The growing role of optical networks in Artificial Intelligence (AI) infrastructure exposes AI researchers to a field still gated by fluency with vendor-specific Yet Another Next Generation (YANG) models and Network Configuration Protocols (NETCONF). Large Language Models (LLMs) can help bridge this gap if applied properly. Specifically, LLMs do not know the YANG data models adopted by commercial Open Reconfigurable Optical Add-Drop Multiplexer (OpenROADM) equipment, and retrieving YANG as flat text loses the hierarchical structure that gives each constraint its meaning.

As 5G networks evolve to meet the growing demands for high data rates, low latency, and superior quality of service, hardware acceleration becomes essential for managing computationally intensive tasks. This paper demonstrates an implementation of Orthogonal Frequency Division Multiplexing (OFDM) symbols (both downlink and uplink transmission) using Field Programmable Gate Arrays (FPGAs), offloading the execution of these critical Low-Physical Layer (Low-PHY) functions away from the general-purpose CPU approach found in the open-source mobile software platform OpenAirInterface (OAI). The full integration of FPGA-generated OFDM symbols with an Open Computing Language (OpenCL) framework and the OAI protocol stack yields significant performance improvements, including a a 90% processing time reduction compared to the traditional CPU-based implementation. This demonstration highlights the effectiveness of FPGA acceleration in enhancing the efficiency of 5G Radio Access Network (RAN) functions implemented by open-source efforts, thus offering a path forward to implementing additional Low-PHY functions on accelerated hardware.

Smart living applications represent a significant group of 5G vertical use cases. For the most part, these use cases require mobile network connectivity and service high-availability. Simply put, two essential requirements for these applications are short connection time and uninterrupted user data service. Coupled with the expectation of supporting billions of connected devices, these requirements can be achieved by exploiting New Generation Radio Access Network (NG-RAN) architectures. One such emerging architecture is Cloud Radio Access Network (C-RAN), whose Next Generation NodeB (gNB) functions are physically decoupled into distinct entities, such as Radio Unit (RU), Distributed Unit (DU), and Central Unit (CU). The CUs are connected to 5G Core Network (CN) and are likely to be virtualized and distributed across multiple (micro and macro) data centers. The virtualized CUs (vCUs) are further decoupled into virtualized CU Control-Plane (vCU-CP) and virtualized CU User-Plane (vCU-UP) to increase flexibility and scalability. As these 5G RAN entities are virtualized, various resiliency schemes, such as container migration, must be considered to overcome possible congestion in or malfunction of the hosting server.In this paper, two distinct cloud-native RAN resiliency scenarios are evaluated while live-migrating gNB-vCU-CP with the objective of maintaining User Equipment (UE) connection time short and user data service uninterrupted in support of smart living and other advanced applications.

The Open ROADM ecosystem enables greater flexibility in deploying optical networks through centralized SDN management and intelligent service orchestration. However, since the maintenance signaling is yet to be standardized and implemented within each device, it is difficult to identify the root cause of issues and manage the network effectively when faults propagate in the network. To tackle this problem, this paper presents a proof-of-concept implementation of an alarm correlation and ticketing system for the multi-vendor Open ROADM ecosystem. The proposed system uses a graph-based method to identify the root cause of alarms and generate tickets for network operations teams. The results of our laboratory tests demonstrate the effectiveness of the proposed system in managing alarms in the multi-vendor Open ROADM ecosystem.

The 5G Radio Access Network (RAN) architecture provides a split option, whereby a gNodeB Central Unit (gNB-CU) is connected to one or more gNB-Distributed Units (gNB- DUs). The CU is in turn connected to the 5G Core Network (CN) and its functions can be virtualized through software containers. This demonstration showcases live migration of a containerized Central Unit (CU) component in a Cloud-native 5G network without loss of service. In terms of resiliency, virtual function live migration can circumvent the failure of the server hosting the gNB-virtualized CU (gNB-vCU) that would otherwise cause an interruption of user-plane (UP) traffic and disconnection of User Equipment (UE). The proposed gNB-vCU container live migration technique reduces the end-user service temporary downtime by 50% when compared to the traditional backup/restore option.

Virtual Optical Networks (VONs) offer scientists the opportunity to test and validate Software Defined Networking (SDN) controllers without requiring access to expensive optical equipment. A key component in VON is the real-time optical layer emulation (OLE) engine that must estimate the OSNR at the virtual receiver of every virtual lightpath that is established in the VON. This study investigates two algorithms for training a two-hidden layer Neural Network (NN) whose aim is to estimate the OSNR penalties caused by a series of virtual Wavelength Selective Switches (WSS) that are traversed by a virtual lightpath before reaching its virtual receiver. The NN solution yields good accuracy and only requires a few microseconds of computation time — a two key requirements for achieving a meaningful.

Edge computing is an attractive architecture to efficiently provide compute resources to many applications that demand specific QoS requirements. The edge compute resources are in close geographical proximity to where the applications’ data originate from and/or are being supplied to, thus avoiding unnecessary back and forth data transmission with a data center far away. This paper describes a federated edge computing system in which compute resources at multiple edge sites are dynamically aggregated together to form distributed super-cloudlets and best respond to varying application-driven loads. In its simplest form a super-cloudlet consists of compute resources available at two edge computing sites or cloudlets that are (temporarily) interconnected by dedicated optical circuits deployed to enable low-latency and high-rate data exchanges. A super-cloudlet architecture is experimentally demonstrated over the largest public OpenROADM optical network testbed up to date consisting of commercial equipment from six suppliers. The software defined networking (SDN) PROnet Orchestrator is upgraded to both concurrently manage the resources offered by the optical network equipment, compute nodes, and associated Ethernet switches and achieve three key functionalities of the proposed super-cloudlet architecture, i.e., service placement, auto-scaling, and offloading.

The lightpath provisioning time or releasing time is adversely affected by the time that optical amplifiers require to adjust to a newly added or terminated signal power. This shortcoming is particularly true with multi-core erbium-doped amplifiers (EDFAs), as multi-core transient-suppressed EDFAs are unavailable at the current time. This paper proposes a fiber span power management scheme based on dummy wavelength signals that are used to shorten the lightpath provisioning and releasing times in multi-core fiber networks. With the shorter time of lightpath provisioning and releasing procedures, the total time that is required to reserve wavelengths in the system is decreased, which means that network resources are used more efficiently. As a result, the blocking performance and average waiting time in the system are improved. To evaluate the performance of the proposed scheme, this paper introduces both analytical model and simulation study. In the introduced model, the ratio of the number of activating and activated dummy wavelengths to the number of dummy wavelengths in each span is considered in the range between 0 and 1. The analysis reveals that the performance of the proposed scheme depends on α, which is the ratio of the number of dummy wavelengths to the number of dummy and lightpath wavelengths in each span, and there exists a point of α where the blocking probability becomes minimum. We further observe that the proposed scheme outperforms the conventional approaches in terms of blocking probability and average waiting time, as traffic loads increase. Finally, we provide the direction on how our introduced model can be considered for a network with multi-span routes.

