Reflections and Multiple Rayleigh Backscattering in WDM Single-Fiber Loopback Access Networks

The optical gain of reflective optical network units (ONUs) may produce a critical amplifying feedback on the single-fiber transmission impairments. In this paper, its influence on the passive optical networks transmission with reflective-ONU is theoretically analyzed and experimentally confirmed. Analytical expressions for the optical crosstalk-to-signal ratio and the $Q$-parameter in presence of Rayleigh backscattering, reflection interferences and ASE noise are given. As a resulting design guideline, the ONU gain should be adjusted to about 3 dB below the total link loss; in addition, component return loss at the drop section must be higher than 30 dB. Experimental results with two basic types of reflective-ONUs, namely a loop structure formed by a Mach–Zehnder modulator and an optical amplifier, and another one employing a reflective-SOA, are in agreement with the theoretical approach.      

Effective Traffic Grooming Algorithms in SONET/WDM Ring Networks

Much work has focused on traffic grooming in SONET/WDM ring networks. Previous work has considered many aspects of traffic grooming, including minimizing the number of ADMs, minimizing the number of wavelengths, considering different traffic models, using different network architectures, incorporating switching capability and so on. In this work, we study traffic grooming in unidirectional ring networks with no switching capability under both uniform traffic and non-uniform traffic models to reduce electronic multiplexing costs. Based on the clustering notion, we derive a general and tighter lower bound for the number of ADMs required in traffic grooming under the uniform all-to-all traffic model. This bound reduces to special cases obtained in previous work. We also derive general, tighter, and closed form lower bounds for the number of ADMs required under two non-uniform traffic models: the distance-dependent traffic model and the non-uniform symmetric traffic model. Cost-effective multi-phase algorithms that exploit traffic characteristics are then designed and studied to efficiently groom traffic streams under different traffic models. Our numerical and simulation results show that the proposed multi-phase algorithms outperform existing traffic grooming algorithms by using a fewer number of ADMs. Our algorithms in several cases also achieve the lower bounds derived.     

Middleware Architecture for Next Generation Heterogeneous Networks

In this paper we present a framework, called Futon, which provides a platform to integrate heterogeneous radio access networks. Futon is a hybrid fibre-radio network that replaces legacy base stations with simple remote antenna units, which are connected to a central unit. As a part of the Futon framework, a generic middleware architecture is discussed in detail, which provides interoperability, cooperative management and service provisioning to both underlying radio access networks (RANs) and IP layer for a heterogeneous network scenario. One of the middleware??s functionality is to provide vertical handover between heterogeneous IP-based radio access technologies and to ensure seamless mobility and service continuity, which is implemented on top of an IPv4/IPv6 Mobile IP (MIP) core. In this paper, the Futon framework and a generic middleware architecture as a part of Futon framework for heterogeneous RANs is discussed. The main modules of the middleware, namely common radio resource management (CRRM), media independent handover, Service/Connection Manager and link selection are explained in detail. Radio over fibre (RoF) Manager is an important part of Central unit, which does performance, fault and security management of network elements. RoF manager helps middleware during handoff, by providing the status of fibre optic links. The implementation of Security management module as a part of RoF manager, and results of authentication with AAA protocol are explained. The CRRM as part of middleware is simulated and the results of experimental evaluation are presented.     

下一代网络的业务互通体系结构

以IP为基础的因特网的出现对传统的电信网络带来了巨大的冲击,它的开放性和业务的灵活性为电信网进一步的发展指出了一个方向.但是,由于IP在提供具有质量保证的等级业务方面缺乏技术的保障;局域网技术、广域网技术的发展使得原来被认为功能简单的第二层传输网络具有越来越强的业务能力,例如QoS、多播、VPN以及安全管理能力,将导致多接入、多业务的下一代网络端到端业务控制和业务集成越来越复杂,使得我们需要重新审视网络互连和业务集成的基本思路,建立下一代网络的新的业务概念.本文对这个问题进行了初步的探讨,结论是:下一代网络具有新的集成业务体系结构,其中的关键是业务互通问题;其中IP用于网络互联,SIP用于建立终端和服务器间的业务会话,提供业务之间的互作用,实现端到端业务能力的集成和最终应用的集成需要新的网格业务技术;下一代网络除要有分别支持网络互联、会话建立和业务集成的能力以外,还必须建立网络、会话和业务之间的新的互作用关系,使得下一代网络的目标得以实现.     

