A novel scheme based on minimum delay at the edges for optical burst switching networks

This paper proposes a novel scheme based on minimum delay at the edges (MDE) for optical burst switching (OBS) networks. This scheme is designed to overcome the long delay at the edge nodes of OBS networks. The MDE scheme features simultaneous burst assembly, channel scheduling, and pre-transmission of control packet. It also features estimated setup and explicit release (ESXR) signaling protocol. The MDE scheme can minimize the delay at the edge nodes for data packets, and improve the end-to-end latency performance for OBS networks. In addition, comparing with the conventional scheme, the performances of the MDE scheme are analyzed in this paper.     

A novel medium access control protocol for optical local networks based on data request ordering

The basic aim of the scheduling algorithms in wavelength division multiplexing (WDM) single-hop optical networks is to construct a short schedule, in order to support quick communication between the nodes of the network. A design of medium access control (MAC) protocol without collisions is introduced for scheduling variable-length data packets based on a broadcast and select architecture. The system includes only data channels and the coordination of the transmissions is achieved via control packets, functioning before the beginning of actual transmissions. The proposed scheme adopts a prediction mechanism in order to eliminate the possible delay introduced by the scheduling computation between the control and data phases of each cycle of transmission. The two common scheduling strategies suggested try to reorder the service sequence of the nodes, by prioritizing the nodes with long data packets, compared with the nodes with short data packets. The final schedule, formed by a scheduling matrix, seems to be much shorter and leads to an increase, in terms of channel utilization. The extensive simulation results show that the novel scheduling techniques offer more free time space for schedule and allow more data to travel on the medium for the same amount of time. Also, the mean packet delay on the queues is reduced and the relation throughput-delay is much better.     

联合空时编码的水声多用户节点协同并行传输多址接人协议设计

针对水声信道长传播时延特点导致水声通信网吞吐量低的问题,提出了一种多节点协同并行传输的多址接入协议。该协议由接收端发起预约,在距离认知的基础上对预约节点划分协同传输小区,从而构建多用户节点的多输入多输出集中式网络架构;采用空时码对数据包编码,并合理规划数据包的发送时刻,使同一小区的多个用户节点发送的数据包在设定时间偏差范围内同时到达接收端,而不同小区的数据包以包链形式到达,实现多用户节点的无干扰、高效并行传输。仿真实验结果表明,与已有的其它两种协议相比,设计的协议通过空时复用的方法大幅缩短了平均端到端时延,显著提升了归一化网络吞吐量。      

一种基于分层的量子分组传输方案及性能分析

大规模量子通信网络中,采用量子分组传输技术能有效提升发送节点的吞吐量,提高网络中链路的利用率,增强通信的抗干扰性能.然而量子分组的快速传输与路由器性能息息相关.路由器性能瓶颈将严重影响网络的可扩展性和链路的传输效率.本文提出一种量子通信网络分层结构,并根据量子密集编码和量子隐形传态理论,给出一种基于分层的量子分组信息传输方案,实现端到端的量子信息传输.该方案先将量子分组按照目的地址进行聚类,再按聚类后的地址进行传输.仿真结果表明,基于分层的量子分组信息传输方案能够有效减少量子分组信息在量子通信网络中的传输时间,并且所减少的时间与量子路由器性能与发送的量子分组数量有关.因此,本文提出的量子分组信息传输方案适用于大规模量子通信网络的构建.     

Time-slot interchange of 40 Gbits/s variable length optical packets using conversion-dispersion-based tunable delays

We demonstrate tunable time-slot interchange of 40 Gbits/s optical data packets using a conversion-dispersion-based tunable optical delay element. Odd and even data packets are extracted from an input signal, delayed relative to one another in a highly dispersive medium, and then multiplexed back together. Tunability is demonstrated by operating with two different packet lengths, 182 and 288 bits/packet, and a bit error rate of <10(-9) is achieved.     

