As optical networks are evolving from traditional opaque networks toward future transparent networks, physical impairments from transmission and switching have become the significant transparent reach limitation for signals. To overcome physical impairments, sparsely deploying optical-electrical-optical regenerators in transparent networks is currently the most economic and reliable solution, namely translucent networks. We study the impairment aware protection issues and propose an impairment aware sharing constraint relaxed path protection (ISRPP) scheme for single-link failures in translucent optical networks. By relaxing the traditional sharing constraint in a limited degree, ISRPP effectively enhances the resource utilization on both wavelengths and regenerators, which contributes to improve the performance of connection blocking probability. Simulation results show that ISRPP can obtain notable resource efficiency and achieve satisfactory tradeoff between blocking probability and vulnerability ratio with respect to its counterpart.
Hybrid waveband/wavelength switching in intelligent optical networks is gaining more and more academic attention. It
is very challenging to develop efficient algorithms to efficiently use waveband switching capability. In this paper, we
propose a novel cross-layer routing algorithm, waveband layered graph routing algorithm (WBLGR), in waveband
switching-enabled optical networks. Through extensive simulation WBLGR algorithm can significantly improve the
performance in terms of reduced call blocking probability.
Checking the great generator's vibration online is difficult because of its strong electric and magnetic field so it needs had better no metal in the sensor. We introduce a method of measuring vibration by using FBG and demodulating it by blazed grating and it doesn't use any metal. We present the design method and the theory of
demodulation. The results of the experiment show that the vibration amplitude of the exciter matches the detected signal under the stable frequency. The experiment also successfully separated the temperature shift and vibration signal.
A novel waveband switching node architecture is proposed using tunable optic filters for arbitrary waveband add/drop. The simulation results show this new architecture achieves lower blocking probability and reduce the scale of ports at switch fabric.
In OBS, JET (Just-Enough-Time) is the classical wavelength reservation scheme. But there is a phenomenon that the burst priority decreasing hop-by-hop in multi-hop networks that will waste the bandwidth that was used in the upstream. Based on the HPI (Hop-by-hop Priority Increasing) proposed in the former research, this paper will do an unprecedented simulation in 4×4 meshed topology, which is closer to the real network environment with the help of a NS2-based OBSN simulation platform constructed by ourselves. By contrasting, the drop probability and throughput on one of the longest end-to-end path lengths in the whole networks, it shows that the HPI scheme can improve the utilance of bandwidth better.
Conventional approaches to QoS (Quality of Service) provisioning in IP networks are difficult to apply in all-optical networks. This is mainly because there is no optical RAM (Random Access Memory) to store packets during contention for bandwidth, so the provision of QoS with OBS (Optical Burst Switching) is a hot issue that has been widely studied. Most of the QoS schemes guarantee the performance of high priority traffic at the cost of low priority traffic's performance. To solve this problem, a novel wavelength assignment scheme for supporting QoS in OBS networks is proposed in this paper, we give the detailed means to increase the priority of the buffed low priority bursts and show it is especially beneficial to improve networks average throughput than that of offset-time-based scheme.
Waveband switching routing is a new problem for research community. It is has some different with the routing of wavelength assign problem. In this paper, we propose a new ideal for agent based Waveband switching network construction. Primary simulation shows that in this way complexity of virtual network topology and blocking probability reduced.
A novel hybrid WDM/TDM optical access network architecture called wavelength shared WDM PON and its media access control mode is proposed. The system is based on a two-stage distribution tree connecting OLT and ONUs.and uses ALOHA protocol for control channel and FIFO scheduler to efficiently assign bandwidth. The packet delay in the system is analyzed and the numerical results demonstrate that the system possesses well performance of packet delay.
Recently, performance evaluation of TCP over Optical Burst-switched Network (OBSN) has drawn more and more attention, but previous work mainly focused on single TCP flow or static traffic model. In this paper, performances of different TCP implementations deployed in OBSN under dynamic competing traffic are investigated.
In this paper, the guideline of wavelength assignment for WDM distribution networks is studied and a novel wavelength assignment algorithm is proposed. The numerical and simulations results demonstrate that this algorithm can improve the system's performance.
