Showing papers in "Photonic Network Communications in 2002"
TL;DR: This study believes that a PON based on polling, with data encapsulated in Ethernet frames, possesses the best qualities, such as dynamic bandwidth distribution, use of a single downstream and a single upstream wavelength, ability to provision a fractional wavelength capacity to each user, and ease of adding a new user.
Abstract: While in recent years backbone bandwidth has experienced substantial growth, little has changed in the access network. “Last mile” still remains the bottleneck between a high capacity LAN or home network and the backbone. Passive optical network (PON) is a technology viewed by many as an attractive solution to this problem. In this study, we discuss and evaluate design issues for PON access networks. Specifically, to drive the cost of an access network down, it is very important to have an efficient, scalable solution. We believe that a PON based on polling, with data encapsulated in Ethernet frames, possesses the best qualities, such as dynamic bandwidth distribution, use of a single downstream and a single upstream wavelength, ability to provision a fractional wavelength capacity to each user, and ease of adding a new user. To support dynamic bandwidth distribution, we propose an interleaved polling algorithm. We then suggest a scheme for in-band signaling that allows using a single wavelength for both downstream data and control message transmission. To obtain realistic simulation results, we generated synthetic traffic that exhibits the properties of self-similarity and long-range dependence. We then analyzed the network performance and its effect on various types of traffic, e.g., best-effort data traffic, VBR video traffic and CBR streams.
373 citations
TL;DR: All the main optical protection techniques proposed as far as now for the WDM layer are classified and reviewed and an example of heuristic network-capacity optimization is presented, discussing results obtained by considering a case-study network.
Abstract: This paper is an introduction to survivability of WDM networks. All the main optical protection techniques proposed as far as now for the WDM layer are classified and reviewed. In particular, commonly adopted protection strategies for ring and mesh networks are explained. Moreover, off-line planning of WDM networks able to support path protection is briefly introduced. Finally, an example of heuristic network-capacity optimization is presented, discussing results obtained by considering a case-study network.
163 citations
TL;DR: This work focuses on developing and implementing comprehensive unified constraint-based routing algorithms within the generalized multi-protocol label switching framework (GMPLS) to provision “sub-wavelength” circuits (low-rate traffic streams).
Abstract: This work focuses on developing and implementing comprehensive unified constraint-based routing algorithms within the generalized multi-protocol label switching framework (GMPLS) to provision “sub-wavelength” circuits (low-rate traffic streams) Constraint-based routing is further augmented in this work by dynamically routing both an active and another alternate link/node-disjoint backup path at the same time in order to provision a given connection request This new integrated approach combines both IP routing and optical resource allocation to setup end-to-end connections
40 citations
TL;DR: There are two preferences, one for the scheme using electronic feedback on the EDFA's pump power, because of good performance, and another for schemes controlling whole links of EDFA cascades by an extra control channel,Because of lower costs.
Abstract: Transmitting optical bursts through a chain of erbium-doped fiber amplifiers (EDFAs) results in dynamic gain changes, which in turn lead to possibly large variations in output power of the data channels. There are many proposals how to control these optical amplifiers in order to minimize or eliminate the power variations. In this paper, we investigate the gain dynamics in a burst switching environment experimentally and numerically. With a categorization of gain control schemes we review the state of the art and discuss advantages and disadvantages of the different approaches particularly with regard to burst switching networks. A comparison of the performance of these methods is given. In our opinion there are two preferences, one for the scheme using electronic feedback on the EDFA's pump power, because of good performance, and another for schemes controlling whole links of EDFA cascades by an extra control channel, because of lower costs.
24 citations
TL;DR: This paper reviews some of the various strategies and approaches proposed so far to intelligently route connections while at the same time providing guaranteed protection against various types of network failures, and explores the tradeoffs associated with these approaches.