基于最小化平均分组跳的分组交换多跳光网的设计

本文研究了支持分组交换通信的波长路由光网的逻辑拓扑设计问题,并将它表示为混合整数线性规划问题(MILP),其目标函数为最小化平均分组跳数目.在约束条件中同时考虑了分组传输时延和排队时延.我们以6结点的网络为例,对于不同的收发机数目和时延边界,数值结果表明最小化平均分组跳数目等价于最小化网络拥塞.小的平均分组跳数目可以保证网络通信时具有较小的时延.最后,对于不同的通信模式,我们比较分析了网格的优化性能参数,这些结果有助于提出更好的启发式算法.     

A Wavelength and Bandwidth Assignment Algorithm to Support Guaranteed Bandwidth Levels in Hybrid Time Division Multiplexing/Wavelength Division Multiplexing Ethernet Passive Optical Networks

Abstract

A novel bandwidth assignment algorithm in wavelength division multiplexing Ethernet passive optical networks, called a dynamic wavelength assignment service level agreement, is proposed to efficiently provide subscriber differentiation. Simulation results show that the dynamic wavelength assignment service level agreement outperforms other bandwidth allocation algorithms in wavelength division multiplexing Ethernet passive optical networks, as it makes a fairer bandwidth distribution than other methods and is able to overcome the non-allowed packet fragmentation of the Ethernet passive optical network standard. Consequently, it greatly increases the achieved throughput and always ensures a minimum guaranteed bandwidth to every priority subscriber. Furthermore, the new algorithm obtains lower mean packet delay and packet loss rate for the highest priority subscribers when compared with other bandwidth distribution schemes in wavelength division multiplexing Ethernet passive optical networks.     

Wavelength division multiplexed loop buffer memory based optical packet switch

Photonic all-optical switching is widely considered as one of the technique to utilize the enormous optical bandwidth. Optical packet switching provides high speed, data rate transparency, data format transparency, efficient use of bandwidth and flexibility. To resolve the conflict during contention, packets are needed to be buffered. Due to the lack of optical RAM, fiber delay lines (FDLs) are the most suited option to buffer the packets. This paper proposes new optical packet switch architecture alongwith feedback shared buffer utilizing the advantage of WDM loop buffer memory. The loop buffer module used in this switch architecture is a new approach towards WDM buffering of packets. The mathematical modeling is done to validate the results obtained from simulation.     

On coding for reliable communication over packet networks

We consider the use of random linear network coding in lossy packet networks. In particular, we consider the following simple strategy: nodes store the packets that they receive and, whenever they have a transmission opportunity, they send out coded packets formed from random linear combinations of stored packets. In such a strategy, intermediate nodes perform additional coding yet do not decode nor wait for a block of packets before sending out coded packets. Moreover, all coding and decoding operations have polynomial complexity.We show that, provided packet headers can be used to carry an amount of side-information that grows arbitrarily large (but independently of payload size), random linear network coding achieves packet-level capacity for both single unicast and single multicast connections and for both wireline and wireless networks. This result holds as long as packets received on links arrive according to processes that have average rates. Thus packet losses on links may exhibit correlations in time or with losses on other links. In the special case of Poisson traffic with i.i.d. losses, we give error exponents that quantify the rate of decay of the probability of error with coding delay. Our analysis of random linear network coding shows not only that it achieves packet-level capacity, but also that the propagation of packets carrying “innovative” information follows the propagation of jobs through a queueing network, thus implying that fluid flow models yield good approximations.     

Design and Performance Evaluation of Optical Ethernet Switching Architecture with Liquid Crystal on Silicon-Based Beam-Steering Technology

A non-blocking optical Ethernet switching architecture with liquid crystal on a silicon-based beam-steering switch and optical output buffer strategies are proposed. For preserving service packet sequencing and fairness of routing sequence, priority and round-robin algorithms are adopted at the optical output buffer in this research. Four methods were used to implement tunable fiber delay modules for the optical output buffers to handle Ethernet packets with variable bit-rates. The results reported are based on the simulations performed to evaluate the proposed switching architecture with traffic analysis under a traffic model captured from a real-core network.     

