Multiclass scheduling algorithms for the DAVID metro network

Abstract—The data and voice integration over dense wavelength-division-multiplexing (DAVID) project proposes a metro network architecture based on several wavelength-division-multiplexing (WDM) rings interconnected via a bufferless optical switch called Hub. The Hub provides a programmable interconnection among rings on the basis of the outcome of a scheduling algorithm. Nodes connected to rings groom traffic from Internet protocol routers and Ethernet switches and share ring resources. In this paper, we address the problem of designing efficient centralized scheduling algorithms for supporting multiclass traffic services in the DAVID metro network. Two traffic classes are considered: a best-effort class, and a high-priority class with bandwidth guarantees. We define the multiclass scheduling problem at the Hub considering two different node architectures: a simpler one that relies on a complete separation between transmission and reception resources (i.e., WDM channels) and a more complex one in which nodes fully share transmission and reception channels using an erasure stage to drop received packets, thereby allowing wavelength reuse. We propose both optimum and heuristic solutions, and evaluate their performance by simulation, showing that heuristic solutions exhibit a behavior very close to the optimum solution. Index Terms—Data and voice integration over dense wavelength-division multiplexing (DAVID), metropolitan area network, multiclass scheduling, optical ring, wavelength-division multiplexing (WDM). I

Design of switch architecture for the geographical cell transport protocol

The Internet is divided into multiple layers to reduce and manage complexity. The International Organization for Standardization (ISO) developed a 7 layer network model and had been revised to a 5 layer TCP/IP based Internet Model. The layers of the Internet can also be divided into top layer TCP/IP protocol suite layers and the underlying transport network layers. SONET/SDH, a dominant transport network, was designed initially for circuit based telephony services. Advancement in the internet world with voice and video services had pushed SONET/SDH to operate with reduced efficiencies and increased costs. Hence, redesign and redeployment of the transport network has been and continues to be a subject of research and development. Several projects are underway to explore new transport network ideas such as G.709 and GMPLS. This dissertation presents the Geographical Cell Transport (GCT) protocol as a candidate for a next generation transport network. The GCT transport protocol and its cell format are described. The benefits provided by the proposed GCT transport protocol as compared to the existing transport networks are investigated. Existing switch architectures are explored and a best architecture to be implemented in VLSI for the proposed transport network input queued virtual output queuing is obtained. The objectives of this switch are high performance, guaranteed fairness among all inputs and outputs, robust behavior under different traffic patterns, and support for Quality of Service (QoS) provisioning. An implementation of this switch architecture is carried out using HDL. A novel pseudo random number generation unit is designed to nullify the bias present in an arbitration unit. The validity of the designed is checked by developing a traffic load model. The speedup factor required in the switch to maintain desired throughput is explored and is presented in detail. Various simulation results are shown to study the behavior of the designed switch under uniform and hotspot traffic. The simulation results show that QoS behavior and the crossing traffic through the switch has not been affected by hotspots

Feedback-based scheduling for load-balanced two-stage switches

A framework for designing feedback-based scheduling algorithms is proposed for elegantly solving the notorious packet missequencing problem of a load-balanced switch. Unlike existing approaches, we show that the efforts made in load balancing and keeping packets in order can complement each other. Specifically, at each middle-stage port between the two switch fabrics of a load-balanced switch, only a single-packet buffer for each virtual output queueing (VOQ) is required. Although packets belonging to the same flow pass through different middle-stage VOQs, the delays they experience at different middle-stage ports will be identical. This is made possible by properly selecting and coordinating the two sequences of switch configurations to form a joint sequence with both staggered symmetry property and in-order packet delivery property. Based on the staggered symmetry property, an efficient feedback mechanism is designed to allow the right middle-stage port occupancy vector to be delivered to the right input port at the right time. As a result, the performance of load balancing as well as the switch throughput is significantly improved. We further extend this feedback mechanism to support the multicabinet implementation of a load-balanced switch, where the propagation delay between switch linecards and switch fabrics is nonnegligible. As compared to the existing load-balanced switch architectures and scheduling algorithms, our solutions impose a modest requirement on switch hardware, but consistently yield better delay-throughput performance. Last but not least, some extensions and refinements are made to address the scalability, implementation, and fairness issues of our solutions. © 2009 IEEE.published_or_final_versio

