The Journal of Optical Networking (JON) is soliciting papers for a feature Issue pertaining to all aspects of reliable components and systems for optical networks and concepts, techniques, and experience leading to high availability of services provided by optical networks. Most nations now recognize that telecommunications in all its forms -- including voice, Internet, video, and so on -- are "critical infrastructure" for the society, commerce, government, and education. Yet all these services and applications are almost completely dependent on optical networks for their realization. "Always on" or apparently unbreakable communications connectivity is the expectation from most users and for some services is the actual requirement as well. Achieving the desired level of availability of services, and doing so with some elegance and efficiency, is a meritorious goal for current researchers. This requires development and use of high-reliability components and subsystems, but also concepts for active reconfiguration and capacity planning leading to high availability of service through unseen fast-acting survivability mechanisms. The feature issue is also intended to reflect some of the most important current directions and objectives in optical networking research, which include the aspects of integrated design and operation of multilevel survivability and realization of multiple Quality-of-Protection service classes. Dynamic survivable service provisioning, or batch re-provisioning is an important current theme, as well as methods that achieve high availability at far less investment in spare capacity than required by brute force service path duplication or 100% redundant rings, which is still the surprisingly prevalent practice. Papers of several types are envisioned in the feature issue, including outlook and forecasting types of treatments, optimization and analysis, new concepts for survivability, or papers on availability analysis methods or results. Customer, vendor, and researcher viewpoints and priorities will all be given consideration. Especially valuable to the community would be papers that include or provide measured data on actual reliability and availability performance of optical networking components or systems.Scope of SubmissionThe scope of the papers includes, but is not limited to, the following topics:

• Reliability and availability measurement techniques specific to optical network devices or services.
• Data on SRLG statistics and frequency of different actual failure causes.
• Real-life accounts or data on failure and repair rates or projected values for use in availability analysis.
• Availability analysis methods, especially for survivable networks with reconfigurable or adaptive failure-specific responses.
• Availability analysis and comparisons of basic schemes for survivability.
• Differentiated availability schemes.
• Design for Multiple Quality of Protection.
• Different schemes for on-demand survivable service provisioning.
• Basic comparisons or proposals of new survivability mechanisms and architectures.
• Concepts yielding higher than 1+1 protection switching availability at less than 100% redundancy.
• Survivable service provisioning in domains of optical transparency: dealing with signal impairments.

Manuscript Submission To submit to this special issue, follow the normal procedure for submission to JON, indicating "Feature Issue: Optical Network Availability" in the "Comments" field of the online submission form. For all other questions relating to this feature issue, please send an e-mail to jon@osa.org, subject line "Feature Issue: Optical Network Availability." Additional information can be found on the JON website: http://www.osa-jon.org/submission/.

The Journal of Optical Networking (JON) is soliciting papers for a feature Issue pertaining to all aspects of reliable components and systems for optical networks and concepts, techniques, and experience leading to high availability of services provided by optical networks. Most nations now recognize that telecommunications in all its forms -- including voice, Internet, video, and so on -- are "critical infrastructure" for the society, commerce, government, and education. Yet all these services and applications are almost completely dependent on optical networks for their realization. "Always on" or apparently unbreakable communications connectivity is the expectation from most users and for some services is the actual requirement as well. Achieving the desired level of availability of services, and doing so with some elegance and efficiency, is a meritorious goal for current researchers. This requires development and use of high-reliability components and subsystems, but also concepts for active reconfiguration and capacity planning leading to high availability of service through unseen fast-acting survivability mechanisms. The feature issue is also intended to reflect some of the most important current directions and objectives in optical networking research, which include the aspects of integrated design and operation of multilevel survivability and realization of multiple Quality-of-Protection service classes. Dynamic survivable service provisioning, or batch re-provisioning is an important current theme, as well as methods that achieve high availability at far less investment in spare capacity than required by brute force service path duplication or 100% redundant rings, which is still the surprisingly prevalent practice. Papers of several types are envisioned in the feature issue, including outlook and forecasting types of treatments, optimization and analysis, new concepts for survivability, or papers on availability analysis methods or results. Customer, vendor, and researcher viewpoints and priorities will all be given consideration. Especially valuable to the community would be papers that include or provide measured data on actual reliability and availability performance of optical networking components or systems.Scope of SubmissionThe scope of the papers includes, but is not limited to, the following topics:

• Reliability and availability measurement techniques specific to optical network devices or services.
• Data on SRLG statistics and frequency of different actual failure causes.
• Real-life accounts or data on failure and repair rates or projected values for use in availability analysis.
• Availability analysis methods, especially for survivable networks with reconfigurable or adaptive failure-specific responses.
• Availability analysis and comparisons of basic schemes for survivability.
• Differentiated availability schemes.
• Design for Multiple Quality of Protection.
• Different schemes for on-demand survivable service provisioning.
• Basic comparisons or proposals of new survivability mechanisms and architectures.
• Concepts yielding higher than 1+1 protection switching availability at less than 100% redundancy.
• Survivable service provisioning in domains of optical transparency: dealing with signal impairments.

