Deployment Of Optical Networks Research Articles

An ILP-based CapEx and OpEx efficient multi-stage TDM/TWDM PON design methodology

Abstract With reference to huge investment needed for greenfield passive optical network (PON) deployment, it is immensely important to define procedures and algorithms aimed towards optimal layout and network planning to reduce the overall expenditure due to capital expenditure and operational expenditure as much as possible. We propose an integer linear programming (ILP) based optimization model that explores optimal network dimensioning and placement of network equipment at appropriate locations so as to minimize the overall expenditure. Based on the number of users [optical network units (ONUs)], user’s bandwidth demand, power budget, maximum distance from optical line terminal (OLT) to users, available number of wavelengths and OLT ports, and geographical locations of ONUs, OLT and candidate locations of remote nodes (RNs), the model selects the number, type, splitting ratio and locations of passive devices. The RN device type is selected to be either power splitter or array waveguide grating. Optimal PON architecture is appropriately identified to be time division multiplexing or time-and wavelength division multiplexing (TWDM) depending on the requirement. It provides complete interconnection details among all devices, the overall expenditure, the number of OLT ports and the number and associated data rates of wavelengths to be used. We show exhaustive results for two deployment regions (viz. urban and rural) with different number of ONUs and bandwidth demands from users.We also show result with actual locations of OLT, ONUs and RNs selected from Google map. The proposed ILP model has low computational complexity and offers optimal solution within a reasonable time limit, without requiring a heuristic approach that provides a sub-optimal solution. The TWDM-PON conforms to next-generation PON stage 2 (NG-PON2) specifications and can be used as a useful tool for setting up NG-PON2.

Nonlinear chirped grating based tunable dispersion compensation using strain

Chirped fiber Bragg gratings (CFBGs) offer an attractive solution for dispersion management in long haul and high capacity point to point optical links. The deployment of reconfigurable optical networks however demands dynamic dispersion compensation schemes to address channel degrading effects. Dynamic correction of dispersion can be achieved by tuning the optical characteristics of the non-linearly chirped FBG using external controls like temperature, strain, magnetic, acousto-optic and electro-optic techniques. In this work, simulations are carried out to evaluate the performance of nonlinear chirped gratings as tunable dispersion compensators. The induced dispersion of the grating is found to be tunable from −800 ps/nm to −2657 ps/nm using strain as external perturbation. BER of 1.85 × 10−118 and 1.71 × 10−116 is achieved after the transmission of the information through 90 and 140 km section of single mode optical fiber respectively. This is achieved by adjusting or tuning the dispersion offered by the nonlinear chirped FBG dynamically in the required range.

A coordinated virtual optical network embedding algorithm based on resources availability-aware over elastic optical networks

Abstract Recent innovations in network virtualization and elastic optical networks enable the flexible deployment of optical networks. However, the spectrum fragmentation and virtual optical links being embedded to the longer lightpaths decrease the spectrum efficiency of elastic optical networks. To address this issue, a coordinated virtual optical network embedding algorithm based on resources availability-aware (RA-CVONE) is proposed. Firstly, we design the node importance metric to embed the neighboring virtual nodes to the closer physical nodes, and then a coordinated embedding approach is adopted, which can further shorten the length of the lightpaths to which virtual optical links are embedded. Moreover, we jointly evaluate the resources availability of a physical lightpath and its node, then select the candidate lightpaths with less spectrum fragmentations and abundant resources for a virtual optical link. Based on the resources availability, a path selection strategy is proposed to determine a physical lightpath of which the vacant spectrum resources can be effectively used. Simulation results show that the RA-CVONE algorithm can significantly shorten the length of the physical lightpaths which are selected to embed virtual optical links, reduce the bandwidth blocking probability of virtual optical network requests, and improve the spectrum utilization of elastic optical networks.

Automated Inspection of Defects in Optical Fiber Connector End Face Using Novel Morphology Approaches.

Increasing deployment of optical fiber networks and the need for reliable high bandwidth make the task of inspecting optical fiber connector end faces a crucial process that must not be neglected. Traditional end face inspections are usually performed by manual visual methods, which are low in efficiency and poor in precision for long-term industrial applications. More seriously, the inspection results cannot be quantified for subsequent analysis. Aiming at the characteristics of typical defects in the inspection process for optical fiber end faces, we propose a novel method, “difference of min-max ranking filtering” (DO2MR), for detection of region-based defects, e.g., dirt, oil, contamination, pits, and chips, and a special model, a “linear enhancement inspector” (LEI), for the detection of scratches. The DO2MR is a morphology method that intends to determine whether a pixel belongs to a defective region by comparing the difference of gray values of pixels in the neighborhood around the pixel. The LEI is also a morphology method that is designed to search for scratches at different orientations with a special linear detector. These two approaches can be easily integrated into optical inspection equipment for automatic quality verification. As far as we know, this is the first time that complete defect detection methods for optical fiber end faces are available in the literature. Experimental results demonstrate that the proposed DO2MR and LEI models yield good comprehensive performance with high precision and accepted recall rates, and the image-level detection accuracies reach 96.0 and 89.3%, respectively.

