Probabilistic Analysis of Cyclic Packet Transmission Scheduling in WDM Optical Networks

We study the packet transmission scheduling problem with tuning delay in wavelength-division multiplexed (WDM) optical communication networks with tunable transmitters and fixed-tuned receivers. By treating the numbers of packets as random variables, we conduct probabilistic analysis of the average-case performance ratio for the cyclic packet transmission scheduling algorithm. Our numerical data as well as simulation results demonstrate that the average-case performance ratio of cyclic schedules is very close to one for reasonable system configurations and probability distributions of the numbers of packets. In particular, when the number of receivers that share a channel and/or the granularity of packet transmission are large, the average-case performance ratio approaches one. Better performance can be achieved by overlapping tuning delays with packet transmission. We derive a bound for the normalized tuning delay Δ such that tuning delay can be completely masked with high probability. Our study implies that by using currently available tunable optical transceivers, it is possible to build single-hop WDM networks that efficiently utilize all the wavelengths.     

Adaptive load-balancing in WDM mesh networks with performance guarantees

In nowadays, wavelength-division multiplexing (WDM) networks, on the one hand, increasingly more users expect the network to provide high-priority QoS services demanding no congestion and low latency. On the other hand, it is significantly more difficult for network operators to forecast future traffic demands, as the packet traffic running over WDM networks fluctuates over time for a variety of reasons. Confronted with a rough understanding of traffic patterns as well as the increasing number of time-sensitive applications, most networks today are grossly over-provisioned. Thus, designing cost-effective WDM networks in an uncertain traffic environment, which includes network planning and robust routing, is both an important and a challenging task. In this paper, we explore adaptive load-balancing to investigate the problems of network planning and robust routing for WDM mesh networks under varying traffic matrices. We first propose an efficient heuristic algorithm called Maximizing Network Capability (MNC) to provision congestion-free and cost-effective WDM networks based on load-balancing to deal with traffic uncertainty. Then, a novel traffic grooming algorithm called Adding Direct Traffic (ADT) is proposed to implement robust routing with partial traffic information. Finally, we demonstrate by simulation that MNC consumes less resources than previous methods and performs quite close to the optimal solution, while ADT achieves the desirable performance in delay, jitter (delay variation), and throughput compared with existing robust routing and traffic grooming algorithms.     

Packet labeling technique using electronic code-division multiple-access for WDM packet-based access networks

We propose and experimentally demonstrate the feasibility of a packet labeling technique using electronic code-division multiple-access for a wavelength-division-multiplexing (WDM) packet-based access network, whereby each wavelength is assigned a unique electronic code-based label on a radio-frequency subcarrier. Such a technique allows individual wavelength channels to be electronically identified without requiring the use of a WDM demultiplexer. We experimentally demonstrate this technique with two WDM channels each with 1.25-Gb/s payload data and 10-Mb/s header coded onto an electronic code at 160 Mb/s. The experimental results and theoretical analysis show that this technique has the potential to support large numbers of WDM channels.     

A prototype broadcast-and-select photonic ATM switch with a WDMoutput buffer

A rack-mounted prototype of a broadcast-and-select (B and S) photonic ATM switch is fabricated. This switch has an optical output buffer utilizing wavelength division multiplexed (WDM) signals. The WDM technology solves. The cell-collision problem in a broadcast-and-select network and leads to a simple network architecture and the broadcast/multicast function. The prototype can handle 10-Gb/s nonreturn-to-zero (NRZ) coded cells and 5-Gb/s Manchester-coded cells and has a switch size of four. In this prototype, the level and timing design are key issues. Cell-by-cell level fluctuation is overcome by minimizing the loss difference between the optical paths and adopting a differential receiver capable of auto-thresholding. The temperature control of delay lines was successful in maintaining the phase synchronization. Using these techniques, we are able to provide a WDM highway with a bit error rate of less than 10^-12. Fundamental photonic ATM switching functions, such as optical buffering and fast wavelength-channel selection, are achieved. We show our experimental results and demonstrate the high performance and stable operation of a photonic ATM switch for use in high-speed optical switching systems as an interconnect switch for a modular ATM switch and an ATM cross-connect switch     