Abstract: Wavelength division multiplexed (WDM)-based mesh network infrastructures that route optical connections using intelligent optical cross-connects (OXCs) are emerging as the technology of choice to implement the next generation core optical networks. In these architectures a single OXC is capable of switching tens of terabits of traffic per second. With such data transfer rates at stake, it becomes increasingly challenging for carriers to (1) efficiently and cost-effectively operate and manage their infrastructure, and (2) cope with network failures while guaranteeing prescribed service level agreements (SLAs) to their customers. Proper routing of primary and backup paths is a critical component of the routing and restoration architecture required to meeting these challenges. In this paper we review some of the various strategies and approaches proposed so far to intelligently route connections while at the same time providing guaranteed protection against various types of network failures. We explore the tradeoffs associated with these approaches, and investigate in particular different, sometimes competing aspects, such as cost/capacity required, level of protection (link vs. node failure), restoration time, and complexity of route computation.
24 citations
TL;DR: This paper extends an earlier analytical model to compute the blocking probability on an arbitrary route in a mesh topology, and proposes heuristic algorithms to place wavelength converters, and results suggest that simple heuristics are sufficient to give near-optimal performance.
Abstract: Wavelength conversion helps improve the performance of wavelength division multiplexed (WDM) optical networks that employ wavelength routing. In this paper, we address the problem of optimally placing a limited number of wavelength converters in mesh topologies. Two objective functions, namely, minimizing the average blocking probability and minimizing the maximum blocking probability over all routes, are considered. In the first part of the paper, we extend an earlier analytical model to compute the blocking probability on an arbitrary route in a mesh topology, given the traffic and locations of converters. We then propose heuristic algorithms to place wavelength converters, and evaluate the performance of the proposed heuristics using the analytical model. Results suggest that simple heuristics are sufficient to give near-optimal performance.
23 citations
TL;DR: This paper presents a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the problem of quality-of-service (QoS)-based protection in terms of the protection-switched time and availability for end-to-end lightpaths in a WDM mesh network.
Abstract: Intelligent methods for automatic protection and restoration are critical in optical transport mesh networks. This paper discusses the problem of quality-of-service (QoS)-based protection in terms of the protection-switching time and availability for end-to-end lightpaths in a WDM mesh network. We analyze the backup lightpath-sharing problem in such networks and study the correlation of the working lightpaths and the impact of the correlation on the sharing of the backup lightpaths. We present a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the protection problem. The proposed algorithm includes intelligent and automatic procedures to set up, take down, activate, restore, and manage backup lightpaths. It greatly reduces the required resources for protection by allowing the sharing of network resources by multiple backup lightpaths. At the same time, it guarantees, if possible, to satisfy the availability requirement even with resource sharing by taking the correlation of working lightpaths into consideration. A simple analysis of the proposed algorithm in terms of computation time and message complexity indicates that the implementation of the algorithm is practical. The illustrative studies that compare the performance of 1:1, unlimited sharing, and QoS-based backup sharing algorithms indicate that QoS-based sharing achieves comparable performance as unlimited sharing, which is much better than the 1:1 backup scheme in terms of connection blocking probability, average number of connections in the network for a given offered load, and network resource utilization.
19 citations
TL;DR: This paper considers scheduling algorithms for multiple access protocols associated with wavelength division multiplexed (WDM) multi-channel optical networks based on the star topology and proposes an on-line scheduling algorithm called OIS (On-line Interval-based Scheduling) to balance these requirements and increase network throughput.
