1) 物理层各子层功能

Reconciliation Sublayer (RS):协调子层。汇聚功能，使不同介质类型对MAC子层透明

Medium Independent Interface (MII):介质无关接口。提供公共接口，屏蔽这些物理层的不同细节

Physical Coding Sublayer (PCS):物理编码子层。编码/解码

Physical Medium Attachment sublayer (PMA):物理介质连接子层。执行并串/串并转换

Physical Medium Dependent sublayer (PMD):物理介质相关子层。信号转换到特定介质上或反向转换

Medium Dependent Interface (MDI):介质相关接口。到传输介质的接口

2) 以太网帧结构

Preamble (PRE)- 7 bytes. The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the frame-reception portions of receiving physical layers with the incoming bit stream.7字节。Pre字段中1和0交互使用，接收站通过该字段知道导入帧，并且该字段提供了同步化接收物理层帧接收部分和导入比特流的方法。

Start-of-frame delimiter (SFD)- 1 byte. The SOF is an alternating pattern of ones and zeros, ending with two consecutive 1-bits indicating that the next bit is the left-most bit in the left-most byte of the destination address.1字节。字段中1和0交互使用，结尾是两个连续的1，表示下一位是目的地址的起始位。

Destination address (DA)- 6 bytes. The DA field identifies which station(s) should receive the frame.目标地址.

Source addresses (SA)- 6 bytes. The SA field identifies the sending station. 源地址.

Length/Type- 2 bytes. This field indicates either the number of MAC-client data bytes that are contained in the data field of the frame, or the frame type ID if the frame is assembled using an optional format.

Data- Is a sequence of n bytes (46=< n =<1500) of any value. (The total frame minimum is 64bytes, maxium is bytes.)

Frame check sequence (FCS)- 4 bytes. This sequence contains a 32-bit cyclic redundancy check (CRC) value, which is created by the sending MAC and is recalculated by the receiving MAC to check for damaged frames.4字节。该序列包括32位的循环冗余校验（CRC）值，由发送方生成，接收方重新进行计算以校验被破坏的帧。

3) IEEE 802.3u Fast Ethernet

3.1) 100BASE-TX

支持全双工模式。使用的是两对抗阻为100欧姆的5类非屏蔽双绞线（UTP），最大传输距离是100米。用线对 1/2(发送), 3/6(接收)。使用RJ-45连接器。PCS子层使用4B/5B编码方式，信号频率为125MHz。PMD子中使用MLT-3(多电平传输-3)编码:若数据为“1”，则从当前电平到下一电平跳变。例如：11111=> +1,0,-1,0,+1，若数据为“0”，则不跳变。