Optical layer survivability-an implementation perspective

This paper looks at several aspects of optical layer protection techniques from an implementation perspective. We discuss the factors that affect the complexity of optical protection schemes, such as supporting mesh instead of ring protection, handling low-priority traffic, and dealing with multiple types of failures. The paper also looks at how the client layer interacts with the optical layer with respect to protection, in terms of how client connections are mapped into the optical layer, and how protection schemes in both layers can work together in efficient ways. Finally, we describe several interesting optical protection implementations, focusing on the ones that are different from conventional SONET-like implementations.     

Failure protection in layered networks with shared risk link groups

The shared risk link group (SRLG) has been widely recognized as a fundamental concept in layered network design by the industry. However, several issues related to SRLG protections that are of both theoretical interest and practical importance have not been explored fully. Two major issues are avoiding failures caused by "traps" in finding backup paths, and minimizing the total network capacity requested by active and backup paths. In this article, we highlight the significance of the trap problem in layered networks with SRLG and evaluate the performance of several existing SRLG protection schemes in terms of trap avoidance and bandwidth efficiency, as well as their complexities. We also demonstrate that a simple yet intelligent heuristic algorithm can achieve good performance.     

Multiple link failure recovery in survivable optical networks

Survivability is of critical importance in high-speed optical communication networks. A typical approach to the design of survivable networks is through a protection scheme that pre-determines and reserves backup bandwidth considering single/double link failure scenarios. In this article, a greedy algorithm is presented to reserve backup bandwidth considering multiple (F > 2) link (SRLG) failure scenarios. A bandwidth-saving joint selection scheme of working and protection paths is presented for protection against random multiple-link failures under dynamic traffic. Simulation shows that the algorithm can achieve maximum sharing of backup bandwidth for protection against random multiple-link failure with significant amount of bandwidth saving.     

Shared risk link group failure restoration with in-band approximate failure localization

This paper proposes a novel failure recovery framework for multi-link shared risk link group (SRLG) failures in optical mesh networks, called failure presumed protection (FPP). The proposed framework is characterized by a failure dependent protection (FDP) mechanism where the optical layer in-band failure identification and restoration tasks for route selection are jointly considered. FPP employs in-band monitoring at each node to obtain on-off status of any working lightpath in case the lightpath is terminated at (or traversing through) the node. Since the locally available failure status at a node may not be sufficient for unambiguous failure localization, the proposed framework reroutes the interrupted lightpaths in such a way that all the suspicious links which do not have 100% restorability under any SRLG failure are kept away. We claim that this is the first study on FDP that considers both failure localization and FDP survivable routing. Extensive simulations are conducted to examine the proposed FPP method under various survivable routing architectures and implementations. The results are further compared with a large number of previously reported counterparts. We will show that the FPP framework can overcome the topological limitation which is critical to the conventional failure independent protection method (e.g., shared path protection). In addition, it can be served as a viable solution for FDP survivable routing where failure localization is considered.     

Spare Capacity Allocation in Two-Layer Networks

In this paper we consider the problem of provisioning spare capacity in two-layer backbone networks using shared backup path protection. First, two spare capacity allocation (SCA) optimization problems are formulated as integer linear programming (ILP) models for the cases of protection at the top layer against failures at the bottom layer. The first model captures failure propagation using overlay information between two layers for backup paths to meet diversity requirements. The second model improves bandwidth efficiency by moving spare capacity sharing from the top layer to the bottom layer. This exposes a tradeoff between bandwidth efficiency and extra cross-layer operation. Next, the SCA model for common pool protection is developed to allow spare capacity sharing between two layers. Our previous SCA heuristic technique, successive survivable routing (SSR) is extended for these optimization problems. Numerical results for a variety of networks indicate that the common pool protection is attractive to enhance bandwidth efficiency without loss of survivability and that the SSR heuristic quickly results in near optimal solutions     

All-optical four-fiber bidirectional line-switched ring

An all-optical four-fiber bidirectional line-switched ring (O-4F/BLSR) architecture is proposed. This new physical layer networking protocol uses wavelengths as tributaries and an optical supervisory channel to carry overhead information. Optical channels can be added and dropped from the ring, and virtual wavelength paths can be provisioned. Both node and link failures of a network can be protected through a two layer protection scheme. Protection switching within the optical multiplex section layer (OMS) restores failure caused by loss of optical continuity in a way similar to the SONET 4F/BLSR line switching. Protection switching within the optical channel layer restores single channel failure using 1:N protection. Test results show that the O-4F/BLSR can restore traffic in less than 50 ms. A self-healing, bandwidth efficient, and scalable all-optical transport network evolving from this O-4F/BLSR architecture is possible     