Heuristic Algorithms for Grooming of Arbitrary Traffic in WDM Ring Networks

In a wavelength division multiplexing (WDM) network, sub-wavelength traffic streams can be elaborately arranged in wavelength channels to minimize the number of required electronic end systems, known as the traffic grooming problem. In this paper, a modified genetic algorithm without crossover operation is proposed to solve the problem using a permutation-based chromosome representation and using a selection strategy of reproducing the best chromosomes, thereby minimizing the number of electronic devices and requiring less wavelengths. Then, three methods are developed to improve the performance of the algorithm and a hill-climbing algorithm is proposed for the same purpose. Computer simulations were performed with plenty of randomly generated traffic patterns in unidirectional rings. The results show that these methods can improve the algorithm considerably. The relationships between the minimized network cost and the number of nodes are also presented.     

双跳波分复用网络的结构和访问控制协议

本文提出了一种无源星形波分复用网，网络中任意两个用户都能在１￣２跳内通信。本文还提出了波长配置算法，沱能使光器件的调谐范围最小，以降低网络对光器件的要求；它同时还使网络的单跳的比例最大，以降低分组时延。本文还对网络性能进行了理论分析和计算机模拟。     

Optical Burst Transport: A Technology for the WDM Metro Ring Networks

We propose a sublambda traffic-grooming scheme on wavelength-division-multiplexing ring networks, named optical burst transport. The network protocol and architecture are designed to support dynamic bandwidth allocation, which is more reasonable for bursty data traffic. To verify our network protocol and architecture, we build a testbed which supports burst-mode transmission. Also, we transmit streaming video over Ethernet as an application     

WDM城域环网中支持可变长分组的节点结构及MAC协议设计

WDM城域环网在升级时,信道数可能是不变的.本文基于此设计了一种新颖的节点结构,它由固定发射器和一组固定接收器组成.基于该结构,文中给出了支持可变长分组的时隙结构及MAC协议.由于实现MAC协议毋需专用波长信道,提高了资源利用率.理论分析和仿真结果证明了本文设计方法可以充分利用空间重用能力,获得很好的网络流量,分组排队时延及分组丢弃率.对于信道数较多,或者网络在升级时信道数也可能变化的情况,本文建议采用固定发射器,一组"准"调谐的接收器结构.该方案可在实现复杂度,网络性能及成本间取得折衷.     

下一代电信网的特点、结构和演进

本文首先分析了新时期的挑战,得出发展下一代电信网是历史必然的结论,然后分别探讨了电路交换网和数据网演进思路,最后给出了一代电信网的特点,结构和演进的思考。     

Dynamic Bandwidth Allocation in WDM Passive Star Networks with Asymmetric Traffic

When asymmetric traffic is offered to a WDM passive star network, the offered bandwidth must be allocated is such a way that each station takes a portion of the available bandwidth proportional to its needs. When the traffic characteristics are fixed and a priori known, then, the bandwidth allocation scheme can be based on these characteristics. Unfortunately, the traffic characteristics are often unknown and time-variable. In this paper, a dynamic bandwidth allocation scheme is presented, which is based on the network feedback information in order to be capable of adapting to the changing traffic characteristics. According to the proposed scheme, a set of learning automata processes the network feedback information and dynamically allocates the available bandwidth to the stations according to their needs.     

下一代多波长光接入网体系架构的研究

介绍了下一代多波长光接入网的主要技术及其体系架构，主要包括WDM—PON技术、WDM／TDM—PON技术、WDM／OCDMA—PON技术。重点介绍了WDM—PON无色ONU的实现方式，其中采用RSOA实现ONU无色化的体系架构有很大的应用前景。分析了下一代基于广播电视的WDM-PON体系架构的研究现状和发展方向。     

自适应TDM/WDM光网络结构

WDM(波分复用)技术极大地利用了光纤的巨大带宽潜力，为此介绍了一种运用WDM技术的光网络结构，其中心局之间通过光交换设备的控制进行自适应的时分交换，同一中心局内的光交换机之间通过预约的时分复用共享所有可用波长，IP(因特网协议)数据包可以直接在该网络中透明传输。该网络结构具有组网灵活，带宽利用率高，扩容性好以及路由方法简单的优点。     

Optimal Wavelength Assignment Algorithms for Permutation Traffic in Multi-Fiber WDM Ring Networks*

Permutation traffic occurs in a number of networking applications. In this paper, the problem of wavelength assignment for permutation traffic in multi-fiber WDM rings with and without wavelength conversion is considered. We focus on a special class of permutation traffic and analyze the bounds on the number of wavelengths required to establish the connections. Lower bounds and optimal algorithms are presented for all the cases. The results indicate that a small number of fibers is sufficient to provide most of the benefits that wavelength conversion provides for this class of permutation traffic.     