Manuscript Submission To submit to this special issue, follow the normal procedure for submission to JON, indicating "Feature Issue: Optical Network Availability" in the "Comments" field of the online submission form. For all other questions relating to this feature issue, please send an e-mail to jon@osa.org, subject line "Feature Issue: Optical Network Availability." Additional information can be found on the JON website: http://www.osa-jon.org/submission/.

In bandwidth abundant optical networks, the Grouped Routing Entity (GRE) concept is a cost-efficient alternative used instead of waveband routing. It offers all the benefits of the waveband routing (i.e., reduced number of ports), without using expensive wavelength cross connects (WXCs) required in hierarchical optical networks. In fact in a GRE-based optical network wavelength channel add/drop operations are accomplished via Wavelength Selective Switches (WSS) or with optical couplers. The objective of this paper is to further investigate the benefits of GRE-based optical networks in a scenario where survivability is required. In this paper a dedicated protection scheme is proposed, where wavelength paths are efficiently routed using mostly disjoint working and backup GRE pipes (i.e., working and backup pipes are allowed to share some common nodes along their paths). Numerical experiments demonstrate that significant hardware scale reduction at the switching nodes can be obtained by using the proposed network design algorithm.

Long-reach passive optical networks (LR-PONs) are able to effectively support the growing demand of traffic originating from residential and business customers. Failures of metro/core (M/C) nodes serving the traffic to/from the access networks covered by LR-PONs, may potentially affect hundreds or thousands of customers. One way of guaranteeing 100% survivability from single-node failures is to apply dual-homing, where each LR-PON is connected to two M/C nodes, and combine it with node-disjoint dedicated-path protection (DPP). In this paper, we present a new approach to provide network survivability against single M/C node failures. Instead of applying dedicated path protection (DPP) strategy, which can require huge amount of extra resources, we combine an unprotected network design with a dynamic multilayer restoration algorithm. Our aim is to determine a suitable amount of resource overbuild (in terms of extra transponders) needed to provide average connection availability close to that guaranteed by DPP. Preliminary results show that dimensioning for the worst-case scenario among a set of predefined M/C node failures, i.e., the one disrupting the highest number of connections, yields to a cost-effective strategy requiring up to 35% less transponders than DPP, while offering the same average connection availability.

We propose a novel energy-efficient and survivable routing algorithm addressing the trade-off caused by conflicting objectives of energy saving and survivability, i.e. energy-efficient routing tends to pack while survivable strategies try to spread the traffic.

Energy consumption in optical backbone networks is increasing due to two main reasons: (i) the exponential growth of bandwidth demands, and (ii) the increase in availability requirements in order to guarantee protection of the ultra high capacity optical channels provided by wavelength division multiplexing (WDM) networks. Although state of the art reliability mechanisms are very efficient in guaranteeing high availability, they do not consider the impact of the protection resources on the network's energy consumption. Dedicated (1:1) path protection (DPP) is a well-known mechanism that provides one extra link-disjoint path for the protection of a connection request. This secondary path is reserved and maintained in an active mode even though it is not utilized most of the time. This means that in-line optical amplifiers and switching nodes/ports are always consuming power even when they are not used to reroute any primary traffic. Moreover secondary paths are on average longer than their respective primary paths. These observations motivated us to investigate the energy savings, when all unused protection resources can be switched into a low-power, stand-by state (or sleep mode) during normal network operation and can be activated upon a failure. It is shown that significant reduction of power consumption (up to 25%) can be achieved by putting protection resources into sleep mode. Moreover, in order to enhance this energy saving figure, this paper proposes and evaluates different energy-efficient algorithms, specifically tailored around the sleep mode option, to dynamically provision 1:1 dedicated path protected connection. The trade-off between energy saving and blocking probability is discussed and an efficient mechanism to overcome this drawback is devised. Our results reveal that a 34% reduction of energy consumption can be obtained with a negligible impact on the network's blocking performance.

