An optical IM/FSK coding technique for the implementation of a label-controlled arrayed waveguide packet router

In this paper, we present a new concept of optical packet/burst switching suitable for generalized multiprotocol label switched (GMPLS)-based optical networks. In such networks, optical labeled switched paths are being established in a similar way as label-switched paths in MPLS. We use a wavelength label as well as an orthogonally modulated label, with respect to the payload modulation format, and which is encoded using either frequency-shift keying (FSK) or differential phase-shift keying (DPSK). Wavelength is used for switching in the node, whereas the orthogonal label defines the label-switched path. We present both simulation and experimental results to assess transmission performance of the proposed combined modulation scheme. In addition, we propose a suitable optical node architecture that can take advantage of this stacked label concept. Toward this, we use widely tunable wavelength converters to efficiently route IM/FSK (or IM/DPSK) optically labeled packets in an arrayed-waveguide grating (AWG)-based node structure. We present performance simulation results in terms of packet loss ratio and internal block probability. Internal blocking is an inherent problem of AWG optical routers, and a specific wavelength assignment algorithm has been developed to minimize it. Finally, the feasibility of IM/FSK transmission is experimentally demonstrated over an 88-km single-mode fiber span, and novel aspects of FSK generation and detection techniques are presented.     

A 1+1 protection architecture for optical burst switched networks

High-capacity optical backbone networks protect their premium customers' information flows by routing two copies of the customer's data over disjoint paths. This scheme, known as 1+1 protection, provides extremely rapid recovery from network failures. We propose an architecture by which 1+1 protection can be extended to optical burst switched (OBS) networks. This architecture is designed by modifying the diversity routing architecture that was originally proposed for nonoptical packet networks and recently applied to networks employing the generalized multiprotocol label switched (GMPLS) architecture. We extend the architecture developed for just-in-time OBS signaling to support 1+1 protection. We also examine design issues that are raised by a difference in the propagation delays of the two disjoint paths across the OBS network. We show that a sufficiently large difference in the propagation delays can cause performance degradations that may result in an unsatisfactory quality-of-service on the protected connection. We examine the impact of this delay mismatch on restoration performance, probability of burst loss, and jitter. Through analysis and simulations, it is discussed how these negative effects can be eliminated.     

基于正交调制PolSK/Inverse-RZ的光标记技术

光标记技术是一种实现光分组交换的重要技术.文章提出并用实验验证了一种基于正交调制PolSK/Inverse-RZ的新型光标记方案,该方案用Inverse-RZ作载荷信号,用PolSK作标记信号.由于Inverse-RZ信号在比特"1"和比特"0"时都具有光功率,在PolSK信号检测时信息一直保持着,因此通常使用ASK信号标记的技术在消光比方面的限制被解决了.     

Network Design and Cost Optimization for Label Switched Multilayer Photonic IP Networks

Dealing with the explosive increase in the amount of Internet traffic requires high-speed and huge capacity Internet protocol (IP) backbone networks. Existing IP backbone networks are constructed using point-to-point wavelength-division-multiplexing (WDM) transmission systems, where all the wavelengths are terminated link-by-link, so that rather expensive optical/electrical conversions are necessary at every node. In these systems, since every IP packet is routed at each intermediate node based on the header information, a header processing bottleneck will occur when the node input traffic exceeds several hundreds of gigabits per second. In order to mitigate these problems, an optical cross-connect (OXC) function that employs wavelength routing of the optical paths (OPs) will provide an effective solution. This paper proposes a network design method where electrical and photonic multiprotocol label switching (MPLS) technologies are used; the network is referred to as a photonic IP network. We first propose new algorithms that minimize the network cost in a multilayered network comprising electrical label switched paths (LSPs) and optical LSPs (optical paths that are controlled using the MPLS mechanism). The particular point of the proposed algorithms is that they include different cost minimization scenarios appropriate for the different OLSP provisioning conditions that are chosen as the first step in the design stage. The effectiveness of the proposed algorithms and the benefits of the OLSPs are quantitatively evaluated through various simulations.     

Optical CDMA for All-Optical Sub-Wavelength Switching in Core GMPLS Networks

Generalized multi-protocol label switching (GMPLS) is a multipurpose control-plane paradigm that extends the MPLS scheme allowing switching without recognizing packet boundaries. In this paper, we present a novel extension that exploits a new physical layer for switching in optical GMPLS. The proposed extension is achieved through adding an optical code switching layer, or code switch capable (CSC) layer, to the existing label mapping layers. Our proposal enables finer granularity at sub-wavelength level in all-optical GMPLS core switches, resulting in significant enhancements to traffic isolation capabilities for all-optical GMPLS core switches. We employ mathematical analysis to derive performance bounds for the proposed scheme, from both the labeling capacity and network throughput points of view. We use our analytical model to derive several optimum operating points for the network, and show that our techniques significantly improve the overall performance of all-optical core networks     

