FATMA—时频多址协议及其性能分析

ＶＳＡＴ网络诉更新，都是以改进网络性能为目标的。本文对ＦＡＴＭＡ－一种新兴的时应多址协议进行了性能分析，结果表明ＦＡＴＭＡ可以大度提高网络的总吞吐亘，具有更好的时延特性和工作稳定性。而且频率个数Ｆ越大，协议性能越好。     

基于输入缓存机制的ATM网络优先级流控策略

提出一种基于输入缓存机制的ＡＴＭ网络优先级流控策略，并运用系统仿真技术对采用该优先级流控及ＦＩＦＯ输入流控两种方案的ＡＴＭ多媒体网络性能进行计算机仿真研究。结果表明：采用优先级流控策略将改善ＡＴＭ多媒体网非实时信元丢失率及实时信元排队时延性能，具有较大实用价值。     

基于输入缓存机制的ATM网络优先级流控策略

提出一种基于输入缓存机制的ＡＴＭ网络优先级流控策略，并运用系统仿真技术对采用该优先级流控及ＦＩＦＯ输入流控两种方案的ＡＴＭ多媒体网络性能进行计算机仿真研究。结果表明：采用优先级流控策略将改善ＡＴＭ多媒体网非实时信元丢失率及实时信元排队时延性能，具有较大实用价值。     

APON的MAC协议设计

本文结合以ＡＴＭ为基础的无源光网络（ＡＰＯＮ）的Ｇ．９８３建议,提出了一种低信元时延变化（ＣＤＮ）、低信元时延（ＣＤ）、无碰撞、公平,高效的媒质接入控制（ＭＡＣ）协议,并对该协议的性能进行了分析。     

无线ATM网介质访问控制协议的研究

近年来无线ＡＴＭ网络得到广泛研究，扩展ＡＴＭ网络的宽带业务至无线环境面临许多方面的问题。介质访问控制（ＭＡＣ）方法是无线ＡＴＭ网的关键技术。ＭＡＣ层协议的好坏直接影响系统性能和移动终端的复杂性。文中综合分析目前已有的无线ＡＴＭ介质访问控制协议及方法，指出设计无线ＡＴＭ网ＭＡＣ层协议的三条原则，提出下一步研究方向。     

基于速率自适应预测的ATM网络ABR业务流量控制

本文深度将自适应预测方法引入ＡＢＲ流控算法中。ＡＴＭ网络的国带宽模型是一非平稳随机过程。高速网络中可用带宽的反馈信息由于线路的传播时延造成了流理控制的滞后。西方节ＡＢ国的这两特点，对ＡＴＭ Ｆｏｒｕｍ的ＴＭ４．０规定进行了一定的修改，采用离散化的ＡＴＭ网传输模型，提出了一种基于速率自适应预测的ＡＢＲ业务流控方法，较好地补偿了时延带来的控制的滞后效应，且具有参数易于选择的优点。通过仿真，论证了该方法     

SDMA技术改进WATM DSA^＋＋ MAC协议快速冲突分解算法的性能

在ＷＡＴＭ（无线异步转移模式）网络中,无线链路与ＡＴＭ（异步转移模式）的光纤链路相比存在着误码率高、时延长和带宽有限等问题。针对ＲＡＣＨ（随机接入信道）,在介绍了ＤＳＡ＾＋＋协议所采用的冲突分解算法的基础上,融入了ＳＤＭＡ（空分多址）技术,得出了分析结果,表明ＲＡＣＨ的吞量和时延性能都得到了很明显的改善。     

ATM在光纤同轴混合网上的应用

文章从光纤同轴混合（ＨＦＣ）网络的结构及传输ＡＴＭ信号的参考模型，ＨＦＣ媒体接入协议等方面探讨ＡＴＭ技术应用于ＨＦＣ网的一些特点，并例举了实际应用情况，将ＡＴＭ技术应用于ＨＦＣ网的优点包括：硬件，软件更实用化，无需改变网络就可以实现新业务，采用灵活有效的方法分配带宽，可减少网络的复杂性，以及易于操作，维护等。     

混合的ATM技术

ＡＴＭ协议体系结构分为物理层，ＡＴＭ层，ＡＬＬ层和高层，如果在终端用户处完全实现这些功能，不仅造价大，还要放弃用户在网卡，网络软件上的投资。而在终端用户的协议栈中采用混全的方案，则能保留现有网络技术的一些协议层次，又加入ＡＴＭ的协议层次，可以在将用户接入ＡＴＭ网的同时，保护用户已有的网络投资。     

基于FDMA的卫星ATM综合宽带通信网

利用卫星将地域上相隔遥远的异地计算机通信网或ＰＡＢＸ专用网互联起来，可以构成综合宽带通信网。这种作法的优点和益处正不断获得人们的共识，而ＡＴＭ技术在卫星综合宽带网中的应用又给这种网络的发展带来诱人的前景，本文拟提出一种基于ＦＤＭＡ的卫星综合宽带通信网，对该网络的结构、地面站终端设备的组成和ＡＴＭ特点接口配置进行论述，并讨论了联网协议和网络管理方面的问题。     

