Practical Integrated Design Strategies for Opaque and All-Optical DWDM Networks: Optimization Models and Solution Procedures

Dense wavelength division multiplexing (DWDM) opaque networks use expensive optical/electrical/optical (O/E/O) conversion at each end of a fiber link. Several technological advances have been used in an attempt to reduce the O/E/O conversion cost component: improved optical amplifiers using distributed Raman amplification allow signals to traverse longer distances without amplification and/or regeneration; optical switches allow the signal to remain in the optical domain most of the time. Networks that use this equipment to eliminate some of the O/E/O conversions are called transparent or all-optical networks and benefit from reduced capital costs at the expense of operational costs and complexity in order to handle potential adjustments in traffic demand. In this investigation, we develop optimization-based algorithms for DWDM network design and traffic routing for both opaque and all-optical networks. This study compares the performance of AMPL/CPLEX implementations of both algorithms on realistically sized networks with up to 36 nodes and 67 links. In all test cases considered the all-optical network design is substantially less expensive than the traditional opaque network design with cost reductions in the range of 12% to 26%.     

Protection cost evaluation of WDM-based next generation optical access networks

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.     

Cost-effective traffic grooming in WDM rings

We provide network designs for optical add-drop wavelength-division-multiplexed (OADM) rings that minimize overall network cost, rather than just the number of wavelengths needed. The network cost includes the cost of the transceivers required at the nodes as well as the number of wavelengths. The transceiver cost includes the cost of terminating equipment as well as higher-layer electronic processing equipment, which in practice can dominate over the cost of the number of wavelengths in the network. The networks support dynamic (i.e., time-varying) traffic streams that are at lower rates (e.g., OC-3, 155 Mb/s) than the lightpath capacities (e.g., OC-48, 2.5 Gb/s). A simple OADM ring is the point-to-point ring, where traffic is transported on WDM links optically, but switched through nodes electronically. Although the network is efficient in using link bandwidth, it has high electronic and opto-electronic processing costs. Two OADM ring networks are given that have similar performance but are less expensive. Two other OADM ring networks are considered that are nonblocking, where one has a wide-sense nonblocking property and the other has a rearrangeably nonblocking property. All the networks are compared using the cost criteria of number of wavelengths and number of transceivers     

The interface between IP and WDM and its effect on the cost of survivability

A summary of research on survivable IP networks overlaid over WDM networks is presented. The WDM networks are part of optical transport service providers, who lease lightpath services to institutions with IP networks. The lightpath services realize IP links for IP networks, and they have different protection grades such as unprotected and protected. The research included considering new network survivability requirements and incorporating them into network design problems. The cost of survivable IP over WDM networks is compared over three scenarios. Each succeeding scenario has the WDM network provide more flexible services, and the IP and WDM networks become more integrated. We consider the problem of setting up lightpaths for an IP network so that the network will remain connected after a fiber link fault. Algorithms to find the lightpaths and minimize cost are given. The network costs under the three scenarios are compared by simulations.     

Architectures and technologies for high-speed optical data networks

Current optical networks are migrating to wavelength division multiplexing (WDM)-based fiber transport between traditional electronic multiplexers/demultiplexers, routers, and switches. Passive optical add-drop WDM networks have emerged but an optical data network that makes full use of the technologies of dynamic optical routing and switching exists only in experimental test-beds. This paper discusses architecture and technology issues for the design of high performance optical data networks with two classes of technologies, WDM and time division multiplexing (TDM). The WDM network architecture presented stresses WDM aware Internet protocol (IP), taking full advantage of optical reconfiguration, optical protection and restoration, traffic grooming to minimize electronics costs, and optical flow-switching for large transactions. Special attention is paid to the access network where innovative approaches to architecture may have a significant cost benefit. In the more distant future, ultrahigh-speed optical TDM networks, operating at single stream data rates of 100 Gb/s, may offer unique advantages over WDM networks. These advantages may include the ability to provide integrated services to high-end users, multiple quality-of-service (QoS) levels, and truly flexible bandwidth-on-demand. The paper gives an overview of an ultrahigh-speed TDM network architecture and describes recent key technology developments such as high-speed sources, switches, buffers, and rate converters     

Translucent optical networks: the way forward [Topics in Optical Communications]

