Lightpath Re-optimization in mesh optical networks

Intelligent mesh optical networks deployed today offer unparalleled capacity, flexibility, availability, and, inevitably, new challenges to master all these qualities in the most efficient and practical manner. More specifically, demands are routed according to the state of the network available at the moment. As the network and the traffic evolve, the lightpaths of the existing demands becomes sub-optimal. In this paper we study two algorithms to re-optimize lightpaths in resilient mesh optical networks. One is a complete re-optimization algorithm that re-routes both primary and backup paths, and the second is a partial re-optimization algorithm that re-routes the backup paths only. We show that on average, these algorithms allow bandwidth savings of 3% to 5% of the total capacity in scenarios where the backup path only is re-routed, and substantially larger bandwidth savings when both the working and backup paths are re-routed. We also prove that trying all possible demand permutations with an online algorithm does not guarantee optimality, and in certain cases does not achieve it, while for the same scenario optimality is achieved through re-optimization. This observation motivates the needs for a re-optimization approach that does not just simply look at different sequences, and we propose and experiment with such an approach. Re-optimization has actually been performed in a nationwide live optical mesh network and the resulting savings are reported in this paper, validating reality and the usefulness of re-optimization in real networks.     

Diverse routing in optical mesh networks

We study the diverse routing problem in optical mesh networks. We use a general framework based on shared risk link groups to model the problem. We prove that the diverse routing problem is indeed NP-complete, a result that has been conjectured by several researchers previously. In fact, we show that even the fiber-span-disjoint paths problem, a special case of the diverse routing problem, is also NP-complete. We then develop an integer linear programming formulation and show through numerical results that it is a very viable method to solve the diverse routing problem for most optical networks found in many applications which typically have no more than a few hundred nodes and fiber spans.     

极低误码下的误码率估计问题

在极低误码率的情况下由于测得的误码点很少,由实测的点来直接估计误码率这一方法变得不可靠。本文提出一种方法,通过牺牲测量值的精度来换取结果的可靠性,即用误码率的上界来描述误码特性。本文还给出了误码率的上界、实际测量得到了误码点数和表示误码率上界可靠性的门限值之间的定量关系。     

Uniform waveband assignment in optical mesh networks

The cost of an optical network in wavelength division multiplexing (WDM) networks can be reduced using optical reconfigurable optical add/drop multiplexers (ROADMs), which allow traffic to pass through without the need for an expensive optical-electro-optical (O-E-O) conversion. Waveband switching (WBS) is another technique to reduce the network cost by grouping consecutive wavelengths and switching them together using a single port per waveband. WBS has attracted the attention of researchers for its efficiency in reducing switching complexity and therefore cost in WDM optical networks. In this paper, we consider the problem of switching wavelengths as non-overlapping uniform wavebands, per link, for mesh networks using the minimum number of wavebands. Given a fixed band size b _s , we give integer linear programming formulations and present a heuristic solution to minimize the number of ROADMs (number of wavebands) in mesh networks that support a given traffic pattern. We show that the number of ROADMs (or number of ports in band-switching cross-connects) can be reduced significantly in mesh networks with WBS compared to wavelength switching using either the ILP or the heuristic algorithm. We also examine the performance of our band assignment algorithms under dynamic traffic.     

Generalized loop-back recovery in optical mesh networks

Current means of providing loop-back recovery, which is widely used in SONET, rely on ring topologies, or on overlaying logical ring topologies upon physical meshes. Loop-back is desirable to provide rapid preplanned recovery of link or node failures in a bandwidth-efficient distributed manner. We introduce generalized loop-back, a novel scheme for performing loop-back in optical mesh networks. We present an algorithm to perform recovery for link failure and one to perform generalized loop-back recovery for node failure. We illustrate the operation of both algorithms, prove their validity, and present a network management protocol algorithm, which enables distributed operation for link or node failure. We present three different applications of generalized loop-back. First, we present heuristic algorithms for selecting recovery graphs, which maintain short maximum and average lengths of recovery paths. Second, we present WDM-based loop-back recovery for optical networks where wavelengths are used to back up other wavelengths. We compare, for WDM-based loop-back, the operation of generalized loop-back operation with known ring-based ways of providing loop-back recovery over mesh networks. Finally, we introduce the use of generalized loop-back to provide recovery in a way that allows dynamic choice of routes over preplanned directions     