Abstract: This paper considers scheduling algorithms for multiple access protocols associated with wavelength division multiplexed (WDM) multi-channel optical networks based on the star topology. To share the available channels among nodes, several demand assignment multiple access protocols based on reservation schemes have been proposed. The core of such reservation-based protocols is the scheduling algorithm, which allocates channels and time slots to the nodes based on traffic demand. The key objectives of the scheduling algorithm design are maximization of network utilization and minimization of packet delay. There is a trade-off between these two requirements: it takes more computation time to achieve a better utilization, which in turn will increase packet delay. This trade-off directly affects the overall network performance. Another important requirement is the consideration of transceiver tuning latencies. In this paper, we propose an on-line scheduling algorithm called OIS (On-line Interval-based Scheduling) to balance these requirements and increase network throughput. We also require that the scheduling algorithms be simple so that hardware implementation is feasible to reduce overall delay. We compare our scheduling algorithm to the Transmission Assignment Algorithm (TAA) studied by Borella and Mukherjee (1996); and to a matrix decomposition algorithm studied by Sivalingam and Wang (1996). We show that our algorithm, although suffering from small utilization loss, requires significantly less computation time and results in higher network throughput. In particular, for higher network speeds such as 2.4 Gbps per channel, the potential improvement using our algorithm is substantial. We also provide conditions when either protocol performs better compared to the other.
18 citations
TL;DR: This paper considers DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes and proposes a new, network state based selection method, and a new method for applying shared protection in dynamic WDM environment.
Abstract: Dense wavelength division multiplexing (DWDM) networks are very attractive candidates for next generation optical Internet and intelligent long-haul core networks. In this paper we consider DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes. The dynamic routing and wavelength assignment (RWA) problem is studied in multifiber networks, assuming both protection strategies: dedicated and shared. We solve the two subproblems of RWA simultaneously, in a combined way using joint methods for the wavelength selection (WS) and wavelength routing (WR) tasks. For the WS problem in contrast to existing strategies we propose a new, network state based selection method, which tries to route the demand on each wavelength, and selects the best one according to different network metrics (such as available channels, wavelengths per fiber and network load). For the WR problem we propose several weight functions for using in routing algorithms (Dijkstra or Suurballe), adapting dynamically to the load of the links and to the length of the path. The combination of different wavelength selection and routing (WS&WR) methods enables wide configuration opportunities of our proposed algorithm allowing good adaptation to any network state. We also propose the extension of the RWA algorithm for dedicated and shared protection and a new method for applying shared protection in dynamic WDM environment. The detailed analysis of the strategies demonstrate that our RWA algorithm provides significantly better performance than previous methods in terms of blocking probability whether with or without protection methods.
10 citations
TL;DR: The need for convergence in the form of a two level protection and restoration scheme with a service independent layer and a mesh restoration capability at the routing layer is shown.
Abstract: This paper argues for the need for convergence of protection and restoration schemes in today's telecommunication networks. Such networks are presented both in a layered context and from an end-to-end perspective. Such convergence is both necessary to ensure inter-working amongst a multitude of technologies deployed and desirable to ensure simplified operations. This paper further identifies the issues and inter-working items that need resolution in today's telecommunication and data networks in order to achieve inter working amongst various existing and emerging restoration and protection schemes in a layered and end-to-end context. End-to-end context covers the access, metro, and long haul dimensions of the network. It also encompasses both the services and the transport layers of the network in the context of multi-domain, multi service provider networks. Layering issues arise from the mix of technologies at several layers for example: optical transmission and CWDM/DWDM at physical layer, SONET/SDH framing and management at layer-1, ATM, MPLS, Ethernet, and resilient packet rings at layer-2, and finally IP and routing protocols at layer-3. Given that some degree of routing and signaling intelligence is migrating down to the optical layer equipment, this whole layering concept is currently in transition. This paper shows the need for convergence in the form of a two level protection and restoration scheme. A service independent layer and a mesh restoration capability at the routing layer.
9 citations
TL;DR: The paper describes theSPR-PW scheme as it is applied to cope with physical link failures, depicts a possible implementation of such a scheme using standard IP/GMPLS signaling capabilities, and numerically demonstrates two properties of the SPR-Pw scheme, i.e., low blocking probability and short restoration times.
