Optical burst switching for service differentiation in thenext-generation optical Internet

In an effort to eliminate the electronic bottleneck, new optical switches/routers (hardware) are being built for the next-generation optical Internet where IP runs over an all-optical WDM layer. However, important issues yet to be addressed in terms of protocols (software) are how to develop a new paradigm that does not require any buffer at the WDM layer, as in circuit switching, and elimination of any layers between which exist mainly due to historical reasons. At the same time, such a paradigm should also efficiently support bursty traffic with high resource utilization as in packet switching. This article surveys design issues related to a new switching paradigm called optical burst switching, which achieves a balance between circuit and packet switching while avoiding their shortcomings. We describe how OBS can be applied to the next-generation optical Internet, and in particular how offset times and delayed reservation can help avoid the use of buffer, and support quality of service at the WDM layer     

Optical homodyne frequency domain reflectometer using an externalcavity semiconductor laser

An external cavity traveling-wave semiconductor ring laser with narrow linewidth is used as a light source for research in frequency domain reflectometry. The optical frequency of the laser is linearly chirped by an intra-cavity phase modulator. The time-delayed reflection signal is mixed with a reference signal to produce a microwave frequency that indicates the position of the reflection. For optical fiber measurement, a spatial resolution of 30 m and a one-way dynamic range of 28 dB for Rayleigh backscattered light have been achieved     

Codes for spectral-amplitude-coding optical CDMA systems

Codes with ideal in-phase cross correlation (CC) are required in spectral-amplitude-coding optical code-division multiple-access (CDMA) systems since these codes eliminate multiuser interference and also suppress the effect of phase-induced intensity noise. However, little research work has been done on such codes although codes with ideal CC have been studied for many years. In a paper by Zhou et al. (2000), such a code has been introduced, but no clear construction method has been presented. In this paper, we first review the construction method of this old code and then construct two new codes with ideal in-phase CC in algebraic ways. Both of the proposed new codes are obtained by modifying former codes with ideal CC. It has been shown that the system performance can be improved significantly by using codes with ideal in-phase CC instead of the Hadamard code. These codes can also be used in the synchronous optical CDMA systems for multiuser interference cancellation.     

Optical time domain reflectometry using an M-ary FSK probe andcoherent detection

This paper proposes a new approach to enhancing the performance of optical time domain reflectometry (OTDR). This approach launches a probe signal modulated in the M-ary FSK format into a test fiber and detects the backscattering by coherent detection, which offers excellent frequency discrimination, followed by simple signal processing to recover the fiber impulse response. Fault location experiments verify the theoretical prediction of that the proposed approach reduces the measurement time to 1/M without sacrificing measurable dynamic range or spatial resolution. They also show that the approach is effective in reducing fluctuations in the OTDR trace. It is experimentally confirmed that OTDR with the proposed approach is feasible for long haul transmission systems     

Performance enhancement of spectral-amplitude-coding optical CDMAusing pulse-position modulation

Spectral-amplitude-coding optical code-division multiple-access (OCDMA) systems are limited by interference between incoherent sources. A detailed analysis of this limit for a system with a balanced receiver is presented. Additional pulse-position modulation (PPM) coding is proposed as a method to improve the system performance beyond this limit. A simple and robust PPM decoding structure is proposed, and the performance analysis of the whole PPM-OCDMA system is presented. The interference-limited performance of the PPM-OCDMA system is found to be superior to that of the original system when the number of simultaneous users is of the order of the PPM word length or larger. In particular, for a PPM word length of two, an increase in spectral efficiency of up to 100% is possible with no change in the signaling rate, data rate, or bit-error rate (BER)     

Feasibility analysis for service differentiation using an FDL bank in OBS networks

A service differentiation scheme in optical burst switching (OBS) networks, which is based on dynamic fiber delay line (FDL) assignment, is shown. The effectiveness of the scheme is validated by numerical analysis and extensive simulations. Especially, the feasibility conditions for the service differentiation scheme, which are considered as the minimum number of FDLs for each sub-FDL group, are displayed. The feasibility conditions are derived numerically, and are verified through extensive simulations. The results of extensive simulations show that the proposed scheme and the feasibility conditions are valid for service differentiation in OBS networks.

