Differentiated QoS for survivable WDM optical networks

Optical networks based on WDM technology have become a promising solution to realize transport networks that can meet the ever-increasing demand for bandwidth. As WDM networks carry a huge volume of traffic, maintaining a high level of survivability is an important and critical issue. The. development of GMPLS switching technology led to the direct integration of IP and WDM. In these IP-over-WDM networks different applications/end users need different levels of fault tolerance and differ in how much they are willing to pay for the service they get. The current trend in network development is moving toward a unified solution providing support for voice, data, and various multimedia services. Therefore, it imperative that WDM networks incorporate fault tolerance to single or multiple component failures, protection bandwidth, recovery time, and recovery granularity besides resource utilization and call acceptance ratio. This article presents a survey of various methods that have been proposed for providing service differentiation in survivable WDM networks and discuss their performance. Such methods are broadly classified under various paradigms such as differentiated reliability, R-connections, quality of protection, and quality of recovery.     

Unslotted deflection routing: a practical and efficient protocolfor multihop optical networks

This paper is concerned with all-optical networks using deflection routing and time division multiplexing. Slotted networks make use of the synchronous arrival of the packets to the routers to minimize locally the number of deflections. We show that the difference in performance between slotted and unslotted networks is mainly due to the fact that unslotted networks cannot easily perform such local optimization. We also show that minimizing locally the number of deflections in unslotted networks gives rise to an NP-complete problem. To overcome this problem, we have designed a heuristic whose aim is to limit locally the number of deflections. We experimentally demonstrate that this heuristic enhances unslotted routing almost at the same performance level as slotted routing. As a consequence, we have shown that unslotted deflection routing can be implemented is a way which makes it a competitive alternative to slotted deflection routing for optical time division multiplexing deflection networks     

Differentiated recovery in WDM networks

A scheme is proposed for supporting dual-failure priority-aware survivability in wavelength division multiplexing (WDM) networks with two classes of working traffic by means of a proportional spare capacity allocation strategy. The proposed scheme not only provides a differentiated recovery capability but also maximizes the capacity utilization. A simple routing strategy for enabling multi-priority delay-aware survivability in WDM networks with three classes of working traffic is also proposed. The simulation results show that the dual-failure recovery scheme achieves the desired restoration ratio for the two classes of working traffic given appropriate settings of the reservation and allocation ratios. In addition, it is shown that the multi-priority delay-aware survivability scheme successfully achieves a delay-sensitive differentiated recovery capability.     

A practical approach for routing and wavelength assignment in largewavelength-routed optical networks

We consider large optical networks in which nodes employ wavelength-routing switches which enable the establishment of wavelength-division-multiplexed (WDM) channels, called lightpaths, between node pairs. We propose a practical approach to solve routing and wavelength assignment (RWA) of lightpaths in such networks. A large RWA problem is partitioned into several smaller subproblems, each of which may be solved independently and efficiently using well-known approximation techniques. A multicommodity flow formulation combined with randomized rounding is employed to calculate the routes for lightpaths. Wavelength assignments for lightpaths are performed based on graph-coloring techniques. Representative numerical examples indicate the accuracy of our algorithms     

Simulation and theoretical results on cluster management anddirectory management in dynamic hierarchical networks

A cluster management scheme for dynamic networks, the purpose of which is to maintain the cluster structure of the hierarchical network as a balanced-tree topology is presented. The theoretical time complexity bounds of the cluster management scheme for node birth and death are derived. The effects of the cluster management on gate-connected fixed-node networks under heavy intercluster traffic situations are discussed. In order to show that the scheme can handle realistic communication networks, routing tables and OD pair shortest path routing are used. The settle-down time, throughput, and end-to-end link delays of a network that uses cluster management and a network of the same topology that only uses flooding are compared     

