Methods for Stabilizing the Gain of EDFAs in Burst Switching Optical Networks

Transmitting optical bursts through a chain of erbium-doped fiber amplifiers (EDFAs) results in dynamic gain changes, which in turn lead to possibly large variations in output power of the data channels. There are many proposals how to control these optical amplifiers in order to minimize or eliminate the power variations. In this paper, we investigate the gain dynamics in a burst switching environment experimentally and numerically. With a categorization of gain control schemes we review the state of the art and discuss advantages and disadvantages of the different approaches particularly with regard to burst switching networks. A comparison of the performance of these methods is given. In our opinion there are two preferences, one for the scheme using electronic feedback on the EDFA's pump power, because of good performance, and another for schemes controlling whole links of EDFA cascades by an extra control channel, because of lower costs.     

Decreasing EDFA transients by power shaping

Multi-wavelength optical networks make extensive use of erbium-doped optical amplifiers (EDFAs) to offset the effects of fiber attenuation and signal power splitting. As optical networking moves towards burst and packet switching, the effects of changes of optical power levels on one wavelength, or channel, can have an impact on the behavior of other wavelengths passing through the same amplifier and impair network performance. We have observed in our simulations of EDFA operation that both the amplitude and duration of EDFA transients will decrease when gradual changes are made to the input power of the EDFA. It was also verified in [D.H. Richards, J.L. Jackel, M.A. Ali, A theoretical investigation of dynamic all-optical automatic gain control in multichannel EDFA’s and EDFA cascades, J. Select. Top. Quantum Electron. 3 (4) (1997)] that the switching time of the channel dropping operation can influence the amplitude and duration of EDFA transients. We show that this effect can be exploited to successfully suppress EDFA transients by power shaping. Our approach is to increase/decrease the power of an added/dropped channel gradually, rather than abruptly. Power shaping can be implemented by adapting existing link layer protocols. It is general and can be applied to amplifiers using different technologies, including EDFAs, solid state and Raman amplifiers.     

The use of a triangular estimator to improve scheduling in optical burst switched networks

In an optical burst switched network, variable‐sized data bursts are switched on the fly using bandwidth previously reserved by their control packets. A key problem in OBS networks is the assignment of wavelengths to incoming bursts, that is, the scheduling of bursts. This paper proposes a new class of burst scheduling algorithms based on a triangular estimator. The proposed tool reduces the complexity of the scheduling scheme (measured in channel checks) without compromising its performance (measured by the burst drop ratio). Simulation results demonstrate both the accuracy and the efficiency of the estimator in a variety of scenarios and under self‐similar network traffic. Copyright © 2009 John Wiley & Sons, Ltd.     

OBS网络中基于优先级的先分割后缓存冲突解决方法

为了有效地降低突发包的丢失率和保证OBS网络中不同优先级业务的服务质量,提出了一种基于优先级的先分割后缓存冲突解决方法。该方法通过在多波长信道系统的输出数据信道上设置光纤延迟线组来缓存被分割的冲突突发包。当冲突发生时,首先基于突发包的优先级和处理完毕时间进行"竞争突发包头部分割或者原突发包尾部分割"处理;无冲突部分进行交换或者直接在事先预留的输出数据信道上处理,冲突部分的分割突发包进行光缓存。仿真结果表明,多波长信道系统中,高优先级突发包的丢失率低于低优先级突发包的丢失率。同时该方法在一定程度上可以有效地减少端到端的传输时延和整个网络的丢包率,从而提高整个OBS网络的性能。     

ASE Analysis and Correction for EDFA Automatic Control

A theoretical model is described that can be used for calculating the amplified spontaneous emission (ASE) at the output of an optical amplifier. The technique can be used to determine the usable optical signal power at the output of an erbium-doped fiber amplifier (EDFA) operating in the constant-output-power control mode. The model was experimentally verified by automating an EDFA to operate in the constant-signal-power control mode using an ASE correction based on our model. Calculated signal-output powers were then compared to the measured values that were obtained using an optical spectrum analyzer.     