Study on a joint multiple layer restoration scheme for IP over WDM networks

In this article we investigate the problem of a restoration scheme for IP over WDM networks. Network reliability is gaining importance with the huge volume of traffic carried by such networks. Providing survivability at the optical layer is inherently attractive, but raises many questions and challenges, given the characteristic of optical aggregated lightpath and relatively coarse traffic granularity. The emergence of MPLS and its extension, MP/spl lambda/S, opens up new possibilities for developing simple integrated protection/restoration schemes that can be coordinated at both the IP and optical layers . This article first presents an overview of existing MPLS/MP/spl lambda/S recovery mechanisms. Then we propose a joint two-layer recovery scheme for IP-centric WDM-based optical networks where the optical layer takes the recovery actions first, and subsequently the upper IP layer initiates its own recovery mechanism, if the optical layer does not restore all affected services. A simulation-based analysis shows the benefits of the proposed two-layer recovery scheme over single-layer recovery schemes. We demonstrate the advantages of finer granularity in IP layer recovery and the effectiveness in speed on the optical layer. The impact of several network parameters on recovery performance is also studied in the paper.     

A New Analytical Model of Shared Backup Path Provisioning in GMPLS Networks

As GMPLS and its supporting set of protocols develop into aviable control plane for optical networks, an important function that they will need to support will be the protection and restoration function that has been a major feature of legacy optical networks. A network with a robust set of protection and restoration mechanisms will be able to support data traffic while allowing faster recovery from failures than can be obtained using layer 3 rerouting. Several models have been proposed for protection with GMPLS using shared backup paths. This previous work has not investigated the effect on recovery time critical to the service or the number of backup paths that are required to meet a desired level of performance. Using both restoration time and recovery blocking probability, we have developed a new analytic model for GMPLS-based recovery in M : N protection groups. Furthermore, we show that smaller backup paths can be reserved by capturing the effect of multiple failures in the case of M : N shared protection with revertive mode in an optical network with a GMPLS control plane.     

Study of LSP arrangement schemes in label switch networks

Label switch paths (LSP) are regarded as the routing components of an end‐to‐end connection in label switching network from the traffic engineering point of view. Thus, an end‐to‐end connection may travel more than one LSP. The QoS of this end‐to‐end connection relies on the performance of each LSP it travels. Therefore, to carefully arrange LSP is an essential step towards QoS networks. Generally speaking, the capacity of a specific link is not allocated for high‐priority LSP because it will cause inflexibility in the scheduling process. In this paper, the best‐fit shortest path (BSP) assignment and the worst shortest path (WSP) assignment schemes are proposed for the arrangement of label switch paths. In order to provide flexibility in packet scheduling, we propose that the BSP scheme to be applied for allocation of low‐priority LSP and the WSP scheme is used for the arrangement of LSP with high priority. Based on these two schemes, we extend them with elastic bandwidth allocation to prevent the bandwidth of the link from being occupied by the higher priority LSP. The experimental results indicate that, compared to the BSP‐only scheme, the proposed hybrid scheme demonstrates a more efficient way of arranging prioritized LSP. Moreover, the proposed elastic constrained bandwidth allocation scheme also illustrates a rather good performance in smoothing the link utilization of high‐priority LSP. Copyright © 2005 John Wiley & Sons, Ltd.     

多协议副载波/波长标签交换技术方案

通过多协议波长交换MtS(Multi-Protocol Lainbda Switching)技术向副载波域的延伸,该文提出了一种全新的宽带光网络技术方案以期实现电视网与Internet网的高效融合基于副载波标签和交换接口的多协议副载波/波长标签交换网络。利用新型复合标签,在独特的副载波/波长双层交换结构的基础上,实现了多层互动的流量工程和灵活的服务质量QoS(Quality of Service)保证,有效利用了波长资源。同时给出了双层标签交换机的框架结构,分析了其性能,并指出了该方案面临的关键问题及相关解决途径。     

A Pre-Planned Local Repair Restoration Strategy for Failure Handling in Optical Transport Networks

Automatic provisioning and recovery of lightpaths with selectable traffic engineering policies are considered basic features of near future optical transport networks (OTN). Worldwide researchers recognize generalized multi-protocol label switching (GMPLS) architecture as the viable control plane solution to achieve these issues in OTN. Growing effort is ongoing to find new recovery models for handling failure conditions in the networks, trying to set up alternative strategies to classical heavy-cost SDH/SONET protection techniques. In this paper, a pre-planned local repair recovery strategy is described. Allocation of primary paths is provided using the interference concept, in order to set a threshold between resources dedicated to working paths and those allocable for local backups in case of failure. Tests of the strategy are shown for a sample national optical transport network, aimed at valuing local-repair recovery times at different failure location and seriousness.     