This paper describes an experimental study of network access delay from the end device to the cloud over a network based on Sub IGHz and LTE based network which may find many practical Internet of Things (IoT) applications when network response time is key and must be closely assessed. For this reason, the authors have built a test-bed using a low cost and ease of deployment wireless sensor network (WSN) based on the IEEE802.15.4g standard that is connected to an LTE modem, providing connectivity to a server in the cloud. The test-bed is used to measure end-to-end packet transfer time from the wireless IoT device to the cloud server, also providing a delay breakdown for every segment of the network. The presented results show the delay performance of the loT network architecture under varying values of the loT device periodic reporting time. While the operation modes of the WSN do not significantly affect the network latency, the LTE backhaul connectivity introduces some delay variability, which depends on the loT device periodic reporting time and other factors. By making use of these results the application designer can estimate the achievable network latency and make sure that the loT application requirements are met.

Industrial IoT faces adversity in radio environment due to harsh physical condition and interference from co-located wireless systems. To mitigate these challenges, channel hopping is leveraged in a number of standards, including IEEE 802.15.4- 2015. The baseline version of the channel hopping described in this standard does not guarantee the best performance, especially in terms of network stability and latency. This paper illustrates the problem by means of a test-bed, and then proposes a channel blacklisting algorithm, which makes use of the channel quality statistics as they are stored in the Cloud. Claims of improvement are corroborated by the results obtained through simulation.

Network administrators are interested in achieving the highest efficiency and utilization of their fiber networks. To this end, routing and wavelength (or more generally spectrum) assignment (RSA) algorithms play an important role, as they determine both the network spectrum fragmentation and the lightpath Quality of Transmission (QoT). If not accurately addressed, the former may unnecessarily decrease the number of lightpaths that can be established in the network and the latter may unnecessarily limit the lightpath achievable transmission data rate. The study in this paper shows that minimizing network spectrum fragmentation and maximizing QoT often are conflicting optimization problems. A RSA algorithm that is designed to minimize network spectrum fragmentation is likely to yield suboptimal QoT. Vice versa, a RSA algorithm that is designed to maximize QoT is likely to yield suboptimal spectrum fragmentation. This trend is documented and quantified for five well-known fiber network topologies.

In dynamic-traffic Wavelength Division Multiplexing (WDM) networks, it is desirable to guarantee each optical circuit a minimum Optical Signal-to-Noise Ratio (OSNR) throughout the circuit's entire lifetime. The objective of this paper is to increase such guaranteed OSNR, which in turn enables bandwidth-efficient modulation formats to be applied to the circuit signals. The guaranteed OSNR is improved by applying OSNR-driven Spectrum Assignment (OSA) constraints to each fiber link in the network, based on its forecast traffic volume (offered load). Applying OSA constraints to fiber links has two conflicting outcomes. On the one hand, circuit requests may experience higher blocking probabilities due to the lack of usable spectrum. On the other hand, the adverse effects of medium nonlinearity may be contained, thus yielding improved circuit OSNR. Two OSA constraints are described and their favorable impact on circuit OSNR (up to 2.75 dB gain) is estimated by using a Gaussian Noise (GN) model and an event-driven simulation of two WDM networks supporting dynamic circuits.

Optical networks are well suited to support massive data exchanges between data centers. Elephant traffic flows can be routed over provisioned and dedicated lightpaths (optical flows) while other (mice) flows, which are routed by electronic switches, are unaffected. In some solutions, Wavelength-Selective Switches (WSSs) are employed in the optical nodes to individually route the lightpath towards its destination. WSSs take time to be switched and delay the lightpath setup time. In this paper, the authors compare three service policies for WSS devices aiming to reduce the lightpath setup and tear down times. The conventional service policy assumes that each setup (tear down) request is handled individually. Two other service policies assume that groups of setup (tear down) requests are handled together by the WSS. These policies are implemented in a discrete event simulator, which is used to estimate the end-to-end lightpath setup and tear down time across an arbitrary mesh network. Simulation results show that group service policies outperform the conventional policy at high loads. The grouping policies are useful to reduce the lightpath setup time especially in the presence of lightpaths that are frequently set up and have relatively short holding time (short duration of elephant-optical flows).

Elastic Optical Networks (EONs) have the potential to improve the fiber spectrum utilization by allocating spectrum resources to multiple traffic requests proportionally to the amount of carried traffic. However, achieving high spectrum utilization in this elastic scenario is hindered by the resulting spectrum fragmentation. A number of studies have addressed and made attempts to mitigate spectrum fragmentation. Most of these studies are based on simulation techniques and target the overall blocking probability experienced by the offered traffic requests due to the lack of available spectrum resources. Some studies have also shown that blocking probability in EON can be uneven, i.e., high-rate circuit requests are more likely to be blocked when compared to low-rate requests due to the shortage of contiguously available spectrum resources. The contribution of this paper is to extend an existing Markov Chain (MC) model previously proposed by the authors to quantify blocking probability in a two-service elastic fiber link. The model extension accounts for a self-limited and partial sharing of the fiber spectrum to accommodate the two types of service. The MC model is used to quantify both the blocking probability and its fairness across the two types of service, documenting how the EON uneven blocking behavior can be significantly mitigated by performing partial (as opposed to full) sharing of the fiber spectrum.

Elastic Optical Networks (EONs) enable optical circuits to be assigned distinct numbers of spectrum slices. Individual circuits can then be assigned an optimal number of slices to best match their target transmission rates. A well-known drawback of EONs is spectrum fragmentation and its resulting uneven blocking probability, which circuit requests experience when the available spectrum slices in the fiber are insufficient or not contiguous. Capturing this spectrum fragmentation problem analytically is a challenging problem. Not surprisingly, most of the existing studies at this time mainly use simulation-based techniques to quantify blocking probability in EONs. In this paper, the authors present a Markov Chain (MC) model that attempts to characterize the fragmentation problem in a simplified scenario, i.e., only two types of circuit services are allowed over a single fiber link. Despite its limited scope, this initial analytical effort is able to accurately capture the non-monotonic behavior of the blocking probability in EONs for the first time.

Distributed and global power control strategies have been successfully applied to cascade of optical amplifiers with the aim of improving circuit OSNR values in WDM networks. For these or similar strategies to achieve their objectives, accurate estimators of the EDFA output power (EOP) are of the essence. These EOP estimators must take into account the amplifier characteristics including unequal power values of the input signals, frequency of each signal and desired target gain for each amplifier. The scope of this paper is to propose and assess the accuracy of three EOP efficient linear estimators. The EOP estimators are part of a framework comprising four modules, which are simple to implement and flexible to use. The proposed estimators are efficient in that they compute EOP estimates in seconds and require only a limited set of EDFA measured data.

In this paper, a Software Defined Networking (SDN) based unified wireless network architecture is proposed to enable distributed mobility management. The proposed approach envisions a virtualized control plane, placed in the Cloud. The user plane is free of typical tunnelling mechanisms and utilizes layer 2 and layer 3 traffic forwarding. The network architecture for cellular users is described first. Then, traffic flow in both upstream and downstream directions, different mobility scenarios, and an efficient address assignment scheme are discussed. An analytical model to estimate the signaling overhead in the Evolved Packet Core (EPC) is presented. The architecture is further extended to support WLAN users in fixed networks, with a description of the signaling schemes required in a number of mobility events.

This paper presents a software defined networking (SDN) based semi-distributed mobility management system. By both using an SDN approach and leveraging layer 2 technology, i.e., carrier grade Ethernet and the 802.1ad standard, it is possible to simplify the network architecture by removing the need for the relatively complex GPRS tunneling protocol currently in use in the user plane. An analytical model is used to evaluate the control overhead of the proposed approach and a proof of concept testbed based on OpenFlow running the Floodlight controller is presented. Obtained results demonstrate that, as long as the SDN controller can quickly react to user mobility, frame loss can be mitigated and the proposed architecture is viable.

