This Special Issue contains a set of remarkable papers covering various recent research advances towards resilient Communication Networks for an hyper-connected World. Papers are organized into five categories: (i) Resilient Architectures for Next-Generation Networks, (ii) Edge, IoT, and Cyber-Physical Systems, (iii) Vehicular, Mobile, and Aerial Networks, (iv) Optical, Hybrid, and Satellite-based Resilient Communications, and (v) Security, Trust, and Resilience in Services and Applications. The editorial begins with an overview of the field and proceeds with a summary of the twenty-two papers included in this Special Issue.

The integration of unmanned aerial vehicles (UAVs) into cellular networks presents significant mobility management challenges, primarily due to frequent handovers caused by probabilistic line-of-sight conditions with multiple ground base stations (BSs). To tackle these challenges, reinforcement learning (RL)-based methods, particularly deep Q-networks (DQN), have been employed to optimize handover decisions dynamically. However, a major drawback of these learning-based approaches is their black box nature, which limits interpretability in the decision making process. This paper introduces an explainable AI (XAI) framework that incorporates Shapley Additive Explanations (SHAP) to provide deeper insights into how various state parameters influence handover decisions in a DQN-based mobility management system. By quantifying the impact of key features such as reference signal received power (RSRP), reference signal received quality (RSRQ), buffer status, and UAV position, our approach enhances the interpretability and reliability of RL-based handover solutions. To validate and compare our framework, we utilize real-world network performance data collected from UAV flight trials. Simulation results show that our method provides intuitive explanations for policy decisions, effectively bridging the gap between AI-driven models and human decision-makers.

This feasibility study deals with Air to Ground (ATG) communications between a 5G type Terrestrial Mobile Communication Network (TMCN) and an User Equipment (UE) installed onboard a passenger aircraft in approach to an airport. The network model is based on real gNodeB (gNB) deployment data and optimized for serving terrestrial UEs. The evaluation concerns a scenario in which the passenger aircraft is supported by a remote operator via an ATG link to assist its safe landing. To mitigate the interference expected to arise in ATG communications, the aircraft is assumed to be equipped with an Active Electronically Scanned Array (AESA). The simulation results discussed in this paper address the Signal to Interference power Ratio (SIR), link availability, and handover process during ATG communications along representative approach trajectories for different AESA configurations and levels of support by the TMCN. It is shown that SIR above 30 dB and link availability upto 97.7% can be achieved by using an 8 x 8 AESA at the aircraft when the network provides support in the form of dedicated radio resources. It is observed that the frequency of handovers increases with improving link quality.

This paper addresses the problem of providing internet connectivity to aircraft flying above the ocean without using satellite connectivity given the lack of ground network infrastructure in the relevant oceanic areas. Is it possible to guarantee a minimum flow rate to each aircraft flying over an ocean by forming an aeronautical ad hoc network and connecting that network to internet via a set of limited number of ground base stations at the coast as anchor points? We formulated the problem as mixed-integer-linear programming (MILP) to maximize the number of aircraft with flow data rate above a certain threshold. Since this multi-commodity flow problem is at least NP-complete, we propose a two-phase heuristic algorithm to efficiently form topology and assign flows to each aircraft by maximizing the minimum flow. The performance of the heuristic algorithm is evaluated over the North Atlantic Corridor, heuristic performs only 8% less than the optimal result with low densities. In high network densities, the connectivity percentage changes from 70% to 40% under 75 Mbps data rate threshold. Furthermore, the connectivity percentage is investigated for different network parameters such as altitude and compared to upper and lower bounds and a baseline algorithm.

Mobility management for terrestrial users is mostly concerned with avoiding radio link failure for the edge users where the cell boundaries are defined. The problem becomes interesting for an aerial user experiencing fragmented coverage in the sky and line-of-sight conditions with multiple ground base stations (BSs). For aerial users, mobility management is not only concerned with avoiding link failures but also avoiding unnecessary handovers while maintaining extended service availability, especially in up-link communication. The line of sight conditions from an Unmanned Aerial Vehicle (UAV) to multiple neighboring BSs make it more prone to frequent handovers, leading to control packet overheads and delays in the communication service. Depending on the use cases, UAVs require a certain level of service availability, which makes their mobility management a critical task. The current mobility robustness optimization (MRO) procedure that adaptively manages handover parameters to avoid unnecessary handovers is optimized only for terrestrial users. It needs to be updated to capture the unique mobility challenges of aerial users. In this work, we propose two approaches to accomplish this: 1) A model based service availability-aware MRO where handover control parameters, such as handover margin and time to trigger are tuned to maintain high service availability with a minimum number of handovers, and, 2) A deep Q-network based model free approach for decreasing unnecessary handovers while maintaining high service availability. Simulation results demonstrate that both the proposed algorithms converge promptly and increase the service availability by more than 40% while the number of handovers is reduced by more than 50% as compared to traditional approaches.