OBS网络中一种基于突发包优先级分割的可控重传方案

在光突发交换(OBS)网络中,突发包会由于竞争OBS核心节点输出端口的有限波长资源而发生冲突。突发包重传能够在一定程度上减少由于突发包在核心节点冲突而导致的数据损失,但重传次数的增加可能会加重网络负荷,反而增加数据丢失率。并且,在多业务存在的OBS网络中,重传方案需要能够实现区分服务以保证网络的服务质量(QoS)。据此,本文提出一种基于突发包优先级分割的可控重传方案,在实施优先级分割的同时,根据网络负荷赋予每次重传不同的概率,并对重传次数加以控制。最后,仿真分析了路径阻塞率和不同优先级业务的字节丢失率(ByLP,byte loss probability)性能。     

Proposal and Analysis of Distributed Reflector‐Laser Diode Integrated with an Electroabsorption Modulator

A novel integrated laser, that is, a distributed reflector laser diode integrated with an electroabsorption modulator, is proposed to improve the output efficiency, single‐mode stability, and chirp. The proposed laser can be realized using the selective metalorganic vapor phase epitaxy technique (that is, control of the width of the insulating mask), and its fabrication process is almost the same as the conventional electroabsorption modulated laser (EML) process except for the asymmetric coupling coefficient structure along the cavity. For our analysis, an accurate time‐domain transfer‐matrix‐based laser model is developed. Based on this model, we perform steady‐state and large‐signal analyses. The performances of the proposed laser, such as the output power, extinction ratio, and chirp, are compared with those of the EML. Under 10‐Gbps NRZ modulation, we can obtain a 30% higher output power and about 50% lower chirp than the conventional EML. In particular, the simulation results show that the chirp provided by the proposed laser can appear to have a longer wavelength side at the leading edge of the pulse and a shorter wavelength side at the falling edge.     

EDFA gain transients: experimental demonstration of a low cost electronic control

Er-doped fibre amplifier (EDFA) gain transients are dynamic performance-degrading effects that need to be effectively suppressed in next-generation reconfigurable optical networks. In this paper, we experimentally assess the feasibility of an electronic dynamic gain control based on low-cost optoelectronic components, showing that a linearized electrical circuit and a control bandwidth smaller than 1 MHz can achieve the same performance as the commonly proposed all-optical feedback solutions.     

Performance of an Adaptive Threshold Receiver in a Dynamic Optical Burst-Switched Network

We compare the performance of a digital receiver operating with both a fixed and adaptive decision threshold in response to gain transients arising from network operation of an optically gain-clamped erbium-doped fiber amplifier. An optical burst switching link, based on a recirculating transmission loop, is used to study the effect of transients accumulated across a number wavelength-routing nodes linked by amplified fiber spans where bursts are added and dropped at each node. The use of an adaptive threshold reduces the amount of optical feedback required by a factor of 6 and, in some cases, allows for unclamped operation.     

Measurement method for output port reflectance of an erbium-doped fiber amplifier

A novel method to measure output port reflectance of an erbium-doped fiber amplifier (EDFA) was demonstrated. This technique was verified through simulating a "black box" EDFA with a reflector prior to the input port of a nonisolated EDFA.     

Evaluation of congestion control protocols for ABR traffic over ATM networks

Congestion control is very important for effective and stable operation of ATM (Asynchronous Transfer Mode) networks. Owing to the bursty and unpredictable characteristic of data network traffic, its congestion control is particularly a challenge for network researchers and designers. The ATM Forum has recently adopted rate‐based congestion control for ABR (Available Bit‐Rate) traffic which is the service class defined for data network applications. However, there is a number of congestion control schemes prevalent. ATM Forum has decided not to specify switch behaviour for ABR traffic; this has further introduced additional ambiguity. Consequently, an evaluation and comparison of the existing protocols would provide valuable guidance for network designers and engineers; it would also give insight for researchers to explore the essence of different congestion control schemes. In the first part of this paper, we investigate the effectiveness of ABR congestion control in the presence of bursty source traffic and the relationship between the burst time scale and the ABR control time scale. Two ABR congestion control schemes, the ABR Explicit Forward Congestion Indication (EFCI) and ABR Congestion Indication (CI) schemes, are compared with Unspecified Bit Rate (UBR) transport which makes no effort to control congestion. Traffic sources of various burst lengths of 100, 1000, 10000, and an equal mix of 100 and 10000 ATM cells are used in simulations. It is found that ABR congestion control schemes effectively control low frequency, medium to long‐term traffic load transients. This is further supported by the result of integrating TCP over ATM congestion control schemes included in the paper. ABR control schemes do not control high frequency, short‐term load transients well, but ABR control is not necessary in such cases since short‐term transients do not require a large amount of buffering. In the second part of this paper, we evaluate and compare six rate‐based congestion control protocols including Scheme I: EFCI, Scheme II: EFCI with separate RM queues, Scheme III: CI, Scheme IV: CI with separate RM queues, Scheme V: the CAPC2 ER (Explicit Rate), and Scheme VI: the EFCI with utilization‐based congestion indication. Each scheme is simulated and compared in the LAN, WAN, and GFC (General Fairness Configuration) environments specified by the ATM Forum. Effects of varying VC (Virtual Circuits) number and changing endsystem–switch distance has been investigated. Their fairness is also compared using the GFC configuration. We have found that ER control scheme performs significantly better than the other five binary control schemes by its faster response to congestion, smoother regulation of bit‐rates, lower queueing delay, shorter buffer queue length, and fairness. Among the other five schemes, the CI scheme performs better than the EFCI scheme. Providing separate RM queues has significantly improved the EFCI scheme in the WAN environment, but has little effect on the CI scheme. Link utilization‐based congestion detection has suffered from either low utilization or an excess cell loss which is unacceptable in most data applications. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental and theoretical analysis of relaxation-oscillationsand spectral hole burning effects in all-optical gain-clamped EDFA's forWDM networks