In this paper we propose the use of Bit Error Rate (BER) as a differentiation of service parameter for connection provisioning in optical Wavelength Division Multiplexing (WDM) networks. This is achieved through the use of Impairment Constraint Based Routing (ICBR), whereby various BER thresholds are set for accepting/blocking requests at the connection provisioning phase, depending on QoS requirements. The performance of the proposed scheme is evaluated through simulations, using dynamic traffic demands as an input at 10 Gb/s bit rate. The evaluation results reveal significant improvement in term of connection blocking, as compared to non-differentiated conventional RWA and ICBR algorithms.

Latest advances in Wavelength Division Multiplexing (WDM) technology make it possible to build all-optical transparent networks, which are considered to be able to satisfy the rapidly growing capacity demand. However, in a transparent WDM network the optical signal transmitted from a source to a destination node might be degraded due to physical layer impairments induced by transmission through optical fibers and components. Several Impairment Constraint Based Routing (ICBR) algorithms have been proposed to consider physical layer impairments during the connection-provisioning phase in order to prevent selecting a lightpath with poor signal quality. However, these algorithms support only a single quality of transmission threshold for all connection requests, while next generation networks and the future Internet are expected to support a variety of services with potentially disparate QoS requirements. In this paper, we propose the use of bit error rate (BER) as a differentiation of service parameter for connection requests in optical WDM networks. This is achieved through the use of ICBR, whereby various BER thresholds are set depending on the QoS requirements for accepting/blocking the connection requests during the connection-provisioning phase. The evaluation results reveal that significant network performance improvement in terms of connection blocking can be achieved, compared to non-differentiated conventional routing and wavelength assignment (RWA) and ICBR algorithms.

In bandwidth abundant optical networks it is important to develop design strategies that are not only cost effective but also able to account for the inherent characteristics of the optical transmission medium responsible for the signal quality degradation. With this objective in mind, the paper proposes a design algorithm able to determine an appropriate placement of regenerators in Grouped Routing Entity (GRE)-based optical networks. The objective of the algorithm is to guarantee a certain signal quality level to all connections while minimizing the number of fibers and switching ports required in the network The proposed design strategy relies on a physical-layer impairment model, specifically introduced in the paper for this purpose, able to estimate the signal quality of an optical path in a GRE-based optical network Simulation results indicate that compared with a single layer optical path network the proposed design algorithm can reduce at least 87% of the switch ports while the increment in the number of fibers is lower than 10%.

We propose and evaluate a Greedy Randomized Adaptive Search Procedure applied to minimize the number of power equalizers (GRASP-PE) needed to limit the propagation of high-power jamming attacks in WDM networks. Simulation results show that GRASP-PE significantly reduces the required number of power equalizers when compared to a greedy approach.

The latest advances in Wavelength Division Multiplexing (WDM) technology are making it possible to build all-optical transparent WDM networks, which are expected to be able to satisfy the rapid growth of today's capacity demand. However, the transparency of such networks makes them highly vulnerable to deliberate attacks, specifically targeting the physical layer. Physical-layer attacks, such as high-power jamming, can cause severe service disruption or even service denial, enhanced by their capability to propagate through a transparent optical network. Several attack-aware routing and wavelength assignment algorithms have been proposed to reduce the possible disruption caused by high-power jamming attacks. However, even with network planning approaches which take network security, specifically physical-layer attacks, into account, resilience to deliberate attacks in such scenarios remains an issue. In this paper, we propose the use of wavelength-selective attenuators as power equalizers inside network nodes to limit the propagation of high-power jamming attacks. Due to the increased cost of optical switching nodes associated with the addition of power equalizers, we aim at minimizing their number through sparse power equalization placement. We developed a set of greedy algorithms to solve what we call the Power Equalization Placement (PEP) problem with the objective of minimizing the number of power equalizers needed to reduce, to a desired level, the propagation of high-power jamming attacks for a given routing scheme. We further improved upon these results by proposing a GRASP (Greedy Randomized Adaptive Search Procedure) heuristic with a somewhat longer execution time, but with significantly superior results. The performance evaluation results indicate that the proposed GRASP heuristic can achieve the same attack propagation reduction as can be obtained by equipping all nodes with power equalizers by placing them at less than 50% of the nodes on average, potentially yielding significant cost savings.

