综合业务局域网的自适应混合多路访问协议

An Adaptive-and-Hybrid Multiple Access Protocol for Integrated Data/Voice Local Area Networks

综合业务局域网正向着高速率、较大地理范围和多工作站的方向发展。所以必须相应发展更有效的介质访问协议。混合多路访问协议结合了随机争用协议和令牌协议的优点,在轻重负载情况下都有好的时延和吞吐量性能。但在中等负载情况下以及在活动站比总站数少很多时,混合多路访问协议不能保持高的效率。为此,本文提出了一种自适应混合多路访问协议ADHYMAP,它是CSMA/CD、隐令牌协议和本文提出的一种预约访问协议的结合。目的是利用预约访问协议改善中等负载特性,以及支持活动站比总站数少很多的情况。因此,ADHYMAP能够支持较大的网络规模,可以应用于大城市网络(MAN)。ADHYMAP是分布式的,具有很高的可靠性。在ADHYMAP中还引入了话音优先权机制和流量控制措施。最后,与其它协议的时延-负载特性以及随活动站数变化的情况进行了计算机模拟对比。

To support high data rates, relatively large areas and a large number of stations, efficient access protocols for integrated data/voice local area networks are required. Hybrid multiple access protocols (HYMAP) combine the advantages of random access mode(e, g. CSMA/CD and its variants) when the bus is lightly loaded with the advantages of ordered assignment mode(e, g. token-passing and implicit token-passing protocols) when the load increases, thereby avoiding the disadvantages of both schemes. However, HYMAP's behavior in middle load is not so perfect and a high channel time cost exists when the number of active stations is much less than the total number of stations. So, an adaptive-and-hybrid multiple access protocol (ADHYMAP) is proposed in this paper, which combines CSMA/CD, reservation and implicit token passing modes to improve HYMAP's characteristics in middle load and reduce the extra costs that token passes to inactive stations. Therefore, ADHYMAP can support a large number of stations when the average number of active stations is in a small percent of total and may be applied in metropolitan area networks(MAN) The prieority scheme of voice stations over data ones and flow control in ADHYMAP are discussed. Finally, a simulation study of ADHYMAP and its comparison with other protocols are yielded.