Multilevel codes: theoretical concepts and practical design rules

This paper deals with 2^l-ary transmission using multilevel coding (MLC) and multistage decoding (MSD). The known result that MLC and MSD suffice to approach capacity if the rates at each level are appropriately chosen is reviewed. Using multiuser information theory, it is shown that there is a large space of rate combinations such that MLC and full maximum-likelihood decoding (MLD) can approach capacity. It is noted that multilevel codes designed according to the traditional balanced distance rule tend to fall in the latter category and, therefore, require the huge complexity of MLD. The capacity rule, the balanced distances rules, and two other rules based on the random coding exponent and cutoff rate are compared and contrasted for practical design. Simulation results using multilevel binary turbo codes show that capacity can in fact be closely approached at high bandwidth efficiencies. Moreover, topics relevant in practical applications such as signal set labeling, dimensionality of the constituent constellation, and hard-decision decoding are emphasized. Bit interleaved coded modulation, proposed by Caire et al. (see ibid., vol.44, p.927-46, 1998), is reviewed in the context of MLC. Finally, the combination of signal shaping and coding is discussed. Significant shaping gains are achievable in practice only if these design rules are taken into account     

Differentiated integrated QoS control in the optical Internet

In order to facilitate convergence of networks and services, this article investigates a new hybrid and integrated QoS control scheme that combines electrical IP layer features with reconfigurable optical layer, and addresses cross-layer design on QoS control in optical Internet (i.e., IP/WDM networks). The proposed integrated QoS control scheme can not only provide appropriate transport service for various types of traffic relating to different service categories in a cost-effective way, but also maintain high flexibility/scalability for integrated services provisioning, which seems to be preferred for QoS provisioning in the next-generation multiservice integrated optical Internet.     

Differentiated reliability (DiR) in wavelength division multiplexing rings

Extant (optical) networks normally offer two degrees of service reliability: full protection in the presence of a single fault in the network, and no protection at all. This situation reflects the historical duality that has its roots in the once divided telephone and data environment. The telephone circuit oriented service requires protection, i.e., provisioning of readily available spare resources to replace working resources in case of a fault. The datagram oriented service relies upon restoration, i.e., dynamic search for and reallocation of affected resources via actions such as routing table updates. The current trend in networking, however, is gradually driving the design of networks toward a unified solution that will jointly support traditional voice and data services, as well as a variety of novel multimedia applications. The growing importance of concepts, such as quality of service (QoS) and differentiated services-which provide multiple levels of service performance in the same network-evidences this trend. Consistently with this evolution, the concept of differentiated reliability (DiR) is formally introduced in the paper and applied to provide multiple reliability degrees (or classes) at the same network layer using a common protection mechanism, i.e., path switching. According to the DiR concept, each connection is guaranteed a minimum reliability degree, or equivalently a maximum downtime ratio, that is chosen by the client. The reliability degree chosen for a given connection is thus determined by the application requirements, and not by the actual network topology, design constraints, robustness of the network components, and span of the connection. An efficient algorithm is proposed to sub-optimally design the wavelength division multiplexing (WDM) layer of a ring and illustrate the advantages of the DiR concept.     

K-terminal reliability in ring networks

The authors present a new formula for computing K-terminal reliability in a communication network whose stations and links (vertices and edges) form a network graph G having a ring topology, where K-terminal reliability is the probability R_K(G) that a subset of R specific terminal stations in G can communicate. This new formula is applied to three Fiber Distributed Data Interface (FDDI) ring-network topologies, and for each topology the authors derive closed-form polynomial expressions of R_K(G) in terms of the failure probabilities of links, network ports, and station common units. The authors define the concept of the K-minimal Eulerian circuit and use combinations of these circuits to obtain K-graphs and their resulting dominations, thus extending the use of K-graphs to ring networks in which data messages, tokens, or other control frames traverse operative network links with an Eulerian tour. Distinct K-graphs having a nonzero sum of dominations are called noncanceled K-graphs and correspond exactly to terms in closed-form polynomial expressions of R_K(G). The authors show that trees have only one K-graph and that counter-rotating dual rings and rings of trees have at most 2K+1 noncanceled R-graphs. These results contribute the first closed-form polynomial R-terminal reliability expressions for the ring-of-trees topology. The results are useful in evaluating dependability, reliability, availability, or survivability of token rings and similar networks     

Differentiated contention resolution for QoS in photonic packet-switched networks

Packet contention is a major challenge in photonic packet-switched networks due to the lack of random access buffers in the optical domain. Existing contention resolution approaches such as wavelength conversion and fiber-delay-line buffering may significantly increase the overall system cost and may be difficult to implement. To avoid such issues, this paper proposes a framework for providing label-based differentiated contention resolution by exploiting recirculation buffering and deflection routing. To accommodate more options for differentiation and to avoid the potential problem of forwarding packets in a network indefinitely, two classes of loopless deflection algorithms are provided. An analytical model is also developed to evaluate the packet loss probability and the end-to-end delay for different buffering and deflection routing schemes. The paper also investigates the effectiveness of the control schemes in providing differentiated loss and delay through simulation and analysis. The accuracy of the analytical model is confirmed by simulation.     