In transparent Wavelength Division Multiplexing (WDM) networks, the signal is transported from source to destination in the optical domain through all-optical channels, or lightpaths. A lightpath may traverse several fiber segments and optical components that in general degrade the optical signal. This effect introduces the need for considering physical layer impairments during the connection-provisioning phase. Physical layer impairments can be divided into linear and non-linear. Both types of impairments are highly dependent on the fiber characteristics, which in turn are sensitive to length, temperature and age. A close look at the fiber infrastructure of today's network operators reveals a situation where old and newly deployed fibers coexist in the network. This heterogeneous fiber plant presents a challenge. A tradeoff should be found between the QoS requirements of connection requests and the use of the available (old and new) network resources. This calls for a provisioning mechanism able to adapt to the various fiber composition scenarios. In parallel, given the need for service differentiation, the authors recently proposed an Impairment Constraint Based Routing (ICBR) algorithm, referred to as ICBR-Diff, supporting differentiation of services at the BER (Bit Error Rate) level in a network with a homogeneous fiber infrastructure. In this paper the ICBR-Diff algorithm is extended to heterogeneous network; particularly, it is evaluated in WDM networks with fiber links having varying Polarization Mode Dispersion characteristics, i.e., with old and new fiber coexisting. Simulation results show that the ICBR-Diff algorithm exhibits high adaptability in a heterogeneous fiber composition scenario. This translates into improved performance in terms of blocking probability, when compared to traditional impairment aware routing algorithms.

We evaluate an Impairment Constraint Based Routing algorithm with service differentiation (ICBR-Diff) applied in WDM networks with fiber links having varying Polarization Mode Dispersion characteristics. Simulation results show high adaptability of the ICBR-Diff approach to this heterogeneous fiber scenario when compared to conventional routing schemes.

We propose and evaluate a novel survivable impairment constraint based routing (ICBR) algorithm with service differentiation at the bit error rate level. Simulations show significant improvement in connection blocking compared to conventional ICBR solutions.

We demonstrate the importance of considering physical impairments in waveband-based optical networks. We propose and evaluate an Impairment-Aware waveband-routing and waveband-assignment (IA-RWBA) algorithm achieving significant improvement in both impairment satisfaction rate and total network cost.

A large variety of access network technologies and architectures that provide wide service portfolio to the customer are available for the network operators. Each of the potential access network architectures and technologies varies in complexity, network functionality, services supported and overall network costs. A detailed comparison of the economic viability of different access network scenarios is crucial for operators due to the high cost of this network segment. This paper identifies all essential elements of a general framework for the techno-economic analysis of different access network technologies and architectures, as well as describes some specific issues/problems related to the techno-economic evaluation of next generation (NG) access networks. The goal is to have at operator’s disposal a methodology allowing the techno-economic comparison of the proposed access network solutions and their introduction/rollout.

In Centralized Radio Access Networks (C-RANs) Baseband Units (BBUs) are decoupled from Remote Radio Units (RRUs) and placed in BBU Hotels. In this way baseband processing resources can be shared among RRUs, providing opportunities for radio coordination and cost/energy savings. However, the failure of a BBU Hotel can affect a large number of RRUs creating severe outages in the radio network. For this reason, the design of a resilient C-RAN is extremely important. This paper focuses on the survivable BBU Hotel placement problem in C-RANs with an optical wavelength division multiplexing (WDM) transport. We first propose an algorithm that jointly decides (i) the placement of a minimum number of BBU Hotels and (ii) solves the Routing and Wavelength Assignment (RWA) problem for the fronthaul connections, ensuring that each RRU is connected to two different BBU Hotels (i.e., one primary and one backup). Then, we present a strategy for maximizing the sharing of backup BBU ports among RRUs, with the aim of reducing the total cost of the C-RAN while guaranteeing uninterrupted service provisioning in case of single BBU Hotel failure. Simulation results show that the proposed strategy helps reducing the overall C-RAN cost. On the other hand, it becomes also evident that the sharing benefits can be maximized only in the presence of a transport network with enough wavelength resources to handle potential bottlenecks that may occur when BBU Hotels are placed quite far from RRUs.

In this paper we take into account the business aspects of building wireless and optical access networks. A detailed view on broadband access network deployment costs, including both capital (CapEx) and operational expenditures (OpEx) is given. Main cost components of optical and wireless access networks have been identified, and the deployment costs of different architectures have also been presented.