Abstract: IP over WDM networking and related GMPLS standards, appear to be attractive solutions for today's and future Internet applications due to their ability to handle multiple traffic flows independently of one another, and reserve wavelengths to carry a large number of aggregated flows. Another advantage of these solutions is the simplified IP over WDM stack, that provides all the vital network functionalities, including network reliability. The paper investigates the use of the stochastic preplanned restoration scheme with proportional weighted path choice (SPR-PW) to design reliable and efficient IP/GMPLS/WDM networks. Upon the disruption of a primary flow determined by a link failure, one of the associated preplanned secondary paths is readily selected by the SPR-PW scheme to continue the flow transmission. The selection of the secondary path is performed on a probabilistic base, without requiring time-consuming coordination among the restoration attempts of the disrupted flows. As a result of this stochastic selection, the SPR-PW scheme has the potential to yield short recovery times. In addition, the SPR-PW required signaling, upon and before the failure occurrence, is limited, which makes SPR-PW a scheme suitable for highly dynamic traffic scenarios, in which flows are subject to frequent changes. The paper describes the SPR-PW scheme as it is applied to cope with physical link failures, depicts a possible implementation of such a scheme using standard IP/GMPLS signaling capabilities, and numerically demonstrates two properties of the SPR-PW scheme, i.e., low blocking probability and short restoration times.
TL;DR: Improvements toMulticommodity flow models are proposed and a method to solve the LTD and the LR problems in a combined manner to keep track of the global design problem when solving each individual step is proposed.
Abstract: Multicommodity flow models are commonly used to formulate the logical topology design (LTD) problem and the lightpath routing (LR) problem as mixed integer linear programming (MILP) problems. In general, MILP formulations are intractable even for relatively small networks due to the combinatorial complexity of the problem. In this paper we propose improvements to these models and a method to solve the LTD and the LR problems in a combined manner. The interest is two fold: firstly, by tackling the two problems with separate models, problem instances of realistic size (up to 14 nodes in this paper) can be dealt with. Furthermore, different combinations of optimization models and objective functions can be investigated in a modular manner. Secondly, the mechanisms proposed to combine the problems allow to keep track of the global design problem when solving each individual step.
TL;DR: A pre-planned local repair recovery strategy is described, provided using the interference concept, in order to set a threshold between resources dedicated to working paths and those allocable for local backups in case of failure.
Abstract: Automatic provisioning and recovery of lightpaths with selectable traffic engineering policies are considered basic features of near future optical transport networks (OTN). Worldwide researchers recognize generalized multi-protocol label switching (GMPLS) architecture as the viable control plane solution to achieve these issues in OTN. Growing effort is ongoing to find new recovery models for handling failure conditions in the networks, trying to set up alternative strategies to classical heavy-cost SDH/SONET protection techniques. In this paper, a pre-planned local repair recovery strategy is described. Allocation of primary paths is provided using the interference concept, in order to set a threshold between resources dedicated to working paths and those allocable for local backups in case of failure. Tests of the strategy are shown for a sample national optical transport network, aimed at valuing local-repair recovery times at different failure location and seriousness.
TL;DR: In this article, the authors proposed a framework for QoS guarantees based on the differentiated MPLS service (DMS) model and QoS recovery schemes against QoS degradation caused by devices failures or attack-induced faults in an AOTN.
Abstract: The Internet is evolving from best-effort service toward an integrated or differentiated service framework with quality-of-service (QoS) assurances that are required for new multimedia service applications. Given this increasing demand for high bandwidth Internet with QoS assurances in the coming years, an IP/MPLS-based control plane combined with a wavelength-routed dense wavelength division multiplexing (DWDM) optical network is seen as a very promising approach for the realization of future re-configurable transport networks. Fault and attack survivability issues concerning physical security in a DWDM all-optical transport network (AOTN) require a new approach taking into consideration AOTN physical characteristics. Furthermore, unlike in electronic networks that regenerate signals at every node, attack detection and isolation schemes may not have access to the overhead bits used to transport supervisory information between regenerators or switching sites to perform their functions. This paper presents an analysis of attack and protection problems in an AOTN. Considering this, we propose a framework for QoS guarantees based on the differentiated MPLS service (DMS) model and QoS recovery schemes against QoS degradation caused by devices failures or attack-induced faults in an AOTN. We also suggest how to integrate our attack management model into the NIST’s simulator—modeling, evaluation and research of lightwave networks (MERLiN).