Optical Flow Switching (OFS) is an end-to-end optical circuit oriented network in which optical circuits are created on demand to directly connect pairs of end-users. Circuits are established across three network segments: the access (distribution), the metro and the wide area network. Once the circuit is reserved, the end-user can then fully utilize the optical channel for large data transfers using efficient and specially designed transport protocols. Scheduling of optical flow transmissions (i.e., optical circuit set up and tear down operations) is a critical component of OFS as resources across the three network segments must be lined up and synchronized to form the end-to-end circuit. The current scheduling solution [1], [2] is designed to be simple and efficient in achieving high utilization of both WAN and Metro optical channels. Its downside is that the distribution network channel utilization must remain low. The contribution of this paper is to improve the OFS scheduling procedure in such a way that medium-high utilization of the distribution network is attainable too. This objective is achieved by adding moderate complexity to the original optical flow scheduling and signaling procedure in order to retain the scalability property of the same. With the proposed extension of the OFS scheduler, the distribution network channel utilization is increased manyfolds.

Given the geographic complexity of the cloud infrastructure distribution, both offline data center dimensioning and link dimensioning as well as online resource allocation strategies play a significant role in enhancing end-to-end performance. In this paper, a three-step offline capacity assignment approach is proposed to select the data center locations, dimension the data centers and network links in an arbitrary mesh topology. Then the performance of the capacity assignment approach is investigated using a number of joint allocation strategies. Simulation results show that by using joint online resource allocation strategies, up to 50% higher load can be offered to the system at a given blocking probability. In addition, the combination of using both optimized capacity assignment approach and joint allocation strategy can reduce the link bandwidth over-provisioning. Results also show that the joint allocation strategy is more robust against sub-optimal offline capacity assignment.

An increasing number of users perform large transfers over data networks. While, for the most part, these transfers are currently performed over the IP network, a number of studies advocate the use of end-to-end optical circuits to support these resource-consuming jobs. One of the major advantages is the ability to carry a large fraction of the overall network traffic using the relatively lower-cost and lower-power optical equipment, when compared to IP routers. For example, in optical flow network, end-to-end optical circuits can be established by reserving wavelength channels only when needed. Once the circuit is established, the large data set is seamlessly transferred across the network without requiring IP routers to be involved in the data transfer. For a circuit to be successfully established the following conditions must be simultaneously met: a transmitter must be available at the sender, a receiver must be available at the destination, and a wavelength channel must be available across the network to connect the sender to the destination. Data transfer can start only when the conditions above are simultaneously met. As a result, a request can experience a delay before being established. Network throughput and delay are affected by the availability of network channels (channel-contention) and end-user's receiver (receiver-contention). The contribution of this paper is twofold. First, channel throughput and delay are analytically estimated. Second, the analytical results are validated using simulation results. A number of experiments are conducted using the presented analytical models and simulation platform to investigate the effect of channel and receiver contention on throughput and delay.

In a recent study about Wavelength Division Multiplexing (WDM) networks, the authors showed that by decoupling the wavelength assigned to the outward circuit from the wavelength assigned to the inward circuit of the same bidirectional unprotected lightpath, it is possible to reduce the total required number of Wavelength Converters (WCs) when compared to the conventional Wavelength Assignment (WA) solution, in which both outward and inward circuits are assigned the same wavelength [1]. The goal of this paper is to generalize the study in [1] to account for dedicated path protection switching mechanisms applied to bidirectional lightpaths. In doing so, a second factor must be accounted for in the study, i.e., the wavelength assigned to the working circuit may be decoupled from the wavelength assigned to the protection circuit. As a result, four design options are possible by either enforcing or relaxing each of the following two constraints: 1) lightpaths are (are not) required to be assigned the same wavelength for the inward and outward circuit; 2) lightpaths are (are not) required to be assigned the same wavelength for the working and protection circuit. The four design options are compared in terms of their required average number of WCs in the network, revealing that the WC usage may differ significantly depending on the design used.

Network element failure may occur due to natural disasters, malfunctioning components, or human errors. Ideally, network failure occurrence should not affect the network performance as it is experienced by the users. For this reason, robust protection mechanisms resort to standby network resources, which are readily available upon failure occurrence, e.g., dedicated path protection. In some network architectures and service models, a less ideal protection approach may still be applicable in exchange for a reduced network and service cost. Graceful degradation of performance upon failure occurrence may be acceptable in this case. The study in this paper explores preemption-based restoration mechanisms applied to optical connections (lightpaths) in Wavelength Division Multiplexing (WDM) networks. The rationale for preempting some of the still functioning lightpaths - while performing rerouting of the failing ones - is to avoid highly unfair scenarios in which some node pairs starve for lightpaths significantly more than other pairs do, as a consequence of a failing network element1.

Wireless media servers and real-time applications are becoming increasingly popular in most homes. Wireless network latency is a key factor in many applications. The objective of this paper is to derive an analytical framework to estimate the latency in terms of the average service time of the most used multiple-rate wireless link protocol, i.e., IEEE 802.11. A number of analytical models for IEEE 802.11 exists in the literature. However, to the best of the authors' knowledge, no general analytical model exists that jointly models IEEE 802.11 latency under the assumption of using multiple transmission rates and unsaturated load traffic. Additionally, the proposed model can also be extended to cooperative variants of IEEE 802.11 which exploit the presence of both multiple nodes and multiple transmission rates to improve network performance. In particular, in this paper, the extension to model COBRA MAC, an opportunistic cooperative variant of IEEE 802.11 is presented. The derived model is validated against simulation results, revealing good match between model and simulation. Also, results showing the performance benefits achieved by COBRA MAC over IEEE 802.11 are presented.

Cross layer optimization is well-known to offer certain cost and performance advantages when designing and operating data networks [1]. It is reasonable to anticipate similar advantages when applying such optimizations across the network layer and the application layer too. In this paper, the authors define one optimization problem whereby the service-to-hosting data center mapping is performed taking into account the available resources in both the data center (CPU cycles) and network (bandwidth) subsystems. The objective function of the optimization problem accounts for the amount of both CPU cycles and bandwidth, which are assigned to each requested service, with the assumption that the user's Quality of Experience (QoE) strictly depends only on these two factors. The problem is formulated using ILP and its numerical results are discussed to gain insights into the potential QoE gains that might result from using this cross layer (cooperative) resource assignment technique.

Multicast transmission offers a bandwidth efficient solution for delivering media content to multiple destinations over the Internet. However, in many existing networks, some (if not all) nodes do not support multicast, i.e., they cannot create multiple outgoing flows with one incoming data flow. In this paper, the authors propose an algorithm for multicast tree computation in networks with multicast incapable nodes. Paths that originate at the source and traversing all destinations are computed first; if such paths cannot be found, destinations are partitioned into subsets and traverse paths are computed over each subset, which is executed recursively until feasible trees can be built based on traverse paths found or no further partition is possible. Two procedures for traverse path computation are presented and their respective advantages are discussed, in terms of both complexity and solution optimality. The algorithm is also shown to be very effective in finding multicast trees even if only a few multicast capable nodes exist in the network.