In this paper, we formulate and solve the optimization problem for joint access point placement and resource allocation for indoor mmWave communications with static users, with a particular focus on airplanes. The proposed scheme obtains the required number of access points (APs) and their locations, for a given data rate threshold and given radio resources such as bandwidth, antenna numbers, and AP co-operation. We first build an airplane cabin environment in a ray-tracing tool to realistically capture the propagation effects. Then, we cast optimal deployment problems considering the performance of different AP cooperation schemes, namely coordinated scheduling (CS), non-coherent joint transmission (NC-JT), and coherent joint transmission (C-JT). The results indicate that full cooperation among the APs with C-JT requires fewer APs, especially under high data rate requirements. Comparing the network deployments in the mmWave and sub-6GHz bands, we observe 9 times higher data rates in mmWave although more APs are required.

This Special Section features research contributions in the area of robust and reliable networks of the future. Modern network infrastructures must support a growing demand for intensive data processing and high-speed communication, that has led, in the last decade, to a constant evolution towards convergence of networking and computing infrastructures. This convergence was made possible by the introduction of network function virtualization and by the emergence of the Software-Defined Networking (SDN) paradigm, and has enabled new forms of cloud and edge computing to cope with the strict requirements of new services and applications, as those in the realm of the Internet of Things (IoT).

Precise indoor positioning systems (IPSs) are key to perform a set of tasks more efficiently during aircraft production, operation and maintenance. For instance, IPSs can overcome the tedious task of configuring (wireless) sensor nodes in an aircraft cabin. Although various solutions based on technologies of established consumer goods, e.g., Bluetooth or WiFi, have been proposed and tested, the published accuracy results fail to make these technologies relevant for many use cases. This stems from the challenging environments for positioning, especially in aircraft cabins, which is mainly due to the geometries, many obstacles, and highly reflective materials. To address these issues, we propose to evaluate in this work an Ultra-Wideband (UWB)-based IPS via a measurement campaign performed in a real aircraft cabin. We first illustrate the difficulties that an IPS faces in an aircraft cabin, by studying the signal propagation effects which were measured. We then investigate the ranging and localization accuracies of our IPS. Finally, we also introduce various methods based on machine learning (ML) for correcting the ranging measurements and demonstrate that we are able to localize a node with respect to an aircraft seat with a measured likelihood of 97 %.

In this paper, the indoor dense space (IDS) channel at 28 GHz is characterized through extensive Ray-Tracing (RT) simulations. We consider IDS as a specific type of indoor environment with confined geometry and packed with humans, such as aircraft cabins and train wagons. Based on RT simulations, we characterize path loss, shadow fading, root-mean-square delay spread, Rician K-factor, azimuth/elevation angular spread of arrival/departure considering different RT simulation scenarios of the fuselage geometry, material, and human presence. While the large-scale fading parameters are similar to the state-of-the-art channel models, the small-scale fading parameters demonstrate richer multipath scattering in IDS, resulting in poorer bit error rate performance in comparison to the 3GPP indoor channel model.

