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Metropolitan Area WDM Networks: An AWG Based Approach provides a comprehensive and technically detailed overview of the latest metropolitan area WDM network experimental systems, architectures, and access protocols. Its main focus is on the novel star WDM networks based on a wavelength-selective Arrayed-Waveguide Grating (AWG). Network researchers, engineers, professionals, and graduate students will benefit from the thorough overview and gain an in-depth understanding of current and next-generation metro WDM networks.

The AWG based metro star WDM network is discussed at length and extensively investigated by means of stochastic analyses and simulations. The book provides:
*an up-to-date overview of ring and star metro WDM networks and access protocols,
*in-depth performance comparison studies of AWG based multihop vs. single-hop WDM networks and AWG vs. Passive Star Coupler based single-hop WDM networks,
*a thorough description of the AWG based network and node architectures and access protocols,
*a novel highly-efficient approach to provide survivability for star WDM networks,
*extensive analytical results for both unicast and multicast variable-size packet traffic and bandwidth on demand,
*supplementary simulation results, including packet header trace files.

Inhaltsverzeichnis

Frontmatter

Introduction

Frontmatter

Chapter 1. Basics

Abstract
In this chapter, we introduce several components which are used in our architectural comparisons and as building blocks for our proposed network. In Section 1.1, we consider these components in isolation and describe their respective properties. In Chapter 5 we will discuss how the components can be connected in order to form our WDM network. Section 1.2 deals with several transmission impairments encountered in optical networks. Their impact on our proposed network will be investigated when discussing the network feasibility in Chapter 8. For an in-depth discussion and detailed information on the following and other components and transmission impairments the interested reader is referred to [Muk97][RS98][MS00].
Martin Maier

Metro WDM Networks

Frontmatter

Chapter 2. Ring Networks

Abstract
Metropolitan are networks (MANs) are located between access and backbone networks, as depicted in Fig. 0.3. MANs have a number of distinctive properties which have to be taken into account in the design of metro network architectures and access protocols:
  • The geographical coverage of MANs is limited. Typically, MANs have a diameter of 50 to 200 km.
  • The number of nodes in a MAN is rather modest in the approximate range from 10 to 250 nodes.
  • Compared to backbone networks, MANs have to be more cost-effective due to the smaller number of subscribers and the traffic in MANs is more bursty.
  • While the nature of data traffic in LANs [LTWW94] and WANs [PF95] have been investigated, defining traffic models for MANs is an open question at the time of writing.
  • While mesh networks are quite common in the backbone, metro networks typically have a ring, bus, or star topology.
Martin Maier

Chapter 3. Star Networks

Abstract
Star metro WDM networks are based on either a PSC or an AWG. In the following star networks communication between any arbitrary pair of nodes — either circuit or packet switched — takes place in one single hop, i.e., transmitted data does not have to be processed and forwarded by intermediate nodes.
Martin Maier

AWG Based Approach

Frontmatter

Chapter 4. Architectural Comparisons

Abstract
We have seen in the previous chapter that metro WDM networks typically have either a ring or star topology. The benefits of a star configuration are numerous [BR99b]. Star configurations are easy to install, configure, manage, and troubleshoot. This has advantages in terms of installation, troubleshooting, and reconfiguration, reducing the cost of installation and ownership for the entire network. In addition, a star network based on a PSC or an AWG is reliable due to its passive nature. As opposed to ring (and bus) topologies it does not suffer from tapping loss which grows linearly with the number of nodes (in dB). However, PSC based star networks suffer from splitting loss (as opposed to the AWG which does not introduce splitting loss). But the splitting loss grows only logarithmically with the number of attached nodes (in dB). Note that star networks exhibit a single point of failure, i.e., when the central hub goes down the entire network connectivity is lost. Therefore, for survivability reasons the central hub has to be protected. This issue is addressed in Chapter 9.
Martin Maier