This paper presents a preliminary study on an effective differentiable network service technique to achieve improved speech recognition under severely poor wireless channel conditions, by leveraging multiple priority levels applied to speech classes. Each speech class is assigned a different priority level based on its level of impact on speech recognition performance. Based on their priority level, frames of each speech class are given distinct levels of network quality of service (QoS) to satisfy the delay requirement and enable speech recognition at the receiver. This proposed Phone Impact (PI) based priority class is compared to the Voiced/Unvoiced (VU) based priority class in this study. The experimental results prove that the proposed scheme is effective at providing wireless network service for robust speech recognition under poor channel conditions, showing up to 2.67 dB and 5.93 dB lower Signal to Noise Ratio (SNR) operating regions compared to the VU based and plain protocols respectively. The PI based method also shows acceptable WERs at lower SNRs where VU and plain systems significantly degrade in speech recognition performance in case of retry limit of 6. Index Terms: Phone Impact, Priority Class, Speech Recognition, IEEE 802.11, Differentiated Maximum Retry Limit.

The growing demand for online media content delivery and multi-player gaming is expected to increase the amount of multicast service requests in both public and private networks. Careful traffic engineering of multicast service requests is becoming increasingly essential, as establishing the lowest cost tree, e.g., shortest path tree, in the network for every individual multicast request does not always ensure a global optimization. In this paper, the authors investigate the use of alternate tree routing, according to which multiple sub-optimal tree candidates are computed for each multicast request. When performing global routing optimization, each request is then assigned one of the tree candidates, in a way that yields the desired result, e.g., to minimize the number of (active) links that are required in the network to bear the entire set of requests. A key component of the investigated approach is the timely construction of the set of alternate trees for every given root and destination set. An algorithm is proposed to compute multiple sub-optimal tree candidates with a guaranteed upper bound on the maximum end-to-end transmission latency. The algorithm builds on the widely used K shortest path algorithm, generalizing the technique of computing K candidate shortest paths to obtain a number of candidate sub-optimal trees with desirable properties. Simulation experiments obtained for a multi-protocol label switching (MPLS) traffic engineering network are discussed to investigate the effectiveness, performance, and scalability of the proposed algorithm.

A careful wavelength assignment (WA) to lambda services must be performed to reduce the total number of wavelength converters (WCs) that are required when the wavelength continuity constraint cannot be met in wavelength division multiplexing (WDM) networks. With the successful introduction of reconfigurable optical add-drop multiplexers (ROADMs), WDM networks are now growing in size, both in the number of optical nodes and the number of wavelengths supported. Fast and memory efficient WA algorithms are required to design cost effective large WDM networks. This paper presents a scalable and efficient WA heuristic algorithm aimed at reducing the total number of WCs that are required in (large) WDM networks bearing static lambda services. The WA algorithm is applied to both unprotected and (dedicated) protected lambda services. In the latter case, the wavelength continuity constraint between the working and protection path of a lambda service is taken into consideration when non-tunable optical transceivers are employed.

The introduction of end-to-end (multi hop) optical circuits (lightpaths) is often seen as the natural extension of a point-to-point (single hop) wavelength division multiplexing (WDM) transmission system, spanning across optical cross-connect nodes. Conventionally, a bidirectional lightpath (whether single or multi hop) comprises two lambda channels in fibers with opposite directions of signal propagation, which are assigned the same wavelength. This constraint is referred to as identical wavelength in bidirectional lightpath (IWBL). While IWBL is a natural and historical choice in point-to-point system, the authors are going to demonstrate that IWBL may unnecessarily increase the number of wavelength converters (WCs), which are required to establish lightpaths in the WDM network when the wavelength continuity constraint cannot be met. In the study, the IWBL constraint is relaxed, thus allowing the assignment of two distinct wavelengths to the same lightpath, one for each direction. A wavelength assignment (WA) algorithm is designed to both take advantage of the IWBL constraint relaxation and minimize the required number of WCs to establish a given set of lightpaths. The algorithm is then applied to a number of network topologies. The outcome is quite surprising, in that the amount of WC reduction obtained by relaxation of the IWBL constraint may be significant under certain conditions.

In this paper the authors present an analytical model that - compared to previously published work - more accurately captures the delay of IEEE 802.11 protocol under low, medium, and near-saturation load conditions. A Markov chain is used to keep track of the instantaneous number of (active) nodes that have a frame to transmit. One advantage of the proposed analytical model is its ability to estimate the IEEE 802.11 protocol latency and delivery ratio in the presence of quality of service (QoS) classes, each class being defined by a specific maximum retransmission count. Such QoS classes can be adopted to support real time applications for which both latency and delivery ratio must be closely monitored for satisfactory operation.

Multimedia applications in Wireless Sensor Networks (WSNs) require different approaches with respect to traditional networks due to the adopted devices' limitations in energy consumption and computational capabilities. This paper proposes a low-complexity algorithm for selecting speech packets according to their perceptual importance for voice transmission over WSNs. The proposed algorithm allows wireless sensor nodes to select which packets to protect during transmission in order to increase speech quality while at the same time minimizing the necessary energy. Experimental results based on cooperative transmission among devices show that the proposed algorithm achieves a good speech quality level while reducing the need to protect packets by 40% when compared to random selection.

Path computation elements (PCE's) are used to compute end-to-end paths across multiple areas. Multiple PCE's may be dedicated to each area to provide sufficient path computation capacity and redundancy. An open problem is to which PCE to send the path computation request. This problem may be a non trivial problem if PCE's have uneven processing capacities. This paper presents a queueing model based on product form to estimate the latencies in path computation while accounting for the arrival rate of path computation requests. The model is used to find the PCE selection policy to minimize the overall expected latencies in path computation. Simulation studies demonstrate that the use of the simplistic product form approach yields reasonable approximations that are within up to 15% of the simulation results at practical offered loads.

Multimedia applications over wireless sensor networks (WSNs) are rapidly gaining interest by the research community in order to develop new and mission critical services such as environmental video monitoring and emergency speech calls. In this work we analyze the possibility of sending voice using a network of wireless tiny motes with the final goal of enhancing speech quality by protecting the most perceptually important packets. We first evaluate the speech quality for a modified version of the ITU-T G.711 standard implemented to fit the particular selected hardware. Hence, we propose a low-complexity measure to evaluate the perceptual importance of speech packets. When performing single-hop experimental data collection, we apply packet redundancy (protection) by using a cooperative mote (relay) which retransmits speech packets that are perceptually important to protect them against potential transmission losses. Collected experimental results are then used to assess multi-hop performance, showing that the combination of the selected hardware and the proposed perceptual marking algorithm achieves good speech quality levels, according to the MOS scale, while reducing the percentage of protected packets by 40% when compared to random protection.

This paper presents an algorithm to find a simple path in the given network with multiple must-include nodes in the path. The problem of finding a path with must-include node(s) can be easily found in some special cases. However, in general, including multiple nodes in the simple path has been shown to be NP-Complete. This problem may arise in network areas such as forcing the route to go through particular nodes, which have wavelength converter (optical), have monitoring provision (telecom), have gateway functions (in OSPF) or are base stations (in MANET). In this paper, a heuristic algorithm is described that follows divide and conquer approach, by dividing the problem in two subproblems. It is shown that the algorithm does not grow exponentially in this application and initial re-ordering of the given sequence of must-include nodes can improve the result. The experimental results demonstrate that the algorithm successfully computes in reasonable time.

