不等长包的CRC约束Turbo译码

约束Turbo译码方法的编码方案是由Turbo码及错误检测码级联而成.该译码方法可以降低Turbo译码的复杂度,同时可以节省译码时间.遗憾的是,由于不正确包满足校验检测导致错误信息的传播,在中低信噪比时,译码性能有所降低.为了减小此类错误包的出现,文中采用不等长包构成一个长帧,在迭代之初,仅对短包进行检测,当不满足校验的短包数量小于给定值时,才对长包进行检测.仿真结果表明,文中给出的方案有效地减小了错误检测的包的数量,在中低信噪比下,译码性能也得到了提高.     

Packet rescheduling in WDM star networks with real-time servicedifferentiation

In this paper, we propose a novel scheduling scheme, namely priority-differentiated scheduling (PDS), which is designed to handle real-time (high-priority) packets in wavelength division multiplexing (WDM) star networks. PDS allows high-priority packets to preempt the prescheduled low-priority (nonreal time) packets. By scheduling the high-priority packets first, and then having the preempted packets rescheduled, PDS guarantees that the high-priority packets can always achieve the earlier transmission than the others in order to meet the quality of service (QoS) requirements. In addition, it does not sacrifice the performance of nonreal-time packets. As a matter of fact, low-priority packets can also benefit from PDS algorithms. This scheme has the capability of handling channel collision and destination conflict, and it supports variable-length packets. This paper also provides an insight into the data channel selection technique along with PDS. With the proposed algorithm that selects a data channel with minimum scheduling latency (MSL), the channel throughput is improved. The performance of the PDS scheme has been extensively studied by means of numerical simulations     

A hybrid beaconless geographic routing for different packets in WSN

The localized operation and stateless features of geographic routing make it become an attractive routing scheme for wireless sensor network (WSN). In this paper, we proposed a novel routing protocol, hybrid beaconless geographic routing (HBGR), which provides different mechanisms for different packets. Based on the requirement of application on latency, we divide the packets of WSN into delay sensitive packets and normal packets. HBGR uses two kinds of Request-To-Send/Clear-To-Send handshaking mechanisms for delay sensitive packets and normal packets, and assigns them different priority to obtain the channel. The simplified analysis is given, which proves that delay sensitive packets have lower latency and higher priority to obtain the channel than normal packets. Moreover, forwarding area division scheme is proposed to optimize the forwarder selection. Simulation results show that HBGR achieves higher packet delivery ratio, lower End-to-End latency and lower energy consumption than existing protocols under different packet generation rates in stationary and mobility scenario. Besides, compared with normal packets, delay sensitive packets have at least 10 % (9 %) improvement in terms of End-to-End latency. The improvement increases with the increasing of packet generation rate, and achieves 58 % (73 %) when the packet generation rate is 24 packets per second in stationary (mobility) scenario.     

Tunnel Restraint to Prevent Out-of-Order Packets for Route Optimization in Proxy Mobile IPv6

Route optimization (RO) developed for Proxy Mobile IPv6 (PMIPv6) aims at reducing the packet transmission cost. However, as we present in this paper, the RO procedure may cause out-of-order packets. In this paper, we propose a tunnel restraint scheme to minimize out-of-order packets during a mobile node (MN)’s handover by utilizing a developed estimation function that calculates an amount of out-of-order packets in the RO procedure. In the proposed tunnel restraint scheme, buffering techniques at proxy mobility agents are adopted to minimize the arrival of out-of-order packets to the MN. The proxy mobility agents taking part in the RO procedure buffer the packets for the MN until they establish the RO tunnel between them. The conducted performance evaluation results show that the traffic rate and the time period of out-of-order packets mainly have effects on the out-of-order packets problem. We also demonstrate that the proposed tunnel restraint scheme enhances the performance of PMIPv6 RO by minimizing the number of out-of-order packets.     