TL;DR: A MILP formalization of the optimal logical topology design (LTD) problem in presence of multicast traffic under a perfectly known (deterministic) traffic pattern and proposes sub-optimal greedy and metaheuristic algorithms for its solution is provided.
Abstract: In this paper we discuss the optimal design of logical topologies in wavelength-routed IP over WDM networks supporting both unicast and multicast transfer of IP datagrams under deterministic and stochastic traffic patterns. The paper brings mainly three original contributions: (i) it provides a MILP formalization of the optimal logical topology design (LTD) problem in presence of multicast traffic under a perfectly known (deterministic) traffic pattern and proposes sub-optimal greedy and metaheuristic algorithms for its solution; (ii) it derives novel, tight optimistic bounds that allow the assessment of the performance of the proposed algorithms; (iii) it investigates the optimal logical topology design problem, when traffic patterns are known with a certain degree of uncertainty, hence characterized with a stochastic description, and it presents approaches for the sub-optimal solution of the problem. Focusing on the current Internet routing algorithms, we explicitly consider the routing of multi-hop flows over the logical topology as an input to the problem, not an optimization target.
TL;DR: A centralized method for optimally selecting the set of active and backup paths in an optical transport network in the cases of shared-path restoration and 1:1 protection schemes and novel mixed integer linear programming (MILP) formulations for both schemes.
Abstract: In this paper we provide a centralized method for optimally selecting the set of active and backup paths in an optical transport network in the cases of shared-path restoration and 1:1 protection schemes We provide novel mixed integer linear programming (MILP) formulations for both the schemes, for a network with full wavelength conversion capability The given formulations are not restricted to consider single link failures: the concept of fault event is introduced to handle the possibility that multiple links go simultaneously under fault The optimization objective includes the total capacity requirement plus an additional term related to the active paths reliability We use a simple decomposition heuristic to support the resolution process The optimization is solved for various sample scenarios in order to evaluate the resource saving achieved with the shared-path restoration scheme The impact of different factors such as topology, traffic demand and structure of failures on the resource saving is analyzed Also, we provide guidelines about handling differentiated levels of protection within the framework of the proposed formulations
TL;DR: This paper conducts extensive simulation experiments to compare and evaluate the effectiveness of different classes of OVPNs for varying network configurations–varying number of fibers, wavelengths on physical links, and number of nodes in OVPN.
Abstract: Wavelength division multiplexed (WDM) networks are matured to provide, scalable data centric infrastructure, capable of delivering flexible, value added, high speed and high bandwidth services directly from the optical domain. Optical virtual private networks (OVPNs) make use of the concept of highly reconfigurable nature of lightpaths offered by WDM, to create secure tunnels of high bandwidth across the intelligent WDM optical transport network. An OVPN is a private connection between two or more edge devices (access nodes), that allows a group of clients to fully exploit the flexibility of the switched intelligent optical network. However, OVPNs will not be a viable alternative unless they can guarantee a predictable bandwidth, availability, response time, and fault-tolerance to users. In this paper, we study the problem of dynamically establishing lightpaths for OVPNs over intelligent optical transport networks to provide varying classes of service based on the type of primary and backup lightpaths and the number of backup lightpaths, when each OVPN is specified by the desired logical connectivity and Class of Service. The type of primary and backup lightpaths determines the QoS parameters such as response time and bandwidth. Whereas, the number of backup lightpaths determines the level of fault-tolerance and availability of OVPN. Based on the service classes, any OVPN in the network falls into one of the six classes viz. single dedicated primary and single dedicated backup (SDPSDB), single dedicated primary and multiple dedicated backups (SDPMDB), single dedicated primary and single shared backup (SDPSSB), single shared primary and single shared backup (SSPSSB), single shared primary and multiple shared backups (SSPMSB), and best-effort (BE). In BE, we consider two variations—(1) OVPN as dedicated logical ring topology (DLRT) and (2) OVPN as shared logical ring topology (SLRT). We conduct extensive simulation experiments to compare and evaluate the effectiveness of different classes of OVPNs for varying network configurations–varying number of fibers, wavelengths on physical links, and number of nodes in OVPN.