Next Generation Access Network Deployment in Croatia: Optical Access Networks and Current IoT/5G Status

ABSTRACTThis paper gives an overview and background of optical access network deployment in Croatia. Optical access network development in Croatia has been put into a global as well as in the European Union context. All the challenges and the driving factors for optical access networks deployment are considered. Optical access network architectures that have been deployed by most of the investors in Croatian telecommunication market are presented, as well as the architectures that are in early phase of deployment. Finally, an overview on current status of mobile networks of the fifth generation and Internet of Things is given.

Optimization of Flexible Non-Uniform Multilevel PAM for Maximizing the Aggregated Capacity in PON Deployments

Non-uniform pulse amplitude modulation (PAM) utilizes unequal distances between its modulation levels. In a multilevel PAM symbol, multiple bits are encoded. Due to the unequal level spacing, some bits can be decoded successfully at a lower received optical power than others. This is well suited for practical passive optical network (PON) deployments wherein the optical powers received by the different optical network units (ONUs) typically vary over a broad range. Thus, more ONUs in the PON can successfully decode non-uniform PAM-4 and PAM-8 than standard PAM-4/8, thereby increasing the aggregated capacity of the network. In systems where signal-dependent noise makes up a significant part of the total received noise level, the non-uniform PAM constellation can be adapted to take this signal-dependent variance into account. In doing so, a lower unequal level spacing can be used, decreasing the received optical power required to successfully decode all the bits in the PAM symbol. The impact of non-uniform PAM on the network throughput is presented by comparison of the experimental results with the actual loss distribution of a commercially deployed PON.

Optimizing of Passive Optical Network Deployment Using Algorithm with Metrics

Various approaches and methods are used for designing of optimum deployment of Passive Optical Networks (PON) according to selected optimization criteria, such as optimal trenching distance, endpoint attenuation and overall installed fibre length. This article describes the ideas and possibilities for an algorithm with the application of graph algorithms for finding the shortest path from Optical Line Termination to Optical Network Terminal unit. This algorithm uses a combination of different methods for generating of an optimal metric, thus creating the optimized tree topology mainly focused on summary trenching distance. Furthermore, it deals with algorithms for finding an optimal placement of optical splitter with the help of K-Means clustering method and hierarchical clustering technique. The results of the proposed algorithm are compared with existing methods.

Adaptation of transmitting signals over joint aged optical fiber and free space optical network under harsh environments

Over the last two decades, a large amount of optical fiber (OF) cables has been deployed as part of the global communication networks. Both the aging of OFs as well as the need to increase transmission data rates, particularly in the backbone, have become hot topics. We present the study of the aged OF deployment in various optical networks including free space optics (FSO) link as a part of modern optical communication networks. Here, we show extended results obtained using a dedicated OF testbed focusing on the long-term monitoring of polarization mode dispersion (PMD) because of its time-varying nature. The adaptation of polarization multiplexed radio over fiber (RoF) and radio over FSO (RoFSO) systems as well as 10Gbps on-off-keying (OOK) non-return-to-zero (NRZ) intensity modulation with the direct detection system, which is common cost-effective transmission system in passive networks, are demonstrated. Moreover, simulation of 100 and 200Gbps return-to-zero (RZ) differential quadrature phase shift keying (DQPSK) with direct detection is outlined to verify the impact of aged OF network connected with FSO under turbulence conditions. Results reveal more than 6dB of power penalty with the aged OF route for 100Gbps systems. In addition, there is a 0.8dB power penalty due to the strong seasonal induced PMD fluctuations. The influence of scintillations in terms of Rytov variance for the FSO link is also investigated for weak to moderate turbulence. Finally, we derive an expression for the long-term mean PMD value determined over one-month measured frequency response.