Emerging Remote Piloting (RP) operations of electrified Unmanned Aerial Vehicles (UAVs) demand low-latency and high-quality video delivery to conduct safe operations in the low-altitude airspace. Although cellular networks are one of the prominent candidates to provide connectivity for such operations, their ground-centric nature limits their capabilities in achieving seamless and reliable aerial connectivity. In this paper, we study the feasibility of supporting RP operations with low latency and high-quality video delivery over commercial cellular networks. By setting up an adaptive bitrate video transmission pipeline with the Google Congestion Control (GCC) and Self-Clocked Rate Adaptation for Multimedia (SCReAM) Congestion Control (CC) algorithms, we analyze the video delivery performance for the RP application requirements and compare the performance of GCC and SCReAM against constant bitrate video delivery. Our results show that low-latency video delivery with < 300 ms playback latency between full-HD and 4K resolution can be maintained up to about 95% of the time in the air. While static bitrate video delivery outperforms adaptive streaming in urban location with abundant link capacity, the latter becomes advantageous in rural locations, where the link capacity is affected by fluctuations. Although the study's findings highlight the capabilities of cellular networks in delivering low-latency video for a safety-critical aerial service, we also discuss the potential improvements and future research challenges for enabling safe operations and meeting the service requirements using cellular networks. We release our collected traces and the video transmission pipeline as open-source to facilitate research in this field.

This Special Section (SI) features the latest research contributions regarding recent advances in the design and management of reliable communication networks. Communication networks are constantly increasing their complexity and scale to satisfy the requirements of network services. The current trend of convergence of networking and computing infrastructures (as in today’s cloud systems and softwarized networks) calls for novel advanced strategies and solutions to support reliable services, as the development of new data-driven solutions for reliable network automation and self-diagnostic tools to ensure resilient network management.

Network support for Unmanned Aerial Vehicles (UAVs) is raising an interest among researchers due to the strong potential applications. However, current knowledge on UAV data traffic is mainly based on conceptual studies and does not provide an in-depth insight on the data traffic properties. To close this gap, we present a measurement-based study analyzing in detail the Control and Non-payload Communication (CNPC) traffic produced by three different UAVs when communicating with their remote controller over 802.11 protocol. We analyze the traffic in terms of data rate, inter-packet interval and packet length distributions, and identify their main influencing factors. The data traffic appears neither deterministic nor periodic but bursty, with a tendency towards Poisson traffic. We further create an understanding on how the traffic of the investigated UAVs are internally generated and propose a model to analytically capture their traffic processes, which provides an explanation for the observed behavior. We implemented a publicly available UAV traffic generator "AVIATOR" based on the proposed traffic model and verified the model by comparing the simulated traces with the experimental results.

Sensors currently deployed on board have wired connectivity, which increases weight and maintenance costs for aircraft. Removing cables for wireless communications of sensors on board alleviates the cost, however, the powering of sensors becomes a challenge inside aircraft. Wireless power transfer (WPT) via radio-frequency (RF) signals is an emerging solution to remotely power sensors for battery-less operation with long-lived capacitors. In this article, we design a WPT system for aircraft IoT-type applications, including low data rate inside (LI) sensors by determining the number, location, and tilt angles of WPT transmitters given constraints based on the cabin geometry and duty cycle of the sensors. We formulate a robust optimization problem to address the WPT system design under channel uncertainties. We also derive an equivalent integer linear programming and solve that for an optimal deployment to satisfy the duty cycle requirements of LI sensors. We perform experiments inside the cabin to validate the wireless avionics intracommunications channel model. Our simulations demonstrate the feasibility of 90% robust design with 14 WPT transmitters for duty cycles less than 0.1% while keeping the human radiation exposure below the recommended reference value of 4.57 W/m2.

While connectivity is available almost anytime and anywhere on ground, aircraft during flight still lack high-throughput communication. We investigate air-to-ground networks consisting of direct air-to-ground, air-to-air and satellite links for providing high throughput to aircraft. We formulate an optimization problem to maximize the minimum throughput of all aircraft. We solve the problem using realistic aircraft and base station positions and also model physical limitations such as maximum number of antennas per aircraft and interference. We investigate different scenarios and parameters and analyze the influence of the parameters on the max-min throughput per aircraft. We show that the satellite and direct air-to-ground links are the bottleneck, as all throughput can be distributed among aircraft. Furthermore we show that air-to-air communication is dispensable for achieving a high throughput when having direct air-to-ground coverage.