Recently, TCP performance over Optical Burst-Switched Networks (OBSN) has drawn more and more attention, but most of previous work were based on small linear network under static traffic, which was much different from the real condition. In this paper, a more realistic OBSN model was set up and dynamic TCP performance over it was investigated with the help of a ns2-based OBSN simulation platform. The impacts of OBSN configuration parameters and different TCP implementations on the overall throughput were discussed.
In this paper, a traffic-grooming problem for multi-granularity traffic of SDH/SONET in WDM grooming mesh networks is investigated. Our objective is to improve the throughput of SDH/SONET WDM mesh networks. We propose a heuristics algorithm to solve this problem. The performances of this traffic grooming heuristics algorithm are evaluated in WDM grooming networks. Finally, we presented and compared the simulation results of this methodology in dynamic traffic grooming WDM mesh networks with that of other methodologies.
KEYWORDS: Global Positioning System, Control systems, Computer simulations, Algorithms, Local area networks, Curium, Surface plasmons, Statistical multiplexing, Standards development
Resilient packet ring (RPR), defined under IEEE 802.17, is a new kind of metropolitan area network technology. Fairness algorithm is one key technology of RPR. Presently, fairness algorithms found in RPR draft and related publications (e.g., DVSR algorithm) have some critical and common limitations, such as oscillation of the allocated bandwidth, high computation complexity or not get high bandwidth utilization. In this paper, we propose a new GPS-based algorithm, FBDRR algorithm, with a view to overcome these limitations. GPS is an ideal scheduling algorithm that can fairly allocate bandwidth to different flows and can also isolate vicious users. Its principle is that when downstream has high demand and make network congested and lost some frames, the low demand traffic from upstream node will has the same loss rate with the downstream one, and if one node does not constrain its stream to its fair share bandwidth, then it can use all of the bandwidth for C class if ring priority scheduling algorithm is used. We analyze the stability of this algorithm. Theoretical analysis and simulation results demonstrate that with this fairness algorithm, each node on the ring can remotely approximate the ideal fair rate for its own traffic at each downstream link, and there is no permanent oscillation, i.e., satisfied stability.
Utilizing optical technologies for the design of packet switches and routers offers several advantages in terms of scal-ability, high bandwidth, power consumption, and cost. However, the configuration delays of optical crossbars are much longer than that of electronic counterpart, which makes the conventional slot-by-slot scheduling methods no longer be-ing the feasible solutions. Therefore, there must find some tradeoff between the empty time slots and configuration overhead. This paper classifies such scheduling problems into preemptive and non-preemptive scenarios, each has its own advantages and disadvantages, and decides whether the traffic in one input queue should be completely transmitted in one switch configuration. Although non-preemptive scheduling is inherently not good at achieving above-mentioned tradeoff, it is shown, however, that the proposed maximum weight matching (MWM) based greedy algorithm is guaranteed to achieve an approximation 2 for arbitrary configuration delay, and with a relatively low time complexity O(N2). For preemptive scheduling, a novel 2-approximation heuristic is presented. Each time in finding a switch configuration, the 2-approximation heuristic guarantees the covering cost of the remaining traffic matrix to have 2-approximation. Simulation results demonstrate that 2-approximation heuristic (1) performs close to the optimal scheduling; (2) outper-forms ADJUST[1] and DOUBLE[3] in terms of traffic transmission delay and time complexity.
In this paper, we propose a novel modified architecture of Optical Burst-Switched Networks, called Reliable Optical Burst Switching (ROBS), which introduces congestion control and retransmission mechanisms of TCP to OBS layer. Design scheme of edge and core nodes for ROBS are both demonstrated. Part of the ROBS function has been implemented on ns-2 platform. Performance improvements due to burst retransmission are simulated and presented.
KEYWORDS: Networks, Failure analysis, Computer simulations, Data transmission, Reliability, Fourier transforms, Error control coding, Local area networks, Telecommunications, Data communications
Resilient Packet Ring (RPR) is a new MAC protocol within metropolitan area network, and Operation, Administration and Maintenance (OAM) function can improve network reliability, simplify network operation and reduce network operating costs. This paper discusses that by sending and receiving OAM control frames OAM function can be implemented in the RPR network. It puts forwards a new hybrid performance management scheme for monitoring the performance on the ring. First an OAM frame is transmitted through the whole ring periodically. If the degradation has happened, the source station can choose serial checking, parallel checking or parallel checking with multicast method to locate the site of the degradation, and consequently QoS is guaranteed. The results of simulations show how to balance bandwidth utilization and station overhead with different methods.
