In the third chapter,all kinds of service prototypes,the control fields and the code regulations of these field are introduced from the MAC layer to the LLC layer.

• 在第三章中,把数据链路层分为逻辑链路控制(Logic Link Control,简称LLC)子层和媒质接入控制(Media Access Control,简称MAC)子层两部分来论述,对各个子层的服务原语,及其各个子层的控制域以及控制编码作了详细的介绍。