全光光孤子WDM到OTDM转换的概念系统

提出了在未来的光孤子波分复／时分复用网络中由ＷＤＭ到ＯＴＤＭ节点处的转换复用的概念系统，主要的模块是完成波长转换的基于交叉增益调制的半导体光放大器，同步和延时及时分复用模块。通过ＳＯＡ可以实现全光的ＷＤＭ到ＯＴＤＭ的波长转换复用，是ＷＤＭ／ＯＴＤＭ网络实用化的一个关键部分。     

Wavelength reuse for efficient packet-switched transport in an AWG-based metro WDM network

Metro wavelength-division multiplexed (WDM) networks play an important role in the emerging Internet hierarchy; they interconnect the backbone WDM networks and the local-access networks. The current circuit-switched SONET/synchronous digital hierarchy (SDH)-over-WDM-ring metro networks are expected to become a serious bottleneck-the so-called metro gap-as they are faced with an increasing amount of bursty packet data traffic and quickly increasing bandwidths in the backbone networks and access networks. Innovative metro WDM networks that are highly efficient and able to handle variable-size packets are needed to alleviate the metro gap. In this paper, we study an arrayed-waveguide grating (AWG)-based single-hop WDM metro network. We analyze the photonic switching of variable-size packets with spatial wavelength reuse. We derive computationally efficient and accurate expressions for the network throughput and delay. Our extensive numerical investigations-based on our analytical results and simulations-reveal that spatial wavelength reuse is crucial for efficient photonic packet switching. In typical scenarios, spatial wavelength reuse increases the throughput by 60% while reducing the delay by 40%. Also, the throughput of our AWG-based network with spatial wavelength reuse is roughly 70% larger than the throughput of a comparable single-hop WDM network based on a passive star coupler (PSC).     

基于光相位信号延时自相干的相位信息高速实时取样系统

提出了一种基于光相位信号自相干的高速光相位实时取样方案。利用时延为10ps的延时干涉仪(DI),将待测光信号的相位信息转换为强度信息;再在高非线性光纤(HNLF)中,利用四波混频(FWM)效应对强度信号进行取样。在接收端,利用不同中心波长的光滤波器(OBPF)即可滤出不同时间点的取样信号,从而在光域同时完成高速光相位信息的实时取样和取样信号的串-并转换。本文方案具有成本低、对测信号码率和波长不敏感的优点。实验中,对9GHz正弦调制以及10Gb/s非归零码调制的光相位信号实现了100G/s的高速实时取样系统,并转换为10路10G/s取样信号输出,最终恢复取样光信号的相位波形。     

一种动态时分／波分复用网络的访问控制协议

本文采用部分可调的光器件，针对多控制通道的单跳星形网络，提出了一种动态时分／波分复用（Ｔ／ＷＤＭ）访问控制协议。本协议中控制通道的传播时延很小。本文对均匀分布的业务情况进行了近似分析。数值结果表明，集中式排队使通道利用率高达１．０，并且分组时延相当小。因此这是高速ＷＤＭ网络中行之有效的一种访问控制协议。     

Can DiffServ guarantee IP QoS under failures?

As ISPs and telcos converge toward all-IP network infrastructures, the problem of service reliability becomes more acute. In this article, we investigate to what extent DiffServ can provide service protection against optical failures in IP over optical (WDM) networks. For this, we propose two mechanisms: a DiffServ/WDM method and a WDM differentiated protection technique that we call DiffProtect. Results show that the priority traffic is equally well protected by both techniques. However, for medium-priority traffic, there is an improvement in delay and jitter under failure when DiffServ is used. Thus, the proposed DiffServ implementation can be used as an affordable and effective fault management technique to protect high-priority traffic with little delay.     