可生存GMPLS网络中带有SRLG约束的路由选择算法

为了提高传统的共享风险链路组(SRLG)约束下的路由选择(TRSSC)算法的成功保护率提出了一种新的RSSC(NRSSC)算法.NRSSC算法的基本思想是,当计算工作路径时考虑SRLG束将SRLG作为链路代价公式的一部分,这样可以在选择工作路径时避免SRLG链路,提高成功保护率.为了提高资源利用率,本算法允许共享备份带宽.另外,NRSSC算法根据用户的不同靠性要求,提供不同等级的保护服务.仿真结果表明,与TRSSC算法相比较,NRSSC算法不仅能够增加成功保护率,而且可以提高资源利用率,有效地改善了网络性能.     

p-Cycle Design in Survivable WDM Networks with Shared Risk Link Groups (SRLGs)

p-Cycle survivable network design under the single link failure assumption has been studied extensively. Shared risk link group (SRLG) is a concept that better reflects the nature of network failures. An SRLG is a set of links that may fail simultaneously because of a common risk they share. The capability of dealing with SRLG failures is essential to network survivability. In this paper, we extend the p-cycle survivable network design from the single link failure model to the single SRLG failure model. An integer linear programming (ILP) formulation that minimizes spare capacity requirement is provided. To avoid enumerating all cycles of a network, we also provide a polynomial-time algorithm to generate a basic candidate p-cycle set that guarantees 100% restorability in case of any single SRLG failure given enough spare capacities. Moreover, we present the SRLG failure detection problem that prevents fast restoration upon an SRLG failure. To solve this problem, we introduce the concept of SRLG-independent restorability, which enables the restoration of each link in a failed SRLG to start immediately without knowing which SRLG has failed. We present an approach to optimal p-cycle design with SRLG-independent restorability and show that it is NP-hard to generate a candidate p-cycle set such that each link can be SRLG-independently restored by at least one cycle in the set.     

IP restoration vs. optical protection: Which one has the least bandwidth requirements?

Survivability in IP-over-WDM networks has already been extensively discussed in a series of studies. While many studies assume an IP restoration scheme and focus on network connectivity in order to ensure proper recovery, few studies deal with optical protection. We investigate this question with the objective of estimating the respective bandwidth requirements of both recovery schemes, subject to single or multiple failures. We also design a mixed recovery scenario where the recovery is taken care at a different layer depending on the type of failures.Results shows that optical protection is by far the most economical recovery scheme in terms of bandwidth requirements.     

Architecture for restorable call allocation and fast VP restorationin mesh ATM networks

This paper presents an architecture for restorable call allocation and fast virtual path (VP) restoration in mesh ATM networks. In this architecture, virtual working and spare capacities needed for call allocation and restoration are reserved and released dynamically on a call-by-call basis at the time of call admission and termination. This obviates the need for advance assignment of spare and working capacities. To shorten the call processing delay, this is done in a parallel-distributed fashion. To provide restorable call allocation, parallel-distributed call processing algorithms of sender-chooser type are suggested. The algorithms integrate, on the call level, virtual bandwidth allocation, virtual spare-capacity assignment, and fixed, alternate, or state-dependent routing. Each routing scheme leads to a particular tradeoff between call processing complexity, call setup delay, and bandwidth efficiency. For each pair of nodes, two sets of VPs are provisioned. The first, working VP (WVP) set, is used for call allocation during the normal operation. The second, spare VP (SVP) set, is used for WVP restoration in the event of failures of network elements. Each SVP protects a preassigned subset of the node pair's WVPs. Each SVP is selected to be link/node disjoint from the WVPs that it is assigned to protect. This assures a protection of the WVP set by a small number of SVPs. Since SVPs are preset and appropriate virtual spare capacities are reserved in advance, the architecture guarantees full restorability and provides very fast restoration. The restoration is done on the VP level in a self-healing manner. The suggested architecture requires only local information to be maintained at each node     

Adaptive cross-layer protection strategies for robust scalable video transmission over 802.11 WLANs

Robust streaming of video over 802.11 wireless local area networks poses many challenges, including coping with bandwidth variations, data losses, and heterogeneity of the receivers. Currently, each network layer (including physical layer, media access control (MAC), transport, and application layers) provides a separate solution to these challenges by providing its own optimized adaptation and protection mechanisms. However, this layered strategy does not always result in an optimal overall performance for the transmission of video. Moreover, certain protection strategies can be implemented simultaneously in several layers and, hence, the optimal choices from the application and complexity perspective need to be identified. In this paper, we evaluate different error control and adaptation mechanisms available in the different layers for robust transmission of video, namely MAC retransmission strategy, application-layer forward error correction, bandwidth-adaptive compression using scalable coding, and adaptive packetization strategies. Subsequently, we propose a novel adaptive cross-layer protection strategy for enhancing the robustness and efficiency of scalable video transmission by performing tradeoffs between throughput, reliability, and delay depending on the channel conditions and application requirements. The results obtained using the proposed adaptive cross-layer protection strategies show a significantly improved visual performance for the transmitted video over a variety of channel conditions.     