Location uncertainty in mobile networks: a theoretical framework

As users, services, databases, and computers become increasingly mobile, so fades the era of the fixed network. Modern networks are becoming mobile networks which must accommodate a broad range services with differing mobility characteristics. Consequently, there is an impetus to understand mobility and its effect on communications systems. Of particular interest are the unique stresses imposed by mobile computing and especially mobile computer programs (agents). As an aid to greater understanding, we propose a theoretical framework for the study of mobility tracking based on user/service/host location probability distributions. We show how this methodology, using stochastic ordering and information theory, can enable quantitative comparison of various mobility management schemes as well as insight into the mobility tracking problem over a wide range of mobility characteristics. This general approach should aid both applications and future research     

Multiservice optical video communication networks — first results and ongoing developments in france

Since 1986, the first operating video communications systems developed by ALCATEL, have been commercially opened in the cities of Rennes, Saint-Cloud, Mantes and Toulon; other plants are under installation in the cities of Evry, Marseille, Massy, Gennevilliers, Lille and Montpellier. The basic infrastructures already installed permit the connection of several tens of thousands of households. Compared with conventional coaxial system, the ALCATEL video communications system presents the following main advantages:

• (a) More efficient operating facilities for audiovisual services offering built-in access control functions, without any additional descrambling terminal on the user's premises, allowing easy introduction of pay-per-view programming, and providing advertising people with adequate audience measurements.
• (b) Flexible and continuous implementation of additional telecommunication services such as telephony, videotex, home security, bidirectional data transmission and professional specialized applications.

Those advantages are a direct consequence of the switched-star network structure, based on fibre-optic technologies. After a brief overview of the architecture, the paper will present design principles and the main technical choices related to the ALCATEL system. The second part of the paper will describe the different subsystems constituting the switched-star network such as the subscriber subsystem and the operating and maintenance organization. Lastly, different evolving schemes for future introduction of narrowband and the broadband telecommunication services will be proposed.     

Survivability in optical networks

Survivability, the ability of a network to withstand and recover from failures, is one of the most important requirements of networks. Its importance is magnified in fiber optic networks with throughputs on the order of gigabits and terabits per second. This article takes a look at the techniques used to achieve survivability in traditional optical networks, and how those techniques are evolving to make next-generation WDM networks survivable.     

光网络的进展研究

光传送网是指光信道接入点所定界的传送网络。光传送网络的物理层采用光纤作为传输媒介，光传送网为客户层信号在很大范围内提供包括传送、复用、路由、管理、抗故障等功能。光传输技术经历了PDH、SDH到WDM的发展过程。在90年代，SONET/SDH网络在容量、可靠性和网络传送效率方面都得到迅速提高。光传送网主要提供如下功能：不同网络客户的透明传送、不同管理域的互联、光信道连接和保护、性能监测和告警监视、网络管理。目前光网络的单信道的传送速率(图1)和网络的传送容量在迅速增加，以满足不断增长的互联网的业务需求。单纤复用的…     

Prolog representation of reliability networks and evaluation of system reliability

The suitabilities of Prolog to represent reliability networks are discussed in this paper. The capabilities of Prolog are illustrated by relevant examples in various reliability network configurations. The network reliability has been estimated by using the recursive nature of Prolog.     

Gigabits-per-second optical interconnection networks:fault-tolerance with and without optical amplifiers

This paper quantifies the power budget concerns with respect to the number of consecutive faults that must be tolerated before a network can fail. In particular, it is shown that multiple consecutive failures may have a serious adverse effect on the speed of gigabit optical networks. Results indicate that, with 20 nodes using simple direct-detection, only passive star networks can operate at Gb/s in the event of multiple consecutive faults. Use of optical preamplifiers is shown to remedy this shortcoming substantially: even with 3 consecutive node failures, optical networks with passive star couplers or single couplers can achieve Gb/s transmission speed for a node spacing of up to 2.3 km