光业务管理是提供多级别城域网业务的关键

随着电信业的发展,传统的运营商和下一代业务提供商为了获得更多的收入而展开了更激烈的竞争。竞争的加剧又促成了新的业务模型的产生,这些新的模型能使运营商通过降低网络成本将其自身与竞争对手区分开来。未来的业务能力将包括按需分配带宽、基于用户的配置、基于使用的计费以及企业网和专用网的线路外租等等。现在标准组织和系统厂商已经将重点放在了窄带和宽带网络基础设施与下一代互连模型的融合上。尽管这样的技术对于业务提供商实现他们的业务和收入目标是十分必要的,但是,这些技术已经不能再为业务提供商和系统厂商提供足够的竞…     

Multi-weight unipolar codes for multimedia spectral-amplitude-coding optical CDMA systems

A novel balanced detection scheme for multi-access interference cancellation in multimedia spectral-amplitude-coding optical code-division multiple-access system is proposed. The receiver is capable of handling both equal and unequal in-phase cross correlation of optical orthogonal codes. A novel class of constant-length variable-weight optical orthogonal codes able to support multimedia services with different quality-of-service requirements is proposed as well. The construction is based on the pairwise balanced designs, or more specifically, on an incidence structure defined on an integer sub-lattice.     

Providing service differentiation for optical-burst-switched networks

This paper proposes a service differentiation scheme called preemptive wavelength reservation protocol (PWRP) to provide proportional quality of service (QoS) for optical-burst-switched (OBS) networks. In the context of service differentiation, traffic is divided into different service classes based on traffic characteristics. A service differentiation scheme then provides different degrees of resource assurance to different classes of traffic in proportion to their service classes. Unlike existing approaches, which may degrade to classless schemes or which may suffer from low wavelength utilization, the mechanism in this paper is robust and efficient and supports an incremental deployment of QoS support. A usage profile for each class is maintained at the router, and a preemptive wavelength reservation mechanism is implemented to ensure QoS. An analytical model is derived and simulations are conducted to evaluate the performance. The results show that the approach described in this paper performs better than existing mechanisms in terms of lower blocking probability and higher resource utilization, making it an excellent QoS mechanism for OBS networks.     

The application of spectral-amplitude-coding optical CDMA in passive optical networks

One code family suitable for passive optical network based on optical code division multiple access is present. Though spatial coding is used for capacity enlargement, the corresponding encoding/decoding devices require less fiber ribbons than that of the spatial/spectral systems proposed previously and the code cardinality is maintained. In addition, the multiple access interference is eliminated in the decoders of the proposed network and the phase-induced intensity noise arising during the photo-detecting process is suppressed further. Therefore, larger capacity can be accommodated in the network with simplified coding hardware.     

Optical time domain reflectometry by photon counting

A photon counting technique has been used to extend greatly the range of optical time domain reflectometry or `back-scatter? for fault location in optical fibre systems. A range of more than 40 dB of one-way fibre loss has been achieved even when the break was index-matched to eliminate any reflection.     

基于光GMPLS接入网中区分服务的QoS研究

通过配置区分服务体系实现基于光GMPLS环状网络的QoS测量,涉及到不同的实时多媒体服务.讨论并分析区分服务结构的三种服务级别的特性.仿真结果表明,在网络过载的情况下,快速转发类和保证转发类都有很好的保护作用.加速转发类适合于实时服务,而最大努力类对任何类型的服务}生能都非常低,同时保证转发非常适合于视频流.     

QoS for wireless sensor networks: Enabling service differentiation at the MAC sub-layer using CoSenS

Providing service differentiation in wireless sensor networks while proposing simple and highly scalable solution is a challenging problem. We retain the use of CSMA/CA as access protocol because of its simplicity, versatility and good scalability properties. We developed CoSenS, a Collect then Send burst Scheme, on top of it to address its weaknesses while facilitating the implementation of scheduling policies. In this article, we propose a simple and scalable service differentiation solution; we implement fixed priority and earliest deadline first on top of CoSenS. The simulation analysis shows that our solution self-adapts to the traffic variation and greatly enhances end-to-end delay, reliability and deadline meet ratio for urgent traffic while not degrading best effort traffic compared to IEEE 802.15.4 original protocol and IEEE 802.15.4 implementing these scheduling policies. Additionally, CoSenS is implemented and tested on motes. The real experimentation results validated our simulation analysis.     