二阶偏振模色散高速光纤通信的影响及补偿

讨论了二阶偏振模色散对光脉冲的影响,模拟结果表明,二阶偏振模色散对信号影响起主要作用的是去偏振项,使得信号波形边缘出现能量过冲;同时也讨论了二阶偏振模色散补偿的方法,利用二段偏振模色散补偿器对二阶偏振模色散进行了有效的补偿,并给出了补偿的实验结果.     

Path enumeration and hot-potato routeing analysis in multihop networks

Using a labelling of the edges of the network graph for a multihop network and a Taylor series expansion of the transfer function of the resulting signal flow graph, we calculate the number of paths of a given length in the multihop network. The derivative of the transfer function and a fixed point algorithm yield the average delay as a function of the packet arrival rate.     

H.263甚低码率视频编码标准的码率控制方法

主要提出ＩＴＵ组织的Ｈ．２６３甚低码率视频压缩编码标准输出码率的控制方案。着重分析了一种通过调整宏观量化器的量化参数来控制Ｈ．２６３编码器输出码率的方法,它能满足在ＰＳＴＮ网上低时延中的码率输出要求。     

Analytical evaluation of improved access techniques in deflectionrouting networks

This paper presents an extension of a known analytical model for the performance evaluation of nonpriority deflection routing networks in uniform traffic. The extension allows the analysis of improved access techniques. The key features of the analytical technique are described by casting it in a very simple setting: nonpriority hot-potato in a two-connected slotted shufflenet (SN) network. Results are presented for three access techniques: transmit-no-hold (TXNH), transmit-hold (TXH), and bypass queuing (BQ)     

瞬态时频内插极低速率图像压缩编码

结合图像信号瞬变、渐变和缓变的特点,从图像信号瞬态非平稳分析与重构角度出发,提出了具有瞬态分析、参数内插和时频重构特点的瞬态时频内插极低速率图像压缩编码方案。瞬态时频分析理论的应用,为今后图像信号处理研究提供了一种新的思路。     

Protecting multicast sessions in WDM optical mesh networks

Recent advances in wavelength-division-multiplexing (WDM) technology are expected to facilitate bandwidth-intensive multicast applications. However, a single fiber (bundle) cut on such a network can disrupt the transmission of information to several destination nodes on a "light tree"-based multicast session. Thus, it is imperative to protect multicast sessions e.g., by reserving resources along backup trees. We show that, if a backup tree is directed-link-disjoint to its primary counterpart, then data loss can be prevented in the event of any single link failure. We provide mathematical formulations for efficient routing and wavelength assignment (RWA) of several multicast sessions (including their backup trees for dedicated protection) at a globally optimum cost. We present these formulations for networks equipped with two kinds of multicast-capable switch architectures: one using the opaque (O-E-O) approach and the other using transparent (all-optical) approach. We expand our formulations to accommodate sparse splitting constraints in a network, in which an optical splitter has limited splitting fanout and each node has a limited number of such splitters. We develop a profit-maximizing model that would enable a network operator to be judicious in selecting sessions and simultaneously routing the chosen ones optimally. We illustrate the solutions obtained from solving these optimization problem formulations for a representative-size network.     

Introduction of very high bit rates for NFC and RFID

This article gives a detailed insight into the very high bit rates (VHBR) technology for the data transfer with NFC and RFID. In the first part enhancements and changes to the ISO/IEC 14443 and related standards are discussed. In the second part an analysis of different bit rates with focus on communication parameters and bit error rates are provided.     

