利用VSAT网实现局域网与Internet互连

Internet在全世界已日益发展和普及。文章简要介绍了利用VSAT网实现局域网（LAN）与Internet互连的特点与方法，为用户尤其是边远地区用户接入Internet提供了一种新的可行的途径。     

交互式VSAT网试验在以色列进行

Gilat卫星网络在以色列进行了世界上最大的、用于接入Internet的交互式VSAT网试验。该网络采用GE公司的Spacenet及Gilat的Skystar VSAT网。     

GPRS网络上MMS业务的实现方法

MMS是运行于GPRS承载网络之上的一个高层应用。而GPRS是在GSM Phase 2 阶段实现的内容，是对GSM网络的一个升级，把分组交换网络引入到了传统GSM的电路交换网络中，从而实现了宽带的移动数据通信。由于GPRS数据交换采用的是IP包交换的方式，从而把Internet网络从固定网延伸到了移动网，极大地改进了Internet网络的通讯接入方式，做到了随时随地都可以接入Internet网络。主要讨论无线终端接入GPRS网络以及MMS消息的具体实现方法。     

应用VSAT卫星通信接入高速互联网

近年来,以Internet和多媒体为代表的信息技术在人们生活和社会发展中占有非常重要的地位,可以预计在即将到来的二十一世纪,Internet和多媒体的普及程度及重要性将超过今天的电话。当前我国Internet业务每年以成倍速度增长,但下载速度太慢是人们普遍感到困扰的问题。虽然利用地面电信网络和CATV可以提供较为满意的宽带Internet接入,由于建设时间太长以及一些技术问题尚不成熟,还不能满足人们的急需,这样就为应用VSAT卫星通信接入宽带Internet和传输多媒体业务提供了一个良好的时间和空间,本文根据国际和国内的发展情况,对这一问题进行了详细的讨论,并介绍了几种应用VSAT接入宽带Internet的技术方案。     

基于MCU的嵌入式Internet技术与网关实现

嵌入式技术和Internet技术的发展，使得嵌入式设备也能够接入Internet网。为此，文中介绍了嵌入式Internet技术的基本原理和实现方案，讨论了MCU应用系统接入Internet网的通信协议。针对嵌入式Internet技术将在实际应用中的技术难点，提出了一种嵌入式网关的设计方案，利用该方案可嵌入式系统通过以太网接入Internet网络中。     

利用卫星通信技术实现Internet接入

随着Internet的快速发展,利用卫星的宽带IP多媒体广播解决Internet带宽的瓶颈问题,通过卫星进行多媒体广播的宽带IP系统逐渐引起了人们的重视,宽带IP系统提供的多媒体(音频、视频、数据等)信息和高速In-ternet接入等服务已经在商业运营中取得一定成效。目前,已有网络使用卫星通信的VSAT技术,发挥其非对称特点,即上行检     

无线接入Internet的两种方式及其关键技术

分析了无线尤其是移动与Internet融合的趋势，对目前移动接入Internet的两种主要方式－无线局域网方式和移动峰窝网方式所涉及的框架体系、主要问题及关键技术等进行了阐述，并对两种接入方式的共性与个性进行了分析。     

Internet的网络结构及信息服务

一、Internet的概念和主要特点Internet是基于通信网络，以TCP／IP协议为基准，以IP地址和域名地址为标识，以路由器和网关为协议转换工具所构成的网络的集合。Internet有五大特点：（l）Internet是一个国际计算机网络，同时也互连了公用电话网（PSTN）。目前，个人用户只要具备电话线、微机、Modem，即可接入Internet。（2）Internet互联的基础是TCP／IP协议，TCP／IP协议就相当于Internet的信令系统，凡遵守TCP／IP协议的计算机网络都可接入Internet。（3）Internet是一个透明性网络，即计算机在与其他网络互联时，用户无…     

VSAT接入技术的商业模式案例分析

Intelsat公司是全球最著名和最早开发利用VSAT技术的卫星运营商之一。因其影响力，该VSAT的技术和规格成为有影响的商业模式。卫星容量接入协议（又称卫星多址协议），网络接入协议和用户数据协议是VSAT网络重要的三层协议，而前两种协议又被人们认为是VSAT网络的关键技术。     

浅谈VSAT系统数据网多址协议

卫星数据网多址协议(access protocol)是发展VSAT数据网的关键技术。依据VSAT数据网所承载的业务特点，ALOHA协议是其采用的重要多址技术，根据端站报文的入网方式，VSAT共享协议可分为固定分配、随机接入、预约三类。主要对这三类共事协议进行扼要的介绍。     

卫星互联网下的VSAT卫星通信

本文介绍了VSAT通信在卫星互联网下的新发展,分析了VSAT系统的互联网接入方式,研究了卫星互联网的技术热点,展望了卫星互联网的发展前景.     