TL;DR: A dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks to join a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as low as possible.
Abstract: Future broadband networks must support integrated services and offer flexible bandwidth usage In our previous work in [1], we explored the optical link control (OLC) layer on the top of optical layer that enables the possibility of bandwidth on-demand (BoD) service directly over wavelength division multiplexed (WDM) networks Today, more and more applications and services such as video-conferencing software and Virtual LAN service require multicast support over the underlying networks Currently, it is difficult to provide wavelength multicast over optical switches without optical/electronic conversions although the conversion takes extra cost In this paper, based on the proposed wavelength router architecture (equipped with ATM switches to offer O/E and E/O conversions when necessary), a dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks The goal is to join a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as low as possible The same algorithm can be applied to other wavelength routing architectures with redefinition of electronic copy cost The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation
TL;DR: The proposed heuristic multicast scheduling algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.
Abstract: The problem of minimizing the number of transmissions for a multicast transmission under the condition that the packet delay is minimum in single-hop wavelength division multiplexing (WDM) networks is studied in this paper. This problem is proved to be NP-complete. A heuristic multicast scheduling algorithm is proposed for this problem. Extensive simulations are performed to compare the performance of the proposed heuristic algorithm with two other multicast scheduling algorithms, namely, the greedy and no-partition scheduling algorithms. The greedy algorithm schedules as many destination nodes as possible in the earliest data slot. The no-partition algorithm schedules the destination nodes of a multicast packet to receive the packet in the same data slot without partitioning the multicast transmission into multiple unicast or multicast transmissions. Our simulation results show that (i) an algorithm which partitions a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than the no-partition algorithm when the number of data channels in the system is limited and (ii) the proposed heuristic algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.
TL;DR: The benefits provided by using MPLS for different VPN models are emphasized, with particular attention to improved scalability, management, and quality of service (QoS).
Abstract: The basic idea, features, and necessity of multiprotocol label switching (MPLS) are given in this paper, with a special focus on virtual private networks (VPN) as one of the most important features that MPLS as technology enables and supports In this context, we first describe the general VPN models, the overlay and the peer model, and than analyze different models, such as the BGP/MPLS virtual private networks and the layer-2 MPLS virtual private networks All over the paper, the benefits provided by using MPLS for different VPN models are emphasized, with particular attention to improved scalability, management, and quality of service (QoS)
TL;DR: Using both restoration time and recovery blocking probability, a new analytic model for GMPLS-based recovery in M : N protection groups is developed and it is shown that smaller backup paths can be reserved by capturing the effect of multiple failures in the case of M: N shared protection with revertive mode in an optical network with aGMPLS control plane.
Abstract: As GMPLS and its supporting set of protocols develop into aviable control plane for optical networks, an important function that they will need to support will be the protection and restoration function that has been a major feature of legacy optical networks. A network with a robust set of protection and restoration mechanisms will be able to support data traffic while allowing faster recovery from failures than can be obtained using layer 3 rerouting. Several models have been proposed for protection with GMPLS using shared backup paths. This previous work has not investigated the effect on recovery time critical to the service or the number of backup paths that are required to meet a desired level of performance. Using both restoration time and recovery blocking probability, we have developed a new analytic model for GMPLS-based recovery in M : N protection groups. Furthermore, we show that smaller backup paths can be reserved by capturing the effect of multiple failures in the case of M : N shared protection with revertive mode in an optical network with a GMPLS control plane.