Measurement and Classification of Out-of-Sequence Packets in a Tier-1 IP Backbone

We present a classification methodology and a measurement study for out-of-sequence packets in TCP connections going over the Sprint IP backbone. Out-of-sequence packets can result from many events including loss, looping, reordering, or duplication in the network. It is important to quantify and understand the causes of such out-of-sequence packets since it is an indicator of the performance of a TCP connection, and the quality of its end-end path. Our study is based on passively observed packets from a point inside a large backbone network-as opposed to actively sending and measuring end-end probe traffic at the sender or receiver. A new methodology is thus required to infer the causes of a connection's out-of-sequence packets using only measurements taken in the "middle" of the connection's end-end path. We describe techniques that classify observed out-of-sequence behavior based only on the previously and subsequently-observed packets within a connection and knowledge of how TCP behaves. We analyze numerous several-hour packet-level traces from a set of OC-12 and OC-48 links for tens of millions connections generated in nearly 7600 unique ASes. We show that using our techniques, it is possible to classify almost all out-of-sequence packets in our traces and that we can quantify the uncertainty in our classification. Our measurements show a relatively consistent rate of out-of-sequence packets of approximately 4%. We observe that a majority of out-of-sequence packets are retransmissions, with a smaller percentage resulting from in-network reordering     

On the coexistence of a primary user with an energy harvesting secondary user: a case of cognitive cooperation

In this paper, we consider a cognitive scenario where an energy harvesting secondary user shares the spectrum with a primary user. The secondary source helps the primary source in delivering its undelivered packets during periods of silence of the primary source. The primary source has a queue for storing its data packets, whereas the secondary source has two data queues: a queue for storing its own packets and the other for storing the fraction of the undelivered primary packets accepted for relaying. The secondary source is assumed to be a battery‐based node, which harvests energy packets from the environment. In addition to its data queues, the secondary user has an energy queue to store the harvested energy packets. The secondary energy packets are used for primary packets decoding and data packets transmission. More specifically, if the secondary energy queue is empty, the secondary source can neither help the primary source nor transmit a packet from the data queues. The energy queue is modeled as a discrete‐time queue with Markov arrival and service processes. Because of the interaction of the queues, we provide inner and outer bounds on the stability region of the proposed system. We investigate the impact of the energy arrival rate on the stability region. Numerical results show the significant gain of cooperation.Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanism of eliminating UDP redundancy control packets in OpenFlow network

Large numbers of redundant control packets produced by connectionless UDP flows may engender serious influence over the performance of the SDN controllers and networks.The endangerment of the redundant control packets for the performance of SDN controllers by testing and modeling was firstly analyzed,and then a basic solution to solve the problem was formed.Therefore,a preinstalling flow-tables & filtering redundant packets (PFFR) mechanism was proposed.By preinstalling flow tables,PFFR limited the initial rate of control packets in UDP flows,and through installing flow tables according to paths and utilizing the redundant packets filtering algorithm,PFFR eliminated redundant packets rapidly.A prototype system based on PFFR was implemented and tested.The experimental results prove that the PFFR mechanism can effectively improve the performance of the controller.     

基于LT码的LBCMP迭代纠错方法

针对删除信道中发生错误的数据包,提出联合信道编码的LBCMP迭代纠错方法,该方法充分利用错误数据包中含有的正确信息,将LT编码包作为冗余纠错包与线性分组码相结合,并采用MP迭代译码方法进行纠错.理论分析及实验结果表明,采用LBCMP迭代方法可以减少为恢复错误数据包所需要的信源编码包数量.     

The Role of Information Update in Flow Control

A common feature of congestion control protocols is the presence of information packets used to signal congestion. We address here the question of how frequently such protocols need to generate information packets in order to optimize their performance. Through a number of congestion control models, we identify and quantify different types of effects of the frequency of generating information packets. We consider both TCP-type protocols, in which controlling the frequency of information packets is done through static or dynamic delayed ACK options, as well as ATM type flow control, where the optimal time spacing between the generation of network management packets is computed. We show how the spacing between information packets influences the throughput and the stability of the system.     