Chapter 5. Architecture and Protocol

Abstract
In this chapter, we specify our metro WDM network architecture and MAC protocol. Based on the results of the previous chapter, we propose a logical single-hop network embedded on a physical star WDM network using an AWG as central hub. In Section 5.1 we first list several requirements of networks in general and metro networks in particular, which we account for in our network design. In Section 5.2 we present the network and node architecture which makes use of the components introduced in Chapter 1. Prior to describing the architecture we explain the underlying principles. Specifically, we discuss what happens when different light source signals are fed into the AWG. We discuss how they can be used for building an efficient and cost-effective network and node architecture. After fixing the architecture we address the dynamic on-demand assignment of wavelengths. Section 5.3 explains the MAC protocol in detail and outlines how the following network requirements are satisfied [Mai01b][Mai01a][MRW02].
Martin Maier

Chapter 6. Performance Evaluation

Abstract
After describing the network at length in the previous chapter, we investigate the impact of various network architecture and protocol parameters on the network performance by means of analysis and/or simulation in this chapter. For tractability reasons we assume Bernoulli packet arrival processes in our analyses. We note that Bernoulli traffic is not an appropriate traffic model for LANs and WANs, as shown in [LTWW94] and [PF95], respectively. But at the time of writing it is an open question which traffic model applies in MANs. While the simulations in this chapter make also use of Bernoulli traffic, in Chapter 8 we provide additional simulations which are driven by packet header trace files that were recorded at the metro level. The performance evaluation proceeds in two steps. First, we consider different network aspects separately from each other in order to provide insight in how they influence the network performance. In Section 6.1, we focus on switching of fixed-size packets and show the positive impact of using multiple FSRs of the underlying AWG on the throughput-delay performance of the network. Next, in Section 6.2 we consider variable-size packets and demonstrate the benefit of spatial wavelength reuse for improving the network flexibility and efficiency. Section 6.3 takes also multicasting into consideration. We show that our network is able to support multicasting efficiently and we examine the interplay between multicast and unicast packet switched traffic.
Martin Maier

Chapter 7. Network Dimensioning and Reconfiguration

Abstract
In the preceding chapter we have gained some insight in how the various network parameters influence the network performance by varying them around their default values. We now go one step further in that we tackle the problem of setting the parameters properly in order to optimize the throughput-delay performance of our AWG based WDM network.
Martin Maier

Chapter 8. Feasibility Issues

Abstract
After specifying, evaluating, and optimizing our network architecture and protocol in the previous chapters, we now investigate the feasibility of the network. For the signalling of reservation requests we adopt a previously reported realization of spectrum spreading. In Section 8.1, we examine the impact of the transmission impairments of Section 1.2 on the transmission limitations of the network. In Section 8.2, we investigate by means of simulations the throughput-delay and packet loss performance of the network using the aforementioned signalling approach. Unlike the analyses and supplementary simulations of Chapter 6, we do not assume Bernoulli traffic in the following simulations. Instead, we use packet header trace files which were recorded at the metro level. The obtained results are discussed in Section 8.3. Section 8.4 provides some conclusions.
Martin Maier

Chapter 9. Protection

Abstract
The central hub of our AWG based single-hop network forms a single point of failure. In this chapter, we address the survivability of our AWG based network. There are different types of network failures comprising node, fiber, and hub failure. While node and fiber failures have only a local effect in our network, the central AWG represents a single point of failure. That is, if the AWG goes down the network connectivity is entirely lost. In the following, we concentrate on the protection of this single point of failure. Under normal operation the proposed protection scheme not only avoids the single point of failure but also enables spatial wavelength reuse at all AWG ports at any given time and allows for transmitting control at significantly higher line rates by replacing the broadband light source with a laser diode. In the following, we highlight the rationale behind the presented protection scheme and show some illustrative results. For detailed information on the analytical performance evaluation, additional results, and an in—depth discussion the interested reader is referred to [FMR03].
Martin Maier

Chapter 10. Conclusions

Abstract
Optical WDM networks can be found throughout the network hierarchy. Due to various inefficiencies current SONET/SDH metro ring networks create the so-called metro gap which prevents high-speed packet switched LANs, access technologies, and service providers from tapping into the vast amounts of bandwidth available in the backbone. This bandwidth bottleneck at the metro level is anticipated to become more severe in the face of the ever increasing number of users and bandwidth-hungry applications and the steadily growing amount of local intra-MAN traffic.
Martin Maier

Backmatter

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