Routing of 40-Gb/s Streams in Wavelength-Routed Heterogeneous Optical Networks

In this paper, we address the design and management issues in routing a mixture of OC-192 and OC-768 streams in wavelength-routed optical networks. We assume that fiber links in the network are heterogeneous with respect to their transmission capability (i.e., links are designed to handle a given maximum bit-rate imposed by regenerator spacing).We investigate the issues of routing connection demands of various bit-rate requirements in such heterogeneous networks. In this environment, we introduce the routing of multirate traffic (RMT) problem. The RMT problem is informally defined as the process of finding the best routing which maximizes the total bandwidth carried in the network, for a set of sessions, within a given TDM equipment budget. We propose a two-phase optimization scheme (two-phase RMT). This scheme first obtains a basis solution used in routing 40-Gb/s traffic only on OC-768 capable links without the use of TDM equipment. In the second phase, an iterative routing, rerouting, and resource allocation step is used to optimize the total bandwidth carried in the network, while allowing 40-Gb/s traffic to be routed on OC-768 incapable links by the proper installation of TDM multiplexors and demultiplexers at some strategic locations in the network. Numerical results reveal the following:. 1) the two-phase RMT optimization algorithm provides substantial savings in terms of both the total TDM equipment installed and number of wavelengths used; 2) noticeable enhancements of the bandwidth utilization and the TDM budget are observed when the route-optimization takes into account the transmission quality of the links; and 3) the use of intermediate TDM multiplexing/demultiplexing functions provides substantial savings, in terms of the total number of channels, over the source-splitting scheme.     

QoS-Friendly Wavelength Assignment in Dynamic Wavelength-Routed Optical Networks

In-band crosstalk has been widely considered as a major transmission impairment that significantly impacts the bit error rate (BER) performance of lightpaths in circuit-switched all-optical wavelength-routed networks. Such crosstalk usually occurs when multiple wavelengths pass through an optical crossconnect node, and the magnitude of the crosstalk is largely dependent on the wavelengths assigned to the lightpaths. Traditional wavelength assignment (WA) schemes pay little regard to the physical layer quality of service (QoS), and hence cannot provide optimized network performance in practical networks with imperfect physical transmission media. In this paper, we first present our categorization of in-band crosstalk based on the location of crosstalk generation, then we propose two QoS-friendly WA approaches, one of which selects the wavelength based on the estimated BERs, and the other based on the weighted crosstalk number counting. The two approaches have different computation complexities. Numerical results show that both approaches can significantly improve the BER blocking rate by suppressing the created in-band crosstalk, but the BER-based approach generally gives the better performance at the price of more extensive computation.This work was supported in part by DARPA Grants #N66001-00-1-8949 and #66001-01-1-8932 (co-funded by NSA).     

应用于分级复用系统的全光网波长分配算法

研究了全光网中采用分级复用系统的波长分配问题,充分考虑到分级复用系统在降低整个网络成本上的重要意义,以最小化光纤数量和波长路径为优化目标,提出一种启发式波长分配算法。     

Blocking Analysis of Dynamic Traffic Grooming in Mesh WDM Optical Networks

Traffic grooming in wavelength division multiplexing (WDM) optical networks routes and consolidates sub-wavelength connections onto lightpaths, to improve network utilization and reduce cost. It can be classified into static or dynamic, depending on whether the connections are given in advance or randomly arrive/depart. In this paper, an analytical model is developed for dynamic traffic grooming, allowing heterogeneous data rates for sub-wavelength connections, arbitrary alternate routing in both logical and physical topologies, and arbitrary wavelength conversion. The accuracy of the model has been verified by numerical results from simulation.     

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.     

Signaling Schemes for Distributed Connection Management in Wavelength-Routed Optical Mesh Networks

The next-generation optical transport network will evolve from point-to-point connectivity to mesh networking, which can provide fast and automatic provisioning with enhanced flexibility and survivability. Signaling is used to support connection setup, maintenance, and teardown in such a network. In this paper, we study the performance of two hop-by-hop and one parallel signaling schemes in wavelength-routed optical mesh networks. Based on the sequence between optical crossconnect (OXC) switching and signaling message processing, we classify hop-by-hop signaling into two types that comply with the requirements of GMPLS signaling protocols. These two types are forward before switching configuration (FBSC) and forward after switching configuration (FASC). Also, we propose a parallel signaling scheme that is different from the existing hop-by-hop GMPLS signaling protocols. Considering OXC architectures and traffic patterns, we compare the FBSC, FASC, and parallel signaling schemes using simulation experiments, in terms of network blocking probability and reservation time. The simulation data reveal that the performance of a signaling scheme depends on the nature of the signaling as well as the network setting (e.g., the OXC architecture and traffic pattern). We analyze reasons for this result and discuss tradeoffs between these signaling schemes. This work offers some insight into designing an efficient signaling protocol for wavelength-routed optical mesh networks.     