In IEEE 802.17 draft standard, bridging technique is suggested to connect multiple resilient packet rings (RPRs). However, we demonstrate that bridging technology may not be a feasible solution because too much of resources and overhead would be occupied or needed to transmit packets across multiple RPR sub-networks. To construct interconnected RPRs and thus solve bridging related issues, this paper introduces a new kind of RPR nodes, namely, RPR-X nodes, to interconnect multiple RPR sub-networks. In our solutions, standard RPR frame defined by IEEE 802.17 is used to transmit packets on the local RPR sub-network, the extended RPR frame (i.e., cross frame) is used to transmit the packets across different RPR sub-networks. For RPR-X node, it can identify and process both standard RPR frame and extended RPR frame. While for RPR-S node (standard RPR node), it can only identify and process standard RPR frame. Based on the extended definitions of standard RPR frame, we give a detailed design of MAC layer reference model of RPR-X node, and propose an original packet cross forwarding algorithm, with a view to transmitting the packets across multiple RPR sub-networks, and at the same time to guaranteeing the cross forwarding algorithm to be compatible with the standard forwarding procedure of RPR-S node. Theoretical analysis and simulation results demonstrate that the proposed methods perform well in terms of performance metrics such as network's throughput and end-to-end delay.
Based on the scenario that the number of wavelengths may be fixed by upgrading the WDM metro ring networks, this paper proposes a novel WDM slotted-ring architecture with nodes employing one fixed transmitter and a set of fixed receivers. It presents a detailed design and analysis of node architecture and MAC protocol, which aim at guaranteeing fairness to each node and achieving efficient bandwidth utilization. The main advantages of this proposed node architecture and its corresponding MAC protocol can be summarized as: 1) Electronic buffer and process delays can be minimized as the packets will not be processed until they arrive at the destination nodes. 2) No contention will occur at the destination nodes. 3) No tunable components used. 4) No dedicated control channel used to transfer the packets. 5) Packets can be stripped by both destination and source nodes, and there is no need to perform O-E-O conversions. It is shown through theoretical analysis and simulation results how the proposed architecture and MAC protocol can achieve a good throughput, low queuing delay and reasonable packet loss probability. In the case of a large number of wavelengths, or if the number of wavelengths increases by upgrading the networks, this paper further proposes an original design method: employing one fixed transmitter and a set of tunable receivers that can only be tuned among partial continuous wavelengths, we show this method can achieve a good trade-off in terms of performance metrics such as network’s throughput, cost and implementing complexity.
This paper investigates the implementing techniques concerning 2-to-1 node receiver for all-optical packet switching. We point out that the state-of-the-art technologies introduced in the literatures are all associated with one main limitation, i.e., even if two incoming packets are directed to the different ports and thus no contention will occur, they can not be directed to the output ports simultaneously. To overcome this problem, a novel node receiver model is proposed in this paper. This work presents a solution that makes use of fiber delay-lines (FDLs) which allow multiple packets to be concurrently stored or transmitted. With a novel switch control, it is shown that this solution is very efficient to resolve contention, and overcomes the limitation existing in the current models (e.g., Quadro, M-Quadro and COD architectures). We describe and analyze the concrete scheduling of the switches. Simulation results based on bursty and non-bursty traffic scenarios demonstrate that the proposed node architecture (1) performs well in terms of performance metrics such as packet loss probability; (2) has a simple control requirement. In addition, we find that the required number of the recirculating time of the packets is minimal.
This paper focuses on the problem of optical buffer control strategies for recirculation shared optical buffer in optical packet switching. Five control algorithms are presented, and their performances are evaluated and compared by computer simulations. Issues on the optimal configuration of optical buffers are also discussed. The numerical results show that the time delay resolution of fiber delay line has significant influence on the system performance in all three discussed switching mode. The results are valuable in designing the optical packet switch.
