Architectural and technological issues for future optical Internetnetworks

This article reports a review of the most significant issues related to network architectures and technologies which will enable the realization of future optical Internet networks. The design of such networks has to take into consideration the peculiar characteristics of Internet traffic. Several architectures have been proposed to provide optical networking solutions, based on wavelength-division multiplexing and compatible with the IP world. These architectures are presented briefly, and the main advantages and drawbacks are discussed. Furthermore, advanced network architectures are reported. In particular, two network paradigms are illustrated and discussed: the optical transparent packet network and optical burst switching. Finally, the key technologies are illustrated     

FSAN OAN-WG and future issues for broadband optical access networks

Network operators are aiming to provide a broadband access network to facilitate the next-generation telecom services. They have established the Full Services Access Networks (FSAN) group in order to find the best way to achieve early and cost-effective deployment of broadband optical access systems. They concluded that a single worldwide broadband access system should be investigated in the FSAN and then standardized in the international standards bodies such as the ITU-T. This article outlines the FSAN organization and the study targets for its Optical Access Network working group, and some key future study issues in terms of optical distribution network requirements and the required system functionalities of the B-PON system. It also describes its standardization strategy and the interaction between the FSAN and ITU-T     

A WDM-based optical access network for wide-area gigabit access services

This article proposes and demonstrates a WDM-based access network that directly connects end users over a wide area to the center node and provides guaranteed full-duplex Gigabit Ethernet access services to each of over 100 users. The center node employs an optical carrier supply module that generates not only the optical carriers for the downstream signals but also those for the upstream signals. The latter are supplied to optical network units (ONUs) at users' homes/buildings via the network. Since the ONUs simply modulate the optical carriers supplied from the center node via the network, they are wavelength-independent.     

Local access optical networks

Both broadcast CATV and switched telephony access networks have evolved, over decades, to deliver their respective services efficiently. But these networks are not necessarily optimal for services that are rapidly emerging. This suggests that the access infrastructure will likely change in the future, driven by demands for new services and the costs of providing them. Will fiber optic networks play an important role? Trade-offs in desirable network properties (low initial costs, high capacity, flexible provisioning, enhanced maintenance and operations, etc.) are strongly influenced by the network architecture. We classify architectures on two characteristics: delivery mode (i.e., broadcast vs. switched) and carrier utilization (i.e., shared vs. dedicated), examining the trade-offs these imply with several examples of existing and proposed architectures. We show that optical networks can, by virtue of recent component development, be reconfigured to change their characteristics without changing the outside plant     

A robust optical flow computation

This paper presents a new method for robust and accurate optical flow estimation. The significance of this work is twofold. Firstly, the idea of bi-directional scheme is adopted to reduce the model error of optical flow equation, which allows the second order Taylor＇s expansion of optical flow equation for accurate solution without much extra computational burden; Secondly, this paper establishs a new optical flow equation based on LSCM （Local Structure Constancy Model） instead of BCM （Brightness Constancy Model）, namely the optical flow equation does not act on scalar but on tensor-valued （matrix-valued） field, due to the two reason： （1） structure tensor-value contains local spatial structure information, which provides us more useable cues for computation than scalar; （2） local image structure is less sensitive to illumination variation than intensity, which weakens the disturbance of non-uniform illumination in real sequences. Qualitative and quantitative results for synthetic and real-world scenes show that the new method can produce an accurate and robust results.     

一种新有用于光码分多址的光相关器

本文提出了一种新的用于光码分多址系统的光相关器,并对光同步和异步系统给出了误比特率公式。数值仿真结果表明,无论是异步还是同步系统,这种光相关器的误比特率性能都优于传统光相关器的性能。     

Architectural design for multistage 2-D MEMS optical switches

Next-generation wavelength routing optical networks requiring optical cross connects (OXC) in the network have the ability to direct optical signals from any input interface to suitable output interfaces by configuring their internal embedded optical switch matrices. Microelectromechanical systems (MEMS) switches are regarded as the most promising technology to achieve such functionality. We consider the construction of a multistage MEMS switch network with single two-dimensional (2-D) MEMS switch blocks. A power loss model is developed that calls on a single MEMS block that is then used to develop the model for a three-stage Clos network. An effective model for maximum loss difference between calls is also developed. Based on these, the paper also proposes three connection patterns [Max + Min greedy (MMG), compressed extended generalized shuffle 1 (C-EGS-1), and compressed extended generalized shuffle 2 (C-EGS-2)] to connect outlet ports and inlet ports between two neighboring stages in a three-stage Clos network. These connection patterns are proved to be optimal and efficient enough to reach the minimums of both the maximum power loss of calls and the maximum loss difference between calls     

Advanced modulation formats for more robust optical transmission systems

Interest in advanced modulation formats for optical communication systems has so far experienced two major waves. The first one was motivated by the potential to enhance receiver sensitivity of thermal noise-limited systems using coherent detection in combination with phase shift keying. It ended with the advent of optical amplification, enabling high sensitivities together with polarization insensitive, simple and stable direct detection. The second wave is still rolling, fueled by the potential of advanced modulation formats to increase robustness of optical transmission systems against signal distortions. Due to performance limitations given by direct detection and nonlinear effects in the transmission fiber, it is not decided yet, whether there will be widespread application in carrier networks.     