复杂信息系统支撑平台研究

保障复杂信息系统(CIS)的安全、互操作、可扩展和可管理非常关键。该文提出安全的CIS体系结构模型以指导CIS的建设或改造。模型把CIS划分为不同层次以降低系统复杂度,采用Web Service技术实现互操作和可扩展,使用密码支撑层、安全防护与可靠性支持层在不同层面保证安全性与可靠性。通过系统管理层与各层交互,实现系统的可管理性。某电子政务试点示范工程案例及其网络统计、网络仿真证明模型不会影响业务系统性能。模型适用于政府、军队、银行等高安全级别的信息系统。适当简化模型中相应层次,模型也可用于相对简单的信息系统。     

MVC和UML在教学管理系统中的研究与应用

MVC(模型-视图-控制器)是一种优秀的编程模型,它可以把用户界面设计、流程控制和事务逻辑进行分离。文中结合南京邮电大学教学平台建设的实践,研究了MVC模式和UML(统一建模语言)在教学管理系统中应用,探索了一种把MVC和UML相结合的方法,提出了基于多层网络应用框架的教学管理系统,即客户应用层、J2EE(Java 2平台企业版)服务器中W eb处理层、J2EE服务器中处理各种复杂教学事务的业务逻辑层、存储数据和文件的企业信息层。其中,业务逻辑层是整个系统的重点,它包含6个EJB(企业Java组件)。实践表明,这种多层结构的软件系统有着良好的推广价值和应用前景。     

Mobility-aware Management of Internet Connectivity in Always Best Served Wireless Scenarios

The widespread availability of portable devices with multiple wireless interfaces, e.g., IEEE 802.11, WiMAX, Bluetooth, and/or UMTS, is leveraging the potential of novel supports to seamlessly and automatically select the proper connectivity technology to exploit at any time for any node and any running application. That selection should be context-dependent and take into account several aspects, at very different abstraction layers, from application-specific bandwidth requirements to expected client mobility, from user preferences to energy consumption. We claim the suitability of mobility-aware middlewares to relieve the application logic from the burden of determining the most suitable interface and connectivity provider for each client/application at service provisioning time. In particular, the paper motivates the need for novel context indicators, e.g., client/connector relative mobility, and describes effective lightweight solutions to estimate them flexibly, depending on dynamically introduced evaluation metrics. The paper presents primary architecture and implementation guidelines to build such a novel middleware solution. The proposed middleware has been experimentally validated and the reported performance results demonstrate the feasibility of the approach: it achieves accurate estimations of node mobility and consequently performs connection establishment/selection with very limited overhead.     

Optimized dimensioning of resilient optical grids with respect to grade of services

An optical grid network geographically integrates distributed computing/information resources with high speed communications. Network dimensioning, maximization of services, and job scheduling are some of today key arising issues in optical grids. Since the last decade, many projects have been conducted in order to provide computational and information facilities in the academic as well as in the business communities. In this paper, we study the network dimensioning and the maximization of IT services in optical grids. We propose a scalable optimization model for maximizing IT services under link transport capacities. We assume the use of the anycast routing principle to identify the server nodes for executing the jobs, and a shared path protection mechanism in order to offer protection against single link/node failures. We also investigate different calculation methods of the link transport capacities in order to maximize the grade of services, while taking into account the bandwidth requirements. Computational results are presented on different traffic distributions. They show that the proposed link dimensioning can save more than 35 % bandwidth in optical grid networks, in comparison with the classical link dimensioning strategies. We also investigate the different protection schemes against single link failures, single node failures, single node and server node failures, and compare their bandwidth requirements, as well as their impact on the grade of services (GoS). Results show that there is no significant increase of the bandwidth requirements and no meaningful impact on the GoS when moving from a single link protection scheme to a single node (including server nodes) protection scheme.     