In-flight Internet connectivity is a necessity for aircraft passengers as well as aircraft systems. It is challenging to satisfy required quality of service (QoS) levels for flows within aircraft due to the large number of users and the highly varying air to ground (A2G) link capacities composed of satellite and direct air to ground communication (DA2GC). To represent service quality variations, we propose models for the generated traffic flows from aircraft and variations in A2G links. We present three different forwarding schemes based on priority, delay requirements and history of the dropped flows metrics. Forwarding schemes schedule the flows in real time by choosing either satellite or direct air to ground link depending on the delay and capacity requirements of flows to maximize the number of accepted flows with required QoS guarantees in terms of dropped packets and delay. Also, the effect of local caching is studied to fully satisfy the QoS requirement of flows in simulated flights. We implement the forwarding procedures and caching in ns-3 and test their performance in a current connectivity scenario of 100 Mbps capacity for both the satellite spot and ground base station in a one-hour flight. Our study shows that although the forwarding procedure based on a combination of priority and delay requirement has relatively better performance than the other schemes, which are based on priority only and weighted average of all metrics, in dropped packet percentage and delay, the current connectivity setup is not able to satisfy all QoS requirements. Furthermore, at least 0.9 cache hit rate is required to satisfy all flows for at least 50% of simulated flights.

Wireless Avionics Intra-Communications (WAIC) is an emerging standard to migrate regulatory and safety-related applications from wired networks to wireless means in next generation aircraft. Removing most of the cables from the fuselage will benefit to the overall efficiency of aircraft. On the other hand, it is a difficult task to achieve the Quality of Service (QoS) performance of wired networks by wireless technologies. Also, the Radio Altimeter (RA) interference in the same spectrum is another obstacle to overcome. Current Long Term Evolution (LTE) and emerging Fifth Generation (5G) technologies advertise promising specifications that can meet the requirements of WAIC networks. Therefore, the goal of this study is to evaluate the feasibility of supporting high data rate WAIC applications with LTE/5G by means of analytical and experimental studies. Measurements conducted in unoccupied mockup cabin and outside environment show that at least one cellular technology can meet the requirements of high data rate WAIC classes in the absence of RA interference. In coupling scenarios, robustness strategies should be considered to improve the network resilience. Finally, a network architecture based on the experimental results is presented to show an example usage scenario of a high data rate WAIC network.

The number of aircraft equipped with broadband connectivity is increasing. With several hundred users per aircraft, a high capacity air-to-ground link needs to be ensured. Today, several systems provide connectivity to aircraft. However, these systems are not optimized for changing aircraft densities in different geographical areas and thus the actual throughput per aircraft varies during the flight. Therefore, we investigate the achievable throughput during any given flight by analyzing actual flight routes in order to determine the relevant parameters to satisfy current and future connectivity needs. We show that multiple air-to-ground communication systems need to be exploited to offer sufficient throughput to all aircraft.

Providing broadband in-flight Internet connectivity to aircraft is challenging. Today's options include satellite communications (SC) and direct air-to-ground communication (DA2GC). To overcome data rate, delay and cost limitations of SC and coverage limitations of DA2GC, one can extend DA2GC with air-to-air communication (A2AC) by enabling multi-hop communication. To investigate the A2AC performance, we construct a mixed integer linear programming (MILP) problem of DA2GC and A2AC, jointly considering interference in topology formation and flow assignment. Our objective is to maximize the number of aircraft that can be connected with a given specific minimum data rate threshold. The evaluation is performed for low aircraft density scenarios over the North Atlantic. We show that in the investigated scenarios, over 90 % of aircraft can have at least 50 Mbps, some being up to 1600 kilometers away from the closest base station (BS). Furthermore, we identify antenna capabilities as an important factor for A2AC performance.

People desire to be connected, no matter where they are. Recently, providing Internet access to on-board passengers has received a lot of attention from both industry and academia. However, in order to guarantee an acceptable Quality of Service (QoS) for the passenger services with low incurred cost, the path to route the services, as well as the datacenter (DC) to deploy the services should be carefully determined. This problem is challenging, due to different types of Air-to-Ground (A2G) connections, i.e., satellites and Direct Air-To-Ground (DA2G) links. These A2G connection types differ in terms of cost, bandwidth, and latency. Furthermore, due to the flights' movements, it is important to consider adapting the service location accordingly. In this work, we formulate two Mixed Integer Linear Programs (MILPs) for the problem of Joint Service Placement and Routing (JSPR): i) Static (S-JSPR), and ii) Mobility-Aware (MA-JSPR) in Space-Air-Ground Integrated Networks (SAGIN), with the objective of minimizing the total cost. We compare S-JSPR and MA-JSPR using comprehensive evaluations in a realistic European-based SAGIN. The obtained results show that the MA-JSPR model, by considering the future flight positions and using a service migration control, reduces the long-term total cost notably. Also, we show S-JSPR benefits from a low time-complexity and it achieves lower end-to-end delays comparing to MA-JSPR model.