A QoS architecture for quantitative service differentiation

For the past decade, a lot of Internet research has been devoted to providing different levels of service to applications. Initial proposals for service differentiation provided strong service guarantees, with strict per-flow bounds on delays, loss rates, and throughput, but required high overhead in terms of computational complexity and memory, both of which raise scalability concerns. Recently, the interest has shifted to class-based service architectures with low overhead. However, these newer service architectures only provide weak service guarantees, which do not always address the needs of applications. In this article we introduce a service architecture that supports strong per-class service guarantees, can be implemented with low computational complexity, and only requires maintenance of a little state information. A key mechanism of the proposed service architecture is that service rate allocation to classes is adaptive, and combined with buffer management. Furthermore, instead of using admission control or traffic policing, the proposed architecture exploits explicit congestion notification for the purpose of regulating the traffic entering the network.     

用无透镜傅里叶变换全息进行光学微分

本文提出用无透镜傅里叶变换全息进行二阶光学微分的新方法,文中给出理论分析及实验结果。     

利用互补光栅编码实现光学图像的微分

一、引言 早在1971年,S.K.Yao和S.H.Lee就在相干光学处理系统中,通过复合光栅在频谱平面上进行空间滤波而实现了微分运算。1984年,冯郁芬又在此方法的基础上,利用非线性记录的复合光栅作频谱滤波,可从+1级和+2级分别输出图像的一阶微分和二阶微分的结果。但是,在这类方法中,由于使用的是相干照明光源,所以输出图像都不可避免地受到相干噪声的干扰。于是人们又研究非相干光学方法,如实时白光图象微分法。这种方法使用白光处理系统,实时地实现了黑白图像的假彩色微分图像。1985年,羊国光等人又利用单色非相干线光源照明,用具有微分脉冲响应的全息滤波器作空间滤波而实现了图像的一维微分运算,其明显的好处是可以有效地抑制相干噪声,提高输出图像的质量。     

A scheduler for relative delay service differentiation

We propose a new delay-based scheduler called asRD-VC (Relative Delay VirtualClock). Since it performs a delay-based service differentiation among flow aggregates, the quality at microflow level is the same as that at aggregate level. This is not easily achievable when the service differentiation is bandwidth-based or loss-based. Unlike theEDF (Earliest Deadline First) scheduler [1], our proposed scheduler self-regulates and adapts the delays according to load changes. This characteristic permits us to implement it in an AF-likePHB providing the relative quantification service in a DiffServ network. Finally, we compare our proposedrd-vc scheduler with two important existing propositions:WTP (Waiting Time Priority) [2, 3] andex-vc (Extended VirtualClock) [4]. Both these propositions are delay-based and have self-regulation property. All three schedulers (RD-VC, WTP andEX-VC) maintain the required service differentiation among aggregates and have comparable long term average performance like mean throughput per aggregate and packet loss ratio etc. However,RD-VC and WTP take an edge overEX-VC at short-term performance like jitter. Bothrd-vc andWTP have good long term and short-term performance. Our proposedrd-vc, compared to existingWTP, has two additional characteristics, i.e. unlike WTP which is limited to architectures with one queue per Qos class, it has no limitation on implementation scope (with or without separate queues per class) and it has lower complexity. This rendersRD-VC an interesting proposition.     

Optical time domain reflectometer using a photon-counting InGaAs/InP avalanche photodiode at 1.3 ?m

We report the first photon-counting optical time domain reflectometer using an InGaAsInP avalanche photodiode. The measured sensitivity at a temperature of ?40°C is comparable to that of the best present conventional PINFET receiver results.     

Optical frequency domain ranging by a frequency-shifted feedbacklaser

This paper describes the theoretical and experimental study of a new technique for optical frequency domain ranging (OFDR) by a frequency-shifted feedback (FSF) laser. In conventional OFDR, a frequency chirped single-mode laser is used as a light source to convert a distance into a beat frequency, and a tradeoff exists between measurement range and resolution. The FSF laser output consists of periodically generated chirped frequency components whose chirp rate is faster than 100 PHz/s (P=10¹⁵), By use of the FSF laser, the tradeoff is removed and long-distance high-resolution OFDR is realized In the experiment, a distance of 18.5 km was measured with a resolution of 20 mm     

Optical interaction with high-field domain nucleation in GaAs

Control of nucleation of high-field domains in GaAs has been reported for essentially one-dimensional samples. The present work reports an optically triggered bimodal form of domain launch in a 3- dimensional sample. The preliminary experiments describing this effect are given, indicating an optically induced time shift in domain launch without a corresponding change in the repetition rate of a domain-generated pulse train. A useful application of this effect to a circulating digital optical memory is described.