Elsevier

Computer Communications

Volume 30, Issue 6, 26 March 2007, Pages 1315-1330
Computer Communications

FARE: An efficient integrated MAC protocol for differentiated services in WDM metro rings

https://doi.org/10.1016/j.comcom.2006.12.017Get rights and content

Abstract

This study investigates the fairness control, collision avoidance and QoS support issues of a particular WDM dual-ring network known as FT2-TR2. This system is an extended version of the original uni-directional FT-TR ring architecture, in which every node is equipped with a fixed-tuned transmitter and a tunable receiver on each ring. This study proposes a novel FAirness and REservation integrated protocol, designated FARE, which incorporates three mechanisms designed specifically to resolve the receiver collision problem, to achieve fairness among all of the network nodes, and to meet the tight delay requirements of multimedia applications. Simulation results are presented to demonstrate that FARE provides a high performance for real-time traffic while simultaneously providing significant performance improvements for best-effort traffic.

Introduction

The increased demand for transport capacity fueled by the explosive growth of Internet traffic in the past few years has prompted the development of high-speed transmission systems and the emergence of Wavelength Division Multiplexing (WDM) techniques. WDM enables hundreds of wavelengths to be carried in a single strand of an optical fiber such that several hundred gigabits of data can be transmitted per second [1]. WDM has emerged as the solution of choice for enhancing transmission capacities in order to satisfy the increased bandwidth demands of broadband networks.

Due to the popularity of distributed content-sharing applications and the installation of local video streaming servers by ISPs, traffic models in Metropolitan Area Networks (MANs) have changed dramatically, rendering current MAN network architectures inadequate. Many studies have been conducted to investigate appropriate WDM-based network topologies and optical packet switching techniques for metropolitan areas [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. WDM metro networks, which typically have either a star [2], [3], [4] or a ring topology [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], have attracted considerable interest recently due to their potential for supporting the development of next-generation metropolitan area networks with huge bandwidth.

The feasibility of designing an optical packet-switched WDM ring network was investigated and demonstrated by the HORNET project [10], [11]. The HORNET network is a uni-directional ring network in which the wavelengths are all slotted with various numbers of fixed-size slots designed to transport fixed-size packets, such as ATM cells [10]. HORNET is a fast TT (tunable transmitter)-FR (fixed-tuned receiver) network structure in which multiple nodes share the same drop wavelength for reception, but each node can choose any wavelength for transmission. When a node transmits a packet, it multiplexes a subcarrier tone onto the packet with a unique subcarrier frequency corresponding to the wavelength occupied by that packet. To ensure collision-free packet transmission, HORNET uses an optical Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol [10], based on the subcarrier multiplexing (SCM) scheme, to govern the transmission of packets.

Besides CSMA/CA, several posteriori buffer selection policies [15], [16] and fairness control issues [17] have been presented for the HORNET network structure. Typically, each node in a TT-FR system maintains separate transmission queues, either one for each destination or one for each wavelength. The aim of the buffer selection strategy is to resolve contention conflicts among the nodes sharing the available wavelengths by selecting an appropriate destination queue for each packet. Although these buffer selection protocols achieve high network efficiency, they generally fail to provide a satisfactory fairness. Therefore, the transmission rate of each individual node must be controlled using fairness control schemes to ensure fairness across the network. Another major issue is the provisioning of quality of service (QoS) support in order to integrate real-time and best-effort (data) traffic streams in the WDM layer. To address the QoS issue, the HORNET network is equipped with an efficient QoS scheme for the integration of real-time and best-effort services [15].

In [12], Jelger and Elmirghani proposed FT (fixed-tuned transmitter)-TR (tunable receiver) system, which is yet another form of packet-switched slotted ring networks. It has been shown that the FT-TR and TT-FR architectures achieve a similar theoretical performance [18]. However, the scalability aspects are far simpler in a FT-TR system than in a TT-FR system [13]. For instance, if the maximum throughput achievable per wavelength and the node transmission rates are known, determining the number of network nodes sharing a common transmission wavelength is straightforward for FT-TR networks. Comparatively, scalability predictions in TT-FR systems are more difficult to obtain.

In a FT-TR network, each node is equipped with one fixed-tuned transmitter and one tunable receiver. Packets are buffered in one single FIFO transmit queue at each node. Unlike TT-FR systems, multiple nodes in FT-TR systems share the same drop wavelength for transmission, but each node can choose any wavelength for reception. Jelger and Elmirghani employed a simple fairness mechanism that prevents a node from reusing the slot it just marked empty in either a source-stripping or a destination-stripping mechanism to avoid a node from starvation. However, this fairness mechanism failed to achieve a complete fairness of transmission rate across all of the nodes, particularly when the network traffic pattern was unbalanced. Moreover, there is no support of QoS requirements to transmit real-time traffic in their FT-TR system.

Another issue of a FT-TR system is that receiver collisions may occur because each node is only equipped with one tunable receiver. Jelger and Elmirghani [14] proposed two Collision Avoidance (CA) strategies to avoid receiver collisions. In the first approach, when multiple packets are destined to the same receiving node at the same time, only one of the packets destined for the receiving node was actually received by the destination; the rest of the colliding packets continued to loop around the ring until they are received one-by-one at the destination. However, this approach not only increases transmission delays, but also increases the number of subsequent receiver collisions since packets sent later to the same destination may collide with earlier packets which are yet to be received. In the second approach, receiver collisions were avoided entirely by replacing the single tunable receiver at each node with an array of W fixed-tuned receivers (one receiver per wavelength). Such a network system is referred to as an FT-FRW system. However, this architecture not only imposes a scalability constraint on the network, but also increases the network costs.