TL;DR: The paper considers the blocking probabilities of all-optical networks when centralized and distributed lightpath allocation schemes are used and considers the routing issues considering dynamic lightpath assignment.
Abstract: This paper considers wavelength routed WDM networks where multiple fibers are used for each communication link. For such networks, the effect of wavelength translation can be achieved without explicit use of wavelength translators. We call this as virtual wavelength translation and study the routing issues considering dynamic lightpath allocation. Using multiple (or a bundle of) fibers for each link also allows us to have bundles of varying sizes to accommodate anticipated differences in traffic through different communication links of the network. The paper considers the blocking probabilities of all-optical networks when centralized and distributed lightpath allocation schemes are used.
TL;DR: A new technique for providing security in a broadcast-and-select, wavelength-division-multiplexed (WDM) optical network that provides privacy of communications by employing a novel challenge-response scheme and exploiting the tuning delay inherent in optical receivers is introduced.
Abstract: We introduce a new technique for providing security in a broadcast-and-select, wavelength-division-multiplexed (WDM) optical network. The approach provides privacy of communications by employing a novel challenge-response scheme and exploiting the tuning delay inherent in optical receivers. The proposed technique can be integrated easily into any existing WDM media-access-control (MAC) protocol that employs tunable receivers. The modified protocol would require every idle user, who is not scheduled to receive data, to tune in to a channel that does not contain sensitive data. A violation of the protocol can be detected with very high probability, and appropriate measures can be taken against the violator. The technique provides features that cannot be achieved with cryptography alone. Significant benefits of the proposed approach include the ability to detect security violations as they occur, and an efficient mechanism to provide privacy for multicast transmissions. We develop two simple solutions to deal with different levels of attack: (1) eavesdroppers working alone, and (2) eavesdroppers working in collaboration. We also introduce a dynamic channel allocation scheme that can further reduce the number of required overhead channels, with minimal loss in the capability to detect eavesdropping violations.
TL;DR: This paper studies the influence of the asymmetric nature of IP traffic on the underlying optical layer and shows how cost(in)efficient this optical capacity is used for IP traffic patterns with varying asymmetry.
Abstract: The main traffic to be carried by a backbone network in the future (or even now) will be (is) IP traffic, which is unidirectional and asymmetric in nature. Today, most backbone networks are still designed for bidirectional, symmetrical services like SDH/SONET. In the future, the transmission links in the optical layer will probably still be symmetric (same amount of capacity installed in both directions of the optical link), and operators will probably continue to lease bidirectional capacity to their customers. However, the traffic that will be conveyed over those bidirectional transmission links will be mainly unidirectional and asymmetric. This paper studies the influence of the asymmetric nature of IP traffic on the underlying optical layer. In case the optical layer contains bidirectional symmetric capacity (as is almost always the case nowadays), it shows how cost(in)efficient this optical capacity is used for IP traffic patterns with varying asymmetry. The comparison is also made with a unidirectional optical layer, in which the capacity (line-systems) installed in the network is asymmetric (more capacity can be present in one direction of an optical link than in the other direction), or in which the capacity that is leased by operators is asymmetric (e.g., an ISP can choose to lease two wavelengths from city A to city B and five wavelengths in the other direction, from city B to city A).
TL;DR: Focussing on aspects of network management, this paper investigates how the mentioned higher-layer protocols may concurrently support WDM.
Abstract: To satisfy the severe requirements involved in future communication networks, commercial and research interest in the applicability of wavelength division multiplexing (WDM) is growing. However, since WDM is merely concerned with transmitting bits over optical fibers, full advantage can only be taken when WDM is efficiently supported by higher-layer protocols. Functionality of higher-layer protocols that could be used in conjunction with WDM originates from synchronous digital hierarchy (SDH) or synchronous optical network (SONET), asynchronous transfer mode (ATM), and the internet protocol (IP). To provide flexible use of services with different levels of quality, various higher-layer protocols may directly support WDM simultaneously by reserving wavelength channels for a specific supporting protocol. Focussing on aspects of network management, this paper investigates how the mentioned higher-layer protocols may concurrently support WDM.