Fast Routing Algorithms for Lightpath Establishment in Wavelength-Routed Optical Networks

In this paper, we study shortest-path routing in wavelength-routed optical networks with an objective to optimize the average-case running time for path computation. Four fast routing algorithms are proposed for dynamically computing the shortest lightpaths or semilightpaths in a network with or without wavelength converters. To reduce the average-case running time for path computation, sequential search, backward routing, and informed search are used in the algorithm design. Simulation results show that the proposed algorithms can significantly reduce the average-case computational overhead for path computation as compared with existing algorithms.      

A Kind of Topology Aggregation Algorithm in Hierarchical Wavelength-Routed Optical Networks

In large scale networks composed of several hierarchical subnetworks, topology aggregation is implemented for both scalability and security consideration. However, due to the special characteristic of optical wavelength-routed networks, existing topology aggregation algorithms cannot be applied directly for topology compression. In this paper, we propose a kind of topology aggregation algorithm suitable for hierarchical wavelength-routed optical networks, thereby considering information of residual wavelengths on network links. Basically, our topology aggregation algorithm is based on a transition matrix technique for constructing a full mesh topology and asymmetric star approach for a more compact topology. Simulations with randomly-generated networks show that topology information compression can be achieved with a little loss of its accuracy: the ratio of border node pairs with representation deviation being well below 10%. Results also indicate that the advantage of our algorithm is also behaved on reducing the amount of link-state-advertisement messages and making networks less vulnerable to propagation delay of these messages over communication links. This work is supported by National 863 Program 2003AA122220.     

WDM光网络中的业务疏导

目前WDM光网络普通用户大量的一般业务请求数目及波长通道带宽的不断增加极大的增加了网络中电层和光层设备的处理负担,增加了网络成本。对低速电信号复用到高速光通道进行优化,减少网络电层设备的使用,降低网络成本的业务疏导(TrafficGrooming)技术成为目前光网络研究的一个热点。本文主要介绍了WDM光网络中的业务疏导问题的基本概念、技术特点、国内外研究现状进行了总结。     

异构无线网络中流量管理模型的研究

首先描述了流量管理在异构无线网络中产生的背景,存在问题及研究现状.然后从博弈论、机制设计和最优化理论学科交叉领域出发,对异构无线网络的流量管理问题进行建模分析.最后对未来发展进行了展望.     

Allocation of Splitting Nodes in All-Optical Wavelength-Routed Networks

In this paper, we introduce the splitter placement problem in wavelength-routed networks (SP-WRN). Given a network topology, a set of multicast sessions, and a fixed number of multicast-capable cross-connects, the SP-WRN problem entails the placement of the multicast-capable cross-connects so that the blocking probability is minimized. The SP-WRN problem is NP-complete as it includes as a subproblem the routing and wavelength assignment problem which is NP-complete. To gain a deeper insight into the computational complexity of the SP-WRN problem, we define a graph-theoretic version of the splitter placement problem (SPG), and show that even SPG is NP-complete. We develop three heuristics for the SP-WRN problem with different degrees of trade-off between computation time and quality of solution. The first heuristic uses the CPLEX general solver to solve an integer-linear program (ILP) of the problem. The second heuristic is based on a greedy approach and is called most-saturated node first (MSNF). The third heuristic employs simulated annealing (SA) with route-coordination. Through numerical examples on a wide variety of network topologies we demonstrate that: (1) no more than 50% of the cross-connects need to be multicast-capable, (2) the proposed SA heuristic provides fast near-optimal solutions, and (3) it is not practical to use general solvers such as CPLEX for solving the SP-WRN problem.     

Sparse Regeneration in Translucent Wavelength-Routed Optical Networks: Architecture,Network Design and Wavelength Routing

In this paper we study an alternate network architecture, called translucent network, to the fully transparent and fully opaque network architectures. In a translucent wavelength-routed optical network, a technique called sparse regeneration is used to overcome the severe lightpath blocking due to signal quality degradation and wavelength contention in a fully transparent network while using much less regenerators than in a fully opaque network. In this paper, we present a node model and a network model that perform sparse regeneration. We address the problem of translucent network design by proposing several regenerator placement algorithms based on different knowledge of future network traffic patterns. We also address the problem of wavelength routing under sparse regeneration by incorporating two regenerator allocation strategies with heuristic wavelength routing algorithms. We compare the performance of different regenerator placement algorithms and wavelength routing schemes through simulation experiments. The benefit of sparse regeneration is quantitatively measured under different network settings.This work was supported by NSF grants (ANI-0074121 and EPS-0091900).Portions of this work have appeared in the Proceedings of the OSA Optical Fiber Communications (OFC 1999) Conference [6] and the Proceedings of the IEEE Global Telecommunications (GLOBECOM 2001) Conference [12].     

