IEEE802.3标准之PHY——初相识
<p .="box-sizing: border-box; margin: 0px 0px 10px; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin-bottom: 10px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">IEEE802.3标准有个框架，框架里分不同的子层（sublayer）,每个子层各司其职，上下子层之间进行沟通协作，彼此间有沟通的方式，最后达到上下贯通、完成信息传递。就好比是一栋办公楼，顶楼分配给总裁，次高层给高管……，一楼分配给一线员工。总裁下达目标，高管负责制定总的执行方针，层层往下传达，每一层又各司其职，对上层下达的任务进行细化，最后达到一线员工手里的就是具体的任务，一线员工再出去服务于客户。<br .="box-sizing: border-box;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box;"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> <img src="http://www.edadoc.com/upload/day_17-0717/14-gscx-01.jpg" alt="" .="box-sizing: border-box; border: 0px none; vertical-align: middle;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; border-width: initial; border-style: none; vertical-align: middle; max-width: 100%;"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">图1 IEEE802.3 Standard构架<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">对于客户来说，面对的就是一线员工，那今天我们就来讲讲这个一线员工，也是很多工程师最为熟悉的子层：PHY。PHY分LAN PHY、WAN PHY，比如基于基带媒介的10GBase Serial PHY就有如下几种：<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><img src="http://www.edadoc.com/upload/day_17-0717/14-gscx-02.jpg" alt="" .="box-sizing: border-box; border: 0px none; vertical-align: middle;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; border-width: initial; border-style: none; vertical-align: middle; max-width: 100%;"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">今天我们着重讲LAN PHY，所以在后文中全部用PHY代替 LAN PHY。讲到PHY，就得提提它的上级：MAC。是不是对它俩很熟？那它们的全名叫什么？各自负责的职责是什么？很多人对它俩的认识停留在似曾相识的阶段，说了解吧可又说不出个所以然来。<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">MAC（Media Access Control），在OSI(开放式系统互连)参考模型下，属于数据链路层，它向上服务的对象有LLC（Logical Link Control逻辑链路控制）子层、或其它ISO/IEC局域网国际标准MAC服务的用户，如下图所示：<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> <img src="http://www.edadoc.com/upload/day_17-0717/14-gscx-03.jpg" alt="" .="box-sizing: border-box; border: 0px none; vertical-align: middle;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; border-width: initial; border-style: none; vertical-align: middle; max-width: 100%;"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">MAC需与其上层沟通，还需与其下层PHY沟通，其中MAC与上层沟通会完成以下两个任务：<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><img src="http://www.edadoc.com/upload/day_17-0717/14-gscx-04.jpg" alt="" .="box-sizing: border-box; border: 0px none; vertical-align: middle;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; border-width: initial; border-style: none; vertical-align: middle; max-width: 100%;"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">在IEEE802.3标准里，任何两个不同子层之间的信息传递必须有依可循，定个沟通的方式（即标准），好让这两个子层之间能顺利给彼此发送消息，不然就是鸡同鸭讲。<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">下面我们把MAC到PHY、PHY到PHY这两个子层之间的通信框架拎出来，把它们放在一个框图下对各个接口协议进行说明，其中PHY如下图红框所示，它包含了许多功能模块。<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> <img src="http://www.edadoc.com/upload/day_17-0717/14-gscx-05.jpg" alt="" .="box-sizing: border-box; border: 0px none; vertical-align: middle;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; border-width: initial; border-style: none; vertical-align: middle; max-width: 100%;"><div .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); text-align: center;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">图2 MAC与PHY框架<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">•<span .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); white-space: pre;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> <span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">MAC和PHY（Physical layer device）之间称为MII（Media Independent Interface，介质独立接口）,它可以有多种协议，比如MII、XMII、GMII、XLGMII……<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">•<span .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); white-space: pre;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> <span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">PHY与PHY之间进行通信的接口称为MDI（Medium Dependent Interface，媒介专用接口），媒介有背板、Cable、光纤……，因媒介的不同就会有不同的通信协议；数率的不同又会有不同的通信协议，媒介和数率两两组合就可以变幻出许多种通信协议,比如10GBase-KR、40GBase-CR4、100GBase-SR10……<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">•<span .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255); white-space: pre;" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> <span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">而PHY这一层里，即PHY内部，它包含了多个功能模块，功能模块间的通信也相应地会有接口协议，比如*AUI、nPPI……<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);">其中，每个PHY的功能模块的多少会因需要的不同而有所增减，比如：<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> 在100Base-T应用场景下没有PMD；<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> 只有10GBase-R、40GBase-R、100GBase-R的PCS需要FEC；<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> 40GBase-R的PCS需要2个PMA、100GBase-R的PCS需要3个PMA；<br .="box-sizing: border-box; color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"><span .="color: rgb(20, 20, 20); font-family: 微软雅黑, Arial, Helvetica, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);" style="word-wrap: break-word; margin: 0px; padding: 0px; box-sizing: border-box; color: rgb(100, 100, 100); font-family: myFont, "Microsoft YaHei"; font-size: 16px; text-align: justify; background-color: rgb(255, 255, 255);"> 只有≥1Gbps以上的背板应用场景才会用到AN； 谢谢分享IEEE802.3标准之PHY 积累知识，学习了，谢谢分享。
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