TL;DR: The design and performances of a strictly non-blocking all-optical cross-connect demonstrator node for WDM wavelength path networks is assessed and its results were validated with the experimental ones.
Abstract: In this paper, we assess the design and performances of a strictly non-blocking all-optical cross-connect demonstrator node for WDM wavelength path networks. The all-optical cross-connect (AOXC) prototype was experimentally tested in a small 2 x 2 WDM network with a STM-16 bit stream per channel. The single and cascaded performance of the AOXC was also simulated and its results were validated with the experimental ones.
TL;DR: The results indicate that a small number of fibers is sufficient to provide most of the benefits that wavelength conversion provides for this class of permutation traffic.
Abstract: Permutation traffic occurs in a number of networking applications. In this paper, the problem of wavelength assignment for permutation traffic in multi-fiber WDM rings with and without wavelength conversion is considered. We focus on a special class of permutation traffic and analyze the bounds on the number of wavelengths required to establish the connections. Lower bounds and optimal algorithms are presented for all the cases. The results indicate that a small number of fibers is sufficient to provide most of the benefits that wavelength conversion provides for this class of permutation traffic.
TL;DR: This paper examines the influence of different parameters such as the speed of recovery actions, changing length of the routes followed by the client data (TCP flows), changes in available bandwidth, etc. on the behavior of TCP, being the ubiquitous protocol used by today's network users.
Abstract: Optical networks based on wavelength-division-multiplexing (WDM) techniques are very likely to be omnipresent in future telecommunication networks. Those networks are deployed in order to face the steady growth of traffic, which is for a large part Internet related. In the resulting IP-over-WDM scenario, TCP/IP constitutes an important fraction of the traffic transported over these networks. As IP networks are becoming increasingly mission-critical, it is of the utmost importance that these networks (and hence the supporting transport networks) be able to recover quickly from failures such as cable breaks or equipment outages. To that end, several IP-over-WDM network scenarios and corresponding protection and restoration strategies have been devised. It is clear that some trade-offs will have to be made in order to choose an appropriate strategy. In this paper, we investigate the effects of such recovery actions on the behavior of TCP, being the ubiquitous protocol used by today's network users. We examine the influence of different parameters such as the speed of recovery actions, changing length of the routes followed by the client data (TCP flows), changes in available bandwidth, etc. Thereby, we focus on what the TCP end-users care about, i.e., the number of bytes transported end-to-end within a certain time interval.
TL;DR: A new architecture is described where the optical transport is done without conversions (except at extreme nodes), and with minimal routing management effort, which is simpler and far more economical than (G)MPL(λ)S arrangements, for instance.
Abstract: Conventional optical wavelength division multiplexing (WDM) networks calls for optoelectronic conversion for each wavelength in every node plus a large management effort for proper packet routing. All-optical networks are still unavailable. Here, a new architecture is described where the optical transport is done without conversions (except at extreme nodes), and with minimal routing management effort. The present basic mechanism is, firstly, to gather (at any source node) the packets demanding for a certain destination node K. Secondly, all these packets are modulated onto wavelength λK. Next, the wavelength is routed towards node K by passive directional devices. As other source nodes reuse wavelength λK, an anti-collision mechanism is presented. This mechanism uses very economic and widely available components. The present arrangement seems to be pre-wired, conveying packets from source to destination nodes almost automatically. The present arrangement is simpler and far more economical than (G)MPL(λ)S arrangements, for instance. Additionally, the present system does not demand for expensive wavelength conversions or central protocols. The disadvantage over (G)MPL(λ)S is that the present arrangement limits its maximum number of operational nodes to the number of wavelenghts WDM is able to support.