A simplified energy consumption model for fiber-based Next Generation Access Networks

ICTs account nowadays for 2% of total carbon emissions. However, in a time when strict measures to reduce energy consumption in all the industrial and services sectors are required, the ICT sector faces an increase in services and bandwidth demand. The deployment of Next Generation Networks (NGN) will be the answer to this new demand and specifically, the Next Generation Access Networks (NGANs) will provide higher bandwidth access to users. Several policy and cost analysis are being carried out to understand the risks and opportunities of new deployments, though the question of which is the role of energy consumption in NGANs seems off the table. Thus, this paper proposes a model to analyze the energy consumption of the main fiber-based NGAN architectures, i.e. Fiber To The House (FTTH) in both Passive Optical Network (PON) and Point-to-Point (PtP) variations, and FTTx/VDSL. The aim of this analysis is to provide deeper insight on the impact of new deployments on the energy consumption of the ICT sector and the effects of energy consumption on the life-cycle cost of NGANs. The paper presents also an energy consumption comparison of the presented architectures, particularized in the specific geographic and demographic distribution of users of Spain, but easily extendable to other countries.     

Applications of 40-Gb/s Chirp-Managed Laser in Access and Metro Networks

We investigate 40-Gb/s cost-efficient transmitter for access and metro networks. This 40-Gb/s transmitter comprises a standard directly modulated distributed-feedback (DFB) laser and a subsequent optical filter. Large dispersion tolerance of this transmitter is realized by chirp control through the phase correlation between adjacent bits for the destructive interference in order to erase the power of “0” bits while enhancing the extinction ratio. The chirp model of the DFB laser and the optimum parameters of the optical filter have been numerically analyzed. The chirp-managed 42.8-Gb/s transmission over 20-km standard single mode fiber (SSMF or SMF-28) without dispersion compensation and a centralized lightwave WDM-PON system are experimentally demonstrated. We have also realized the transmission over 100-m graded index plastic optical fiber (GI-POF). Moreover, the application in the metro network over 240-km SSMF or SMF-28 has also been investigated in this paper.      

Improved Approaches for Cost-Effective Traffic Grooming in WDM Ring Networks: Uniform-Traffic Case*

To fully utilize the capabilities of a SONET/ADM network, traffic grooming is needed to multiplex a number of lower-rate traffic streams into a higher-rate stream, and vice versa. Although the capacity of a SONET ring network can be upgraded by operating it over multiple wavelengths, the corresponding network design may be costly if it employs a large number of ADMs. A cost-effective design attempts to minimize the total number of ADMs used in the network while carrying the offered traffic. We introduce and evaluate the performance characteristics of two new traffic-grooming approaches for WDM ring networks, called single-hop and multihop. Our single-hop implementation uses the simulated-annealing heuristic. After placing all the traffic on virtual circles, we group the circles in order to reduce the number of ADMs in the network. Our multihop implementation places an ADM at each node based on the requested traffic in the traffic-demand matrix; then, it tries to groom the wavelengths which can be groomed. We select one of the nodes to be the hub node which has an ADM for each wavelength. The hub node, therefore, can bridge traffic between all of the wavelengths. Each algorithm is specified and illustrated by a simple example. Our results demonstrate that it is beneficial to use a single-hop approach based on simulated annealing for a small grooming ratio, but for a large grooming ratio and node number, we advocate the use of the multihop approach.     

下一代网络的运营支撑系统

由于管制的放松以及前所未有的技术进步，电信业正经历着一场革命。在这一革命中，最引人注目的是利用下一代网络（NGN）系统提供数据、语音、集成多媒体业务。竞争性本地网运营商（CLEC）、本地数据网运营商（DLEC）、互联网服务商ISP）、应用服务商（ASP）、无线数据服务商、城域以太网服务商、卫星通信服务商、光纤批发运营商以及公共设施提供者均是推动NGN发展的重要成员。何谓NGN？NGN是利用分组交换网络提供实时通信，包括电话，视/音频会议以及多媒体协同业务的公用基础设施。在迎合最终用户需求方面，服务商当前和将来均…     

面向NGN的综合接入万门局

融合是电信网络发展的必然趋势和一直追求的目标，从普遍认可的三网合一的理念，到现在的综合接入和NGN软交换技术的实现，越来越强烈地传达着网络融合的信息，体现着网络融合现实而快速的发展。     

面向NGN的综合接入万门局

NGN是一个业务驱动型的网络，但同时又是一个综合建设运营方面高性价比的网络。NGN在生产成本，使用成本、发展成本等多个方面都得到了更大的优化。