THEORY OF ORTHONORMAL M-BAND WAVELET PACKETS

In recent years, M-band orthonormal wavelet bases, due to their good characteristics, have attracted much attention. The ability of 2-band wavelet packets to decompose high frequency channels can be employed to improve the performance of wavelets for time-frequency localization, which makes more kinds of signals for analyzing by wavelets. Similar to the notations from the extension of 2-band wavelets to 2-band wavelet packets, the theoretic framework of M-band wavelet packets is developed, a generalization of the notations and properties of 2-band wavelet packets to that of M-band wavelet packets is made and the corresponding proofs are given.     

Performance analysis of a random packet selection policy formulticast switching

This paper studies a random packet selection policy for multicast switching. An input packet generates a fixed number of primary copies plus a random number of secondary copies. Assuming a constant number of contending packets during a slot, the system is modeled as a discrete time birth process. A difference equation describing the dynamics of this process is derived, the solution of which gives a closed form expression for the distribution of the number of packets chosen. Then this result is extended to the steady state distribution through a Markov chain analysis. It is shown that the old packets have larger fanout than the fresh packets and the copy distribution of the mixed packets is determined. The packet and copy throughput taking into account the old packets have been obtained. We determined the mean packet delay as well as an upperbound for packet loss probabilities for finite buffer sizes. The asymptotic distribution of the number of packets is also given for large switch sizes under saturation by applying results from the renewal theory. Finally, simulations are done to determine the performance of the switch under mixed (unicast plus multicast) traffic     

Smoothing transcoded MPEG-1 video streams for Internet transmission

An efficient smoothing scheme for the real-time transmission of MPEG-1 transcoded video over 'best-effort' IP networks is presented. The scheme uses intelligent partitioning and multiplexing of the packetised bit stream. Bit-rate smoothing is achieved by partitioning packets according to their picture type (I, P or B). Subsequently, the partitioned packets are multiplexed in such a way that each packet from an anchor (I and P) picture is followed by two packets from B-pictures. The proposed scheme smooths the bit rate of the encoded video, making it more suitable for adaptive video streaming applications. In such applications, the transmission bit rate is varied so as to adapt to the available network bandwidth. The scheme reorganises the transmission order of the packets, spreading the less important packets from the B-pictures into the more important packets from the anchor pictures. This indicates a reduction in the likelihood of losing more important anchor packets as the bandwidth bottleneck increases, implying an improvement in the quality of transmitted video. A variety of simulations results are presented to demonstrate these points.     

M带正交子波包理论

M带正交子波基由于所具有的优良特性得到了广泛关注。2带子波包具有划分较高频率倍频程的能力,可用于改善子波对时间-频率局部化的性能,推广了信号的适用范围。本文用类似于从2带正交子波基扩展到2带子波包的概念,建立了M带子波包的的理论框架,并把有关2带子波包的定义、概念和性质推广到一般的M带子波包,给出了相应的证明。     

基于机会式网络编码的低时延广播传输算法

为了提高无线网络中数据包广播传输的效率,本文提出了一种基于机会式网络编码的广播传输算法.该算法在发送端按一定顺序选择不同终端的丢包,并采用异或运算编码重传包,在终端采用从重传包中解码数据包的方法恢复丢包.该算法优先恢复时间重要性较高的丢包,并使多个终端同时从单个重传包恢复其丢包,因此有效地提高了广播传输效率并降低了传输...     

Packets flow watermarking method based on the inter-packet delay with smooth crossed grouping

To improve the self-correction ability and resist the entropy-based detection,a flow watermarking approach based on the inter-packets delays with smooth crossed grouping was proposed.Such an approach extended the watermarking methods using both the convolutional code and the smooth group methods to embed the watermarks into packet flows.By adjusting the inter-packets delays of the crossed packets,the transmission time distribution of the watermarked packets can indefinitely approach to that of any normal packets transmission times.Furthermore,the approach can mitigate the negative consequences introduced by packets transmission jitters,packets losses,packets aggregations and packets divisions for the watermarks detection.Both theoretical analysis and experimental results show that the proposed approach overweight the known watermarking methods from the aspects of identification accuracy,robustness and hiddenness.     