This paper proposes a FT-TR system, known as the FT2-TR2 system, for the WDM metro ring and investigates the aforementioned issues on the proposed network system. Similar to a slotted single ring system, e.g., HORNET, the performance of FT2-TR2 network relies primarily on the manner in which optical resource sharing takes place among the different access nodes. Hence, establishing a collision-free operation and a fairness mechanism for all of the network nodes is very important. On the other hand, many applications, e.g., multimedia traffic, require a QoS with respect to throughput, delay, and jitter. To meet these requirements, a network must be able to provide differentiated services for real-time and best-effort traffic, respectively. Therefore, it is essential to design a QoS scheme for WDM networks such that these two types of traffic stream can share the available bandwidth efficiently while satisfying their QoS requirements. Although the collision avoidance protocol [10], QoS mechanism [15], and fairness control schemes [17] proposed for HORNET networks work well in TT-FR based systems, they are not readily applicable to FT-TR based systems, i.e., the FT2-TR2 system considered in this study. Hence, this paper develops an effective Media Access Control (MAC) protocol, designated the FAirness and REservation integrated protocol (FARE), which comprises three separate mechanisms: (i) collision-free access, (ii) QoS provisioning, and (iii) fairness control. By employing the FARE integrated protocol, FT2-TR2 systems can achieve high performance, avoid receiver collisions, guarantee fair access for all nodes, and support QoS provisioning.

The remainder of this paper is organized as follows. Section 2 presents the architecture of the FT2-TR2 system and the proposed collision-free MAC protocol. Sections 3 QoS provisioning mechanism, 4 Fairness control mechanism introduce the QoS provisioning mechanism and the fairness control scheme of the FARE integrated protocol for FT2-TR2 systems. Section 5 presents the simulation results. Finally, Section 6 draws some brief conclusions.

Section snippets

FT2-TR2 system description and MAC design

This section presents the underlying system architecture of the current WDM dual-ring and its node structure and discusses the receiver collision free MAC protocol proposed previously by the current authors in [23]. Together, the network system and the receiver collision free MAC protocol form the technological basis for the proposed access protocols which are described in the following sections.

QoS provisioning mechanism

In order to transmit real-time data without exceeding the acceptable delay, a QoS provisioning mechanism is required to regulate the transmission. In general, in WDM metro ring networks, traffic with a stringent delay requirement is supported via the reservation of network resources using such schemes as those presented in [15], [20], [21]. However, these schemes are all designed for TT-FR network systems. Therefore, this study proposes a QoS mechanism based on a reservation scheme which

Fairness control mechanism

Concerning the fairness issue in terms of best-effort traffic, when the network is operated under a heavy load with a non-uniform distribution traffic pattern, fairness problems are likely to arise. This section addresses two common fairness problems, namely cross-wavelength fairness and in-wavelength fairness, and develops corresponding reverse-direction based fairness control protocols to evenly allocate the available network bandwidth across the individual nodes. In the proposed approaches,

Performance study

This study performed a series of computer simulations developed using the C programming language to analyze the performance of the proposed protocols running on an FT2-TR2 network system.

Conclusions

This paper has presented a WDM metro slotted dual-ring architecture employing a novel integrated MAC protocol to arbitrate access to the network. The proposed integrated MAC protocol, designated as FARE, comprises three key protocols, namely (i) CSMA/RCA, (ii) reservation QoS provisioning, and (iii) M-FECCA with a TAC fairness control scheme. The CSMA/RCA protocol avoids collisions at a node with a single tunable receiver, but introduces a potential cross-wavelength fairness problem. To resolve

Hui-Tang Lin received B.S. degree in Control Engineering from National Chiao-Tung University, Taiwan, in 1989, the M.S. and the Ph.D. degrees both in Electrical Engineering from Michigan State University, East Lansing, MI, in 1992 and 1998, respectively.

He is currently an assistant professor at the Electrical Engineering Department and the Computer and Communication Institute of National Cheng-Kung University, Taiwan. Prior to joining the EE department of National Cheng-Kung University, he was

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  • Cited by (0)

    Hui-Tang Lin received B.S. degree in Control Engineering from National Chiao-Tung University, Taiwan, in 1989, the M.S. and the Ph.D. degrees both in Electrical Engineering from Michigan State University, East Lansing, MI, in 1992 and 1998, respectively.

    He is currently an assistant professor at the Electrical Engineering Department and the Computer and Communication Institute of National Cheng-Kung University, Taiwan. Prior to joining the EE department of National Cheng-Kung University, he was a Member of Technical Staff (MTS) at Agere Systems (former Lucent Microelectronics), where he worked on the design and implementation of high-speed networking ICs. Before he followed the company’s spin-off decision to Agere Systems, he was a MTS at Advanced Technologies division of Bell Laboratories in Lucent Technologies, where he worked on an industry-leading silicon solution for ATM and IP switching and port processing. His research interests include QoS of high-speed networks, optical networks, switch architecture, wireless networks, sensor networks, and network security.

    Wang-Rong Chang obtained his B.S degree in Electronic Engineering from Southern Taiwan University of technology, Taiwan, in 2000, the M.S. degree in Computer Science and Information Engineering from National Taipei University of Technology, Taiwan, in 2003. He is currently working towards the Ph.D. degree in the department of Electrical Engineering at National Cheng-Kung University, Taiwan. His research interests include the areas of optical networks and wireless sensor networks.

    Ho-Ting Wu received his B.S. degree from National Taiwan University in 1986, and both the M.S. and Ph.D. degrees from University of California, Los Angeles in 1989 and 1994, all in electrical engineering. Since 1996, he has been on the faculty at National Taipei University of Technology, Taiwan, where he is currently an associate professor in the department of computer science and information engineering. His current research interests include multimedia communications, optical and wireless networks.

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