The transmission reach of signals in optical transmission systems is limited. To go beyond these transparent reach limits, signal regeneration is necessary to re-amplify, reshape, and retime the optical signals. Translucent optical networks are a type of optical transport network specifically devised to address such a concern by allowing for sparse but strategic signal regeneration in the network. Translucent optical networks seek a graceful balance between network design cost and service provisioning performance, and can achieve performance comparable to that of an all-electronic switching network, but requiring far fewer signal regenerators. Despite massive progress, there are many outstanding issues regarding the implementation of translucent networks planning and operation. This article reviews a range of translucent optical networks and discusses various research issues, particularly involving network planning, lightpath routing and wavelength assignment, and network survivability. We also suggest other potential research topics such as traffic grooming, fault detection, and multicasting for translucent networks     

Performance analysis and dimensioning of multi-granular optical networks

Recent years have demonstrated the limited scalability of electronic switching to realize transport networks. In response, all-optical switching has been identified as a candidate solution to enable high-capacity networking in the future. One of the fundamental challenges is to efficiently support a wide range of traffic patterns, and thus emerges the need for equipment that is both practical and economical to construct and deploy. We have previously proposed the use of multi-granular optical cross-connects (MG-OXC), which support switching on both the wavelength and sub-wavelength level. To this end, the MG-OXCs are equipped with cheap, highly scalable slow switching fabrics, as well as a small number of expensive fast switching ports. The goal of this work is two-fold: first to demonstrate that a small number of fast switching ports suffices to support a wide range of traffic requirements, and second that multi-granular optical switching can offer cost-benefits on a network-wide scale. The first objective is studied through simulation analysis of a single switching node, and results indicate that a limited number of fast switching ports can significantly improve burst blocking performance over slow only switches. Furthermore, under certain circumstances, the MG-OXC can even approach the performance of a fast only switch design. Secondly, we introduce an Integer Linear Programming model for the total network installation cost, and our evaluation indicates that multi-granular optical switching can be a cost-effective solution on the network level, in comparison to slow only or fast only approaches. Furthermore, we can achieve reduced costs of individual OXC nodes, which allows us to minimize scalability problems corresponding to emerging fast switching fabrics.     

Power consumption modeling in optical multilayer networks

The evaluation of and reduction in energy consumption of backbone telecommunication networks has been a popular subject of academic research for the last decade. A critical parameter in these studies is the power consumption of the individual network devices. It appears that across different studies, a wide range of power values for similar equipment is used. This is a result of the scattered and limited availability of power values for optical multilayer network equipment. We propose reference power consumption values for Internet protocol/multiprotocol label switching, Ethernet, optical transport networking and wavelength division multiplexing equipment. In addition we present a simplified analytical power consumption model that can be used for large networks where simulation is computationally expensive or unfeasible. For illustration and evaluation purpose, we apply both calculation approaches to a case study, which includes an optical bypass scenario. Our results show that the analytical model approximates the simulation result to over 90% or higher and that optical bypass potentially can save up to 50% of power over a non-bypass scenario.     

Hybrid Link/Path-Based Design for Translucent Photonic Network Dimensioning

The advancement of ultralong-haul transmission technology has dramatically enhanced the all-optical reaches. However, the actual situations of installed fiber and sites for terrestrial network often prevent implementing a purely transparent network, and thus, opaque reshaping retiming regenerating (3R) regeneration is required to guarantee optical signal reachability. Since 3R regenerators based on optical/electrical/optical conversion tend to dominate the total network costs, an efficient network design method that allocates a minimum number of 3R regenerators to optimum locations is essential to build a cost-effective photonic network. In this paper, we propose such a network-dimensioning method by combining the advantages of link-based and path-based design approaches. It first guarantees optical signal reachability for any possible traffic demand in each segmented linear link. After combining all the links, excessive regenerators are eliminated based on the optical signal quality check with -factor calculation for each wavelength path. A trial design of a large-scale mesh network demonstrated a significant cost savings of more than 30% in comparison with a conventional link-based design. In the trial, the impact of fiber loss coefficient over the total network cost was investigated quantitatively, addressing the importance of such quantitative modeling and analysis.     

The Economics and Performance of Satellite Packet Switching

The economics and performance of packet-switched satellite systems operating in a broadcast mode are studied and compared to landline-based systems similar to the ARPANET. The fixed-packet length inefficiencies and the satellite channel utilization of the satellite systems are presented as functions of the message length distribution, the number of earth stations, the average message delay, and the average number of messages generated at each earth station. Some of the economic factors in the design of packetswitched satellite networks are discussed, including hardware costs as a function of technology and system performance. Satellite network configurations with or without backhaul facilities are compared and it is concluded that configurations using backhaul facilities consisting of two 30 mile private leased lines (each 50 kbits/s) are more expensive. Parameters and estimated costs of satellite system configurations are presented and an engineering estimate of the cost function for satellite packet-switched networks is derived and presented in the form of long range average cost curves. Economies of scale with respect to network traffic and diseconomies of scale with respect to the number of network earth stations are found to be present.     