Cooperative link layer protocols are typically used in single hop networks to enhance the link layer capabilities using a special node, called relay. In multi-hop networks, a frame is sent from an original source to the final destination through a series of intermediate nodes. The performance benefits of cooperation at link layer can be channeled into multi-hop networks as well. This paper addresses the challenge in finding multi-hop routes accounting for relays at the link layer by proposing the cooperative expected transmission time (CETT) metric. CETT is used to compute the route, i.e., the sequence of intermediate nodes in terms of the minimum end-to-end average transmission time taking into account the cooperative nature of the link layer.

WiFi, i.e., IEEE 802.11 is one of the most widely used technologies to implement internet access in today's networks. Typical frame error rates in IEEE 802.11 are much higher than in wired links. This negatively impacts the behavior of TCP, which assumes that packet loss is due to congestion. This paper presents LN-MAC, a cross-layer solution based on explicit loss notification (ELN), where the IEEE 802.11 MAC is enhanced to provide loss notifications to the TCP layer. Extensive simulation results demonstrate the benefits of LN-MAC. Numerical results demonstrate that under any condition TCP throughput is always higher when using LN-MAC than when using conventional IEEE 802.11.

The two transport protocols DCCP and UDP-Lite can make use of data that are known to be erroneous, provided that the link layer hands over such data. A similar functionality has been suggested for TCP. In order to investigate the potential of these mechanisms in WiFi networks, we carried out a measurement study where we examined how often information about corrupt data reaches the transport layer when the corruption control at the link layer is disabled. Our results suggest that this may be a rare occurrence in certain scenarios.

In cooperative ARQ protocols, data frame retransmissions may be performed by a neighboring node (the relay) that has successfully overheard the source's frame transmission. One advantage is the diversity provided by the relay. The three-way (source, destination, relay) frame exchange sequence required in the cooperative ARQ protocols may however introduce extra latency when compared to non-cooperative ARQ protocols. To take advantage of cooperative ARQ protocols, it is then necessary to resort to selective repeat solutions. The focus of the paper is to derive a delay model for cooperative selective repeat ARQ protocols in slotted radio networks. The derived analytical model quantifies, with closed formulas, the queueing and transmission delay experienced by Poisson arriving data frames, whose retransmissions are performed by a single relay.

One class of wireless sensor networks makes use of sensor nodes that recharge their batteries by harvesting energy from the surrounding environment. Being continuously recharged, the battery does not need to be replaced regularly and the sensor node is maintenance-free. A key module in such sensor network solutions is the data link automatic repeat request (ARQ) protocol, which must be designed to reliably deliver sensor nodes data at the minimum energy cost. With this objective in mind, two ARQ protocol classes are compared. In one class, each sensor node operates individually. In the other, the concept of cooperative communications is adopted, whereby neighboring sensor nodes help each other during the retransmission process. It is shown that the use of cooperative ARQ protocols in energy harvesting sensor networks enables sensor nodes to balance their energy consumption to match their own battery recharge rate. In turn, a balanced energy consumption-to-recharge rate ratio has the potential to improve the network throughput. Both classes of ARQ protocols are analyzed and compared. Estimated throughput gains are discussed under various network scenarios.

This paper demonstrates that cooperative ARQ protocols have the desirable property of increasing the saturation throughput of fixed multiplexed access radio networks, subject to non-uniform offered traffic. The throughput gain is found to be increasing as the source-to-destination channel quality deteriorates and the source-to-relay channel quality ameliorates. Asymptotically, such gain approaches that of the optimum solution, i.e., the perfect statistical multiplexing.

MPLS Fast Reroute advocates local protection mechanisms to rapidly reroute traffic onto pre-computed and signaled bypass tunnels. When the network is subject to multiple element failures, it becomes challenging to handle all the possible failure scenarios, for they are more disruptive and may require many more bypass tunnels to be dealt with. The objective of this paper is to adapt the MPLS local recovery schemes to deal with multi-failure scenarios, while retaining as much as possible the simplicity and the fast failure detection feature of current (single failure) local recovery mechanisms. This objective is achieved by optimally grouping failure patterns into clusters and minimizing the overall additional network resources - i.e., bypass tunnels and bidirectional forwarding detection sessions - while yielding full recovery from such failure patterns.

The generic autonomous platform for sensor systems (GAP4S) is a maintenance-free wireless sensor network in which the sensor node battery does not need to be replaced. Power is delivered to the sensor node via a microwave signal that is radiated by a base-station. The base-station also acts as the entry point to a wider communication network, e.g., the Internet. The paper describes an automatic repeat request (ARQ) protocol that may be used in GAP4S to yield reliable and fair data transmission from the sensor nodes to the base-station. The protocol takes advantage of cooperative communication, whereby neighboring sensor nodes help during the retransmission process. The transmission power level is optimized at each sensor node to increase the saturation throughput of the ARQ protocol.

MPLS-TE (traffic engineering) fast reroute proposes a local protection mechanism to reroute protected TE LSPs (label switched paths) quickly onto precomputed and signaled bypass tunnels. The paper explores the case of multiple network element failure scenarios. The undesired complexity inherent in the multiple failure scenario originates from the fact that those failure scenarios are more disruptive, and may require multiple bypass tunnels to cope with them. The paper adapts the MPLS local recovery schemes to multi-failure scenarios, while controlling the number of bypass tunnels that are required. This is achieved by mapping multi-failure scenarios onto probable failure patterns (PFPs). PFPs are characterized by their probability (or frequency) of occurrence during the network lifetime. A number of bypass tunnels is then computed to cope effectively with the PFPs according to their frequency or probability of occurrence. It is shown that by properly choosing how the PFPs are grouped, and how the corresponding bypass tunnels are computed, it is possible to trade the required number of bypass tunnels for their average length and outage probability, i.e., the probability that the local recovery scheme cannot cope with the occurrence of a multi-failure pattern.

This paper introduces a centralized admission control mechanism, referred to as threshold-based blocking differentiation (TBDiff), to differentiate the blocking probability experienced by various service classes in a circuit switched WDM network. The mechanism is based on multiple class-thresholds that indicate the minimum amount of capacity that must be available, prior to accommodating a request for a given service class. The performance of TBDiff is studied by means of an analytical framework and also an event-driven simulator. The results show a thorough matching of the analytical and simulation results and also demonstrate that high blocking differentiation among service classes can be obtained, without excessively increasing the overall (average) network blocking probability.

In this paper, the authors investigate the use of two destination-initiated wavelength-weighted reservation (DW/sup 2/R) protocols for the distributed setup of dynamic lightpaths in wavelength division multiplexed (WDM) rings. The two protocols are based on a weight-based wavelength selection heuristic, recently proposed for mesh topologies. The main objective of the DW/sup 2/R protocols is to reduce the probability of service denial due to multiple and concurrent wavelength reservation attempts, initiated by distinct sources. A detailed performance study based on simulation experiments on ring topologies reveals for the first time a number of desirable scalable properties of the DW/sup 2/R protocols.

In reliable wavelength division multiplexed (WDM) networks, the optimal choice of routing and wavelength assignment (RWA) for the working and protection path-pair is often a complex problem to solve. To cope with such problem complexity, this paper presents the disjoint path-pair matrix (DPM) approach. With the DPM approach, the RWA problem complexity - i.e., the size of the solution space - can be significantly reduced by limiting the number of candidate path-pairs considered in the optimization. Simulation results are collected using the DPM approach to solve the online RWA problem in a network based on the shared path protection switching scheme with differentiated reliability. When compared to the conventional k-shortest paths approach, the DPM approach requires up to one order of magnitude less candidate path-pairs. In addition, the DPM approach finds solutions with reduced hop length of both the working and protection paths by up to 3% and 14%, respectively.