Design of Routers for Optical Burst Switched Networks

Optical Burst Switching (OBS) is an experimental network technology that enables the construction of very high capacity routers using optical data paths and electronic control. In this dissertation, we study the design of network components that are needed to build an OBS network. Specifically, we study the design of the switches that form the optical data path through the network. An OBS network that switches data across wavelength channels requires wave-length converting switches to construct an OBS router. We study one particular design of wavelength converting switches that uses tunable lasers and wavelength grating routers. This design is interesting because wavelength grating routers are passive devices and are much less complex and hence less expensive than optical crossbars. We show how the routing problem for these switches can be formulated as a combinatorial puzzle or game, in which the design of the game board determines key performance characteristics of the switch. In this disertation, we use this formu-lation to facilitate the design of switches and associated routing strategies with good performance. We then introduce time sliced optical burst switching (TSOBS), a variant of OBS that switches data in the time domain rather that the wavelength domain. This eliminates the need for wavelength converters, the largest single cost component of systems that switch in the wavelength domain. We study the performance of TSOBS networks and discuss various design issues. One of the main components that is needed to build a TSOBS router is an optical time slot interchanger (OTSI). We explore various design options for OTSIs. Finally, we discuss the issues involved in the design of network interfaces that transmit the data from hosts that use legacy protocols into a TSOBS network. Ag-gregation and load balancing are the main issues that determine the performance of a TSOBS network and we develop and evaluate methods for both

On greening optical access networks

With the remarkable growth of fiber-based services, the number of FTTx subscribers has been dramatically increasing in recent years. Owing to the environmental concern, reducing energy consumption of optical access networks has become an important issue for network designers. In Ethernet passive optical network (EPON), the optical line terminal (OLT) located at the central office broadcasts the downstream traffic to all optical network units (ONUs), each of which checks all arrival downstream packets to obtain those destined to itself. Since traffic of ONUs changes dynamically, properly defining the sleep mode for idle ONUs can potentially save a significant amount of energy. However, it is challenging to shut down an ONU receiver as the ONU needs to receive some downstream control packets to perform upstream transmission. In this framework, a novel sleep control scheme is proposed to address the downstream issue which can efficiently put ONU receivers to sleep. This dissertation further defines multiple levels of power saving in which the ONU disables certain functions based on the upstream and downstream traffic load. The proposed schemes are completely compatible with the multi-point control protocol (MPCP) and EPON standards. Elimination of the handshake process makes the sleep control schemes more efficient. Currently, OLTs also consume a significant amount of energy in EPON. Therefore, reducing energy consumption of OLT is as important as reducing energy consumption of ONUs; such requirement becomes even more urgent as OLT keeps increasing its provisioning data rate, and higher data rate provisioning usually implies higher energy consumption. Thus, a novel energy-efficient OLT structure, which guarantees services of end users with a smallest number of power-on OLT line cards, is proposed. More specifically, the number of power-on OLT line cards is adapted to the real-time incoming traffic. Also, to avoid service disruption resulted by powering off OLT line cards, a proper optical switch is equipped in OLT to dynamically configure the communications between OLT line cards and ONUs. By deploying a semi-Markov based technique, the performance characteristics of the sleep control scheme such as delay and energy-saving are theoretically analyzed. It is shown that, with proper settings of sleep control parameters, the proposed scheme can save a significant amount of energy in EPON

Load-balanced optical switch for high-speed router design

A hybrid electro-optic router is attractive, where packet buffering and table lookup are carried out in electrical domain and switching is done optically. In this paper, we propose a loadbalanced optical switch (LBOS) fabric for a hybrid router. LBOS comprises N linecards connected by an N-wavelength WDM fiber ring. Each linecard i is configured to receive on channel λ i. To send a packet, it can select and transmit on an idle channel based on where the packet goes. The packet remains in the optical domain all the way from an input linecard/port to an output linecard/port. Meanwhile, the loading in the ring network is perfectly balanced by spreading the packets for different destinations to use different wavelengths, and packets for the same destination to use different time slots. With the pipelined operation of the LBOS, we show that LBOS is an optical counterpart of an efficient load-balanced electronic switch, and close-to-100% throughput can be obtained. To address the ringfairness problem under the inadmissible traffic patterns, an efficient throughput-fair scheduler for LBOS is also devised. ©2010 IEEE.published_or_final_versio