With advances in the information and communication technology (ICT), connected vehicles are one of the key enablers to unleash intelligent transportation systems (ITS). On the other hand, the envisioned massive number of connected vehicles raises the need for powerful communication and computation capabilities. As an emerging technique, fog computing is expected to be integrated with existing communication infrastructures, giving rise to a concept of fog-enhanced radio access networks (FeRANs). Such architecture brings computation capabilities closer to vehicular users, thereby reducing communication latency to access services, while making users capable of sharing local environment information for advanced vehicular services. In the FeRANs service migration, where the service is migrated from a source fog node to a target fog node following the vehicle's moving trace, it is necessary for users to access service as close as possible in order to maintain the service continuity and satisfy stringent latency requirements of real-time services. Fog servers, however, need to have sufficient computational resources available to support such migration. Indeed, a fog node typically has limited resources and hence can easily become overloaded when a large number of user requests arrive, e.g., during peak traffic, resulting in degraded performance. This paper addresses resource management in FeRANs with a focus on management strategies at each individual fog node to improve quality of service (QoS), particularly for real-time vehicular services. To this end, the paper proposes two resource management schemes, namely fog resource reservation and fog resource reallocation. In both schemes, real-time vehicular services are prioritized over other services so that their respective vehicular users can access the services with only one hop. Simulation results show that the proposed schemes can effectively improve one-hop access probability for real-time vehicular services implying low delay performance, even when the fog resource is under heavy load.

Fog computing is expected to be integrated with communication infrastructure, giving rise to the concept of fog-enhanced radio access networks (FeRANs) to support various mission-critical applications. Such architecture brings computation capabilities closer to end users, thereby reducing the communication latency to access services. In the context of FeRAN, service migration is needed to tackle limited resources in a single fog node and to provide continuous service for mobile end users. To support service migration, high capacity and low latency are required in mobile backhaul networks. Passive optical networks can be a promising solution for such mobile back-haul, in which bandwidth is shared by both migration traffic and that which is not associated with service migration. In this paper, we propose a bandwidth slicing mechanism, in which the bandwidth can be provisioned to the migration traffic and non-migration traffic dynamically and effectively to meet their different delay requirements. Simulation results verify that the proposed delay-aware bandwidth slicing scheme can handle the migration traffic properly, i.e., sending it within a required time threshold, while limiting the impact of the migration traffic on the latency and jitter of the non-migration traffic, particularly that with high priority.

We present the flexible RAN concept and evaluate its performance in different radio coordination scenarios considering an optical transport network. Results show the benefits of flexible RAN compared to C-RAN in terms of wavelength usage and transponder cost.

Cloud computing is increasingly based on geographically distributed data centers interconnected by high performance networks. Application of Software Defined Networking (SDN) is studied as an emerging solution to support dynamic network resource management for distributed data centers (DCs) jointly with extensive use of Network Function Virtualization (NFV). SDN/NFV operation takes advantage of orchestration of network control functions according to distributed DCs communication needs. Orchestration relies on a set of logical information related to the underlying infrastructure, called abstraction, which offers different levels of visibility of available resources, depending on the abstraction strategy adopted.

We propose to add optical amplifier(s) to passive optical interconnect (POI) at top-of-rack in datacentres and validate this approach by introducing impairment constraints into POIs design. It is shown that one amplifier can improve scalability by a factor of 16.

A framework is developed for modeling the fundamental impairments in optical datacenter interconnects, i.e., the power loss and the receiver noises. This framework makes it possible, to analyze the trade-offs between data rates, modulation order, and number of ports that can be supported in optical interconnect architectures, while guaranteeing that the required signal-to-noise ratios are satisfied. To the best of our knowledge, this important assessment methodology is not yet available. As a case study, the trade-offs are investigated for three coupler-based top-of-rack interconnect architectures, which suffer from serious insertion loss. The results show that using single-port transceivers with 10 GHz bandwidth, avalanche photodiode detectors, and quadratical pulse amplitude modulation, more than 500 ports can be supported.