A secure wireless mission critical networking system for unmanned aerial vehicle communications

A privacy-preserving secure communication in ad hoc (without infrastructure) mission critical wireless networking system suitable for unmanned aerial vehicle communication systems is introduced and analyzed. It is expected that in a critical condition, few ad hoc (without infrastructure) mission critical wireless networking systems will work together. To make the simple and low cost privacy-preserving secure communication among the same network, each transmitting mobile node generates packets in such a way that its wanted receiving mobile nodes can read the message packets easily. On the other hand, the unwanted receiving mobile nodes from other networks cannot read those message packets. In addition, the unwanted receiving mobile nodes receive ‘jamming packets’ if they try to read them. This mechanism prevents the malicious receivers (readers from other networks) from reading the packets and obtaining information from this network. Results show that the throughput is very high and does not detect any jamming packets, if the receiving nodes of a network try to read packets transmitted by the nodes from the same networks.     

Queueing analysis of an integrated services TDM system using amatrix-analytic method

A matrix-analytic method is used to analyze the queueing behavior of small time division multiplexing (TDM) integrated services systems. Such systems have priority services for time-critical traffics in which adjacent packets exhibit a strong interdependency. The TDM frame with a capacity of M packets is used to transmit the high-priority packets at every time step. Any unused capacity is utilized to transmit low-priority packets. The system can be modeled as a discrete-time system with a fluctuating number of servers for the low-priority packets. Because the number of servers is small and adjacent packets are dependent, the birth-and-death analysis is not appropriate. An algorithm, based on a modification of Neuts' method, is used to determine the boundary points required in the queuing analysis. Numerical results for two integrated services systems, each with different characteristics, are presented to demonstrate the feasibility of the analysis method and the computational algorithm     

IPv6高速网络环境下数据分组捕获技术的研究

针对传统的数据分组捕获技术在IPv6高速网络环境下表现出的严重分组丢失问题,采用"零拷贝"的思想设计并实现了一个适用于IPv6高速网络环境的数据分组捕获平台(HSPCP)。以Intel82541GI吉比特网卡驱动程序e1000为基础,对网络数据分组的接收流程进行改进,在内核中注册一个杂项设备,实现了其mmap和ioctl方法,并编写了与改进后零拷贝驱动相对应的用户空间报文捕获程序。通过实验将HSPCP与Libpcap进行了分组捕获效率对比测试,实验证明HSPCP相对于传统的Libpcap分组捕获方式在性能上有较明显的提高。     

Reorder notifying TCP (RN‐TCP) with explicit packet drop notification (EPDN)

Numerous studies have shown that packet reordering is common, especially in networks where there is high degree of parallelism and different link speeds. Reordering of packets decrease the TCP performance of a network, mainly because it leads to overestimation of the congestion in the network. In this paper, we analyse the performance of networks when reordering of packets occur. We propose a proactive solution that could significantly improve the performance of the network when reordering of packets occurs. We report results of our simulation experiments, which support this claim. Our solution is based on enabling the senders to distinguish between dropped packets and reordered packets. Copyright © 2005 John Wiley & Sons, Ltd.     

GSM/GPRS分裂信道高效重分配策略

现有GSM/GPRS系统各种信道分裂策略都仅限于话音呼叫,即仅允许分裂信道分配给话音呼叫而不允许分配给包呼叫.因而,当系统没有空信道时,即使可以提供分裂信道,一个新到达的包呼叫也将被阻塞.本文提出的分裂信道重分配策略允许话音呼叫和包呼叫均可获得分裂信道,论文还研究了包呼叫得到分裂信道的条件.研究结果表明,允许将分裂信道分配给新到达包呼叫可以获得更优越的性能;在本文的参数设置下,在门限参数θ＝2/3时,新策略的话音阻塞率和平均包传输时间没有明显恶化,而包阻塞率和平均信道利用率却得以显著改善.