A constraint-based parallel local search for the edge-disjoint rooted distance-constrained minimum spanning tree problem

Many network design problems arising in areas as diverse as VLSI circuit design, QoS routing, traffic engineering, and computational sustainability require clients to be connected to a facility under path-length constraints and budget limits. These problems can be seen as instances of the rooted distance-constrained minimum spanning-tree problem (RDCMST), which is NP-hard. An inherent feature of these networks is that they are vulnerable to a failure. Therefore, it is often important to ensure that all clients are connected to two or more facilities via edge-disjoint paths. We call this problem the edge-disjoint RDCMST (ERDCMST). Previous work on the RDCMST has focused on dedicated algorithms and therefore it is difficult to use these algorithms to tackle the ERDCMST. We present a constraint-based parallel local search algorithm for solving the ERDCMST. Traditional ways of extending a sequential algorithm to run in parallel perform either portfolio-based search in parallel or parallel neighbourhood search. Instead, we exploit the semantics of the constraints of the problem to perform multiple moves in parallel by ensuring that they are mutually independent. The ideas presented in this paper are general and can be adapted to other problems as well. The effectiveness of our approach is demonstrated by experimenting with a set of problem instances taken from real-world passive optical network deployments in Ireland, Italy, and the UK. Our results show that performing moves in parallel can significantly reduce the elapsed time and improve the quality of the solutions of our local search approach.

Itinerant Routing in Elastic Optical Networks

We state a new problem of \emph{itinerant routing} in elastic optical networks, which we define as the establishment and reconfiguration of an \emph{itinerant connection}. In an itinerant connection, one of the connection end nodes is allowed to change. Itinerant routing could also be considered a form of connection restoration, where a connection has to be restored to a different end node. With the introduction of new mobile-network architectures, the progressing integration of wireless and optical networks, the continuing growth of wireless high-bitrate services, and the eventual deployment of elastic optical networks, there is a need to support this itinerant routing in the elastic optical networks. We present and discuss two major use cases of the itinerant routing, and propose a \emph{novel reconfiguration algorithm}. Our algorithm does not deteriorate the network performance, and requires half as many new links to configure as the shortest-path reconfiguration algorithm. The performance evaluation was carried out with 46800 simulation runs using randomly-generated realistic transport networks.

北海道東川町における光ファイバ整備と企業のインターネット利用への影響(シンポジウム デジタル時代の情報生成・流通・活用,2012年度秋季学術大会)

北海道東川町における光ファイバ整備と企業のインターネット利用への影響(シンポジウム デジタル時代の情報生成・流通・活用,2012年度秋季学術大会)

Key performance indicators for elastic optical transponders and ROADMs: The role of flexibility

Flexible optical networks will provide the required service diversity to manage unpredictable traffic patterns and growth. However, a key challenge is to quantify flexibility in order to indicate the associated performance of individual components and subsystems required to support networks and correlate it with other figures of merit. Measurable key performance indicators will aid the process towards the design and deployment of cost effective and efficient optical networks. Moreover, the design and placement of network elements within a network influences the resultant network-wide flexibility and performance. In this paper, we highlight critical design parameters for key optical components, optical transmission and switching subsystems using flexibility as an additional figure of merit. We derive models to measure the flexibility of key optical components, optical transmission and switching subsystems based on entropy maximization. Using these models, we evaluate flexibility and design trade-offs of the presented enabling technologies with other key performance indicators such as spectral efficiency, lightpath reach, total capacity, normalized cost, connectivity and others. This study provides an advanced and more informed set of design rules that quantify and visualize the different degrees of flexibility of enabling technologies and associated performance based on required specification and/or functionality.

Increasing Flexibility and Capacity in Real PON Deployments by Using 2/4/8-PAM Formats

Current passive optical networks (PONs) use on–off keying (OOK) modulation throughout the entire network regardless of actual path losses. Statistics of commercial gigabit passive optical network (GPON) deployments show significant path loss differences among the optical network units (ONUs). Flexible 4- and 8-level pulse amplitude modulation (4/8-PAM) allocation for the better-situated ONUs can significantly increase the PON’s aggregated data rate. By keeping to intensity modulation direct detection (IM-DD) modulation and a constant symbol rate, the introduction of adaptive, multilevel PAM does not require expensive optics investments; additionally, 8-PAM is made feasible with zero-overhead data-aided equalization. Two scenarios for distributing the extra capacity are explored: first, controlling the dynamic bandwidth allocation of the time division multiplexed PON (TDM-PON) to provide equal time-length slots to both 4/8-PAM ONUs and OOK ONUs, thereby providing maximum aggregated capacity increase; and second, setting up the dynamic bandwidth allocation to provide equal capacity slots to the various ONUs so the entire ONU population in the same PON can benefit from the extra capacity. Both scenarios result in a larger aggregated capacity of the PON and provide additional options for the network operator during the network design phase.