Hierarchical cache design for enhancing TCP over heterogeneous networks with wired and wireless links

TCP is a reliable transport protocol tuned to perform well in traditional networks made up of links with low bit-error rates. Networks with higher bit-error rates, such as those with wireless links and mobile hosts, violate many of the assumptions made by the transmission control protocol (TCP), causing degraded end-to-end performance. We propose a two-layer hierarchical cache architecture for enhancing TCP performance over heterogeneous networks with both wired and wireless links. A new network-layer protocol, called new snoop (NS), is designed. The main idea is to cache the unacknowledged packets at both the mobile switch center (MSC) and base station (BS), to form a two-layer cache hierarchy. If a packet is lost due to transmission errors in the wireless link, the BS takes the responsibility to recover the loss. When a handoff occurs, the packets cached at the MSC can help to minimize the latency of retransmissions due to temporal disconnection. NS can preserve the end-to-end TCP semantics and is compatible with existing TCP applications. Its implementation only requires code modification at the BS and MSC. Simulation results show that NS is significantly more robust in dealing with unreliable wireless links and handoffs as compared with the original snoop scheme, as well as some other existing TCP enhancements.     

A Co-optimization Routing Algorithm in Wireless Sensor Network

The MACORA is presented to solve the collision between mobile agent and multicast suppression in channel competitive process. With two-layer graph model, the channel converter problem in the dual-channel wireless sensor networks can be simplified into a routing problem over the two-layered graph, so we can search for routes in the control plane and transport traffic in the data plane synchronously. Then, the control plane and the data plane are integrated into a two-layered network, and searching for route for each traffic in the two-layer networks synchronously. The MACORA can make full use of the idle resource in different layers, this strategy deals with the collision between mobile agent and multicast suppression in channel competitive process well, so the blocking probability of networks and the error rate of packet transmission can be cut down. Simulation results show that the MACORA performs better in improving success rate of packet transmission.     

Novel scheme for packet forwarding without header modifications in optical networks

We present a novel scheme for packet forwarding in optical packet-switched networks and we further demonstrate its good scalability through simulations. The scheme requires neither header modification nor any label distribution protocol, thus reducing component cost while simplifying network management.     

Demonstration of all-photonic spectral label-switching for optical MPLS networks

All-photonic label-switching of weight four spectral packet labels (concurrent quadruple wavelength conversion) is demonstrated for optical multiprotocol label-switching networks. The experimental setup is based on cross-gain modulation in a fiber ring laser using a semiconductor optical amplifier gain medium and uses commercially available components. Static transfer functions and step response measurements for various input-output label-switching combinations show that a noisy input label with small extinction ratio can be switched to a clean, amplified, output label.     

CFR: A cooperative link failure recovery scheme in software‐defined networks

Software‐defined networking that separates the control plane from the data plane is envisioned as a promising technology to enable resilient and flexible network management. Tolerating link failures is a fundamental problem in enhancing such network resilience in software‐defined networking. Reactive and proactive fault tolerant schemes for conventional networks may not well balance the fault recovery time and network performance, since the proactive scheme typically underutilizes resources and the reactive scheme usually incurs a longer recovery time. In this paper, we propose a cooperative link failure recovery scheme to find a fine‐grained trade‐off between resource utilization and recovery time by combining reactive and proactive methods. We formalize the problem of link failure recovery as a multiobjective optimization problem and devise a 2‐stage algorithm for it. The first stage of the algorithm guarantees connectivity restoration in an acceptable recovery interval based on fast failover feature supported in OpenFlow protocol, meanwhile it assigns virtual local area network tags to back up paths for achieving a lower memory consumption. The second stage of the algorithm guarantees the quality of service for different applications by adjusting the backup paths after rapid connectivity restoration. Extensive simulations highlight that cooperative link failure recovery scheme can satisfy both the carrier‐grade recovery requirements and quality of service requirements in terms of delay and network bandwidth.     

FB-banyans and FB-delta networks: Fault-tolerant networks for broadband packet switching

Many fast packet switches for the broadband integrated services digital network (BISDN) in the literature are based on banyan networks. Although banyan networks possess nice properties such as a simple control and a low hardware cost, they are unique-path networks. Since there is a unique path from an input to an output in a banyan network, a single component failure may disrupt services of some nodes connected to such a network. Moreover, banyan networks are also blocking networks; packets can be lost within the networks. To reduce the packet loss, buffered banyan networks can be used. In an earlier work we have proposed the addition of backward links to otherwise unidirectional banyan networks to create B-banyans (and B-delta networks). Backward links not only function as implicit buffers for blocked packets, but also provide multiple paths for each input-output connection. However, the multiple paths in B-banyans may not be disjoint. In this paper, we enhance B-banyans and B-delta networks in such a way that the resulting networks can provide disjoint multiple paths for each input-output pair. The existence of disjoint multiple paths has a significant effect on the network fault-tolerance. The new networks, called FB-banyans and FB-delta networks, are k fault-tolerant, where k is the number of backward links per switch and is less than the switch size. They are also robust to more than k faults, depending on the locations of faults. The maximal fault-tolerance is achieved when k is the switch size minus 1. The performance of the new networks is analysed and compared to that of other networks of interest. FB-banyans and FB-delta networks can be used as a switch fabric for fast packet switches to provide performance comparable to that of buffered banyan networks and good fault tolerance.     

