum number of transceivers. In most cases, tunable transceivers are shown to reduce the number of ports per node by as much as 60%. We also consider the case where traffic can dynamically change among an allowable set of traffic demands. Tunability is again shown to significantly reduce the port requirement for a nonblocking ring, both with and without rearrangements.     

Photonic packet WDM ring networks architecture and performance

This article reviews various WDM ring architectures and pays special attention to their implementation in the metropolitan environment. A number of possible network architectures as well as protocols are reviewed. The article also proposes and analyses a WDM slotted-ring network architecture with nodes that use one fixed transmitter and fixed receivers. Used as a metropolitan access network, it is shown through simulation how a simple slotted MAC protocol can be implemented in this network to achieve efficient bandwidth utilization. Throughput, delay and packet dropping probability results are presented under Poisson and self-similar traffic.     

Dynamic load balancing in WDM packet networks with and without wavelength constraints

We develop load balancing algorithms for WDM-based packet networks where the average traffic between nodes is dynamically changing. In WDM-based packet networks, routers are connected to each other using wavelengths (lightpaths) to form a logical network topology. The logical topology may be reconfigured by rearranging the lightpaths connecting the routers. Our algorithms reconfigure the logical topology to minimize the maximum link load. In this paper, we develop iterative reconfiguration algorithms for load balancing that track rapid changes in the traffic pattern. At each reconfiguration step, our algorithms make only a small change to the network topology hence minimizing the disruption to the network. We study the performance of our algorithms under several dynamic traffic scenarios and show that our algorithms perform near optimally. We further show that these large reconfiguration gains are achievable in systems with a limited number of wavelengths.     

A novel architecture of hybrid (WDM/TDM) passive optical networks with suitable modulation format

In this paper, we have analyzed the performance and feasibility of a hybrid wavelength division multiplexing/time division multiplexing passive optical network (WDM/TDM) PON system with 128 optical networks units (ONUs). In the proposed network, the triple play services (video, voice and data) are successfully transmitted to a distance of 28 km to all ONUs. In addition, we investigate and compare the proposed hybrid PON for suitability of various modulation formats for different distance. It has been observed that the most suitable data format for hybrid PON network is NRZ Rectangular.