In this paper, we investigate the somewhat untraditional approach of contention resolution in WDM optical packet switches. The most striking characteristics of the developed switch architecture are that (1) contention resolution is achieved by a combined sharing of fiber delay-lines (FDLs) and tunable optical wavelength converters (TOWCs); (2) FDLs used for contention resolution is in non-degenerate form, i.e., buffers are achieved by non-uniform distribution of the delay lines; (3) TOWCs just can achieve wavelength conversion in partial continuous wavelength channels, i.e., sparse wavelength conversion. We describe and analyze the concrete configuration of FDLs and TOWCs under non-bursty and bursty traffic scenarios. Simulation results demonstrate that for a prefixed packet loss probability constraint, e.g., 10-6, the developed architecture provides a different point of view in the optical packet switching (OPS) design. That is, combined sharing of FDLs and TOWCs can, effectively, obtain a good tradeoff between the switch size and the cost, and TOWCs which are achieved in sparse form can also decrease the implementing complexity.
It has been proved that through burst segmenting, and thus dropping the segment of one burst that is overlapped with another burst, the packet loss probability will be significantly improved for optical burst switched networks. Based upon this, two main segment dropping strategies, head- and tail-dropping, can be used to resolve contention. In this paper, we point out that tail-dropping policy, which is adopted in most literatures, may not be a feasible solution, while head-dropping policy, even though it may make the packets to arrive out of order, is in deed a solution which can resolve the contention effectively. Moreover, with respect to tail-dropping policy, the increase of the disorder of packet arrivals for head-dropping policy is trivial. To support service differentiation and decrease the disorder of packet arrivals generated by contention resolution, we further propose a new threshold-based hybrid-assembly scheme. The most striking characteristic of the hybrid-assembly scheme is that the low and high packet classes are aggregated into one burst simultaneously. Once contention occurs, head-dropping policy is adopted to drop the overlapping packets. We describe the concrete implementation of QoS supporting, and the corresponding dropping strategy -- improved head-dropping policy, which aims at guaranteeing a better QoS support and a feasible implementation, is also detailed. Simulation results demonstrate that the proposed burst assembly scheme, together with the head-dropping policy, perform well in terms of performance metrics such as the average packet loss probability and service differentiation.
A novel, simple and controllable bandwidth allocation scheme, called bandwidth on Demand (BoD), is proposed for optical burst-switched network in this paper. It assures every service class to consume bandwidth no more than its granted percentage by examining the bandwidth usage of each class periodically. The burst loss ratios under arbitrary input loads are theoretically analyzed as well as numerically simulated. The theoretical descriptions accord with the simulated results very well. The scheme can be used as an effective scheme of bandwidth allocation and management.
As a new solution of all optical networks, Optical burst switching (OBS) has been wildly studied in recently years for its high traffic throughput and high resource utilization at current technology level. In this paper we address some issues of efficient contention resolution: burst segmentation and deflection routing. Under the Just-Enough-Time (JET) protocol based OBS networks architecture, control packet is the guider for corresponding data burst during the transmission. Taking these into consideration, here we propose a novel segmentation strategy - current burst segmentation (CBS) and a modified deflection routing strategy fit for JET based OBSN. Through analysis and simulation, it is shown that these new strategies perform well.
Integrated routing is a routing approach to support the peer interconnection model in IP over WDM networks. To have a better network link load distribution and network usage in IP over WDM networks, in which network nodes may have the ability to handle traffic in fine granularities, it is important to take into account the combined routing at the IP and WDM layers. Based upon this, this paper develops an algorithm for integrated dynamic routing of bandwidth guaranteed paths in IP over WDM networks. For newly dynamic arriving requests, as the developed algorithm takes into account the combined topology and resource usage information at the IP and WDM layers, and the routing procedure makes full use of the statistic information of the users’ bandwidth requirement and considers carefully both the routing cost and the corresponding length of the routing path, thus a better link load balancing and network usage can be achieved. Simulation results show that the developed scheme performs well in terms of performance metrics such as the number of rejected demands and the network link load balancing.