The objective of this paper is to compare three well-known WDM network architectures (first-generation, single-hop, and multi-hop) when they are deployed to accommodate dynamic end-to-end connections with sub-wavelength transmission rates. The comparison is based on a performance figure that is uniquely defined to take into account the various architecture costs determined by the cost of the deployed network elements. The defined performance figure permits also to compare the three architectures for all possible line-to-node cost ratio values.

The label stacking mechanism of MPLS is studied in this paper. LSP encapsulation is shown to be able to reduce the MPLS control plane workload, while maintaining the data network blocking probability at acceptable levels.

A method is presented to compute a fundamental traffic engineering parameter, the end-to-end blocking probability, when both traffic and reliability aspects are taken into account. Additionally, link failures are not assumed independent. This situation is justified by the practical scenario of logical network, even if the physical link failures are independent, after mapping the failures into the logical network, the logical links do not fail independently. Dependent link failures can also occur as a result of a node failure.

Optical burst switching (OBS) provides statistical multiplexing capabilities at the optical layer with relaxed hardware requirements when compared to optical packet switching. One of the open challenges of OBS is to assemble as many packets as possible in the same burst, while at the same time ensuring low latency of the transmitted packets. The authors propose the use of OBS to realize a geographically distributed packet switch for metro rings. High efficiency of the ring bandwidth and low packet latency are obtained at the ring node by combining a multi-token based protocol for contention less and loss-free transmission of bursts, known as the lightring protocol, with the creation of bursts that contain packets belonging to multiple traffic flows (classified by priority and destination). As illustrated in the paper, the proposed solution yields throughput that is significantly higher than that one offered by a centralized packet switch connected to the ring nodes via dedicated optical circuits. Latency of real time packets is kept at few dozens of milliseconds under a variety of network scenarios. The solution scales well geographically for metro applications.

Reliability of data exchange is becoming increasingly important. In addition, applications may require multiple degrees of reliability. The concept of differentiated reliability (DiR) was recently introduced in [A. Fumagalli and M. Tacca, January 2001] to provide multiple degrees of reliability in protection schemes that provision spare resources. With this paper, the authors extend the DiR concept to restoration schemes in which network resources for a disrupted connection along secondary paths are sought upon failure occurrence, i.e., they are not provisioned before the fault. The DiR concept is applied in two dimensions: restoration blocking probability i.e., the probability that the disrupted connection is not recovered due to lack of network resources - and restoration time - i.e., the time necessary to complete the connection recovery procedure. Differentiation in the two dimensions is accomplished by proposing three preemption policies that allow high priority connections to preempt resources allocated to low priority connections. The three policies trade complexity, i.e., number of preempted connections, for better reliability differentiation. Obtained results indicate that by using the proposed preemption policies, it is possible to guarantee a significant differentiation of both restoration blocking probability and restoration time. By carefully choosing the preemption policy, the desired reliability degree can be obtained, while minimizing the number of preempted connections.

Remote sensing technologies have long since been relegated to the implementation of airborne or spaceborne configurations. We recognize that distributed sensors in all configurations can contribute to improved sensor performance and expanded measurement configurations. These new sensor systems require designs that can be scaled to hundreds to potentially thousands of individual sensors or sensor components. This paper describes a novel sensor network design strategy and some suggested operational scenarios. Mega-Mesh sensor networks require special design to support effective communication protocols. There will be a requirement for reliable sensor-to-sensor communication, ad-hoc self organizing network, multiple individual communication network structures, wireless base stations, remotely charging techniques, etc. All of these approaches dictate unique network architectures that eventually interface to conventional communication infrastructure and/or legacy networks.

Network survivability provided at the optical layer is a desirable feature in modern high-speed networks. For example, the wavelength division multiplexed (WDM) self-healing ring (or SHR/WDM) provides a simple and fast optically transparent protection mechanism against any single fault in the ring. Multiple self-healing rings may be deployed to design a survivable optical mesh network by superposing a set of rings on the arbitrary topology. However, the optimum design of such a network requires the joint solution of three subproblems: the ring cover of the arbitrary topology (the RC subproblem); the routing of the working lightpaths between end node pairs to carry the offered traffic demands (the WL subproblem); and the provisioning of the SHR/WDM spare wavelengths to protect every line that carries working lightpaths (the SW subproblem). The complexity of the problem is exacerbated when software and hardware requirements pose additional design constraints on the optimization process. The paper presents an approach to optimizing the design of a network with arbitrary topology protected by multiple SHRs/WDM. Three design constraints are taken into account, namely, the maximum number of rings acceptable on the same line, the maximum number of rings acceptable at the same node, and the maximum ring size. The first objective is to minimize the total wavelength mileage (working and protection) required in the given topology to carry a set of traffic demands. The exact definition of the problem is given based on an integer linear programming (ILP) formulation that takes into account the design subproblems and constraints and assumes ubiquitous wavelength conversion availability. To circumvent the computational complexity of the exact problem formulation, a suboptimal solution is proposed based on an efficient pruning of the solution space. By jointly solving the three design subproblems, it is numerically demonstrated that the proposed optimization technique yields up to 12% reduction of the total wavelength mileage when compared to solutions obtained by sequentially and independently solving the subproblems. The second objective is to reduce the number of wavelength converters required in the solution produced by the ILP formulation. Two approaches are proposed in this case that trade the required wavelength mileage for the number of wavelength converters.

Storage area networks (SAN) are important components of today's corporate networks. Two key features of SAN are the ability to provide distributed access to stored files of any size in a timely manner, and to use network bandwidth efficiently. To achieve these goals, the paper proposes a novel bandwidth reservation scheme for the LightRing - a recently proposed all-optical WDM ring with distributed multi-token access control. For each file transfer, the proposed scheme reserves a bandwidth that: (1) is proportional to the file size; and (2) takes into account the ring latency. The file is then transmitted using one or more optical bursts. As shown in the paper, the proposed reservation scheme achieves both of the goals, i.e., a good utilization of the ring bandwidth and fast file transfer time under a variety of file sizes.

The authors (Fumagalli and Tacca (2001)) introduced the concept of differentiated reliability (DiR) applied to dedicated path protection (DPP) switching in wavelength division multiplexing (WDM) rings. By means of the DiR concept, a network can be designed to provide multiple degrees of reliability and efficiently satisfy the user-specific requirements, yet minimizing the network total cost. This paper extends the DiR concept to the case of shared path protection (SPP) switching in arbitrary (mesh) topology, the so called SPP-DiR. A time efficient algorithm is proposed to determine the primary and backup path of each demand in both conventional SPP and SPP-DiR (WDM) networks. When compared to DPP, results obtained for the pan-European network by using the proposed algorithm indicate cost reductions of about 16% when SPP is applied, and up to 34% when SPP-DiR is applied.

A number of bandwidth reservation schemes have been proposed for multi-channel rings, generally classified as centralized and distributed. Besides simulation results, the existing analytical models address only the blocking probability and achievable throughput of such schemes. However, in determining the properties and advantages of each reservation scheme (especially the LightRing, a scheme previously proposed by the authors) the above performance figures are not sufficient, as network latency plays a determinant role when fast bandwidth provisioning is of the essence. This paper presents an analytical framework that allows one to derive the response time and throughput of such schemes under the assumption that a single request for bandwidth can be stored and processed by the source at a time. Numerical results obtained using the proposed model reveal a number of interesting properties of the existing bandwidth reservation schemes.