There is a strong demand in the aviation industry to replace cables in airplanes by wireless connectivity to gain flexibility and reduce weight. Such in-plane wireless communications must be reliable and robust against interference. As part of our activities in this domain, we present a proof-of-concept for an ultra-wideband (UWB) sensor network deployed in a mockup of a small passenger cabin of a commercial aircraft with a few passengers and report experimental results on the packet loss rate with off-the-shelf IEEE~802.15.4-2011 compliant UWB transceivers. It is shown that a combination of spatial and temporal diversity can significantly lower the packet loss rate of different link types without degrading throughput.

Even though both delay and availability are of high importance for cloud services, it is mostly impossible today to guarantee a certain latency and availability for end-to-end cloud services traversing the telecommunication networks. An enabler is network virtualization with isolated virtual networks and combined control for network and IT resources. In this paper, we introduce two fundamental architectural alternatives in resilience design for cloud services using virtual networks, where in the former, resilience is provided solely by the physical infrastructure provider and in the latter only by the virtual network operator. We show that the resilience design plays a key role in terms of latency of the cloud services. Our simulation results show that the guaranteed maximum delay for the cloud services can differ by more than 90% depending on the implemented resilience design. This can have a big impact on the service performance in large networks especially for today's applications, where each millisecond might count.

This paper details approaches to resilience in optical multilayer and multidomain networks. Principal challenges and solutions have been described using exemplary settings and models. In addition, we have also shared an outlook to future research topics within this paper.

For long-term operated networks, pre-planning is a challenging task due to uncertainty in future demand requests. In this paper we first address the question of how severe the impact of demand uncertainty on the network costs really is. Results indicate that only for special cases, uncertainty is interesting to be addressed in the planning process itself. Additionally, we introduce a Stochastic Programming model in order to handle the influence of such a special case. It can be observed that including an improbable demand development into the planning process leads to cost efficient network solutions for all considered scenarios.

Significant cost reductions can be achieved through the deployment of alternative homing architectures. These reductions, however, come at the expense of increased recovery time. In this paper we focus on the dual homing with shared backup router resources (SBRR) architecture and propose an analytical recovery time model based on GMPLS signaling. Case studies are presented showing recovery times ranging from 100 ms to around 2500 ms. Simultaneously, the dominating time contributing factors are identified, while the impact of varying parameters such as the network edge length is quantified. We proceed to show how service-imposed maximum outage requirements have a direct effect on the configuration of the SBRR architecture.

Ethernet's success in local area networks (LANs) is fueling the efforts to extend its reach to cover metro and long-haul networks. This new Ethernet is refereed to as Carrier Ethernet. Among the various transport infrastructures for realizing Carrier Ethernet, wavelength-division multiplexing (WDM) optical network is a strong candidate for this purpose. Optical transmission rates per channel are increasing from 10 to 40 Gb/s and even 100 Gb/s, and they can also coexist in the same fiber. Along with the flexibility associated with such a network with mixed-line rates (MLR), signal-related constraints at high rates become a challenge for cost-efficient routing. Among these issues is the maximum nonregenerated optical distance that a signal can travel before its quality degrades or maximum transmission range (TR). TR is rate-dependent: The higher the rate, the shorter the range. While high-rate pipes may require signal regeneration to restore the signal's quality, they support more traffic and, hence, can save resources. We study the problem of cost-efficient routing of multi-bit-rate (1/10/40/100 Gb/s) Ethernet tunnels using MLR over a carrier's WDM optical network with signal-transmission-range constraints. We studied the effect of TR for mixed-rate signals (10/40/100 Gb/s) on the network's cost to determine the optimal TR of each bit rate. We present an analytical model based on a mixed-integer linear program (MILP) to determine the optimal TR of a small network. Since MILP has scalability constraints that makes it hard or sometimes impossible to solve for real network topologies, we propose a graph-based solution that constructs a mixed-line-rate auxiliary (MLR-AUX) graph to capture the network's heterogeneity and a weight-assignment approach that allows the routing to be cost-efficient. Our algorithms were tested on a U.S. nationwide network topology. We found that it is possible to reduce the network's cost by using short TR and that the optimal TR depends strongly on traffic characteristics and on the TR values of different bit-rate signals.