An optimal burst assembly approach employing traffic shaping (OBATS) for OBS

Optical burst switching (OBS) aims at combining the strengths of packet and circuit switching and is considered as a promising technology for implementing the next generation optical Internet, required to cope with the rapid growth of Internet traffic and the increased deployment of new services. In this paper, an optimal burst assembly approach employing traffic shaping (OBATS) for OBS networks has been proposed in order to improve network performance in terms of reduced blocking probability, congestion control and better utilization of bandwidth. Particularly, the proposed scheme aims at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. Simulation results show that the proposed burst assembly approach gives better network performance in terms of burst drop, resource contention and delay as compared to conventional burst assembly approaches.     

一种光突发交换网络中降低填充开销的突发组装算法(英文)

针对光突发交换(OBS)网络现有组装算法在输入业务量较小时组装填充开销较大的性能缺陷,提出了一种新的突发组装算法,称之为BPRA算法.该组装算法通过改变突发生成时间,在不增加端到端时延的条件下利用偏置时间来延长突发组装时间,从而可以有效降低填充空闲比特的数目.同时提出一个近似分析模型来计算空闲比特填充概率.分析和仿真结果表明BPRA算法可以明显降低组装填充开销.     

Wave packet echoes in the motion of trapped atoms

We experimentally demonstrate and systematically study the stimulated revival (echo) of motional wave packet oscillations. For this purpose, we prepare wave packets in an optical lattice by nonadiabatically shifting the potential and stimulate their reoccurrence by a second shift after a variable time delay. This technique, analogous to spin echoes, enables one even in the presence of strong dephasing to determine the coherence time of the wave packets. We find that for strongly bound atoms it is comparable to the cooling time and much longer than the inverse of the photon scattering rate.     

Route selection for interference minimization to primary users in cognitive radio ad hoc networks: A cross layer approach

An opportunistic routing problem in a cognitive radio ad hoc network is investigated with an aim to minimize the interference to primary users (PUs) and under the constraint of a minimum end-to-end data rate for secondary users (SUs). Both amplify-and-forward (AF) and decode-and-forward (DF) relaying techniques are considered for message forwarding by SU nodes in the network. Unlike popular transmit power control based solutions for interference management in cognitive radio networks, we adopt a cross layer approach. The optimization problem is formulated as a joint power control, channel assignment and route selection problem. Next, closed form expression for transmission power is derived and corresponding channel selection scheme and routing metric are designed based on this solution. The proposed route selection schemes are shown to depend not only on gains of the interference channels between SUs and PUs but also on the values of the spectrum sensing parameters at the SU nodes in the network. Two distributed routing schemes are proposed based on our analysis; (i) optimal_DF and (ii) suboptimal_AF. The routing schemes could be implemented using existing table driven as well as on demand routing protocols. Extensive simulation results are provided to evaluate performance of our proposed schemes in random multihop networks. Results show significant reduction in PUs’ average interference experience and impressive performance as opportunistic routing schemes can be achieved by our schemes compared to traditional shortest path based routing schemes. Performance improvement is also reported over prominent recent schemes.     

Scheduling for end-to-end performance in multi-rate CDMA/HDR systems

An interesting feature of the third generation (3G) cellular networks is their ability to support multiple data rates for data services. Thus, it is important to understand the end-to-end delay and throughput performance over these multi-rate cellular systems. In this work, we consider a multi-rate system such as High Data Rate (HDR) and represent the possible data rates using a Markov chain. Using a M/G/1 queuing model, we calculate the expected data rate and the corresponding link layer delay for each of the initial states. We study the effects of various link layer scheduling techniques for the radio link protocol (RLP) frames destined for multiple user. Though the commonly used link layer scheduling techniques work well, they do not provide the best performance for when end-to-end semantics need to be maintained. In this regard, we propose a scheduling algorithm that aids the transport protocol, for example TCP. Our research shows that the proposed remaining frames first scheduler enhances the transport layer performance compared to the commonly used “best channel scheduler”. Comparative results, based on simulations, are shown with respect to radius of cell, distance of user, number of users, and varying bit error rate.     

