Multi-period design of survivable wireless access networks under capacity constraints

Design of survivable wireless access networks plays a key role in the overall design of a wireless network. In this research, the multi-period design of a wireless access network under capacity and survivability constraints is considered. Given the location of the cells and hubs, the cost of interconnection, and the demands generated by the cells, the goal of the designer is to find the best interconnection between cells and hubs so that the overall connection cost is minimized and the capacity and the survivability constraints are met. Integer programming formulations for this problem are proposed and the problems are solved using heuristic methods. Using different combination of network sizes, demand patterns and various time periods, a number of numerical experiments are conducted and all of them are found to yield high quality solutions.     

Server capacity planning for Web traffic workload

The goal of the paper is to provide a methodology for determining bandwidth requirements for various hardware components of a World Wide Web server. The paper assumes a traditional symmetric multiprocessor (SMP) architecture for the Web server, although the same analysis applies to an SMP node in a cluster. The paper derives formulae for bandwidth demands for memory, processor data bus, network adapters, disk adapters, I/O memory paths, and I/O buses. Since the Web workload characteristics vary widely, three sample workloads are considered for illustrative purposes: 1) standard SPECweb96; 2) a SPECweb96-like workload that assumes dynamic data and retransmissions; and 3) WebProxy, which models a Web proxy server that does not do much caching, and thus has rather severe requirements. The results point to a few general conclusions regarding Web workloads. In particular, reduction in memory/data bus bandwidth by using the virtual interface architecture (VIA) is very desirable, and the connectivity needs may go well beyond the capabilities of traditional systems based on the traditional PCI-bus. Web workloads also demand a significantly higher memory bandwidth than data bus bandwidth and this disparity is expected to increase with the use of VIA. Also, the current efforts to offload TCP/IP processing may require a larger headroom in I/O subsystem bandwidth than in the processor-memory subsystem     

Adaptive scheduling for integrated traffic on WDM optical networks

One of the important issues in the design of future generation of high-speed networks is to provide differentiated service to different types of traffic with various time constraints. In this paper, we study the problem of providing real-time service to either hard or soft real-time messages and normal transmission service to variable-length messages without time constraints in WDM optical networks. We propose an adaptive scheduling algorithm for scheduling message transmissions in order to improve the network performance when both real-time and non real-time messages are transmitted in one topology. We have analyzed the complexity of the algorithm to show its feasibility. We have conducted extensive discrete-event simulations to evaluate the performance of the proposed algorithm. The study suggests that when scheduling message transmission in WDM networks differentiated services should be considered in order to meet time constraints of real-time messages while non real-time messages are being served so that the overall performance of the network could be improved.     

Maximizing the capacity of mobile cellular networks with heterogeneous traffic

We propose a novel adaptive reservation scheme that handles, in an integrated way, heterogeneous traffic of two types: streaming and elastic. The scheme adjusts the rates of streaming sessions to meet the QoS objective, adapting to any mix of traffic and enforcing a differentiated treatment among services, in both fixed and variable capacity systems. The resource utilization achieved by streaming traffic is close to the one obtained by an optimal policy, while the efficiency in the use of resources achieved by elastic traffic is greatly improved by limiting the abandonment probability. The performance evaluation carried out verifies that the QoS objective is met with an excellent precision and that the scheme converges rapidly to new operating conditions. We also compare the new adaptive scheme with two previous ones verifying that ours performs better in terms of carried traffic and convergence rate. The proposed scheme has low complexity which makes it practical for real cellular networks.     

OBS网络中的静态业务量疏导技术

现有的光突发交换(OBS)网络中的业务量疏导技术都没有考虑全网业务量优化问题,对此提出OBS网络的静态业务量疏导机制和两种算法:基于相同目的地址的静态业务量疏导算法和基于相同下一跳地址的静态业务量疏导算法.使用OPNET仿真工具对两种算法进行仿真,结果表明,低负载情况下,该疏导机制指导下的两种算法均能提高链路利用率,降低IP分组丢包率,改善网络性能.同等条件下,基于相同下一跳地址的疏导算法更为有效.     

复杂业务需求下的光网络规划问题的研究*

研究了复杂业务需求下的光网络规划问题,建立了支持多种业务需求和保护需求的ILP数学模型;针对大型光网络相应的整数线性模型规模过大、难以求解的困难,引入了Bender数学分解方法。计算结果表明,利用Bender分解可以有效地求解复杂业务需求和保护需求下的光网络规划问题,同时降低时间和内存的消耗。     

Solving dimensioning tasks for proportionally fair networks carrying elastic traffic

The paper studies optimal dimensioning problems associated with the notion of “proportional fairness” (PF) considered for packet networks carrying elastic (greedy) traffic, i.e. the traffic streams that can use up, perhaps within certain assumed bounds, any bandwidth that is assigned to them. We give effective, simple and explicit solutions to the introduced optimisation tasks based on the dual optimisation theory, and illustrate them with numerical examples. The explicit solutions can guide a network operator how to proceed when introducing PF into his network.     

