一种卫星网络中基于Agent的可靠组播传输协议

IP 组播技术是一种可以把单个数据信息同时分发到不同的用户去的网络技术。卫星网络固有的广播信道特性使得它很适合组播应用。然而目前针对卫星网络的可靠组播服务研究很少,虽然已经有一些关于地面Internet组播协议建议,但他们并不适合于卫星网络。在卫星网络组播传输中的一个关键技术是传输协议设计。该文提出一种基于Agent的宽带卫星网络可靠组播传输协议(ASMTP)。该协议利用接收端Agent来实现卫星组播,采用分组级FEC和本地差错恢复纠正传播中的非相关错误和相关错误。在ASMTP中,还实现了流量控制和拥塞控制机制。仿真结果表明,在卫星网络环境中,ASMTP性能优于MFTP(Multicast File Transport Protocol),同时具有较好的网络可扩展性。     

IP网组播的实现机制（下）

广域网上的组播实现有多种技术方式，但是最常用的实现方式是采用PIM—SM组播路由协议。PIM—SM协议与单播路由协议无关，并可同时支持基于源的组播树和共享树两种组播方式，特别是它是实现跨AS域组播的基础。因此，当前多数网络是以PIM—SM作为其组播路由协议。下面，将针对实例详细介绍PIM—SM的组播实现方式。     

IP组播路由算法及协议

该文主要介绍了在IP组播中使用的各种构造组播树的路由算法,以及相关的路由协议和几种新的协议。     

WDM层实现IP组播

WDM Multicast的关键问题是如何在WDM层建立组播树。本文深刻分析WDM网络上实现组播所面临的难题，并指出其与传统的IP组播的区别。在此基础上提出了两种可行的WDM Multicast方案。一种是对现有组播协议不加修改，但是需要增加一个中间层来实现WDM层组播树的构建；另外一种修改现有组播路由协议，使其充分考虑到WDM层的光分路能力，并设计新的波长路由分配算法来建WDM层组播树。本文对这两种方案详细分析并以目前广泛使用的DVMRP协议为例来说明它们各自的特点。     

MAODV路由协议的研究与仿真

组播通信有效地节约了网络资源,在资源受限的无线网络环境中引入组播有着非常重要的意义。本文分析了MAODV组播路由协议的路由机制,用NS2仿真分析了在不同组规模情况下网络的性能。仿真结果表明该组播协议减少了开销、降低了时延,可以有效地支持无线网络中的组播应用。     

移动自组网组播路由协议的分析

移动自组网是无中心、自组织、可快速展开、可移动的对等式网络,组播作为群组服务在移动自组网中应用广泛。移动自组网具有节点移动频繁、能源和带宽有限等特点,它要求组播协议能在节点频繁移动下具备良好的健壮性,传统的组播协议已不适用。文章介绍了移动自组网组播路由协议,描述了几种组播路由协议的基本运行过程,并对其性能进行了分析和比较,最后论述了组播协议在能源、安全、组播服务(QOS)、利用位置信息等方向的应用前景及面临的问题。     

基于卫星网络的移动可靠组播技术

本文首先介绍了基于卫星网络的可靠组播的优势,然后详细讨论了移动可靠组播及卫星网络可靠组播所面临的新的问题,最后提出了卫星网络中移动可靠组播的解决方案。     

MLD协议与PIM-SM协议实现IPv6组播

文章主要介绍IPv6组播的原理机制，当前用于实现IPv6组播的两个基本协议MLD协议与PIM—SM协议，以及MLD协议与PIM-SM协议之间的互操作。同时还详细描述了组播共享树和最短路径树的建立过程。     

IP组播技术研究与实现

主要介绍了IP组播技术、IP组播协议的分类及域内组播路由协议比较;详细地给出了综合业务交换机上IP组播软件的实现框架,并对PIM-SM组播路由模块、IGMP协议模块和组播数据转发模块的设计进行了简要的说明。IP组播技术的应用将不断得到重视和扩大。     

IP组播技术在多协议标记交换(MPLS)中的应用

对MPLS和组播技术分别进行了介绍，详细论述了IP组播技术在MPLS中的应用、与MPLS技术相关的组播特性以及这些特性与各组播路由协议的对应关系，并阐述了组播VPN在MPLS VPN中的应用。     

Transport protocols in multicast via satellite

In a wide variety of broadband applications, there is a need to distribute information to a potentially large number of receiver sites that are widely dispersed from each other. Communication satellites are a natural technology option and are extremely well suited for carrying such services because of the inherent broadcast capability of the satellite channel. Despite the potential of satellite multicast, there exists little support for multicast services over satellite networks. Although several multicast protocols have been proposed for use over the Internet, they are not optimized for satellite networks. One of the key multicast components that is affected when satellite networks are involved in the communication is the transport layer. In this paper, we attempt to provide an overview of the design space and the ways in which the network deployment and application requirements affect the solution space for transport layer schemes in a satellite environment. We also highlight some of the issues that are critical in the development of next generation satellite multicast services. Copyright © 2004 John Wiley & Sons, Ltd.     

