Intel 82559 用户手册

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A flow control frame is identified by a special type field (bytes transmitted left to right): 88 to 80. 
The reception of a FC frame can be done either through the regular individual address filtering 

mechanism or by a special multicast address detection mechanism. Since the transmitting MAC 

may not know the individual address of the other station, it may not be able to send FC frames to 
the individual address of the other node. A special multicast destination address is defined for use 

in FC frames. Special address filtering is used to receive frames addressed to that multicast 

address. The address is (bytes transmitted left to right): 01-80-C2-00-00-01.

When a station’s receive buffer reaches a high watermark (running out of storage space for 
incoming packets), it may send its link partner a pause frame (also known as an XOFF frame).

When the station receives the pause request, it stops transmitting for a number of slot times as 

specified by the time parameter in the pause frame. The time parameter is a 2 byte field.

The reaction time for a transmitting station (the congester) is 512 bit times from the end of the 

received pause frame. If the congester is transmitting when the time expires, it should complete the 
transmitted frame. The congester should not start transmitting a frame after the 512-bit time period. 

Transmission is restarted upon expiration of the pause timer or upon reception of a pause request 

with a time parameter of zero (also known as an XON frame).

Note: The 82557 does not support flow control functionality.

one byte

up to 6 bytes

one byte

6 bytes

6 bytes

2 bytes

2 bytes

4 bytes

one byte