Enabling the Digital Economy

In this contribution we argue the importance of an ubiquitous high speed broadband infrastructure in Europe based on an analysis of subsequent technological revolutions, each characterized by a specific core infrastructure which enables the broad deployment of innovations, which in turn leads to a structural improvement in productivity.To reap the full benefits of the current ICT-driven technological revolution adaptation of the institutional environment is essential, as overtime rules and regulations have been optimized for the previous techno-economic paradigm. A fundamental adaption has been the liberalization of the sector in the late 1990s. This enabled the deployment of Pan-European optical backbone networks. We argue the importance of infrastructure-based competition in the development of broadband access networks, but also recognize the limits of the market-driven model. Hence, we emphasize the important role of governments where and when commercial models fail to supply broadband. Here, research has shown a large diversity in alternative approaches and bottom-up solutions across Europe, based on initiatives by municipalities, non-telco entrepreneurs, cooperatives and communities of users. In closing the broadband gap we recommend these initiatives to be leveraged and facilitated by national, regional and local governments.Next to ubiquitous coverage and affordable broadband, a high degree of usage is critical. This leads to the importance of the other Pillars of the Digital Agenda for Europe on digital literacy, skills and a safe and secure Internet. Research also suggests that the economic benefits will only materialize if investments in ICT hardware and software are complemented with investment in human capital, i.e. in skills development, and the reconceptualization of the business models and business processes. Early examples are the change from ‘print distribute’ to ‘distribute print’ and the disintermediation of the ‘middle man’. More recent examples are Airbnb, Uber and Snappcar.An investigation into Internet usage, in particular the average peak rates which are indicative for the broadband capacity available to end-users, suggests that leading countries in Europe are at par with leading states in the USA, while there is still a gap with South Korea and Japan. South Korea and Japan benefit from a higher starting point enabled by the broad deployment of fibre. Nonetheless, if the leading countries in Europe keep up the current growth rate of 30% demonstrated over the past 8 years the gap with South Korea will be closed by 2020. Hence, policy focus should be on keeping the momentum in the leading countries and on closing the gap by the other countries in Europe.While legacy copper networks have been crucial for providing the early broad access to the Internet, increasingly higher data rates require increasing use of fibre. Medium and large business users have already the opportunity to be connected by fibre. For residential users this will in the short term likely be in the form of upgrades from fibre to the cabinet to fibre to the distribution point/last amplifier and fibre to the basement, with full fibre deployment in greenfield situations. On the longer term this will have to be all fibre deployments to all users to accommodate the projected growth towards Gigabit data rates in 2025.

Signal monitoring and performance stability evaluation tool in a high speed optical communication network

The diverse communication systems in South Africa have changed drastically over the last few years and are envisioned to continue to improve as evidenced by the deployment of high speed optical fibre networks, in both access and metro networks. The key task in the design of any communication network is to come up with a tool that monitors and evaluates the performance stability of the entire communication link. A cost effective, reliable and reconfigurable bit error ratio (BER) signal analyzer was designed and implemented to monitor and evaluate the overall performance stability of a high speed optical communication link. The reconfigurable digital signal processing (DSP) assisted optical receiver is an alternative technology to the expensive and complex hardware receivers, based on its ability to be repurposed to adapt to different modulation formats. BER is a figure of merit that allows different optical communication systems to be evaluated in a fair and consistent manner. In this experimental work, a reconfigurable DSP signal analyzer tool was developed and implemented to evaluate the performance stability of an unamplified transmission through a 25km G. 655 fibre at 1550nm. The developed DSP algorithm was authenticated and validated by comparing its performance with results obtained from a commercial BER tester. A transmission penalty of 2dB was attained on comparing the back-to-back to a transmission over 25km of fibre. The cost effective DSP assisted receiver is a valuable tool to monitor and evaluate the performance fidelity of a high speed optical communication link.

Multitenant Transport Networks With SDN/NFV

We propose the combination of optical network virtualization and network function virtualization (NFV) for deployment of on-demand OpenFlow-controlled virtual optical networks (VON). Each tenant SDN controller is run on the cloud, so the tenant can control the deployed VON. This paper demonstrates the feasibility of the proposed use case and provides implementation details in the ADRENALINE testbed of an NFV orchestrator, which is able to provide multitenancy on top of an heterogeneous transport network by means of network orchestration and virtualization.