Key Management in Secure Satellite Multicast Using Key Hypergraphs

Satellite networks play an important role in today’s information age because they can provide the global coverage services. Information security is an important concern in satellite multicast communications, where eavesdropping can be performed much easier than the fixed terrestrial networks. In this work, a novel multicast key management scheme based on key hypergraph for satellite networks on a predefined communication scenario is proposed. We use logical key hierarchy and distributed-logical key hierarchy as reference models for performance comparisons. It is shown that the proposed multicast key management scheme is scalable to large dynamic groups and minimizes satellite bandwidth usage.     

A Distributed Multicast Routing Scheme for Multi-Layered Satellite IP Networks

In this paper, a distributed multicast routing scheme is introduced for multi-layered satellite IP networks, which include GEO, MEO, and LEO layers. This scheme aims to minimize the total cost of multicast trees in the satellite network. Multicast trees are constructed and maintained in the dynamic satellite network topology in a distributed manner. Simulation results are provided to evaluate the performance of the new scheme in terms of end-to-end delay and multicast tree cost.     

适于低轨卫星IP网络的特定源组播算法

为了解决低轨卫星IP网络中现有特定源组播算法的信道资源浪费问题,本文提出了一套新的特定源组播算法,即基于核心群的特定源组播算法(CSSM)和加权的CSSM算法(w-CSSM).CSSM算法以源节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,所得的树代价最小,从而大大提高了网络的带宽利用率和传输效率.在w-CSSM算法中,加权因子可以自适应调整以适度增大树代价、降低端到端传播时延,以支持某些有严格端到端时延要求的实时组播业务.通过与低轨卫星IP网络中典型特定源组播算法MRA的仿真比较,可以看出CSSM和w-CSSM算法的树代价性能比MRA有较大改善,不过端到端传播时延略高.     

卫星星座网络中的IP路由选择

本文从中、低轨道卫星星座网络的动态特性出发,介绍了目前用于解决星座网络中实现IP路由选择功能的一些策略和方法,并对它们进行了分析和讨论。     

Efficient support of IP multicast in the next generation of GEO Satellites

Satellites are expected to have an important role in providing the Internet protocol (IP) multicast service to complementing next-generation terrestrial networks. In this paper, we focus on the deployment of IP multicast over the next generation of digital video broadcasting-based geosynchronous earth orbit satellites supporting multiple spot beams and on-board switching technologies. We propose a new encapsulation scheme optimized for IP multicast, which has two distinct modes enabling two alternative on-board switching approaches: the self-switching and the label-switching. We also detail a set of mechanisms and protocols for ground stations, as well as for the on-board processor to allow an efficient multicast forwarding in this type of environment, while reducing the load of control and data messages in the satellite segment, and building efficient multicast delivery trees reaching only the spot beams containing at least one member of the corresponding multicast session. To integrate satellite links in the terrestrial Internet, we present satellite multicast adaptation protocol (SMAP), a protocol which is implemented in satellite stations to process incoming protocol independent multicast-sparse mode (PIM-SM) messages sent by terrestrial nodes to the satellite system. SMAP helps to update the tables required for the mapping between IP packets and MPEG-2 data segments, their switching on board the satellite, and their filtering at the satellite receivers.     

一种新的移动卫星综合信息网构架

移动卫星综合信息网与现有的移动卫星通信网有着很大的区别。本文提出一种可反映移动卫星综合信息网特点的天基信息综合系统（SI^3），给出SI^3的网络模型，分析了这种分层网络模型的优缺点，并给出一个具体的参考星座组网例子，最后分析了SI^3建设中面临的技术问题。     

Effects on TCP of routing strategies in satellite constellations

A broadband satellite network uses a constellation of a number of similar satellites to provide wireless networking services to the Earth. A number of these constellation networks are under development. This article introduces the types of satellite constellation networks, and examines how overall performance of TCP communications carried across such a network can be affected by the choice of routing strategies used within the network. Constellations utilizing direct intersatellite links are capable of using multiple paths between satellites simultaneously as a strategy to spread network load. This allows more general routing strategies than shortest-path routing, but we show these strategies to be detrimental to the performance of individual TCP connections     

Walker星座卫星网络拓扑结构动态性分析

对低轨道(LEO)、Walker星座类型的卫星网络拓扑结构动态变化特征进行量化,给出了精确计算系统周期内网络时间片数量和时间片长度的公式。通过研究,一方面弥补了卫星网络研究中对拓扑结构时间片特征的简单假设,另一方面也为未来卫星网络星座的设计提供一定的指导。