The queuing delay analysis at relay node based on cooperative GBN-ARQ protocols

In this paper, a single relay cooperative diversity network model is proposed, analyzing queuing delay of the packets at relay node. Using dynamic radio link adaptation in wireless networks, based on the character of GBN-ARQ protocol and the queuing theory, the paper solves the problem that packets wait to transmit at relay, and presents a relay node to destination node queuing analysis model for GBN-ARQ protocol with fixed feedback delay. The paper establishes Markov model of packet transmission, and the delay statistics at relay node are figured out by using matrix geometric methods.     

Scheduling Strategy Design Framework for Cyber–Physical System with Non-Negligible Propagation Delay

Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form a closed-loop. When such CPS are deployed for time-sensitive applications such as remote control, the uplink and downlink propagation delay are non-negligible. However, existing studies on CPS/WNCS usually ignore the propagation delay of the uplink and downlink channels. In order to achieve the best balance between uplink and downlink transmissions under such circumstances, we propose a heuristic framework to obtain the optimal scheduling strategy that can minimize the long-term average control cost. We model the optimization problem as a Markov decision process (MDP), and then give the sufficient conditions for the existence of the optimal scheduling strategy. We propose the semi-predictive framework to eliminate the impact of the coupling characteristic between the uplink and downlink data packets. Then we obtain the lookup table-based optimal offline strategy and the neural network-based suboptimal online strategy. Numerical simulation shows that the scheduling strategies obtained by this framework can bring significant performance improvements over the existing strategies.     

时隙光分组交换网络中一种新的光缓存优化配置方案

研究了时隙光分组交换网中的光缓存配置方案,针对反馈共享式缓存结构,通过对传统的连续分布式光缓存结构中不同延迟粒度的光缓存丢包的分布情况仿真结果研究,发现在传统的连续分布式光缓存结构中,丢包主要发生在小粒度的光缓存上,为此,提出通过适当增加小粒度的光缓存的方法,达到有效地降低丢包率,仿真结果显示,这种光缓存方案可以明显降低节点的丢包率.     

Resource allocation for LTE-based cognitive radio network with queue stability and interference constraints

We consider the problem of interference management and resource allocation in a cognitive radio network (CRNs) where the licensed spectrum holders (primary users) share their spare capacity with the non-licensed spectrum holders (secondary users). Under such shared spectrum usage the transmissions of the secondary users should have a minimal impact on the quality of service (QoS) and the operating conditions of the primary users. Therefore, it is important to distinguish the two types of users, and formulate the problem of resource allocation considering hard restrictions on the user-perceived QoS (such as packet end-to-end delay and loss) and physical-layer channel characteristics (such as noise and interference) of the primary users. To achieve this goal, we propose to assign the bandwidth and transmission power to minimize the total buffer occupancy in the system subject to capacity constraints, queue stability constraints, and interference requirements of the primary users. We apply this approach for resource allocation in a CRN built upon a Third Generation Partnership Project (3GPP) long-term evolution (LTE) standard platform. Performance of the algorithm is evaluated using simulations in OPNET environment. The algorithm shows consistent performance improvement when compared with other relevant resource allocation techniques.     

Delay-Sensitive NOMA-HARQ for Short Packet Communications

This paper investigates the two-user uplink non-orthogonal multiple access (NOMA) paired with the hybrid automatic repeat request (HARQ) in the finite blocklength regime, where the target latency of each user is the priority. To limit the packet delivery delay and avoid packet queuing of the users, we propose a novel NOMA-HARQ approach where the retransmission of each packet is served non-orthogonally with the new packet in the same time slot. We use a Markov model (MM) to analyze the dynamics of the uplink NOMA-HARQ with one retransmission and characterize the packet error rate (PER), throughput, and latency performance of each user. We also present numerical optimizations to find the optimal power ratios of each user. Numerical results show that the proposed scheme significantly outperforms the standard NOMA-HARQ in terms of packet delivery delay at the target PER.