基于Q学习算法的Ad Hoc网络自适应DSR协议研究

提出了一种用于Ad Hoc网络改进的基于Q学习算法的自适应动态源路由(DSR)协议。该协议能在网络状态较好的情况下减小开销,在网络状况较差的情况下改善端到端时延和吞吐量性能。仿真结果表明,自适应Q-DSR协议能够提升传统DSR协议的性能,是简单高效的路由协议。     

An enhanced MAC protocol based on the IEEE 802.11 for data relay satellite systems

Data relay satellite (DRS) systems play an important role in space information networks. Characterized by highly dynamic topology and discontinuous communication links, it is suggested that the IEEE 802.11 protocol employed in such a network could be more flexible. However, such a terrestrial network protocol could not be applied to DRS systems directly, nor supports a fast response due to the long propagation delay and severe packet collision. To address this challenge, we proposed an enhanced media access control (MAC) protocol based on the IEEE 802.11 protocol providing multiaccess for low earth orbit (LEO) distributed constellations. In this paper, we investigated the access delay performance of the proposed protocol in our model. Then, we derived a contention window adaption by using an iteration algorithm that can dynamically adjust the values of the contention window depending on the number of user satellites in the communication coverage. Simulation results show that the average access delay does not exceed 20 seconds, which is significantly lower than the standard protocol. Moreover, the traffic threshold is increased to 0.6, and the maximum throughput has doubled compared with the standard protocol. It is proved that the enhanced MAC protocol shows a better performance in DRS systems.     

基于DSR的改进型综合源路由协议

在无线Mesh网络中,动态源路由(Dynamic Source Routing,DSR)协议是一种广泛应用的协议,其路由的建立与维护都从源节点发起。然而,由于DSR协议在路由发现与建立的过程中存在局限性,因此仍需要进一步研究。基于DSR协议通过引入一种综合了路径负载率、时延和跳数的负载均衡机制,并加入能量状态监控和多径路由,提出了一种改进型综合源路由协议(Improved Comprehensive Multi-path Source Routing,ICMSR),能够更好地实现网络负载均衡,节约网络能源,提升网络性能。最后,使用Opnet仿真验证了算法的有效性。仿真结果表明,改进协议在网络生存时间、分组投递率、端到端时延和网络吞吐量等性能指标上,相较于现有DSR协议都有较大的提升。     

A hybrid reservation-based MAC protocol for underwater acoustic sensor networks

Due to the characteristics of underwater acoustic channel, such as long propagation delay and low available bandwidth, media access control (MAC) protocol designed for the underwater acoustic sensor network (UWASN) is quite different from that for the terrestrial wireless sensor network. However, for the contention-based MAC protocols, the packet transmission time is long because of the long preamble in real acoustic modems, which increase the packet collisions. And the competition phase lasts for long time when many nodes are competing for the channel to access. For the schedule-based MAC protocols, the delay is too long, especially in a UWASN with low traffic load. In order to resolve these problems, a hybrid reservation-based MAC (HRMAC) protocol is proposed for UWASNs in this paper. In the proposed HRMAC protocol, the nodes reserve the channel by declaring and spectrum spreading technology is used to reduce the collision of the control packets. Many nodes with data packets to be transmitted can reserve the channel simultaneously, and nodes with reserved channel transmit their data in a given order. The performance analysis shows that the proposed HRMAC protocol can improve the channel efficiency greatly. Simulation results also show that the proposed HRMAC protocol achieves better performance, namely higher network throughput, lower packet drop ratio, smaller end-to-end delay, less overhead of control packets and lower energy overhead, compared to existing typical MAC protocols for the UWASNs.     

基于OPNET的水声通信网MAC层协议的研究

AC（Multiple Access）协议是水声通信网络的重要研究内容,利用OPNET网络仿真软件对ALOHA协议和MACAW协议下水声通信网络的性能进行仿真研究,分析比较这两种协议在不同业务量下的网络性能。仿真结果表明,在水声通信网络中,MACAW协议的性能优于ALOHA,但两者均可应用于低数据业务量网络中。     

A medium access protocol exploiting multiuser-detection in CDMA ad-hoc networks

A new medium access protocol which exploits the physical layer capability of multiuser detection is proposed to help in improving the throughput/delay performance of ad-hoc networks. When more than one node has packets buffered for a common node in the neighborhood, all such nodes can simultaneously transmit their packets to the common receiver after reserving their surrounding channel. This is achieved in our protocol by extending the (sender-initiated) CSMA/CA collision avoidance framework by the receiver-initiated medium access technique and incorporating the transmission power control. We analyze the improvement in the throughput that can be achieved over the basic sender-initiated collision avoidance protocol in the network. Since the throughput improvement via multi-packet reception is influenced by the network layer activity as well, the performance of our protocol rolls back to that of the basic sender-initiated protocol in case of no coordination from the network layer. For the evaluation of performance of our protocol we simulate ad-hoc networks for different network topologies and traffic configurations. We observe the scheme to be capable in significantly improving the throughput/delay performance of the network.     

基于WiFi的自组织网络路由协议算法研究

以基于WiFi的自组织网络为应用背景,本文利用仿真平台OPNET对四种经典自组网路由协议的性能进行了仿真比较。实验结果表明,反应式路由协议的性能总体优于先应式路由算法,而AODV协议由于其备份路由的特性,性能更优。为满足战场环境下车载自组织网的大规模组网要求,以及火控数据的时延传输要求,结合AODV算法的优势,本文提出了一种新的分层自组网路由算法CRP,其分簇结构的设计减少了网络拓扑变化对寻由过程的影响和路由发现过程中的洪泛开销,加速了路由的查找过程,仿真结果显示该算法的综合性能优于AODV算法及经典分簇路由协议ZRP算法,端到端传输时延明显减小。     

Moralism: mobility prediction with link stability based multicast routing protocol in MANETs

In recent research, link stability is getting tremendous attention in mobile adhoc networks (MANETs), because of several impediments that occur in a reliable and robust network. Link stability metric is used to improve network performance in terms of end-to-end delay, data success delivery ratio (DSDR) and available route time (ART). Energy consumption, bandwidth and communication delay of major concern in ad hoc networks. A high mobility of MANET nodes reduces the reliability of network communication. In a dynamic networks, high mobility of the nodes makes it very difficult to predict the dynamic routing topology and hence cause route/link failures. Multicast in MANETs is an emerging trend that effectively improves the performance while lowering the energy consumption and bandwidth usage. Multicast routing protocol transmits a packet to multicast a group at a given time instant to achieve a better utilization of resources. In this paper, node mobility is considered to map better their movement in the network. So, the links with long active duration time can be identified as a stable link for route construction. Variation in signal strength is used to identify whether the direction of the node is towards or away from estimating node. We consider signal strength as QoS metric to calculate link stability for route construction. Efforts are made to identify the link with highly probable longer lifetime as the best suitable link between two consecutive nodes. We predict the movement time of nodes that define the route path to the node destination. Exata/cyber simulator is used for network simulation. The simulation results of the proposed routing protocol are compared with on-demand multicast routing protocol and E-ODMRP, which works on minimum hop count path. Analysis of our simulation results has shown improvement of various routing performance metrics such as DSDR, ART, routing overhead and packet drop ratio.     

DIChirp: direct injection bandwidth estimation

Ideally, network bandwidth estimation algorithms should be independent of the end system performance. If end system capabilities are involved, then the measurement will be of the system throughput and will not indicate a correct assessment of network bandwidth. Packet dispersion‐based active bandwidth estimation schemes including Pathload, TOPP and pathChirp use delay correlation where the network‐induced delay on packets transmitted at certain rates is translated into bandwidth estimation. Since packet dispersion‐based active measurement schemes use delay correlation, bandwidth estimations are distorted by the host protocol stack‐induced delay variations. Studies revealed that the host protocol stack‐induced delay variations due to context switching are stovepiped in the network‐induced delay variations and impact the measurement process. This study explores the delay variations introduced by the host protocol stack in packet dispersion‐based techniques. The impact of host protocol delay variations and context switching on bandwidth estimation is analyzed and a new active bandwidth estimation tool minimizing the impact of context switching is proposed. Direct Injection Chirp (DIChirp) bypasses the TCP/IP protocol stack and directly interfaces with the network hardware. It uses the kernel for scheduling the outgoing packets, thus achieving more accurate estimation of bandwidth. Experiments revealed that the host protocol and context switching‐induced delay variations can be as high as 800µs and could result in bandwidth estimation errors near 20%. Experiments also revealed that the DIChirp is superior to the pathChirp implementation in performance estimation since the datapath utilized by DIChirp is less prone to delay variations induced by context switching. Copyright © 2007 John Wiley & Sons, Ltd.     

Delay Analysis of All-Optical Packet-Switching Ring and Bus Communications Networks

We study the delay performance of all-optical packet communication networks configured as ring and bus topologies employing cross-connect switches (or wavelength routers). Under a cross-connect network implementation, a packet experiences no (or minimal) internal queueing delays. Thus, the network can be implemented by high speed all-optical components. We further assume a packet-switched network operation, such as that using a slotted ring or bus access methods. In this case, a packet's delay is known before it is fed into the network. This can be used to determine if a packet must be dropped (when its end-to-end delay requirement is not met) at the time it accesses the network. It also leads to better utilization of network capacity resources. We also derive the delay performance for networks under a store-and-forward network operation. We show these implementations to yield very close average end-to-end packet queueing delay performance. We note that a cross-connect network operation can yield a somewhat higher queueing delay variance levels. However, the mean queueing delay for all traffic flows are the same for a cross-connect network operation (under equal nodal traffic loading), while that in a store-and-forward network increases as the path length increases. For a ring network loaded by a uniform traffic matrix, the queueing delay incurred by 90% of the packets in a cross-connect network may be lower than that experienced in a store-and-forward network. We also study a store-and-forward network operation under a nodal round robin (fair queueing) scheduling policy. We show the variance performance of the packet queueing delay for such a network to be close to that exhibited by a cross-connect (all-optical) network.