Optical Tandem Single-Sideband-Based WDM Interface for Millimeter-Wave Fiber-Radio Multisector Antenna Base Station

We propose and demonstrate a spectrally efficient wavelength division multiplexed (WDM) optical interface for millimeter-wave radio access networks with the capability of being integrated within a standard 100-GHz WDM infrastructure. The proposed WDM optical interface is realized by the use of a multiport optical circulator in conjunction with fiber Bragg grating filters. The interface supports demultiplexing of wavelength-interleaved optical tandem single-sideband modulated signals for a millimeter-wave fiber radio backbone with a sectorized antenna interface at the remote base station. The functionality of the interface is verified experimentally for RF signals at 29 and 31.6 GHz with 155-Mb/s binary phase-shift keying data. The effects of optical impairments on the transmission performance of WDM channels are experimentally analyzed. The experimental results demonstrate that the WDM optical interface performs efficiently with very low channel impairments due to optical crosstalk.      

Transmission edge filters for power equalization of EDFA's

We propose and demonstrate the use of transmission edge filters based on apodized linearly chirped fiber Bragg gratings for providing power equalization among different wavelength channels in an erbium-doped fiber amplifier module. The filters we fabricated provide a dynamic range of ≈13 dB, an amplitude variation of ±0.5 dB from an ideal linear edge, and negligible group delay in transmission. Using the grating filters, we demonstrate power equalization, with no observed variation in signal levels after compensation, for three WDM signals having >6-dB difference in power levels before amplification. Our technique can also be extended to provide active power equalization by incorporating a feedback loop     

Providing deterministic quality-of-service guarantees on WDM optical networks

A major challenge in the design of future generation high-speed networks is the provision of guaranteed quality-of-service (QoS) for a wide variety of multimedia applications. In this paper we investigate the problem of providing QoS guarantees to real-time variable length messages (e.g., IP packets) in wavelength division multiplexing (WDM) optical networks. In particular, we propose a systematic mechanism comprised of admission control, traffic regulation, and message scheduling that provide guaranteed performance service for real-time application streams made up of variable-length messages. We formulate an analytical model based on the theory of max-plus algebra to evaluate the deterministic bounded message delay in a WDM network environment using our proposed QoS guarantee mechanism to determine the "schedulability conditions" of multimedia application streams, We also conduct a series of discrete-event and trace-driven simulations to verify the accuracy of the analytical model. The simulation results demonstrate that the analytic delay bound we obtained for our WDM optical network is valid and accurate.     

Demonstration of timing skew compensation for bit-parallel WDM datatransmission with picosecond precision

We demonstrate transmission of seven wavelength-division-multiplexed (WDM) bit-parallel channels with a total of 15-nm spectral span over a 2.5-km standard single-mode fiber/dispersion-compensating fiber link with less than 3-ps timing skew. The synchronized WDM channels are generated by spectrally slicing pulses from a single femtosecond fiber laser using a femtosecond pulse shaper. The small residual timing skew arises from the residual dispersion slope of the link. We measure a dispersion slope of D'=0.017 ps/km/mn², which is roughly four times less than for an equivalent length of dispersion-shifted fiber. Our work shows that the dispersion-compensating fiber technique could significantly reduce the timing skew for WDM bit-parallel transmission over a several-kilometer fiber link     

Self-tuning PID controller using Newton-Raphson search method

A new algorithm for self tuning of proportional-integral-derivative (PID) controllers is proposed. A combined least-squares estimation and Newton-Raphson search technique is used to determine the ultimate gain and period of an unknown system for the purpose of automatic tuning of PID controllers based on Ziegler and Nichols (ZN) or refined Ziegler and Nichols (RZN) formulas. The proposed algorithm can be applied to systems with known time delay, as well as those with unknown dead time. Simulation studies are used to demonstrate the performance of this algorithm. The performance of this PID self tuner is also compared with a popular commercial auto-tuner for simulated systems and a laboratory-scale real plant     

An AWG-based WDM-PON architecture employing WDM/TDMA transmission for upstream traffic with dynamic bandwidth allocation