Routing in sparse splitting optical networks with multicast traffic

In this paper, we investigate the problem of Multicast Routing in Sparse Splitting Networks (MR-SSN). Given a network topology with the multicast capable nodes distributed uniformly throughout the network, and a multicast session, the MR-SSN problem is to find a route from the source node of the multicast session to all destinations of the multicast session such that the total number of fibers used in establishing the session is minimized. In this paper, we develop a rerouting algorithm for a given Steiner tree, which makes it feasible to route a multicast session using a tree-based solution in sparse light splitting optical networks. In addition, we present a heuristic based on Tabu Search (TS) that requires only one transmitter for the source node and one wavelength for each multicast session. To evaluate the performance of heuristics, we formulate the MR-SSP problem as an integer linear program (ILP), and optimally solve small instances using the commercially available linear solver, CPLEX. We test our heuristic on a wide range of network topologies. Our experimental results show that: (1) The difference between our solution and ILP optimal solution, in terms of the number of fibers used for establishing a multicast session, is within 10% in almost all the instances and within 5% in about half of the instances. (2) The average delay, taken over all destination nodes, falls within three times the optimal value. (3) A sparse light splitting all-optical network with 30% of multicast capable cross-connects has an acceptable low cost and relatively good performance. (4) The improvement achieved by TS heuristic increases considerably when the session size is large, the number of Splitter-and-Delivery cross-connects is small, and the network connectivity is dense.     

Estimating traffic capacity for weaving segments using neural networks technique

The impact of weaving vehicles on the capacity of freeway segments is uncertain due to the complexity in operation. The Highway Capacity Manual (HCM) 2000 provides values for capacity on various weaving segments (Exhibit 24-8) based on sets of conditions (configuration, speed, length, volume ratio, and number of lanes). However, to find capacity for a given set of conditions, an iterative process should be carried out using a properly programmed spreadsheet. This paper suggests alternative and convenient procedure for estimating capacity on weaving segments. Two capacity prediction models are developed using regression and neural networks (NNT). Although, linear regression (LR) technique showed satisfactory results, neural network technique outscored linear regression in the prediction performance, and generalization ability. The trained neural network architecture represented by weight and bias values for each layer is simply used to predict capacity for weaving segments under new conditions.     

规则网络上提高交通处理能力不同路由策略研究*

针对交通拥挤问题,提出了一个基于随机选择最短路径的简单交通流模型,并研究了这个模型的动力学行为。为了提高规则网络上的相变点的值,提出了几种改进的路由策略,并作了详细的仿真对比研究。最后,给出了更好的提高网络整体性能的路由策略,并提出了应对交通问题的一些合理性建议。 结果显示,规则网络上交通流存在一个从自由相到拥塞相的相变。相变点的值可以用来衡量网络处理交通流的能力。     

On providing elastic QoS in optical burst switched networks

Integrated services schemes have not been used to support QoS in OBS networks, largely because of the high control overhead involved in monitoring bursts continuously at intermediate nodes. In this paper, we propose for the first time, an integrated services scheme to support elastic QoS in OBS networks. Our scheme relieves intermediate nodes of the burden of monitoring individual bursts continuously, thus largely decreasing the control overhead. We show how absolute bandwidth guarantees can be provided, and how bandwidth used by each connection can be made elastic. We demonstrate the effectiveness of our scheme using both analytical and simulation studies.     

Rerouting schemes for dynamic traffic grooming in optical WDM networks

Traffic grooming in optical WDM mesh networks is a two-layer routing problem to effectively pack low-rate connections onto high-rate lightpaths, which, in turn, are established on wavelength links. The objective of traffic grooming is to improve resource efficiency. However, resource contention between lightpaths and connections may result in inefficient resource usage or even the blocking of some connections. In this work, we employ a rerouting approach to alleviate resource inefficiency and improve the network throughput under a dynamic traffic model. We propose two rerouting schemes, rerouting at lightpath level (RRLP) and rerouting at connection level (RRCON) and a qualitative comparison is made between the two. We also propose two heuristic rerouting algorithms, namely the critical-wavelength-avoiding one-lightpath-limited (CWA-1L) rerouting algorithm and the critical-lightpath-avoiding one-connection-limited (CLA-1C) rerouting algorithm, which are based on the two rerouting schemes. Simulation results show that rerouting reduces the blocking probability of connections significantly.     

Impairment-aware fixed-alternate BSR routing heuristics applied to elastic optical networks

The Journal of Supercomputing - The introduction of elastic optical networks (EONs) leads to new challenges, such as the problem of routing, modulation level, and spectrum assignment. In...     