Optical networks carry an increasing amount of traffic due to the rapid growth of IP and multimedia services. Therefore the impact of network failures on this traffic and thus user services is growing fast. In addition some network services are heavily dependent upon the availability of communication resources. Consequently, network operators have to deal with the steadily growing availability requirement. Thus, survivability mechanisms need to be provided in the networks to meet the connection availability requirement. There are several protection schemes that can be applied to improve connection availability in the network. Shared Path Protection (SPP) scheme is selected in this paper due to its efficiency in resource utilization .In many works the SPP scheme has been studied to solve a single failure problem. However, in large networks the occurrence of multiple concurrent failures cannot be neglected [1]-[3]. In this respect we studied the SPP scheme for mesh optical transport networks with multiple failure scenario and developed connection availability model with multiple failure assumption instead of traditional single failure assumption. In this paper we present the analytical model for connection availability in SPP mesh network with multiple failure assumption. Our model is more general than the traditional model adopted for single failure assumption and also is more general than the work for two protection paths. We also developed a simulator to evaluate our analytical model. The results show that the connection unavailability obtained by simulations is very close to the theoretical value, which approve that our algorithm is accurate.

Reliability in optical access networks is becoming a crucial issue for both operators and users due to the enormous increase of capacity and the importance of uninterrupted access to network services. Consequently, the growing number of users requesting penalties for connection interruptions is motivating for investing in protection mechanisms in fiber access networks. The investments involved depend on several aspects such as technology and covered area (population density, distance, type of users, etc.). Moreover, the passive optical network is considered one of the most beneficial fiber access solutions from the capital expenditures point of view; in particular, we are witnessing a wide deployment of TDM PONs. Keeping in mind that cost is a major issue in the access part of the network, in this article we propose a cost-efficient way to provide protection in a TDM PON considering different deployment scenarios in respect to population density in the access network area. The cost efficiency is obtained by taking advantage of investment cost reduction caused by sharing the same duct by both working and protection fibers. In order to evaluate the investment associated with the deployment of the proposed protection schemes, we take into account three different approaches: provide protection in the access network from the beginning, invest initially on an unprotected architecture keeping in mind a future upgrade with protection resources, and roll out an unprotected access network and, if needed in the future, invest in deployment of protection resources. The cost parameters considered in this article include investment in the infrastructure and installation, as well as the operational expenditures associated with failure reparation and service interruption penalties. Our results confirm that the proposed reliable PON architectures can achieve significant reduction of service interruption at very low increase in investment cost, leading to a great decrease of the total cost of ownership. Finally, some useful guidance for cost-efficient deployment of protection in fiber access networks is provided along with a sensitivity study to point out the key cost factors.

A new way to provide protection in TDM PONs is proposed and evaluated. It is shown that very low investment is needed to provide protection. In this way the total cost can be reduced due to the diminution of the OPEX related to the failure management.

Optical access networks are being widely deployed due to their high capacity and scalability. The reliability of these networks is a key issue because of the impact of failures on both the number of interrupted services and significance of the service interruptions for the community. Consequently, the service interruption penalties that a network operator would need to pay are directly related to the network reliability performance. Nowadays, penalties are paid to business customers when the service interruption time is longer than the value of the Service Level Agreement agreed with the operator. However, the number of users requesting penalties increases, which has triggered the need of protection mechanisms in access networks. In this paper, the investments required to offer protection for different planning approaches will be compared for different optical access technologies (TDM, WDM, AON and P2P). The evaluation of the costs associated to each scenario such as infrastructure, equipment, power consumption, failure reparation etc. is presented. The overall cost reduction when investing on infrastructure protection is highlighted.

The paper provides the methodology to evaluate the tradeoff between the consumed energy, the connection availability and the connection interruption time for survivable hybrid passive optical converged networks in different deployment areas.

Along with the competition on the telecom market and high reliability requirements of the emerging services operators and service providers are forced to increase connection availability of all users supported by their network. For economical reason most of the investment related to providing protection resources has been so far limited to the core and metro networks. On the other hand, increasing requirement for interrupted access to the network services is moving the focus for protection towards the end user. However, the cost to offer protection in access networks is a limiting factor. In this paper, a protection scenario for passive optical network in dense urban area is proposed. The cost of this protection approach is analysed, and furthermore, the key cost drivers are identified. It is shown that the failure rates of fiber and Optical Network Units (ONUs) and basic salary of technicians are the main cost drivers for the considered dense urban area.

Reliability is becoming a crucial issue for service providers, operators and users in optical access networks. The increase of network capacity and the importance of reducing service interruption times, force network operators to implement protection mechanisms in optical access networks. However, so far providing backup resources in access networks has been considered too expensive. In order to assess the impact of protection on capital and operational expenditures, the evaluation needs to study the impact to aspects such as the required infrastructure and equipment costs, failure reparation costs, and expected service interruption time. This work deals with the cost and reliability evaluation of time-division-multiplexing (TDM) and wavelength-division-multiplexing (WDM) passive optical networks (PONs). Three strategies to offer protection are evaluated: 1) provide protection in the access network directly from the greenfield, 2) invest initially on an unprotected architecture keeping in mind a future upgrade with protection resources, and 3) roll out an unprotected access network and if needed in the future, invest in deployment of protection resources. The impact of these strategies on the overall cost is studied.