The concept of differentiated reliability, (DiR) was recently introduced by the authors to provide multiple reliability degrees (or classes) at the same network layer using a common protection mechanism, e.g., path switching. According to the DiR concept, each connection at the layer under consideration is guaranteed a minimum reliability degree, defined as the maximum failure probability allowed for that connection. 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. In the paper the DiR concept is applied to designing the wavelength division multiplexing (WDM) layer of a ring network in which wavelength conversion is not available. To solve the routing and wavelength assignment problem at the WDM layer an efficient algorithm is proposed that resorts to reusable protection wavelengths while guaranteeing the required reliability degree of each connection. Lower bounds on the network bandwidth required by two approaches-respectively based on non-reusable and reusable protection wavelengths-reveal interesting properties of the DiR concept and the proposed algorithm.

By means of optical transparency wavelength division multiplexing (WDM) networks with multi-rate transmissions are becoming a reality. The potential advantages of individually selecting the transmission rate for each lightpath are however not yet fully understood. A recent work studied for the first time multi-rate and multi-hop (M&M) networks in which tributary signals are transmitted over a concatenation of lightpaths, each one operating at its own transmission rate. The study revealed that the problem of designing M&M networks is NP-complete and optimal solutions are practically available only for small networks. The paper presents a heuristic algorithm for designing M&M ring networks that yields efficient sub-optimal solutions in polynomial time. The algorithm determines the rate for each lightpath taking into account a number of factors including the node's interface, amount of multiplexed traffic and cost of the network components. The potential advantages provided by the M&M network when compared to first generation optical networks (i.e., SONET/SDH), single- and multi-hop (constant bit rate) optical networks, are discussed in the paper and documented with numerical results. Presented results show that the network cost reduction achieved by the M&M design is a function of the cost ratio between the optical bandwidth (wavelengths) and the optical terminals.

One of the approaches currently pursued to provide an optical network architecture for supporting the next generation Internet consists of transmitting the Internet protocol (IP) packets directly over the wavelength division multiplexing (WDM) layer. The challenge of this approach is to make the optical bandwidth directly accessible to IP with the statistical multiplexing necessary to support the bursty nature of IP traffic in a cost effective way. This paper proposes a WDM ring architecture with a multitoken interarrival time (MTIT) access protocol designed to achieve a bandwidth efficient multiplexing technique in local and metropolitan network applications. The MTIT protocol achieves efficient multiplexing of all-optically transmitted packets by means of multiple control tokens whose rotation speed along the ring is regulated via the "token interarrival time," as opposed to the "token rotation time" adopted in existing standards. The proposed WDM architecture and protocol provide a unique medium access control that allows one to maintain the channel access delay at a node within a limited range of values, possibly reaching average values that are below the roundtrip propagation time of the ring. In the paper it is shown that the MTIT protocol efficiency grows with the number of wavelengths-in agreement with today's WDM technology trends-and it is not a function of the packet size-a mandatory feature to support IP traffic.

This paper proposes an efficient contention resolution switching architecture which can serve as the basis for all-optical switching nodes. The presented solution builds on fiber delay lines used as temporary optical storage and 2/spl times/2 space photonic switches, a solution principle also known as Quadro or switched delay lines (SDLs). The efficiency of SDLs is fundamentally linked to its storage capacity, i.e., the length of the fiber delay lines, while its cost depends on the number of 2/spl times/2 photonic switches, i.e., the number of stages in the switch. This work presents a solution that makes use of multibuffer fiber delay lines which allow multiple packets to be concurrently stored (propagated) on each line. With a novel switch control, it is shown that this solution increases the total storage capacity and significantly improves switch and network performance, without increasing the number of the 2/spl times/2 switches in the system, i.e., its cost.

One of the concepts currently pursued to provide the ideal network architecture for supporting the next generation Internet consists of transmitting the Internet protocol (IP) packets directly over the wavelength division multiplexing (WDM) layer of extant optical networks. The challenge of this concept is to make the optical bandwidth directly accessible to IP with the statistical multiplexing necessary to support the bursty nature of IP traffic in a cost effective way. This paper proposes the multi-token inter-arrival time (MTIT) access protocol designed to achieve a bandwidth efficient multiplexing technique in WDM ring networks. The network throughput is maximized without violating the desired access delay requirement by controlling the "token inter-arrival time" as opposed to controlling the "token rotation time" as proposed in existing standards, e.g., FDDI. It is shown that the MTIT protocol efficiency grows with the number of wavelengths-in full agreement with the WDM technology trend-and does not depend on the packet length-a feature ideal for IP implementation. In addition, the protocol provides a unique token control technique that allows to maintain the channel access delay at a node bounded even within the round trip propagation time of a ring.

The design of survivable all-optical mesh networks based on bidirectional line-switched WDM (wavelength division multiplexed) self-healing rings (SHR/WDM) to provide full protection against any single line fault requires the solution of three sub-problems: determining the ring cover of the mesh topology, determining the routing of the working lightpaths (paths of light) between the node pairs that originate traffic demands, determining the allocation of the spare wavelengths in each ring required to protect every line in the mesh that supports traffic. A working lightpath can span over multiple rings, thus requiring one crossconnect I/O port at each node that connects two adjacent rings along its path. This paper addresses the problem of minimizing the total number of optical crossconnect I/O ports that are required in the mesh to support a set of traffic demands. The problem is solved under two design scenarios. In the first scenario we derive the minimum number of crossconnect ports necessary in a mesh network with a given ring cover and given routes for the working lightpaths. Once the number of crossconnect ports are minimized, the network total (working and protection) wavelength mileage is minimized by balancing the traffic in each ring. In the second scenario the ring cover, the routing for the working lightpaths and the spare wavelengths in each ring are first computed in such a way to minimize the total wavelength mileage. With this network configuration we then minimize the number of crossconnect ports. The presented solutions provide the designer with two alternative approaches that trade one cost function, i.e., the number of crossconnect ports, for the other, i.e., the total wavelength mileage.

The design of survivable all-optical networks based on self-healing WDM rings (SHR/WDM) to provide 100% protection from any single link failure requires the joint solution of three sub-problems. These are the ring cover of the mesh topology (the RC sub-problem), the routing of working lightpaths between node pairs to support traffic demands (the WL sub-problem) and the selection of the SHR/WDM spare wavelengths for the protection of every link traffic (the SW subproblem). This paper presents an integer linear programming (ILP) formulation of the problem of minimizing the total wavelength mileage (/spl lambda/-miles) required to support a set of given traffic demands in a given network topology using SHR/WDM employing 1:N line protection mechanism (the WRL problem). This formulation allows to jointly and optimally solve the three subproblems, and yields up to 15% reduction of the total /spl lambda/-miles required by existing solutions that separately resolve the sub-problems. A simplified sub-optimal solution of the WRL problem is also provided, that yields results few percent worse than the optimal solution and that is tractable for networks whose size is on the order of the pan-European network, i.e., 19 nodes.