Seamless session mobility scheme in heterogeneous wireless networks

The next generation wireless communication system will likely be heterogeneous networks, as various technologies can be integrated on heterogeneous networks. A mobile multiple‐mode device can easily access the Internet through different wireless interfaces. The mobile multiple‐mode device thus could switch to different access points to maintain the robustness of the connection when it can acquire more resources from other heterogeneous wireless networks. The mobile multiple‐mode device therefore needs to face the handover problem in such environment. This work introduces Session Initiation Protocol (SIP)‐based cross‐layer scheme to support seamless handover scheme over heterogeneous networks. The proposed scheme consists of a battery lifetime‐based handover policy and cross‐layer fast handover scheme, called the SIP‐based mobile stream control transmission protocol (SmSCTP). This work describes the major idea of the proposed scheme and infrastructure. The proposed scheme has been implemented in Linux system. The simulation and numerical results demonstrate that the proposed SmSCTP scheme yields better signaling cost, hand‐off delay time, packet loss and delay jitter than SIP and mSCTP protocols. Copyright © 2010 John Wiley & Sons, Ltd.     

Scheduling algorithms for shared fiber-delay-line optical packet Switches-part II: the three-stage clos-network case

In all-optical packet switching, packets may arrive at an optical switch in an uncoordinated fashion. To prevent packet loss in the switch, fiber delay lines (FDLs) are used as optical buffers to store optical packets. However, assigning FDLs to the arrival packets to achieve high throughput, low delay, and low loss rate is not a trivial task. In the authors' companion paper, several efficient scheduling algorithms were proposed for single-stage shared-FDL optical packet switches (OPSs). To further enhance the switch's scalability, this work was extended to a multistage case. In this paper, two scheduling algorithms are proposed: 1) sequential FDL assignment and 2) multicell FDL assignment algorithms for a three-stage optical Clos-Network switch (OCNS). The paper shows by simulation that a three-stage OCNS with these FDL assignment algorithms can achieve satisfactory performance.     

MPLS security: an approach for unicast and multicast environments

Multi-Protocol Label Switching (MPLS) network architecture does not protect the confidentiality of data transmitted. This paper proposes a mechanism to enhance the security in MPLS networks by using multi-path routing combined with a modified (k, n) threshold secret sharing scheme. An Internet Protocol (IP) packet entering MPLS ingress router can be partitioned into n shadow (share) packets, which are then assigned to maximally node disjoint paths across the MPLS network. The egress router at the end will be able to reconstruct the original IP packet if it receives any k share packets. The attacker must therefore tap at least k paths to be able to reconstruct the original IP packet that is being transmitted, while receiving k???1 or less of share packets makes it hard or even impossible to reconstruct the original IP packet. In this paper, we consider the multicast case in addition to the unicast. To our best knowledge, no work has been published for MPLS multicast security. We have implemented our model and measured its time complexity on variable packets size.     

Interleaved coding and sequential transmission scheme for packet‐level forward error correction over burst loss channels

Burst packet loss is a common problem over wired and wireless networks and leads to a significant reduction in the performance of packet‐level forward error correction (FEC) schemes used to recover packet losses during transmission. Traditional FEC interleaving methods adopt the sequential coding‐interleaved transmission (SCIT) process to encode the FEC packets sequentially and reorder the packet transmission sequence. Consequently, the burst loss effect can be mitigated at the expense of an increased end‐to‐end delay. Alternatively, the reversed interleaving scheme, namely, interleaved coding‐sequential transmission (ICST), performs FEC coding in an interleaved manner and transmits the packets sequentially based on their generation order in the application. In this study, the analytical FEC model is constructed to evaluate the performance of the SCIT and ICST schemes. From the analysis results, it can be observed that the interleaving delay of ICST FEC is reduced by transmitting the source packets immediately as they arrive from the application. Accordingly, an Enhanced ICST scheme is further proposed to trade the saved interleaving time for a greater interleaving capacity, and the corresponding packet loss rate can be minimized under a given delay constraint. The simulation results show that the Enhanced ICST scheme achieves a lower packet loss rate and a higher peak signal‐to‐noise‐ratio than the traditional SCIT and ICST schemes for video streaming applications.