Ku-Band satellite data networks using very small aperture terminals—part I: Multi-access protocols

This two-part paper presents a comprehensive overview on the technology of very small aperture terminal (VSAT)-based satellite data networks, which have received increasing attention in recent years because of a combination of technical and economic factors. Ku-band networks with customer-premise earth-stations can overcome the inherent local access bottleneck in wide-area terrestrial data networks by suitably exploiting the unique multi-access and broadcast features of satellite communication. In this part of the paper, the issue of multiple access, which is an important critical path technology in the ongoing evolution of VSAT data networks, is considered in detail. Satellite multi-access protocols are classified in terms of channel synchronization (slotted and unslotted) and the qualitative nature of message access (fixed assigned, contention and reservation). In addition to well known techniques such as ALOHA, slotted ALOHA, tree CRA, packet CDMA and demand assigned (DAMA) TDMA, a number of new approaches to efficient unslotted access, including selective reject (SREJ) ALOHA, time-of-arrival CRA and locally synchronous reservation, are discussed. The general review is followed by a detailed performance comparison of a number of candidate first-generation VSAT protocols, namely ALOHA, slotted ALOHA, SREJ-ALOHA, DAMA with TDMA reservation access and DAMA with slotted ALOHA reservation access. The performance evaluation, based on detailed simulations with VSAT equipment and transaction traffic parameters, is summarized by curves of average delay and throughput vs. number of VSATs per channel for each of the protocols considered. Higher-order differences in delay performance are illustrated with appropriate delay distribution results and the sensitivity of performance with respect to key equipment and traffic parameters is investigated. For the transaction traffic model under consideration, the results suggest the use of SREJ-ALOHA among contention techniques or DAMA with slotted ALOHA reservation among controlled access alternatives. The trade-off between contention and reservation access is shown to be more complex, depending on the combination of average delay, peak delay, transmission cost and equipment complexity suited to the particular application. In Part II

1 To published in the next issue

of this paper on Ku-band VSAT networks, the issue of overall system design is considered.     

VSAT Networks—an overview

This paper examines the technology and constraints of very small aperture terminals (VSAT) networks, a special type of wide-area thin-route satellite network that represents a recent innovation in the field of satellite communications. VSAT network architectures suitable for both data and voice communications are studied in this paper. Several issues concerning the frequency of operations, that is, C-band versus Ku-band are examined, and trade-offs between non-spread spectrum and spread spectrum techniques, as well as modulation and multiple access schemes, are considered in detail. Link design examples are given to illustrate the performance of various types of VSAT networks.     

DVB-RCS卫星互动网络的研究

DVB-RCS卫星互动网络,应用前景广阔。DVB-RCS标准是为了在单向的卫星广播网络中(DVB-S)实现双向互动网络而采纳的一系列技术规范,但标准中仅规定了空中接口,没有提到如何实现一个网络的MAC接入层。卫星网络的实现结构是其MAC接入层协议的重要组成部分。本文设计了一个DVB-RCS卫星互动网络的网络结构,重点解释了它的多址接入方式和资源分配方式,最后描述了它的入网过程。     

浅谈VSAT卫星通信系统设计方法

本首先介绍了VSAT卫星通信技术的一般概念及特点，然后介绍了VSAT通信系统规划需要注意的事项，其次着重探讨VSAT卫星终端站的设计方法，特别对卫星终端站天线尺寸的选择和安装位置进行了详细的论述，并提出了一些卫星终端站设计中应遵守的原则，最后结合VSAT卫星通信的特点展望了其未来的应用前景。     

走向宽带化的VSAT卫星通信

受数据音频视频广播、计算机卫星宽带交互接入和音视频会议等业务的推动,VSAT卫星通信网向宽带业务发展巳成为必然趋势。分别对应以上业务的VSAT卫星通信网也日益趋于融合成一个统一的宽带VSAT通信网。发展宽带VSAT通信网的关键技术涉及到宽带数据广播、宽带多址接入、卫星通信规程、网络综合管理和宽带虚拟子网等。     

VSAT卫星通信小站设备常见故障原因与解决

随着卫星通信技术的发展,VSAT卫星通信设备在气象部门正得到广泛的应用。本文针对VSAT卫星通信小站设备在通信中常见的故障进行了原因分析,并提出了具体的解决方法。     

VSAT communications networks-an overview

The very-small-aperture-terminal (VSAT) fixed satellite communication network is a star network in which many dispersed micro terminals attempt to send data in a packet form through a random access/time-division multiple-access (RA/TDMA) satellite channel with transmission delay. The basic concept of the VSAT and its service potential are discussed. Two classes of traffic are addressed, namely business-oriented low-rate-data traffic and bulk data traffic of corporate networks. Satellite access, throughput, and delay are considered. The size of the network population that can be served in an RA/TDMA environment is calculated. User protocols are examined. A typical VSAT business scenario is described     

Simulation models for performance evaluation of satellite multipleaccess protocols

Simulation models are described for the performance evaluation of satellite multiple-access protocols used in VSAT (very small aperture terminal) data networks. Since the design of VSAT-based wide-area networks for interactive applications is critically dependent on the delay-throughput characteristics of the channel access protocol used, detailed simulation models have been developed to augment analytical performance-evaluation methods. Simulation models for several candidate VSAT access protocols, including random-access techniques such as Aloha, selective reject Aloha and slotted Aloha and demand-assignment multiple-access based techniques, are discussed in terms of traffic-source models, access algorithms, and performance-evaluation criteria. Numerical results for a realistic interactive data VSAT network environment are presented