An autonomous recovery mechanism against optical distribution network failures in EPON

Ethernet Passive Optical Network (EPON) is chosen for servicing diverse applications with higher bandwidth and Quality-of-Service (QoS), starting from Fiber-To-The-Home (FTTH), FTTB (business/building) and FTTO (office). Typically, a single OLT can provide services to both residential and business customers on the same Optical Line Terminal (OLT) port; thus, any failures in the system will cause a great loss for both network operators and customers. Network operators are looking for low-cost and high service availability mechanisms that focus on the failures that occur within the drop fiber section because the majority of faults are in this particular section. Therefore, in this paper, we propose an autonomous recovery mechanism that provides protection and recovery against Drop Distribution Fiber (DDF) link faults or transceiver failure at the ONU(s) in EPON systems. In the proposed mechanism, the ONU can automatically detect any signal anomalies in the physical layer or transceiver failure, switching the working line to the protection line and sending the critical event alarm to OLT via its neighbor. Each ONU has a protection line, which is connected to the nearest neighbor ONU, and therefore, when failure occurs, the ONU can still transmit and receive data via the neighbor ONU. Lastly, the Fault Dynamic Bandwidth Allocation for recovery mechanism is presented. Simulation results show that our proposed autonomous recovery mechanism is able to maintain the overall QoS performance in terms of mean packet delay, system throughput, packet loss and EF jitter.     

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.     

On joint protection/restoration in IP-centric DWDM based opticaltransport networks

Previous advances in WDM technology are now beginning to shift the focus more toward optical networking and network-level issues. Providing survivability at the optical layer is inherently attractive, but whether it makes practical sense, given similar mechanisms that are already available at the higher layers, poses serious challenges and raises many questions. Today's core network architecture model has functional overlap among its layers, contains outdated functionality, and is too slow to scale. If IP can be mapped directly onto the WDM layer, some of the unnecessary network layers can be eliminated, opening up new possibilities for developing a simple and integrated-protection/restoration scheme that can be coordinated at both the IP and WDM layers. This article presents an overview of existing optical protection/restoration schemes. Then we present a novel mesh-based hybrid optical protection scheme that utilizes multifiber physical links along with a hierarchical OXC structure. An overview of the envisioned IP-centric DWDM-based optical data network architecture is then presented. The basis of how to implement a more direct IP standard-based approach for closer and efficient IP-WDM integration is also discussed. Finally, we articulate a view of how to provide a joint protection/restoration scheme that is coordinated at both the IP and WDM layers     

On the synergy between adaptive physical layer and multiple-access control for integrated voice and data services in a cellular wireless network

We propose a novel design to exploit the synergy between the multiple-access control (MAC) layer and the physical layer of a cellular wireless system with integrated voice and data services. As in a traditional design, the physical layer (channel encoder and modulator) is responsible for providing error protection for transmitting the packets over the hostile radio channel, while the MAC layer is responsible for allocating the precious bandwidth to the contending users for voice or data connections. However, a distinctive feature of our proposed design is that in the physical layer, a variable-rate adaptive channel encoder is employed to dynamically adjust the amount of forward error correction according to the time-varying wireless channel state such that the MAC layer, which is a reservation-based time-division multiple-access protocol, is able to make informed decisions as to bandwidth allocation. Specifically, based on the channel state information provided by the physical layer, the MAC protocol gives higher priority to users with better channel states. This novel synergistic mechanism between the two protocol layers can utilize the system bandwidth more effectively. The multiple-access performance of the proposed scheme is compared with two baseline systems. The first baseline system consists of the same reservation-based MAC protocol but with a traditional fixed-rate physical layer. The second system consists of the same reservation-based MAC protocol and the same channel adaptive physical layer, but without interaction between the two layers. All three protocols have a request queue, which stores the previous requests that survive the contention but are not allocated information slots. Our extensive simulation results demonstrate that significant performance gains are achieved through the exploitation of the synergy between the two protocol layers.     

Architecture Design of Fine Grain Quality Scalable Encoder with CABAC for H.264/AVC Scalable Extension

In addition to coding efficiency, the scalable extension of H.264/AVC provides good functionality for video adaptation in heterogeneous environments. Fine grain scalability (FGS) is a technique to extract video bitstream at the finest quality level under the given bandwidth. In this paper, an architecture of FGS encoder with low external memory bandwidth and low hardware cost is proposed. Up to 99% of bandwidth reduction can be attained by the proposed scan bucket algorithm, early context modeling with context reduction, and first scan pre-encoding. The area-efficient hardware architecture is implemented by layer-wise hardware reuse. Besides, three design strategies for enhancement layer coder are explored so that the trade-off between external memory bandwidth and silicon area is allowed. The proposed hardware architecture can real-time encode HDTV 1920×1080 video with two FGS enhancement layers at 200 MHz working frequency, or HDTV 1280×720 video with three FGS enhancement layers at 130 MHz working frequency.