Quality of service requirements and the increasing amount of data transmission demand for efficient protection mechanisms. Existing mechanisms like 1+1 and 1+N path protection offer instantaneous recovery but they suffer from high capacity needs and nodal degree requirements, respectively. The high nodal degree requirement makes an implementation of the 1+N mechanism in transport networks difficult. In this paper, we develop two new mechanisms by applying network coding on a virtualized protection scheme. These mechanisms are more resource-efficient compared to 1+1, and are implementable in transport networks even under stringent nodal degree constraints. The difference between the two mechanisms lies in complexity and performance. Therefore, either of them can be preferred as a good compromise between 1+1 and 1+N in different scenarios according to the needs and available resources.

For simplified network operations, demands are often routed on shortest paths, e.g., with physical length as metric. We propose a new controlled shortest path routing concept for multiperiod planned networks, formulated as optimization model. This routing concept minimizes the network costs (capital expenditures) under the constraint of using shortest path routing within the lit fiber network. Within a single optimization step, fibers on candidate topology edges are chosen to become lit, constituting a (lit) fiber network, such that cost-optimal results are obtained under shortest path routing within this selected fiber network. In case studies our new routing and dimensioning approach is compared with shortest path routing in the candidate topology and general cost-optimal routing. For lightly to medium loaded networks, case studies show that controlled shortest path routing can achieve significantly lower cost results than shortest path routing, while being comparable in cost to cost-optimal routing.

Many networks today are composed of numerous subnetworks or domains. The connection points of these domains are important and vulnerable parts of the communication. Therefore, one of the key points of protection schemes today is being able to protect these interconnections. Hence, in this type of networks a protection mechanism is applied, where there is 1+1 protection inside each domain and dual homing at the borders. With this mechanism, the breakdown due to the failure of the interconnection elements is prohibited. This system enables the network to survive any node or link failure in each domain. However, it suffers from the high capacity need on the border links, where data has to be transmitted bidirectionally for each single demand. We are showing that combining network coding with this protection mechanism gives a realization, which outperforms the existing mechanism by providing high resource savings. We present the theoretical basis and the application methodology of the proposed method.

Shared protection promises the benefits of lower network capacity utilization without sacrificing the availability level of dedicated protection. Shared protection is often evaluated in terms of its spare capacity efficiency, but seldom in terms of real-world CAPEX (capital expenditure) costs. In this paper, we investigate the design of several shared protection architectures under a standardized cost model for the WDM layer, developed recently within the European NOBEL project. This paper presents a comparative study of the implementations and costs of these architectures under this model. Findings show a counterintuitive relationship between network capacity utilization and design cost when the network is lightly loaded.

The hybrid wireless-optical broadband access network (WOBAN) architecture provides a new and promising architecture for access networks by combining the beneficial properties of wireless and optical technologies. Thus it can achieve low deployment costs (as no cable infrastructure is necessary for the last mile) and provide a mobile yet economically viable end-user access. However, the integration of these technologies (optical and wireless) also has its challenges: While optical links have high availabilities (especially with modern protection techniques), the performance of wireless links depends on a variety of external parameters, which in many cases can be only described statistically. In this work, we evaluate the availability performance of a WOBAN in different demand scenarios and study the influence of various routing strategies (shortest paths with different link metrics, specialised routing algorithms for a WOBAN and multi-path routing). Our results show that we can significantly improve availability for end-users by using shortest path routing with link unavailability as the link cost metric. Using multi-path routing, further gains can be achieved.

The paper derives lower bounds on the redundancy, the protection capacity to working capacity ratio, needed by link-protection or link-restoration. Homogeneity conditions, on which the well-known redundancy bound 1/(dmacr1) holds for a network, are also identified, where dmacr is the average nodal degree.

Multiperiod network planning is, especially for cost intensive and long term operated core networks, a necessity to provide cost efficient long term solutions. In this paper we give an overview on commonly used multiperiod planning approaches and compare their cost allocations and dependencies on cost decreasing factors. Furthermore, we propose a new multiperiod approach, which aims at a complete new orientation: Instead of minimizing network costs, a restricted budget is used not only to satisfy occurring demand but also to purchase equipment for future demand requests. With this approach we obtain long term solutions for optical networks with a restricted budget. This Budget-Restricted approach has a strong relation to applications in industry and public authorities. We use for our studies an integer linear optimization model which takes cost optimal routing and also the wavelength assignment into account. Additionally we provide a detailed cost function with a special interest on node costs.