Experimental and theoretical analysis of the gain dynamics of all-optically stabilized multichannel erbium-doped fiber amplifier (EDFA) and the impact on wavelength division multiplexed (WDM) networks performance requirements is presented. In particular, we focus on precise analysis of the detailed transient response of the surviving channel and the relaxation oscillations of the compensating (lasing) signal. The main objective of this work is to experimentally and theoretically analyze and examine some of the critical factors such as, lasing wavelength, gain recovery time, relaxation oscillation frequency of the feedback loop, and the number of channels dropped/added, that affect the transient power excursions in the surviving channel. First, we consider the applicability of laser automatic gain control (AGC) to control fast power transients in WDM optical networks and reports the first high resolution measurements of transients in such gain controlled EDFAs. Second, the experimental results are compared with those predicted from a numerical simulation of the dynamic of the gain controlled EDFA     

光突发交换网络基于优先级与突发包分割的光缓存方法

为了保证光突发交换(OBS)网络中不同优先级业务的服务质量(Qos)和有效地降低突发包的丢失率,提出了一种基于优先级与突发包分割的光缓存方法.该方法通过在输出数据信道上设置光纤延迟线组来缓存被分割的冲突突发包.当冲突发生时,基于突发包的优先级进行"竞争突发包头部分割或者原突发包尾部分割,,处理;无冲突部分进行交换或者直...     

Hybrid offset‐time and burst assembly algorithm (H‐OTBA) for delay sensitive applications over optical burst switching networks

Optical burst switching (OBS) is the most favourable switching paradigm for future all‐optical networks. Burst assembly is the first process in OBS and it consists of aggregating clients packets into bursts. Assembled bursts wait for an offset time before being transmitted to their intended destinations. Offset time is used to allow burst control packet reserve required resources prior to burst arrival. Burst assembly process and offset‐time create extra delay in OBS networks. To make OBS suitable for real time applications, this extra latency needs to be controlled. This paper proposes and evaluates a novel offset time and burst assembly scheme to address this issue. Constant bit rate (CBR) traffic that has stringent end‐to‐end delay QoS requirements is used in this study. The proposed scheme is called hybrid offset‐time and burst assembly algorithm (H‐OTBA). The objective of the paper is achieved by controlling maximum burst transfer delay parameters of CBR. The proposed scheme was evaluated via network simulation. Simulation results demonstrate that, H‐OTBA has effectively reduced end‐to‐end delay for CBR traffic compared with current solutions. Copyright © 2014 John Wiley & Sons, Ltd.     