In this article, we examine a candidate architecture for wavelength-division multiplexed passive optical networks (WDM-PONs) employing multiple stages of arrayed-waveguide gratings (AWGs). The network architecture provides efficient bandwidth utilization by using WDM for downstream transmission and by combining WDM with time-division multiple access (TDMA) for upstream transmission. In such WDM-PONs, collisions may occur among upstream data packets transmitted simultaneously from different optical networking units (ONUs) sharing the same wavelength. The proposed MAC protocol avoids such collisions using a request/permit-based multipoint control protocol, and employs a dynamic TDMA-based bandwidth allocation scheme for upstream traffic, called minimum-guaranteed maximum request first (MG-MRF), ensuring a reasonable fairness among the ONUs. The entire MAC protocol is simulated using OPNET and its performance is evaluated in terms of queuing delay and bandwidth utilization under uniform as well as non-uniform traffic distributions. The simulation results demonstrate that the proposed bandwidth allocation scheme (MG-MRF) is able to provide high bandwidth utilization with a moderately low delay in presence of non-uniform traffic demands from ONUs.     

A novel medium access control protocol for WDM-based LAN's andaccess networks using a master/slave scheduler

We describe an architecture and medium access control (MAC) protocol for wavelength-division multiplexing (WDM) networks. Our system is based on a broadcast star architecture and uses an unslotted access protocol and a centralized scheduler to efficiently provide bandwidth-on-demand in WDM networks. To overcome the effects of propagation delays the scheduler measures the delays between the terminals and the hub and takes that delay into account when scheduling transmissions. Simple scheduling algorithms, based on a look-ahead capability, are used to overcome the effects of head-of-line blocking. An important application area for this system is in optical access networks, where this novel MAC protocol can be used to access wavelengths in a WDM passive optical network (PON)     

Performance Constraint Analysis of WDM LANs with Nonzero Propagation Delays and Destination Conflicts

In this paper, we study the effect of the round trip propagation delay on performance measures of wavelength division multiplexing (WDM) networks. Even though the impact of propagation delay is substantial in the optical network's behavior, most of the studies ignore the effect of this time component in throughput and delay evaluation. We assume a WDM local area network (LAN) where the round trip propagation delay is less or equal to a data packet transmission time. The proposed asynchronous transmission policy avoids data channel collision. In the analysis, we take into account the propagation delays and the effect of receiver collision for a system with a finite number of stations.     

A collision-free with propagation latency WDMA protocol analysis

The substantial role of propagation delay latency in WDM networks is examined in this paper in conjunction with a multi-channel control architecture (MCA) that reduces the processing overhead of control information for synchronous transmission in passive star topology. We exploit the peculiarity of propagation delay latency in WDM networks and its impact in the performance measures to introduce a simple multiple access algorithm avoiding data channel conflicts, aimed at improving of system utilization. Also we examine the effect of receiver collisions to performance measures evaluation developing analytic Markovian models for finite population.     

All-Optical Data Vortex Node Using an MZI-SOA Switch Array

We propose and demonstrate a new structure of a Data Vortex switch node for all-optical routing of wavelength-division-multiplexing (WDM) 10-Gb/s optical packets. The proposed node consists of two Mach-Zehnder interferometers with integrated semiconductor optical amplifier: an optical and gate and a high-speed optical switch. In the experiment, WDM 10-Gb/s data packets are successfully routed with 1-dB power penalty at a bit-error rate of 10^-9.     

Demonstration of RSOA‐Based 20 Gb/s Linear Bus WDM‐PON with Simple Optical Add‐Drop Node Structure

We demonstrate a linear bus wavelength‐reused gigabit wavelength‐division multiplexing passive optical network (WDM‐PON) with multiple optical add‐drop nodes. A commercially available reflective semiconductor optical amplifier‐based WDM‐PON has a sufficient power budget to provide multiple optical add/drop nodes in 16 WDM channels. Sixteen 1.25 Gb/s WDM channels are successfully transmitted over 20 km of single‐mode fiber with four optical add/drop multiplexers, even with 32 dB reflection and chromatic dispersion in the link.