Cost Comparison of Optical Circuit-Switched and Burst-Switched Networks

This paper examines the economic viability of two technologies—optical circuit-switched (OCS) networks and optical burst-switched (OBS) networks—in the core network. We analyze and dimension OCS network (OCSN) and OBS network (OBSN) architectures for a range of traffic demands given the constraints on the network element capacities. We investigate the effect of traffic grooming for both of these architectures. We evaluate these network architectures for a national core network in Australia in terms of their capital costs and packet-blocking probabilities. We observe that OBSNs with traffic grooming at the optical layer may become more cost effective than OCSNs with traffic grooming at both the IP and optical layers for the same quality of service in terms of blocking probability. The cost advantage of OBSNs over OCSNs grows as the capacity of the core network increases. Hence, among the all-optical networking options that do not involve buffering at the core, OBS appears to be an attractive option especially for high-capacity core networks.      

Designing long reach optical access networks

The long reach optical access concept promises to reduce the cost of a future BT network through simplification. This is achieved by extending the reach and split of today’s passive optical network systems (PONs) to 100 km and 1024 respectively, thus eliminating the need for separate backhaul equipment. Compact, low-power optical amplifiers are used at exchange locations requiring very low electrical power consumption. Ultimately this could effectively eliminate local exchange buildings and consolidate BT’s network to around a hundred metro nodes, drastically reducing operational costs. In this paper we describe research to date on the techniques to overcome physical layer impairments at costs appropriate for residential access. We also highlight from an operator’s point of view the protocol requirements of the LR-PON concept, point out the necessary changes to the GPON protocol, and describe an experiment to show its suitability to work over 100 km distances at 10 Gbit/s.     

Plug-and-play sensors in wireless networks

The availability of these self-configuring networks of wireless sensor data will accelerate the ongoing trend toward automation ranging from the factory floor to the office to the warehouse and outdoors. Lower installation costs, lower operating costs, and the improved factory efficiency will provide significant cost savings. Technicians will be able to walk near a machine and obtain data on its existing state and its history, enabling better monitoring of the equipment condition and avoiding expensive downtime. Open standards like Bluetooth and IEEE 1451 are key to supporting the proliferation of these technologies     

Optical Network Design With Mixed Line Rates and Multiple Modulation Formats

With the growth of traffic volume and the emergence of various new applications, future telecom networks are expected to be increasingly heterogeneous with respect to applications supported and underlying technologies employed. To address this heterogeneity, it may be most cost effective to set up different lightpaths at different bit rates in such a backbone telecom mesh network employing optical wavelength-division multiplexing. This approach can be cost effective because low-bit-rate services will need less grooming (i.e., less multiplexing with other low-bit-rate services onto high-capacity wavelengths), while a high-bit-rate service can be accommodated directly on a wavelength itself. Optical networks with mixed line rates (MLRs), e.g., 10/40/100 Gb/s over different wavelength channels, are a new networking paradigm. The unregenerated reach of a lightpath depends on its line rate. So, the assignment of a line rate to a lightpath is a tradeoff between its capacity and transparent reach. Thus, based on their signal-quality constraints (threshold bit error rate), intelligent assignment of line rates to lightpaths can minimize the need for signal regeneration. This constraint on the transparent reach based on threshold signal quality can be relaxed by employing more advanced modulation formats, but with more investment. We propose a design method for MLR optical networks with transceivers employing different modulation formats. Our results demonstrate the tradeoff between a transceiver's cost and its optical reach in overall network design.      

Optimal topology planning of optical networks with respect to overall design costs

The planning of optical networks aims to design a configuration that meets the desired requirements while reducing the overall expenses. Many attributes of a network ultimately depend on the underlying physical topology. This work investigates an optimal topology design for given node locations based on a traffic forecast. Our goal is to minimize the total equipment costs, including the dimensioning of node and span capacities. We identify three main cost terms, namely duct costs for the span infrastructure, expenses that can be assigned to the fiber medium, and costs that involve switching functionality. Resilience against single or dual failures is guaranteed by constructing an appropriately meshed network structure that offers path diversity. We develop a mathematical program formulation and investigate a case study.     