Management of terminal handovers is one of the challenges in mobile wireless ATM (W-ATM) systems due to the connection-oriented nature of ATM. When the ATM connection is re-established to follow the terminal roaming from one base station to another, seamless handover is necessary to guarantee the required quality of service (QoS). A promising procedure is based on the use of handover buffers at the (destination) base station. This paper proposes a technique to reduce the buffer requirements in seamless handovers by introducing the concept of buffer sharing at the base station (B/sup 2/S/sup 2/): connections requiring handover at the same time and towards the same base station share a common pool of buffers available at the base station. When compared to the standard dedicated buffer (DB) approach B/sup 2/S/sup 2/ achieves the required QoS with a reduced total buffer size, and consequently with a reduced cost of the base station. Simulation and numerical results are discussed to quantify this reduction.

This paper introduces an approach to solving the fundamental scalability problem of all-optical packet switching wavelength-division multiplexing (WDM) access networks. Current optical networks cannot be scaled by simply adding nodes to existing systems due to the accumulation of insertion losses and/or the limited number of wavelengths. Scalability through bridging requires, on the other hand, the capability to switch packets among adjacent subnetworks on a wavelength basis. Such a solution is, however, not possible due to the unavailability of fast-switching wavelength sensitive devices. In this paper, we propose a scalable WDM access network architecture based on a recently proposed optical switching approach, termed photonic slot routing. According to this approach, entire slots, each carrying multiple packets (one on each wavelength) are "transparently" routed through the network as single units so that wavelength sensitive data flows can be handled using fast-switching wavelength nonsensitive devices based on proven technologies. The paper shows that the photonic slot routing technique can be successfully used to achieve statistical multiplexing of the optical bandwidth in the access network, thus providing a cost-effective solution to today's increasing bandwidth demand for data transmissions.

We analyze the worst-case behavior of general connection-oriented networks, with first-in-first-out (FIFO) queueing policy, forwarding packets along an arbitrary system of routes. A worst-case bound is proven for the end-to-end queueing delay and buffer size needed to guarantee loss-free packet delivery, given that sources satisfy a given source rate condition. The results are based on a novel deterministic approach and help in reconciling the discrepancy between the unstable worst-case behavior of FIFO-based networks and their good practical performance.

Photonic slot routing (PSR) is a promising approach to solving the fundamental scalability problem of all-optical packet switched WDM networks. In this approach adjacent subnetworks can exchange wavelength sensitive traffic through bridges using wavelength non-selective devices which can be constructed using proven technologies. With photonic slot routing, packets sharing a common subnetwork destination are aggregated to form a photonic slot which is individually routed in order to reach the destination subnetwork. Photonic slots from different subnetworks can originate contentions at the bridge, leading to potential penalties of slot loss and retransmission. This paper shows how slot contention penalties can be reduced through the use of switched delay lines (SDL) at the bridges. The combination of these two innovative techniques, the photonic slot routing and the switched delay lines, leads to a unique solution that is shown to nearly achieve throughput and delay performance obtainable in absence of slot contentions.

This paper presents an approximate analytical model for the evaluation of throughput and access delays in high-speed all-optical networks with slotted multi-channel ring topology, where each channel is shared in statistical time division by all nodes transmitting to one destination using a collision- and contention-free access protocol based on a channel inspection capability. Nodes are assumed to have only one queue to store packets for all destinations; two configurations are considered: the single buffer queue and the infinite buffer queue. Simulation results are used to assess the accuracy of the approximate model.

Resource contention in packet switched all-optical networks is being addressed in this paper through the combined use of fiber delay lines and 2/spl times/2 space photonic switches. With this basic approach, also known as Quadro or switched fiber delay lines (SDL), the solution efficiency is linked to its storage capacity, determined by the combined length of the fiber delay lines. In the past, this capacity was given by the number of 2/spl times/2 photonic switches used, i.e., the number of stages in the receiver, which limited the solution by cost, mainly determined by the switch component, and by the signal power loss and crosstalk introduced by each switch. This work presents and analyzes the use of "multibuffer" fiber delay lines, in Quadro, so termed since in it multiple packets are allowed to be concurrently stored (propagated) on each delay line. In this way the total storage capacity is increased, while the proposed design utilizing novel switch control is shown to significantly improve receiver and network performance, without increasing the number of the 6/spl times/2 space photonic switches in the system, i.e., its cost.

The implementation of optical packet-switched networks requires that the problems of resource contention, signalling and local and global synchronization be resolved. A possible optical solution to resource contention is based on the use of switching matrices suitably connected with optical delay lines. Signalling could be dealt with using subcarrier multiplexing of packet headers. Synchronization could take advantage of clock tone multiplexing techniques, digital processing for ultra-fast clock recovery, and new distributed techniques for global packet-slot alignment. To explore the practical feasibility and effectiveness of these key techniques, a consortium was formed among the University of Massachusetts, Stanford University, and GTE Laboratories. The consortium, funded by ARPA, has three main goals: investigating networking issues involved in optical contention resolution (University of Massachusetts), constructing an experimental contention-resolution optical (CRO) device (GTE Laboratories), and building a packet-switched optical network prototype employing a CRO and novel signaling/synchronization techniques (Stanford University). This paper describes the details of the project and provides an overview of the main results obtained so far.

This paper proposes an original approach to controlling WDM Passive optical stars, termed queuing arrivals for delayed reception operation (Quadro). In WDM stars the fundamental problem of receiver conflicts leads to severe performance degradation. In current solutions conflicts are prevented by scheduling transmissions or resolved by retransmissions. Both approaches waste bandwidth and involve electronic processing and buffering. The proposed approach is conceptually different in introducing a local conflict resolution mechanism at each receiver incorporating delay lines. This solution brings optical star networks a step closer to an all-optical realization. In addition, it allows an almost total utilization of the channels, as obtainable until now only by TDM control. Contrary to TDM, however, the proposed solution does not suffer performance degradation under heterogeneous traffic conditions and increasing number of nodes. It is thus unique in offering the potential of an all-optical solution providing at the same time high throughput, low delay, small buffer requirements, and robustness under all traffic conditions.>

An electronically controlled optical packet deflection switch that is based on space and time switching at intermediate nodes is described. The switch uses optical delay lines to store and switch packets in the optical domain so that optical bandwidth can be achieved across the network. The optical switch is controlled by an associated electronic mechanism that provides the necessary versatility and processing power. This approach combines the advantages of the optics and the electronics. The use and performance of the switch are demonstrated in the context of the Manhattan deflection network.>

The authors introduce a common modeling framework making it possible to develop tractable analytic models of optical star networks with reservation-based control. Reservation-based wavelength division multiplexing (WDM) optical star systems, and in particular the Quadro-based receiver design, have the performance advantages of high capacity, low response time, and adaptability to changing traffic flows. Using the modeling framework introduced, tractable approximate models of reservation-controlled WDM stars were derived. It was shown that the framework allows the representation of different control strategies, while resulting in only a very small error.>

TOP/PDT, a toolkit for the development and the simulation of communication protocols, is presented. A protocol is described by a high-level language, derived from SDL, and named PDL, short for protocol description language. A compiler translates PDL programs into C programs; these are then compiled and linked using the utilities of the host operating system. TOP/PDT is an open environment: to add functionalities or to optimize a protocol, users can add their own functions, usually written in C, to the existing function library. The validation of the protocol is done by simulation. PDL allows the characterization of the data link(s) used to transmit and provides a set of measurement functions to evaluate the protocol performance. The modular structure of TOP/PDT and the use of the C programming language make it easily portable. The executable program generated using TOP/PDT can also run without a host operating system, since the PDT kernel provides a minimal operating system able to handle an unlimited number of processes and ensures their mutual exclusion in the access to shared data.>