IP over Optical网络联合流量工程研究

对IPoverOptical网络的流量工程进行了深入的研究。问题,给出了两种流量工程体系结构,重叠流量工程和联合流量工程,然后对这两种流量工程体系进行了比较,并给出了联合流量工程的实现框图以及需要解决的关键问题。     

Analysis of Traffic Distribution and Blocking Probability in Future Wireless Networks

Future wireless networks are envisioned to provide good quality multimedia services to mobile users anywhere at anytime. Traditional analysis of teletraffic in such networks assumes that call arrivals follow a Poisson process, as each cell is being modeled as an M/G/c/c queueing system. This does not reflect the real situation since handoff traffic arrivals are not generally Poissonian. In this paper, we propose to model each cell in future wireless networks as a G/G/c/c queueing system. As such a model has not been explicitly addressed in the literature, our main contribution is to propose a solution which enables to evaluate both traffic distribution and blocking probability within each cell of the service area. Result analysis reveals that coefficient of variation of call arrivals has more impact on the network performance than coefficient of variation of channel holding time.     

WDM网络中基于阻塞公平性的业务疏导和波长分配

在具有多速率级别连接请求的WDM网络中，通过为较高速率的请求预留更多的波长集合，结合网络节点对较低速率业务更强的输导能力，解决网络的阻塞公平性和全网的流量问题。在中国教育科研网的仿真实验，本文的策略比First-fit算法取得了更好的阻塞公平性能，并接纳了更多的网络流量。当负载为170Erlang时，多接纳的流量约为12％。     

WDM光网络多跳业务量疏导算法

针对具有多跳疏导能力的WDM光网络进行了研究,提出了一种基于固定备选路由的多跳业务量疏导算法（FO-HC-MH）。该算法对备选路由的跳数进行限制,因而可以节约使用网络的收发器资源。仿真实验表明,与FO-MH算法相比,在网络负载较低的情况下该算法节约效果明显。     

On the Traffic Offloading in Wi-Fi Supported Heterogeneous Wireless Networks

Heterogeneous small cell networks (HetSNet) comprise several low power, low cost (SBSa), (D2D) enabled links wireless-fidelity (Wi-Fi) access points (APs) to support the existing macrocell infrastructure, decrease over the air signaling and energy consumption, and increase network capacity, data rate and coverage. This paper presents an active user dependent path loss (PL) based traffic offloading (TO) strategy for HetSNets and a comparative study on two techniques to offload the traffic from macrocell to (SBSs) for indoor environments: PL and signal-to-interference ratio (SIR) based strategies. To quantify the improvements, the PL based strategy against the SIR based strategy is compared while considering various macrocell and (SBS) coverage areas and traffic–types. On the other hand, offloading in a dense urban setting may result in overcrowding the (SBSs). Therefore, hybrid traffic–type driven offloading technologies such as (WiFi) and (D2D) were proposed to en route the delay tolerant applications through (WiFi) (APs) and (D2D) links. It is necessary to illustrate the impact of daily user traffic profile, (SBSs) access schemes and traffic–type while deciding how much of the traffic should be offloaded to (SBSs). In this context, (AUPF) is introduced to account for the population of active small cells which depends on the variable traffic load due to the active users.     

大容量光网络异构互联及控管研究

多种类型的网络设备并存造成光网络严重异构化,且难以实现真正意义上的互联互通,成为阻碍光网络进一步发展的＂瓶颈＂。文章针对大容量光网络异构互联及优化控管问题,对一些相关新技术和研究成果进行介绍,包括集中式与分布式相结合的异构多域大规模光网络广义控管架构、K随机最短路域间路由优化技术、基于＂边缘环＂的多域网络拓扑架构、路由重定向信令技术,以及异构多域光网络试验平台搭建等。     

WDM光网络动态业务流量的可重构疏导

流量疏导是当今光网络研究中一个学术与商业价值并重的研究热点。在WDM(波分复用)光网络中使用流量疏导技术不仅能够有效地降低网络成本，也能够使网络性能得到必要的优化。为了适应当前网络中普遍存在的突发多变的业务分布，引入了一种称为网络可重构动态流量疏导的新型流量疏导概念，并对疏导进行了分类，较全面地论述和评价了近年来这方面的研究，最后对今后的研究作了一番展望。