High-Q SAW filter and submicron process technology for timingextraction in high bit rate optical communications system

A new surface acoustic wave (SAW) filter configuration that consists of 3λ/8-wide meander-type electrodes and 3λ/8-wide excitation electrodes on ST-cut quartz was designed for use in a 2.5-Gb/s optical communications system. New submicron process techniques using the phase shifting method as well as several types of resist were investigated to fabricate this filter. It had an insertion loss of less than 14 dB and a Q of about 700, and satisfied all required system specifications over a temperature range from 0 to 60°C     

Congestion-aware fair rate control in wireless mesh networks

This paper presents a fair and efficient rate control mechanism, referred to as congestion-aware fair rate control (CFRC), for IEEE 802.11s-based wireless mesh networks. Existing mechanisms usually concentrate on achieving fairness and achieve a poor throughput. This mainly happens due to the synchronous rate reduction of neighboring links or nodes of a congested node without considering whether they actually share the same bottleneck or not. Furthermore, the achievable throughput depends on the network load, and an efficient fair rate is achievable when the network load is balanced. Therefore, existing mechanisms usually achieve a fair rate determined by the mostly loaded network region. CFRC uses an AIMD-based rate control mechanism which enforces a rate-bound to the links that use the same bottleneck. To achieve the maximum achievable rate, it balances the network load in conjunction with the routing mechanism. Furthermore, it allows the intra-mesh flows to utilize the network capacity, and the intra-mesh flows achieve a high throughput. Finally, we investigate the performance of CFRC using simulation in ns-2, and the results demonstrate that CFRC increases the throughput with the desired fairness.     

Effective utilization of optical transponders in WDM mesh networks

We consider a multi-degree optical node configuration, which can provide multiple fiber links to the other nodes in wavelength-division-multiplexing (WDM) mesh networks. In the node, optical transponders are utilized for the wavelength channels sources and 3R-wavelength converters. It is shown that blocking originated from both the limited signal impairment threshold (SIT) problem and wavelength contentions can be resolved by the optical transponders. Moreover, the number of optical transponders per fiber link can be reduced down to half of the number of wavelength channels without degrading the network performance.     

Output characterization of constant bit rate traffic in FIFO networks

We provide an analytical proof that the departure rate of a CBR flow at an overloaded link with FIFO buffers is proportional to the flow?s share of the total offered load at the link. This property of FIFO scheduling was recently validated in [1] in a series of traffic measurement experiments. An extension of the analysis to a multi-node scenario shows that the output rate of a flow in a network with many overloaded FIFO switches approaches the pessimistic values given by blind multiplexing.     

Loopback recovery from double-link failures in optical mesh networks

Network survivability is a crucial requirement in high-speed optical networks. Typical approaches of providing survivability have considered the failure of a single component such as a link or a node. We motivate the need for considering double-link failures and present three loopback methods for handling such failures. In the first two methods, two edge-disjoint backup paths are computed for each link for rerouting traffic when a pair of links fails. These methods require the identification of the failed links before recovery can be completed. The third method requires the precomputation of a single backup path and does not require link identification before recovery. An algorithm that precomputes backup paths for links in order to tolerate double-link failures is then presented. Numerical results comparing the performance of our algorithm with other approaches suggest that it is possible to achieve almost 100% recovery from double-link failures with a moderate increase in backup capacity. A remarkable feature of our approach is that it is possible to trade off capacity for restorability by choosing a subset of double-link failures and designing backup paths using our algorithm for only those failure scenarios.     

Control and management protocols for survivable optical mesh networks

This paper considers the problem of online provisioning and restoration of sharable, restorable connections in a mesh-based optical network. First, we propose a new framework called distributed path selection with local information (DPLI) and discuss in detail a control and management protocol to set up and tear down connections and determine restoration capacity sharability in a distributed manner. Since only local information is maintained at each node, protocol scalability is not a big concern. Second, we discuss the important problem of the network's ability to quickly recover from element failures. We propose a new rapid restoration signaling that minimizes the service interruption time upon the occurrence of a failure in a network with preplanned restoration paths. The significant contribution of this new algorithm is that the connection restoration time is found to be independent of the restoration path length (i.e., eliminating the effect of the propagation delay), of the accumulation of the switch configuration time along the restoration path, and of the switch configuration waiting time at any particular node when multiple configuration requests arrive simultaneously. We evaluate through simulation experiments the effectiveness of the proposed protocols.