Ethernet is a success story in Local Area Networks (LAN). Efforts for extending its boundaries beyond LAN to the carriers' backbone networks are in progress. We study the problem of designing reliable and cost-efficient high-rate (100 Gbit/s) carrier-grade Ethernet in a multi-line-rate telecom network under signal transmission-range constraints. Reliability is achieved using shared-path protection at two levels: (1) Protection-at-Connection (PAC) level, or (2) Protection-at-Lightpath (PAL) level. We study the two cases for their impact on network cost and other performance parameters. We construct a graph, called Mixed Topology (MT), using which it is possible to: (1) identify traffic grooming possibilities, (2) select a path which requires the minimum amount of 3R regeneration, and (3) effectively choose the data rate of a lightpath to be established. Our algorithms, tested on the 17-node German network, lead to the following findings: (1) for both PAL and PAC, our MT-based algorithm resulted in lower network cost and higher lightpath utilization compared with other schemes; and (2) in general, PAL incurs slightly higher cost than PAC.

The parallel existence of different transport technologies in today's networks is a challenging aspect for network planning and operation. Due to the grooming and multiplexing possibilities at multiple layers, the routing complexity increases dramatically. We develop a network model and an integer linear program (ILP) formulation to compute the optimal network design. The novel ldquopath over pathrdquo concept maps traffic demands into grooming flows that are provisioned as transparent lightpaths. This approach enables scalability of the problem size by limiting the number of eligible grooming configurations and transparent lightpaths. The optimization objective is to minimize the overall capital expenditures with respect to the deployed network equipment. Case study results show that the cost relation transponders/muxponders and restrictions on the equipment have a significant impact on the routing and network configuration.

We suggest methods for achieving high dual-failure restorability in p-cycle networks that are optimally designed only to withstand all single failures, or have minimized amounts of additional capacity for dual failure considerations. In one set of circumstances we consider static p-cycles (that cannot be rearranged once established) and propose strategies to enhance the dual-failure restorability based on concepts of failure spreading and limiting the maximum number of protection relationships of any p-cycle. We then consider the case of reconfigurable p-cycles, in which the spare capacity can be reconfigured dynamically, creating a new set of p-cycles that are optimized to withstand possible second failures. Results show significant improvements of the dual-failure restorability obtained by limiting the number of protection relationships in static design. For 100% dual-failure restorability, p-cycle reconfiguration reusing most of the existing p-cycles and adding some new ones appears to be the most promising approach.

p-Cycles can attain high capacity efficiency and fast protection switching times in WDM networks. The number of deployed p-cycles and the ability to survive dual fiber duct failures are further important characteristics which are considered in a pan-European network case study. We show that the dual failure restorability and the protection capacity can vary significantly for cycle-configurations with different numbers of deployed p-cycles.

We investigate the deployment of p-cycles (preconfigured protection cycles) in WDM mesh networks with and without wavelength conversion. We develop optimization models for the configuration of the cycles and apply these on a case study for a pan-European network. The results in particular for wavelength converting networks show that p-cycles achieve high efficiency.

This paper describes an approach for the optimal configuration of lightpaths in transparent and static WDM networks for IP traffic. The approach involves finding the virtual topology for IP demands and a routing and wavelength assignments (RWA) on the WDM layer. The problem is split into several subproblems and solved by heuristic algorithms.

Based on queuing theory, we develop an analytical approximation for low and high priority packet delays in a spatial reuse protocol (SRP) ring. SRP is a MAC layer protocol for ring based media (e.g., optical rings) that can carry IP and ATM client (prioritized) traffic (see Tsiang, D. and Suwala, G., "The Cisco SRP MAC Layer Protocol", RFC 2892, 2000). This protocol is one basis for the evolution of the currently standardized resilient packet ring, IEEE 802.17 (see http://www.ieee802.org/rprsg/). We develop approximative formulae for the transfer delay on a SRP ring and determine the maximum network throughputs for a traffic pattern. The formulae are instrumental in performance considerations and in quasi-validations of simulators.