Output power excursions in a cascade of EDFAs fed by multichannelburst-mode packet traffic: experimentation and modeling

A serious problem facing wavelength-division multiplexed (WDM) networks with fiber amplifier cascades is transient cross-gain saturation or gain dynamics of fiber amplifiers. Attention has been focused primarily on circuit-switched scenarios. When the number of WDM channels transmitted through a circuit-switching network varies, channel addition/removal will tend to perturb signals at the surviving channels that share all or part of the route. Even more serious bit error rate deterioration can arise in WDM packet switched burst mode networks. In this paper, we present experimental and theoretical results demonstrating the effect of fast power transients in erbium-doped fiber amplifiers (EDFAs) on packetized traffic transmitted through a chain of five EDFAs. Traffic of a local-area network has been transmitted over three channels. The effect of EDFA cross-gain saturation due to the burstiness of the traffic has been observed in a continuous-wave monitoring channel. The stabilizing effect of gain clamping of the first EDFA in the cascade has been investigated. The experimental results are extended to eight-channel WDM system using a large signal numerical analysis     

Burst scheduling for differentiated services in optical burst switching WDM networks

Optical burst switching (OBS) is one of the most important switching technologies for future optical wavelength division multiplexing (WDM) networks and the Internet. The model of differentiated services has been proposed to support quality of service (QoS) in the IP‐based Internet. It is also very important to have differentiated service support in OBS networks. When the burst scheduling in an OBS network is set up appropriately, network can support differentiated services. In this paper, we proposed a new burst scheduling scheme, called differentiated scheduling with identical priority offset time (DSIPO). In DSIPO, the same priority offset time is used for all the bursts destined to the same edge node regardless of their priorities. Differentiated services in terms of burst loss probability are achieved by processing the control packets of higher priority class bursts, thus reserving resources for their data bursts, more promptly upon their arrival than those of lower priority class bursts. Each intermediate (core) node can adjust the burst loss probabilities of various burst classes by choosing its own differentiated processing delay value for each priority class or its own differentiated processing delay difference value between any pair of adjacent priority classes. We model and analyse DSIPO in terms of the burst loss probability for each priority class with simulation validation. The performance of DISPO is evaluated by simulation. Copyright © 2004 John Wiley & Sons, Ltd.     

Prioritized burst segmentation and composite burst-assembly techniques for QoS support in optical burst-switched networks

We address the issue of providing quality-of-service (QoS) in an optical burst-switched network. QoS is provided by introducing prioritized contention resolution policies in the network core and a composite burst-assembly technique at the network edge. In the core, contention is resolved through prioritized burst segmentation and prioritized deflection. The burst segmentation scheme allows high-priority bursts to preempt low-priority bursts and enables full class isolation between bursts of different priorities. At the edge of the network, a composite burst-assembly technique combines packets of different classes into the same burst, placing lower class packets toward the tail of the burst. By implementing burst segmentation in the core, packets that are placed at the tail of the burst are more likely to be dropped than packets that are placed at the head of the burst. The proposed schemes are evaluated through analysis and simulation, and it is shown that significant differentiation with regard to packet loss and delay can be achieved.     

Highly Utilized Fiber Plant with Extended Reach and High Splitting Ratio Based on AWG and EDFA Characteristics

In this paper, we propose a hybrid time‐division multiplexing and dense wavelength‐division multiplexing scheme to implement a cost‐effective and scalable long‐reach optical access network (LR‐OAN). Our main objectives are to increase fiber plant utilization, handle upstream and downstream flow through the same input/output port, extend the reach, and increase the splitting ratio. To this end, we propose the use of an arrayed waveguide grating (AWG) and an erbium‐doped fiber amplifier (EDFA) in one configuration. AWG is employed to achieve the first and second objectives, while EDFA is used to achieve the third and fourth objectives. The performance of the proposed LR‐OAN is verified using the Optisystem and Matlab software packages under bit error rate constraints and two different approaches (multifiber and single‐fiber). Although the single‐fiber approach offers a more cost‐effective solution because service is provided to each zone via a common fiber, it imposes additional losses, which leads to a reduction in the length of the feeder fiber from 20 km to 10 km.     

Surface‐Mountable 10 Gbps Photoreceiver Module Using Inductive Compensation Method

We propose an inductive compensation method for a surface‐mountable 10 Gbps photoreceiver module. Since many typical 10 Gbps photoreceiver modules consist of a photodetector and low‐noise pre‐amplifier, the impedance mismatch between the photodetector and preamplifier, as well as package parasitics, may reduce the frequency bandwidth. In this paper, we inserted an inductive component between the photodetector and pre‐amplifier in order to create frequency bandwidth expansion. From the measurement results, we have found that the proposed technique can increase the ?3 dB bandwidth about 4.2 GHz wider compared with an uncompensated module. And, from a bit‐error rate (BER) test, we observed ?15.7 dB sensitivity at 10^?12 BER. This inductive compensation can be implemented easily and is compatible with common manufacturing processes of photoreceiver modules.