Resilient Packet Ring (RPR) is an emerging network architecture and technology designed to meet the requirements of packet-based metropolitan area network (MAN). IEEE 802.17 RPR Draft Standard[1] defines RPR dual-ring topology discovery protocol. In this paper, we propose a new RPR multi-ring interconnected network. RPR multi-ring interconnected network has better resource availability and better bandwidth utilization than RPR dual-ring topology. So how to extend RPR dual-ring topology to RPR multi-ring interconnected network really deserves our attention. RPR multi-ring network is formed by decreasing the scale of standard RPR and interconnecting several small scale standard RPR rings together through cross-stations. The new topology discovery algorithm uses the method of multi-layer subnet topology discovery in clockwise implemented by the multi-ring automatic topology discovery module in cross-station’s MAC control layer. Furthermore, we bring forward the unit structure of tree-like bi-direction list and of topology information list. The paper mainly contains the two parts: RPR standard topology discovery algorithm and RPR multi-ring interconnected topology discovery algorithm.
In this paper we investigate the fairness problem of offset-time-based quality of service (QoS) scheme proposed by Qiao and Dixit in optical burst switching (OBS) networks. In the proposed schemes, QoS relies on the fact that the requests for reservation further into the future, but for practical, benchmark offset-time of data bursts at the intermediate nodes is not equal to each other. Here, a new offset-time-based QoS scheme is introduced, where data bursts are classified according to their offset-time and isolated in the wavelength domain or time domain to achieve the parallel reservation. Through simulation, it is found that this scheme achieves fairness among data bursts with different priority.
In this paper, inefficiencies of the QoS scheme based on extra-offset-time-based priority for variable-length optical burst-switched network were pointed out, and a novel fixed-length burst assembly scheme is proposed. This scheme is not only practical, but also able to decrease the latency of bursts at the edge nodes. Compared to variable-length (traditional) scheme, a smaller blocking probability for the highest priority service and almost one third offset time delay for every class were obtained in fixed-length scheme.
P-cycle based protection has been proved to be an effective way for WDM networks’ survivability design. In IP over WDM networks, p-cycle can also be constructed through GMPLS technology to protect a number of IP links. In this paper, we demonstrate that there are some drawbacks associated with the current p-cycle searching algorithms, e.g., 1) none of the them take the hop-count constraint into account, which means some requests may not able to be protected by their associated p-cycles; 2) to protect those failures occurred on the straddling links, the algorithms demand the traffic to be split in half over each p-cycle segment, which may not be a resource efficient solution, and the routing procedure may be prohibited by hop-count constraints, also, it may introduce extra link propagation delays and causes IP packets to arrive out of order. We propose an improved object function, and give a novel p-cycle searching algorithm. Simulation results obtained from CERNET-like physical topology and the national backbone networks show that the developed algorithm performs well in terms of performance metrics such as the connection blocking probability and the success rate of the protection.
The problem of integrated routing in multifiber IP over WDM networks is studied in this paper. To solve this problem, a layered-graph is constructed and an algorithm, called integrated cost-based shortest path (ICSP) algorithm, is then proposed. ICSP can not only balance the traffic uniformly but also make a dynamic tradeoff between all the links in the layered-graph. A parameter rl is introduced to characterize the resource richness of an IP over WDM Network. Simulation results show that ICSP outperforms other algorithms significantly in terms of blocking probability in all the cases we studied, and the performances of other algorithms are affected by rl greatly. Because a multifiber network can be functionally equivalent to a single fiber network with limited wavelength conversion (WC), we make the first known attempt to investigate the impact of WC on dynamic integrated routing by studying the multifiber networks. Results show that the effect of WC depends on the granularities of label switched path (LSP) requests. If the granularity of each request is large, WC will improve the network performance; if the granularity of each request is small, WC will worsen the performance.
In this paper, two switch models -- MOD1, employs a set of nondegenerate fiber delay-lines (FDLs) shared among the input lines, and MOD2, employs a set of degenerate FDLs and tunable wavelength converters (TOWCs) shared among the input lines, are proposed to handle contention. We demonstrate that for a prefixed packet loss probability constraints, e.g., 10-6, and for nonbursty traffic, if the wavelengths per fiber is no less than 8, a very small number of FDLs is sufficient to obtain a reasonable packet loss probability for both models, i.e., without the need to use TOWCs for MOD2, used for MOD1 equals to those of the FDLs and TOWCs used for MOD2, MOD2 performs much better than MOD1 even if no TOWC is used. With the increase of the average burst length, the number of TOWCs needed by MOD2 needs to be increased so as to maintain a reasonable packet loss probability. However, even for the traffic with high degree of burstness, MOD2 is still a cost effective and robust solution.