Abstract Video streaming and video-on-demand are gaining popularity nowadays which dictates a need of bandwidth upgrade for Internet users. Many next generation optical access network architectures have been proposed to meet high capacity requirement on a per-user basis. However, the capacity upgrade in access networks, may lead to a huge traffic growth in the aggregation/core network. One way to avoid this problem is to keep the traffic locally (i.e., inside the access network area) as much as possible. It can be obtained by using locality-aware peer-to-peer (P2P) applications for content distribution and has the potential to offload the core segment. However, various optical access network architectures accommodate the P2P traffic in different ways. Thus, it is important to study these differences in order to identify the best architecture option for capacity offloading in the core network, energy efficiency and network resource utilization. By deploying a proper architecture in the access segment along with an efficient traffic locality aware strategy, the extra investment and capacity upgrade of the expensive core network resources needed to support the future traffic expansion can be minimized. However, to the best of our knowledge this kind of assessment is so far not available. Therefore, in this paper, we analyze the efficiency of supporting locality-aware P2P video distribution algorithm in three main types of optical access network architectures, i.e., active optical network (AON), wavelength division multiplexing passive optical network (WDM PON) and time/wavelength division multiplexing PON (TWDM PON). Our goal is to provide important design guidelines for the next generation broadband access architectures, while minimizing the need for the core network upgrade. We obtain this objective by utilizing the unique characteristics of each access network architecture in accommodating P2P video delivery applications. We have done an extensive literature study and for the first time we have compared performance of these architectures with respect to the amount of the traffic on the links in different aggregation levels, power consumption taking into account sleep mode functionality at the user premises, and required switching capacity in the nodes. Our results reveal that both active and passive architectures have good ability to localize P2P traffic, whereas they show distinct performance with respect to the other aforementioned aspects. This is caused by the different number of aggregation levels, link capacity, and resource allocation protocols. Considering the overall performance evaluation, it is shown that TWDM PON is the most promising option for the future broadband access, where locality-aware P2P video distribution is applied, thanks to its low energy consumption and required switching capacity of the network equipment needed to deliver this service. This conclusion is against the general intuition because of the PON׳s centralized control plane and passive infrastructure without switching capability in the field. Our unexpected conclusion can be of particular interest to operators as it is perfectly aligned with next generation optical access architecture identified by Full Service Access Networks (FSAN).

Individual users and enterprises are increasingly relying on the access to internet services and cannot accept long interruption time as easily as before. Moreover, the main characteristics of next generation optical access (NGOA) networks, such as long reach and a large number of users per feeder line, turn the network reliability to an important design parameter to offer uninterrupted service delivery. In this regard, protection mechanisms become one of the crucial aspects that need to be considered in the design process of access networks. On the other hand, it should be noted that not all users can afford to pay a high extra cost for protection; hence, it is important to provide resilience in a cost-efficient way. A PON combining WDM and TDM technologies, referred to as hybrid WDM/TDM PON or HPON, is one of the most promising candidates for NGOA networks due to its ability to serve a large number of subscribers and offer high capacity per user. For these reasons, in this article, we propose HPON architecture offering different degrees of resilience depending on the user profiles (i.e., partial and full protection for residential and business access, respectively). Also, the investment cost of providing resilience for the proposed schemes is investigated considering various protection upgrade road maps. Our results confirm that protecting the shared part of network with a large number of users is required in order to keep the failure impact at an acceptable level, with less than 5 percent increase of investment cost compared to the unprotected case. Meanwhile, the proposed end-to-end protection for business users considerably reduces the risk of service interruption for this type of demanding user without a need to duplicate the deployment cost of an unprotected connection. Furthermore, a sensitivity analysis is performed to investigate the impact of changes in business user percentage and protection upgrade time on the deployment cost. The results may be used as advice on cost-efficient deployment of reliable fiber access networks.