企业级大用户光纤接入的方案比较

本文比较了三种目前在FTTP领域有竞争力的光纤接入层网络技术和设备，基于SDH的MSTP自愈环和弹性分组环（RPR），多业务的千兆EPON和多业务网络光端机（一种在传输汇聚层上将TDM电路和以太网混合传输的星形网络设备），并指出在FTTP领域，EPON和多业务网络光端机是适合大多用户的普遍接入的解决方案。     

高生存性光接入网结构分析

从网络结构方面对光接入网生存性进行了研究,在对各种网络接入结构生存性初期分析的基础上,利用共享链路组(SRLG)的概念定量分析了各种接入拓扑结构的网络生存性,表明了星型环接入网结构在网络生存性方面较现行各种网络结构的优越性;提出了改进的网络生存率计算算法,利用分层计算和等价归并结合的方式,减少了计算量,提高了计算效率,尤其在总故障数目多的情况下可以大大减少计算时间,快速计算网络生存率.     

Novel field installable optical fiber splice and connector for optical access networks

We have developed two types of field installable connection techniques. One is mechanical splicing, which is used to connect coated optical fibers without the need for stripping or cleaning procedures. The other is a field assembly connection technique, which employs a new type of field installable connector that makes it possible to realize a physical contact connection with chamfer grinding. Mechanical splicing is achieved by precisely aligning and directly connecting coated fibers with a capillary. The assembled splice is installed with 1.3-μm single-mode fibers that have an 80-μm cladding and a 125-μm coating and they exhibit good optical performance with a low average insertion loss of 0.2 dB. Connection is achieved with our developed field installable connector by using a chamfered fiber endface and the compression force of the buckled fiber. The assembled connectors achieve physical contact with the chamfered fiber endface, which provides good optical performance with a low insertion loss of 0.11 dB.     

Architectural issues of ATM based connectionless overlay network

Connectionless service such as SMDS, or its European equivalent CBDS, can be provided by an ATM network by building a separate connectionless overlay network (CLON) on top of the ATM bearer service. A CLON is composed of a number of connectionless servers, CLSs, which provide the routing function, connected by semipermanent virtual paths (VPs). In this paper, architectural issues related to the design of a CLON are studied. In particular, we address the question of the optimal number of CLSs and their interconnection topology, assuming the underlying ATM network and the mean connectionless traffic load are known. The objective of the design process is to meet given design criteria with minimum costs. The QoS requirements of the SMDS/CBDS service are briefly reviewed and a simple cost model for the CLON network is given. The dimensioning of the logical links is also considered. Then the design process to find the optimal solution for the whole network is outlined. A simplified procedure was applied in numerical studies of the topological optimization. In order to find the general dependence of the optimal number of CLSs on the size of the network and other network parameters, the optimization procedure was applied to a large number of sample ATM networks, generated by an algorithm which is briefly described. Results from these studies are presented and discussed.     

Developments in optical access networks

Optical fibre access network technology has become more complex over the last few years with bit rates steadily increasing. PONsystems are available with bit rates in the range 155 Mbit/s to, currently, 622 Mbit/s. Newly designed systems, both PON andpoint-to-point, will allow this trend to continue with 2.5 Gbit/s systems becoming practicable in the near future.With this increase in technology has come an increase in the opportunities for fibre systems to cost-reduce more of the network,including the metro space – a fact which increases the appeal of the technology.Some of the newer PON systems are being designed using Ethernet as the underlying technology with a promise of reducing theprice of the technology still further. How this will occur in practice, however, is still unclear.What is certain is that optical access technologies are expanding and are sure to find openings in real networks in the foreseeablefuture.     

光接入网技术研究

文章介绍了宽带光纤接入网系统和其中的几种主流接入方式，并详细比较了几种接入技术在应用上的优缺点，最后给出了建议和展望。     

A network management architecture for robust packet routing in meshoptical access networks

We describe an architecture for an optical local area network (LAN) or metropolitan area network (MAN) access. The architecture allows for bandwidth sharing within a wavelength and is robust to both link and node failures. The architecture can be utilized with an arbitrary, link-redundant mesh network (node-redundancy is necessary only to handle all node failures), and assumes neither the use of a star topology nor the ability to embed such a topology within the physical mesh. Reservation of, bandwidth is performed in a centralized fashion at a (replicated) head end node, simplifying the implementation of complex sharing policies relative to implementation on a distributed set of routers. Unlike a router, however, the head end does not take any action on individual packets and, in particular, does not buffer packets. The architecture thus avoids the difficulties of processing packets in the optical domain while allowing for packetized shared access of wavelengths. We describe the route construction scheme and prove its ability to recover from single link and single node failures, outline a flexible medium access protocol and discuss the implications for implementing specific policies, and propose a simple implementation of the recovery protocol in terms of state machines for per-link devices