This paper proposes a new 2x1 node receiver architecture for all-optical packet switched networks, whose basic principle can be extended to construct a larger buffer if more 2x2 switches and fiber delay lines (FDLs) are available. The most striking characteristic of the architecture is that the buffer is achieved by a combined use of feed-forward and feedback FDLs. We describe and analyze the concrete two-stage FDL architecture which is the cheapest and simplest multi-stage solution. As for control strategy, we demonstrate that bottom control strategy (BCS), which uses FDL that is arranged in the feed-forward form when both feed-forward and feedback FDLs are available, is a more robust solution against bursty and non-bursty traffic. Simulation results show that the developed scheme (1) performs well in terms of performance metrics such as packet loss probability; (2) has a simpler control requirement and a better packet loss probability than M-Quadro architecture.
In this paper, we analyze the drawback of tail-dropping contention resolution in optical burst switched networks. Once contention occurs, we adopt modified head-dropping policy to resolve contention. This policy drops the head of the contending burst only if the overlapping region of the two bursts is less than the whole contending burst size, otherwise drops the whole contending burst. In order to have a better support of differentiated service, a new burst assembly policy, namely, Priority-based Proportional Mixed Burst Assembly, is proposed. Simulation results show that the proposed scheme performs very well in terms of performance metrics such as the times of contention and packet loss probability.
To obtain the partial information of network's resources, which indicates what fraction of each link's bandwidth, is currently used by working paths, and is used by protection paths, is feasible in IP over WDM networks using Multi-Protocol Label Switching (MPLS) technology. Based upon this partial information scenario, this paper proposes a new integrated dynamic routing algorithm of path-based protection design for IP over WDM networks. For working paths selection, the algorithm makes a tradeoff between the routing costs and the corresponding routing path length. While for protection paths, a tradeoff between the sharing of the protection paths and the associated routing path length is made. We find that the developed routing scheme is beneficial to achieve a good link load balancing. Simulation results show that the developed algorithm performs well in terms of performance metrics such as the number of rejected requests and the network link load balancing.
In this paper, we propose a new threshold-based mixed-assembly technique with QoS support in optical burst switched networks. The most striking characteristic of the mixed-assembly policy is that both the low and high packet classes are aggregated into one burst simultaneously. Once contention occurs, there will be an overlap between the tail of the earlier arriving burst and the head of the contending burst. Combing with burst segmentation technique, we drop the tail of the earlier arriving burst that is mainly made up of low priority packets, thus the packet loss probability of the high packet classes will be guaranteed. Simulation results show that the proposed burst assembly scheme performs well in terms of performance metrics such as the average packet loss probability and the packet loss probability of the high class of traffic.
In Optical Burst Switched (OBS) networks, the requirements on packet loss probability vary for different class users. In order to meet different packet loss probability demands, besides the traditional methods to support Differentiated services (DiffServ) by resource allocation and contention resolution, the scheduling of control
packets should also support DiffServ. A new type of scheduling strategy, Priority-based Weight Fair Queuing (PWFQ) scheduling strategy, is proposed. An equivalent analysis model is also presented to simplify the solving process of scheduling weight of each class. We also define a parameter, normalized deviation factor, to evaluate
the validity of our analysis model as well as the fairness of scheduling strategy on supporting DiffServ. Numerical results confirm that, it is feasible to analyze queue system, in which PWFQ scheduling strategy is adopted, with our equivalent model. At the same time, it confirms that our scheduling strategy performs well on providing fair DiffServ in terms of packet loss probability.
In this paper, a priority-based wavelength assignment algorithm, Dynamic Threshold Method (DTM), is proposed. A set of wavelengths, Preferred Wavelength Set (PWS), is pre-allocated for each priority request. Based on the usage of wavelength in the PWS of a priority request, a threshold is dynamically calculated to decide whether the wavelengths for the higher priority request can be allocated to the lower. By using DTM, the blocking probability of the high priority request is guaranteed to be a lower degree, and at the same time performance of the low priority request is improved. So the network's average blocking probability is minimized. Simulation results of the network performance show that the proposed algorithm performs well in different dynamic traffic load situation.
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