Field measurements show that more than half of the Internet traffic could be able to take advantage of the local data storage and distribution by utilizing the peer–to–peer (P2P) technique, which in many cases can offer higher scalability and lower price than the client–server based applications. However, typically Internet service providers (ISPs) are limiting P2P applications, because P2P traffic may unnecessarily travel through areas managed by other ISPs and hence cause additional cost when transmitting outside the ISP’s network. In this paper we employ a locality–aware content fetching strategy for the P2P application and investigate the influence of systems utilizing locally stored content on the traffic load distribution between core, metro and access networks. Moreover, we quantitatively evaluate the improvement of the resource utilization in an access network along with the inter–ISP bandwidth saving. Our simulation results show that using locality aware content fetching in access network can reduce traffic loads in the metro and core networks by keeping it closer to the access via local bridging. The big amount of localized P2P traffic in the access network may introduce a new challenge for next generation access networks to cost–efficiently handle the local traffic.

New technologies and advanced network devices make it possible to move towards high capacity access networks able to satisfy the growing traffic demand. Wavelength division multiplexing (WDM) is considered as one of the promising technologies for the next generation access networks since it offers higher bandwidth and longer reach compared to the current technologies (such as time division multiplexing (TDM) based networks). However, the migration to a new technology is typically based on an overall techno-economic study which should assure the network operator that the new implementation is cost effective and profitable while able to provide the required services to the users. Another important aspect in the access network design is the network reliability performance, which can be improved by providing a certain level of protection for equipment and/or infrastructure with high failure impact ratio in order to prevent a big number of the users being affected by a single failure. The cost of protection should be carefully evaluated since providing the backup resources may be too expensive for a network operator. In this paper, we investigate the capital and operational expenditures for two next generation optical access (NGOA) networks based on the WDM technology in dense urban areas. Three scenarios with different splitting ratios are studied for each technology, with and without protection. The aim of this work is to investigate the impact of providing protection on the total cost of NGOA networks. The results show that in the dense urban areas the fibers and digging costs are highly shared among the end users but still vary according to the splitting ratios for different scenarios and the fiber layout. It also can be seen that with a proper fiber layout design, minor extra investment for protection of NGOA networks can make a significant saving on failure related operational cost and that operational expenditures depend significantly on the fiber layout.

Wireless heterogeneous networks (HetNets) based on small cells are a cost and energy efficient alternative to provide high capacity to the end users. On the other hand, the cost and energy consumption of backhaul network aggregating data traffic from a large number of base stations may limit the benefits brought by the use of small cell. In HetNet deployments it becomes thus essential to be able to assess the total cost of ownership (TCO) of the backhaul network. This paper presents for the first time a comprehensive cost evaluation methodology to compute the TCO of mobile backhaul networks. The presented model can be instrumental to identify the most critical cost drivers in the backhaul networks and to have a better understanding of the backhaul TCO dynamics when small cells are deployed. The proposed TCO model is then used in a case study where two technology options for the backhaul are considered, i.e., microwave and fiber. The results from the case study show how it is possible to identify the most critical cost factors, thus easing the way towards a cost efficient backhaul design strategy.

High-capacity architecture is proposed aiming to fulfill stringent latency constraint for coordinated multipoint transmission in mobile networks. It offers obviously lower delay, cost and energy consumption as well as better resiliency than the conventional solutions. © 2015 OSA.

The absence of electrical regenerators in transparent WDM networks significantly contributes to reduce the overall network cost. In transparent WDM networks, a proper resource allocation requires that the presence of physical impairments in Routing and Wavelength Assignment (RWA) and lightpath provisioning be taken into account. In this article a centralized, a hybrid centralized-distributed and two distributed approaches that integrate information about most relevant physical impairments in RWA and lightpath provisioning are presented and assessed. Both centralized and hybrid approaches perform a centralized path computation at the management-plane level, utilizing physical impairment information, while the lightpath provisioning is done by the management plane or the control plane, respectively. The distributed approaches fall entirely within the scope of the ASON/GMPLS control plane. For these two approaches, we provide functional requirements, architectural functional blocks, and protocol extensions for implementing either an impairment-aware real-time RWA, or a lighpath provisioning based on impairment-aware signaling.

The Service Oriented Optical Network is a project committed to introduce the concept of service virtualization in optical metro/core networks, by improving the Automatic Switched Transport Network (ASTN) architecture thanks to the introduction of an extra functional layer, namely Service Plane, designed according to the ITU-T Intelligent Network Conceptual Model. An implementation of the Service Plane is presented highlighting the software architecture and the technology details. In particular it is applied to a testbed that implement a VPN topology request from a client application.