Performance Analysis of Smart Optical Burst Switching Networks for Different Signaling Protocols

A future optical transport network needs an extremely high capacity to satisfy the rapid increase in traffic. Many technologies have been developed to increase throughput and energy efficiency and simplify the deployment of optical transport networks. Internet Protocol traffic transmission precedes optical transport networks in requiring new approaches for network nodes. Although optical fiber has a tremendous capacity, switching nodes limit the performance of optical networks. An optical burst switched network concept has been introduced as a promising solution to overcome this problem. Optical burst switched technology effectively utilizes the advantages of both circuit switching and packet switching networks, and also eliminates their drawbacks. Two important issues in achieving the best performance in optical burst switched networks are scheduling bursts and signaling protocols. In this paper, we provide a comprehensive analysis of optical burst switched signaling protocols. We study three protocols for signaling in optical burst switched networks that are used for various traffic types. The Tell-and-Wait and Just Enough Time protocols are used in extreme cases of loss-sensitive and delay-sensitive traffic, respectively. The third signaling protocol, called Intermediate Note Initiation, is a promising solution with an ability to adjust parameters depending upon traffic requirements. We analyze the blocking probability of core nodes with respect to the number of buffers and wavelengths for each signaling protocol. The simulation results show that when the number of optical buffers are five or higher, blocking probability tends to be zero, regardless of the number of wavelengths. Therefore, this tends to decrease loss due to a burst, and improves the overall performance of optical burst switched networks. The burst outstripping problem in optical fiber has been solved by determining a proper buffering policy for each burst, after considering the burst priorities and time delays between consistent bursts.

Exploring parallelism and desynchronization of TCP over high speed networks with tiny buffers

The buffer sizing problem is a big challenge for high speed network routers to reduce buffer cost without throughput loss. The past few years have witnessed debate on how to improve link utilization of high speed networks where the router buffer size is idealized into dozens of packets. Theoretically, the buffer size can be shrunk by more than 100 times. Under this scenario, widely argued proposals for TCP traffic to achieve acceptable link capacities mandate three necessary conditions: over-provisioned core link bandwidth, non-bursty flows, and tens of thousands of asynchronous flows. However, in high speed networks where these conditions are insufficient, TCP traffic suffers severely from routers with tiny buffers.To explore better performance, we propose a new congestion control algorithm called Desynchronized Multi-Channel TCP (DMCTCP) that creates a flow with parallel channels. These channels can desynchronize each other to avoid TCP loss synchronization, and they can avoid traffic penalties from burst losses. Over a 10 Gb/s large delay network ruled by tiny buffer routers, our emulation results show that bottleneck link utilization can reach over 80% with much fewer number of flows. Compared with other TCP congestion control variants, DMCTCP can also achieve much better performance in high loss rate networks. Facing the buffer sizing challenge, our study is a new step towards the deployment of optical packet switching networks.

Experimental performance evaluation of software defined networking (SDN) based data communication networks for large scale flexi-grid optical networks.

Software defined networking (SDN) has become the focus in the current information and communication technology area because of its flexibility and programmability. It has been introduced into various network scenarios, such as datacenter networks, carrier networks, and wireless networks. Optical transport network is also regarded as an important application scenario for SDN, which is adopted as the enabling technology of data communication networks (DCN) instead of general multi-protocol label switching (GMPLS). However, the practical performance of SDN based DCN for large scale optical networks, which is very important for the technology selection in the future optical network deployment, has not been evaluated up to now. In this paper we have built a large scale flexi-grid optical network testbed with 1000 virtual optical transport nodes to evaluate the performance of SDN based DCN, including network scalability, DCN bandwidth limitation, and restoration time. A series of network performance parameters including blocking probability, bandwidth utilization, average lightpath provisioning time, and failure restoration time have been demonstrated under various network environments, such as with different traffic loads and different DCN bandwidths. The demonstration in this work can be taken as a proof for the future network deployment.

Elastic optical networks: The global evolution to software configurable optical networks

Worldwide operator deployment of high-speed 100G coherent optical networks is currently underway. To ensure a competitive solution offering significant performance improvements to cope with the ever-increasing traffic demand, a novel network concept has been proposed for improved resource utilization based on “elasticity”; specifically, the ability to make a number of previously fixed transmission parameters tunable, for example optical data rate or channel spacing. The benefits are numerous, including increased network capacity, lower cost per bit, and improved energy efficiency and scalability. In this paper, we review the work carried out within the Cooperation for a Sustained European Leadership in Telecommunications (CELTIC) Elastic-Optical NETwork (EO-Net) project towards advancing the state of software-configurable optical networking. We identify the key building blocks for enabling elastic optical networks to provide desired performance improvements over static optical networks. We examine the design of elastic transponders capable of data rate adaptation, interfaces between client packet devices and transponders supporting flexible traffic aggregation, and associated algorithms for traffic grooming and routing. We also perform network cost/energy analyses. Finally, we review the experimental demonstration of such elastic functionalities.