IP/Network

  

 

 

 

Ethernet : Pause Frame

 

Pause Frame is a special type of control frame transmitted by MAC layer to control the rate of incoming packet. Basically this packet says "I am now overwhelmed, please don't send any frame for this amount of time".

 

you can easily find Pause frame from wireshark with the filter "macc.opcode == pause" as shown below.

 

 

Here you see "pause_time" and you would ask "what is the unit of the time ?". It is a special unit called 'bit quanta' in IEEE 802.2 31B.2. I bit quanta is equal to 512 bit time for each implementation.

It is what they call "Bit Time". The Bit Time conversion to physical timing varies depending on physical layer data rate as follows.

 

Rate

physical time / 1 bit time

Fast Ethernet

10 nano seconds

Gigabit Ethernet

1 nano second

10 Gigabit Ethernet

0.1 nano second

 

If an Ethernet port wants to allow the incoming frame before pause_time expires, it can send another Pause frame with pause_time = 0.