Study on Methods for Constructing Layered Protocols in High-Speed Satellite Data Networks

卫星数据网络可以用来满足日益增长的需求，即可以在多个站点之间高速传输和交换大量信息。如何构建通信协议是高速数据网络发展中需要解决的重要问题之一。本课题的目标是研究在高速卫星数据网络中构建有效的分层协议的方法。首先比较了面向连接的(CO)逻辑链路控制(LLC)协议和无连接(CL)LLC协议在采用TDMD预留多址协议的高速卫星分组网络中的性能。特别是，我们考察了信道传输速率如何影响两种LLC协议的性能，然后确定哪种LLC协议更适合于任何给定的系统环境。比较表明，随着信道传输速率的提高，CL-LLC协议比CO-LLC协议具有更多的优势，CL-LLC协议的适用范围随着接收缓存容量的增加和网络负载的降低而变宽。在隔离类型中，独立于其LLC协议定义MAC协议，而组合类型具有与其LLC协议相关的MAC协议。本文研究了TDMA预留和时隙ALOHA两种MAC协议，以及一种面向连接的LLC协议。对这两种方法进行了比较，发现采用TDMA预留协议的混合型协议的性能总是优于相应的隔离型协议，而采用时隙ALOHA协议的两种类型的性能差别很小。此外，我们还研究了局域网中的链路级连接控制方案，作为通过卫星链路互连局域网的初步研究。

Satellite data networks can be used to meet an increasing demand that a large amount of information can be transmitted and exchanged at high speeds among many sites. One of the most important problems to be solved in the development of high-speed data networks is how to construct communication protocols. The objective of this project is to develop some methods for constructing efficient layered protocols in high-speed satellite data networks.We first make a performance comparison between a connection-oriented (CO) Logical Link Control (LLC) protocol and a connectionless (CL) LLC protocol in a high-speed satellite packet network with the TDMD-Reservation multiple access protocol. In particular, we examine how the channel transmission rate affects the peformance of the two LLC protocols and then determine which LLC protocol is more suitable for any given system environment. The comparison indicates that the CL-LLC protocol has more advantages over the CO-LLC protocol as the channel transmission rate increases and that the suitable region for the CL-LLC protocol becomes wider as the receive-buffer capacity increases and as the network load decreases.Next, we propose two methods for constructing the data link protocol satellite data networks : the isolated type and combined type. In the isolated type, a MAC protocol is defined independent of its LLC protocol, whereas the combined type has a MAC protocol related to its LLC protocol. We study here two MAC protocols, TDMA-Reservation and Slotted-ALOHA, and a connection-oriented LLC protocol. We compare the two methods and then see that the combined type with the TDMA-Reservation protocol always outperforms the corresponding isolated type, while the performance difference between the two types with Slotted-ALOHA is very small.In addition, we also study link-level connection control schemes in local area networks (LAN's) as a preliminary research on interconnecting LAN's by satellite links.