Multiple link failures survivability of optical networks with traffic grooming capability

This paper investigates the problem of survivable traffic grooming (STG) in shared mesh optical networks and proposes different frameworks for improving the survivability of low speed demands against multiple near simultaneous failures. Spare capacity reprovisioning has recently been considered for improving the overall network restorability in the event of dual failures; here, after the recovery form the first failure, some connections in the network may become unprotected and exposed to new failures. Capacity reprovisioning then allocates protection resources to unprotected and vulnerable connections so that the network can withstand a future failure. In this paper, we propose two different reprovisioning schemes (lightpath level reprovisioning, LLR, and connection level reprovisioning, CLR); they differ in the granularity at which protection resources are reprovisioned. Further, each of these schemes is suitable for a different survivable grooming policy. While LLR provides collective reprovisioning of connections at the lightpath level, CLR reprovisions spare bandwidth for lower speed connections instead. We use simulation methods to study the performance of these schemes under two grooming policies (PAL and PAC), and we show that while CLR reprovisions substantially many more connections than LLR (i.e., potentially more management overhead) CLR yields a much better network robustness to simultaneous failures due to its superior flexibility in using network resources.     

混合光交换网络中不确定业务下的优化路由方案

在结合了OCS和OBS优点的混合光交换网络背景下,提出了一种业务矩阵不确定的情况下的优化路由方案。在给定的波长数目下,该方案首先给OBS预留若干个波长;然后构建OCS虚拓扑;最后利用预留的波长,采用优化方法得到OBS路由。以最小化丢包率作为优化网络性能指标。仿真结果表明,在给定波长数目的情况下,与最短路由相比,采用优化路由能有效地减少整个网络的丢包率;同时,为了描述业务矩阵的不确定性,引入了不确定因子。随着不确定因子的减小,优化路由下整个网络的丢包率就越小。     

On the complexity and algorithm of grooming regular traffic in WDM optical networks

In SONET/WDM networks, a high-speed wavelength channel is usually shared by multiple low-rate traffic demands to make efficient use of the wavelength capacity. The multiplexing is known as traffic grooming and performed by SONET Add-Drop Multiplexers (SADM). The maximum number of low-rate traffic demands that can be multiplexed into one wavelength channel is called grooming factor. Since SADMs are expensive, a key optimization goal of traffic grooming is to minimize the total number of SADMs in order to satisfy a given set of traffic demands. As an important communication traffic pattern, all-to-all traffic has been widely studied for the traffic grooming problem. In this paper, we study the regular traffic pattern, which is considered as a generalization of the all-to-all traffic pattern. We focus on the Unidirectional Path-Switched Ring (UPSR) networks. We prove that the traffic grooming problem is NP-hard for the regular traffic pattern in UPSR networks, and show that the problem does not admit a Fully Polynomial Time Approximation Scheme (FPTAS). We further prove that the problem remains NP-hard even if the grooming factor is any fixed value chosen from a subset of integers. We also propose a performance guaranteed algorithm to minimize the total number of required SADMs, and show that the algorithm achieves a better upper bound than previous algorithms. Extensive simulations are conducted, and the empirical results validate that our algorithm outperforms the previous ones in most cases. In addition, our algorithm always uses the minimum number of wavelengths, which are precious resources as well in optical networks.     

复杂网络加边扩容策略研究

网络扩容策略是近年来复杂网络的研究热点,目前针对网络删边扩容研究已经颇为成熟,但加边扩容的研究还较为匮乏.根据网络容量与网络节点介数的最大值成反比的结论,提出了一种复杂网络加边扩容的策略,并与最低度添加边和最长最短路径添加边策略进行分析比较.实验表明:在添加边数目相同的条件下,提出的添加边策略不仅能有效减少网络平均最短路径,还可以最大化提高网络的容量.     

Modulation format independent blind polarization demultiplexing algorithms for elastic optical networks

We demonstrate a novel modulation format independent algorithm for adaptive blind polarization demultiplexing for elastic optical networks (EONs). We compare the proposed algorithm with traditional constant modulus algorithm (CMA) and radius-directed algorithm (RDA), in terms of performance in PM-QPSK, PM-16QAM and PM-64QAM coherent system, by simulating in back-to-back (BTB) and transmission sceneries. The simulation result shows that the modulation format independent algorithm can achieve universal adaptive blind polarization demultiplexing for PM-mQAM signals and gain slightly better performance in condition of lower optical signal noise ratio (OSNR). Furthermore, we also carry out experiments to investigate the performance of the proposed algorithm in BTB and 800 km transmission scenarios for 16 GBaud PM-QPSK and PM-16QAM. The experimental results demonstrate the conclusion of the numerical simulations.     

Performance analysis of a novel traffic scheduling algorithm in slotted optical networks

This paper considers the scheduling problem in a new slotted optical network called Time-Domain Wavelength Interleaved network (TWIN). The TWIN architecture possesses interesting properties, which may offer solutions for next-generation optical networks. Besides, better Quality of Service (QoS) could be achieved in TWIN by minimizing two parameters: queueing delay and delay variance. However, to the best of our knowledge, most of the existing scheduling algorithms in TWIN ignored consideration of QoS and focused mainly on maximizing the throughput. In this paper, we formulate the scheduling problem into an Integer Linear Programming (ILP) problem and propose a novel heuristic – Destination Slot Set (DSS) algorithm to solve it fast and efficiently. Besides, we derive an analytical model for TWIN and investigate the performance of DSS in it. By means of simulations, we demonstrate that our analytical model approximates the TWIN network very well; moreover, DSS incurs smaller queueing delay and delay variance, which ensures better QoS.