New Adaptive Compandor for LTE Signal Compression Based on Spline Approximations

With the constant increase in network traffic, wireless operators are finding it more challenging to keep network hardware costs to a minimum. At the same time, the energy cost associated with operating a network has increased proportionally. Therefore, the search for higher network capacity is simultaneously accompanied by the search for a cost‐efficient network deployment. In this paper, we show that a saving in transmitted signal energy can be achieved at the signal design level by deploying very specific signal processing techniques. Using an orthogonal frequency‐division multiplexing signal for Long‐Term Evolution networks as an example, we utilize a novel non‐uniform companding quantizer to save a transmitted signal energy. Our results show that by using non‐uniform quantization it is possible to further optimize 4G wireless networks.     

IP over optical cross-connect architectures [Topics in Optical Communications]

IP over optical network architectures have been extensively discussed within the research literature over the past few years. However, although signaling protocols between IP routers and optical cross-connect networks have been standardized, large IP backbones are not typically deployed over optical cross-connect networks with automatic reconfigurability features, such as automatic restoration or dynamic establishment of new IP links. One of the most important criteria in determining whether an IP backbone should be carried over such an optical cross-connect network is economic viability. In this article we analyze and explore four architectures for a typical large ISP backbone. In contrast with some other published claims, our results suggest it is more economically attractive to bypass an intermediate cross-connect network, given current equipment and IP backbone network design requirements. However, for ISPs who also provide a large volume of private line services, we propose an integrated architecture for IP over optical cross-connect networks that may provide an attractive alternative for providing rapid and cost-effective restoration from network failures     

采用分级光交换的全光网络成本分析

采用分级光交换的WDM全光网,考虑其端H需求和成本,分类分析了网络业务模式和结构形式,进而提出一般数学模型。由计算得出：采用分级光交换结构的网络可以减少对设备端H数的需求,从而大幅度降低整个网络的成本,如有19个节点的环网可节省65％左右。该模型不仅适用于环网,也适用于环带链、多环以及格状网等结构;不仅可用于集中型、分布型业务模式,还可以延伸到任意的业务模式情况。     

A comparison of the implementation and annual operating costs of IDR and TDMA in the intelsat system

The outcome of a preliminary systems cost study which compares the cost of operating INTELSAT intermediate data rate (IDR) and time division multiple access (TDMA) stations under various conditions is reported. The differences in the annual cost of operating the two candidate methods over the range of 1 to 1000 terrestrial channels are derived under the conditions of no CME, DSI only and the use of DCME. For DCME the effect of one, two, three and four destinations per DCME is considered. The results show that while the initial cost of the TDMA equipment is higher than with IDR, the annual cost of operating the systems is dominated by the space segment costs. For this reason the greater bandwidth efficiency, inherent multidestinational capability and ease of capacity expansion of the TDMA system give it a lower annual operating cost, even at fairly moderate earthstation capacities (e.g. for DCME with two destinations TDMA becomes cheaper than IDR for capacities in excess of about 300 channels). There are attributes of both systems which will also influence the network planners' decision. The IDR system is modular in that costs associated with implementation are incurred more gradually than with the TDMA system. Furthermore, IDR is to a great extent an extrapolation of the current FDM/FM/FDMA practice. However, since the equipment costs are small compared to the space segment charges, it may prove advantageous to adopt the lowercost system as soon as possible. In addition, the TDMA system offers significant long-term advantages of low-cost expansion and the ability to reconfigure the system with minimal or no loss of traffic.     

On Multicast Routing for Wavelength-Routed WDM Networks with Dynamic Membership

Future broadband networks must support integrated services and offer flexible bandwidth usage. In our previous work in [1], we explored the optical link control (OLC) layer on the top of optical layer that enables the possibility of bandwidth on-demand (BoD) service directly over wavelength division multiplexed (WDM) networks. Today, more and more applications and services such as video-conferencing software and Virtual LAN service require multicast support over the underlying networks. Currently, it is difficult to provide wavelength multicast over optical switches without optical/electronic conversions although the conversion takes extra cost. In this paper, based on the proposed wavelength router architecture (equipped with ATM switches to offer O/E and E/O conversions when necessary), a dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks. The goal is to join a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as low as possible. The same algorithm can be applied to other wavelength routing architectures with redefinition of electronic copy cost. The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation.