基于移动代理的卫星网路由性能研究

通过仿真方法分析代理系统中影响基于移动代理卫星网路由算法性能的关键因素,给出了拟仿真的路由算法及其NS2仿真方案,详细阐述了使用Grasshopper、JADE和Linux、运行于局域网环境、支持代理的卫星网仿真平台构建方案,包括仿真平台的系统结构、卫星节点功能实体、路由代理交互接口、星际链路仿真模块等。通过与NS2中的仿真结果对比,得出了高链路时延下的移动代理迁移效率是影响路由算法性能的关键因素,并通过代理系统间横向比较,给出了路由算法开发以及仿真平台构建过程中代理系统的选择建议。     

LEO卫星网络中基于蚂蚁算法的分布式QoS路由

低地球轨道(Low Earth Orbit,LEO)卫星系统因能够提供多媒体通信服务而成为卫星通信研究的热点.有效的路由算法设计是LEO卫星网络中的一个关键问题.为了满足多媒体应用的服务质量(Quality of Service,QoS)要求,卫星的路由算法应当考虑切换的影响.文章提出了一种基于启发式蚂蚁算法的分布式的QoS路由策略,可以满足延时限制,同时避免链路拥塞.仿真结果显示在不同的延时限制条件下,相对于最短路径优先算法,该算法具有较低的呼叫阻塞概率.     

基于UWB技术的无线移动多媒体QoS路由协议

随着UWB技术的出现,无线移动多媒体业务在自组网中的应用成为可能。为了满足无线移动多媒体传输的需要,设计了一种新的针对多媒体业务的QoS路由协议,给出了协议的详细描述。由于该协议充分利用了UWB技术的速率和距离互换特性,考虑了传输速率、时延和链路拥塞程度3个QoS参数,并借鉴无线移动自组网基本路由协议DSR和AODV,因此不仅能够获得满足业务要求的路由,且能提前预测链路的中断,以便及时切换替代路由。与目前已提出的基于UWB技术的路由协议相比,该协议更适合于无线移动多媒体业务的传输。     

LEO／MEO卫星网络中的一种抗毁动态路由算法

要首先分析了目前卫星网中流行的离线路由算法由于无法获知当前网络中流量的分布和链路的状态，因此无法对路由进行优化．也无法绕开故障链路的缺陷。针对这些缺陷，提出了一种抗毁动态路由算法。该算法首先通过一种基于簇的星问链路状态信息传递子算法，以较低的带宽开销将链路状态信息传遍全网；然后利用边界卫星源路由子算法。对链路状态、路由切换等因素进行综合优化。在Iridium系统模型的基础上对离线路由算法和抗毁动态路由算法进行了仿真，仿真结果证明后者具有更好的性能，尤其在部分链路故障时，优势更加明显。     

移动自组网QoS路由的DNA计算模型

QoS路由问题是移动自组网应用面临的一个重要问题,其中如何根据移动自组网动态拓扑结构和单向链路的特点来设计路由算法是关键。DNA计算是一种基于生化反应的新型计算方法,高度的并行性和海量存储能力是其最大的特点。文章首先给出了QoS路由问题模型,然后介绍了DNA的分子结构和DNA计算的基本原理,最后依据Adleman进行DNA计算的编码方法,给出了移动自组网QoS路由问题的DNA计算模型,为解决多约束QoS路由问题提供了一种新的思路。     

基于蚁群算法的移动自适应网QoS路由算法

在移动自适应网中,由于无线环境的不稳定性及终端的移动性造成网络拓扑结构不断变化,使网络中端对端的服务质量随时间不断变化.为移动自适应网提供服务质量保证的关键是移动自适应网的QoS路由问题.提出了一种适用于移动自适应网的QoS路由算法.该算法将蚁群算法与移动自适应网的特点相结合,可以高效地在该网络中寻找满足延迟、延迟抖动、带宽、包丢失率、节点跳数和费用等多项指标的QoS路由,从而显著地提高移动自适应网的QoS路由性能.     

一种应用于LEO QoS网络的路由策略

从减少连接切换频率并合理利用网络资源的角度出发,为LEOQoS网络提出了一种路由策略。介绍了根据给定连接切换目标概率来选择具有适当生命期的星际链路作为QoS路径的方法,并给出了仿真结果。     

分层蜂窝网络中基于移动速度、方向的流量均衡

在异构无线网络中,使用有效的流量均衡可以服务更多的移动用户。文章为异构分层无线网络提出了一种基于移动速度、方向和位置的流量均衡算法,其原理是选择逗留时间较长的移动用户执行垂直切换,从负载较重的小区转移到负载较轻的重叠覆盖小区。同时,快速切换呼叫在一定条件下可以接入到微小区,慢速切换呼叫也可以切换进入宏小区。仿真实验结果表明,该算法改善了新呼叫阻塞率和切换呼叫掉线率等方面的性能。     

基于蚂蚁代理的QoS多播路由算法

现有的基于蚂蚁代理的路由算法都没有考虑到状态信息的非精确性对蚂蚁选路过程的影响。本文中，我们为状态信息不精确的包交换网设计出一种有带宽和延迟保证、基于蚂蚁代理的多播路由新算法——QMRA。在我们的算法中，蚂蚁使用链路满足QoS约束的概率以及它所经过路径的代价，而不是它的旅行时间或年龄来决定信息素的铺设。因此，蚂蚁代理的移动过程比较简单，控制参数也较少，并且能够容纳状态信息相当程度的不精确性。仿真结果显示了QMRA在状态信息不精确的情况下，具有较低的路由阻塞率和数据包的平均延迟，并且能够快速收敛。     

基于空间光链路的双层卫星网络路由算法研究

在分析传统多层卫星网络路由算法的基础上,提出了一种基于空间光链路传输的双层卫星网络结构及其相应的基于拉格朗日松弛算法的LDSR算法。该结构根据空间光链路的特点及双层卫星网络的优势,在考虑适合该体系接入策略的同时提出将MEO作为天基网接入域的组成部分,由MEO星座进行路由信息的会聚及分发业务,同时LEO卫星则基于拉格朗日松弛算法来确定其选用的路由并预留带宽。仿真结果表明,该算法可以在充分利用卫星网络的通信容量的同时提供较好的QoS路由性能。     

LEO卫星中模拟实时通信量确保保护信道的分配

由于LEO（Low Earth Orbit）卫星网络中不断变化的点波束小区实时通信量负载无法估计,提出了一种根据系统仿真过程中当前通信量状态优化动态保护信道算法（ODGCS）。该分配策略引入呼叫间隔时间和切换呼叫中断间隔时间来获悉系统的实时性能状态,由仿真中通信量状态预测当前系统切换呼叫的中断概率,根据比较计算的呼叫中断概率和预先设定的QoS（Quality of Service）值,动态调整预留给切换呼叫使用的保护信道数。仿真结果表明,与传统的静态预留保护信道的算法相比,该算法能有效提高LEO卫星系统的性能稳定性。在负载较轻时,ODGCS算法保证切换呼叫QoS的同时,降低了新呼叫阻塞概率。     

Optimization for adaptive bandwidth reservation in wireless multimedia networks

In future wireless multimedia networks, user mobility management for seamless connection regarding realtime multimedia applications is one of the most important problems. In this paper we propose an opportunity-cost concept-based approach for adaptive bandwidth reservation with admission control for handover calls utilizing network traffic information. Excessive reservation guarantees low blocking probability of handover calls at the cost of high blocking probability of new calls. According to our survey, however, it may degrade bandwidth utilization while no prioritization for handover admissions degrades quality of service (QoS) for ongoing calls. We consider both QoS assurance and bandwidth utilization in order to optimize the amount of bandwidth to reserve for handover admissions. We believe that our scheme could be utilized as a guideline for cost-effective radio resource allocation in mobile multimedia networks.     

Performance evaluation of product form cellular mobile communications networks

This paper proposes and analyzes a queueing network model of a cellular mobile communications network including the multiway connection. This model is formulated as a queueing network with multiple call classes and state-dependent transition rates. As the performance measure a handover blocking probability is evaluated based on the product form equilibrium distribution and the constraint matrix whose elements consist of the mean arrival and service rates for individual cells. As a numerical example, an eight-cell cellular system is considered and blocking probabilities for a two-way handover between neighbouring cells are calculated for several network loads and constraint matrices. Since results represent the characteristics depending on individual cells or neighbouring cells, it can be emphasized that this model is useful for the control of QoS taking account of the spatial traffic.     

Agent-based load balancing routing for LEO satellite networks

To ensure an intelligent engineering of traffic over entire satellite networks, a distributed routing scheme for low-earth orbit (LEO) satellite networks, agent-based load balancing routing (ALBR), is presented. Two kinds of agents are used. Mobile agents migrate autonomously to explore the path connecting source and destination, to gather inter-satellite link (ISL) cost, identifier and latitude of visited satellites. Meanwhile, stationary agents employ exponential forgetting function to estimate ISL queueing delay, calculate ISL cost using the sum of propagation and queueing delays; evaluate path cost considering satellite geographical position as well as ISL cost, finally update routing items. Through simulations on a Courier-like system, the proposed scheme is shown to achieve better load balancing, and can especially decrease packet loss ratio efficiently, guarantee better throughput and end-to-end delay bound in case of high traffic load. Furthermore, results from the implementation complexity analysis demonstrate that with the aid of agent technology, ALBR has lower on-board computation, storage, signaling requirements than other on-board routing schemes.     

LEO卫星网络中的一种分布式路由算法

在LEO卫星网络中，由于卫星高速运动导致的网络拓扑变化和不同卫星覆盖城内流量的非规整性给设计其特殊路由算法带来很大挑战。结合卫星网络的固有特点，本文提出一种基于路径信息压缩的分布式路由算法CPDR（Compressed Path Information based Distributed Routing）。该算法使用分布式分层链路状态收集策略和简洁的路径信息编码机制，能够在不引入额外信令开销基础之上提供多路径路由能力，实现卫星网路中的流量负载平衡、优化网络带宽应用、提高星际链路利用率。     

基于SDN的高性能QoS保障低轨道卫星星间路由算法

低轨道卫星通信系统具有全球覆盖性、移动性、可扩展性等优势,在提供全球互联网服务、灾难应急处理等方面发挥重要作用,但由于星上有限的存储和计算资源,传统路由算法不适用于低轨道卫星通信网络。结合软件定义网络架构,提出一种支持服务质量（QoS）的高性能低轨道卫星星间路由算法。根据剩余链路持续时间定义星间链路生存时间,确定每条星间链路的稳定度,缓解由于链路切换导致的业务路径重构问题。基于高轨道卫星得到的星间链路的流量状态,定义链路负载矩阵,给出星间链路负载度函数,并利用标签交换路径集合获得每条路径的负载度,避免节点拥塞,实现网络负载均衡。针对不同要求的业务服务类型定义权重因子矩阵,通过调整因子来减小瓶颈节点对路由算法的影响,满足多用户的QoS要求。仿真结果表明,在不同的QoS要求下,该算法在业务时延、系统吞吐量、网络负载均衡等方面均具有明显优势,且算法复杂度低,大幅节省了有限的星上存储与计算资源。     

Probability based dynamic-alternate routing and the corresponding converter placement algorithm in all-optical WDM networks

This paper proposes a new dynamic-alternate routing algorithm and its corresponding converter placement algorithm in order to reduce the connection blocking probability for all-optical WDM networks. The main idea in the proposed dynamic-alternate routing algorithm is to try to route the traffics according to a predefined optimal probability distribution. The problem for finding the optimal probability distribution was shown as a convex optimization problem. The problem can be solved by flow deviation method or other standard optimization techniques. Simulation results show that the proposed routing algorithm yields lower connection blocking probabilities than the previous works. The proposed routing algorithm produces similar traffic pattern as the optimal traffic pattern. The similarity between the traffic pattern produced by the proposed dynamic-alternate routing algorithm and the optimal traffic pattern can be further employed for solving other network designing problems such as converter placement problem. Since the optimal traffic pattern can be easily predicted, the optimal traffic pattern which minimizes the blocked traffic intensity is utilized for finding the locations of wavelength converters. The key idea is to place the wavelength converters at the nodes where they are needed most. Simulations have been performed to study the performance of the proposed wavelength converter placement method. The simulation results have shown that the proposed placement method combined with the proposed probability based dynamic-alternate routing algorithm yields smaller connection blocking probability than the two converter placement methods with their corresponding alternate routing algorithms.     

一种基于时隙划分的三层卫星网络QoS路由协议

提出了一种基于低轨/中轨/高轨（LEO/MEO/GEO）卫星网络体系结构（TLSN）和时空分割思想的QoS路由协议（TDRP）,详细阐述了时空分割思想和时隙优化方法,重点研究了QoS路由的实现框架和路由算法（BDA）的实现原理.在此基础上,卫星网络体系结构和路由协议的性能得到了详细分析和仿真验证.相同负载情况下,TLSN中端到端时延和时延抖动性能明显好于LEO卫星网络;同Dijkstra算法相比,BDA算法在端到端时延、时延抖动、丢包率、吞吐量方面具有更好的QoS保证能力.     

Availability guarantee in survivable WDM mesh networks: A time perspective

Since availability is an important quality-of-service (QoS) factor in mesh networks, different service provision with availability guarantee have been discussed by many researchers in the literature. However, with the increasing demand for mesh networks to support both data and real-time multimedia traffic, multiple availability requirements may be made during one connection’s holding time. The traffic of different availability requirements has to be routed by special wavelengths. In this paper we discuss availability guarantee in mesh networks from the perspective of time and propose a new scheme called Time Aware Availability Guarantee (TAAG). The routing paths of each connection are adjusted according to the different availability requirements in different time spans. Simulation results show that the proposed scheme outperforms the previous schemes such as Time Unaware Availability Guarantee (TUAG) in terms of resource utilization, blocking probability and traffic throughput.