Hello, if anyone can help me explain in detail how flow control works it would be great.

I have a part of a network that looks like this:

main site

750Mb/s FD Airfiber24

1st point

360Mb/s FD Alcoma 10GHz

2nd point

wap link 1Gb/s HD

3rd point

lhg60 link 1Gb/s HD

4th point

lhg60 link 1Gb/s HD

5th point

and more (lets say up to 10)

on every point I have some AP for clients...
tcp btest looks like this
When I measure speed from client on 3rd to main I get 300Mb/s
When I measure speed from client on 4th to main I get 300Mb/s
When I measure speed from client on 5th to main I get 60Mb/s
When I measure speed from client on 5th to 2nd I get 500Mb/s
When I measure speed from client on 5th to 1st I get 60Mb/s

Clients from 5th place and far away have problems with speed... Every point is routed with ospf... no bridges or switches.

So i thought that the router on the 1st just cannot handle that anymore and replaced hex poe with 5009poe but the problem remained.

Today out of a despair i tried to poke with flow control between 1st and 2nd point.

I turned rx and tx on on both sides and here it comes... full speed of the link when i start the speed from the client on 5th place to the main.

I said to myself... i dont want to be limiting speed when an interface is full and others are not so I switch from tx on / rx on to tx on / rx off and the problem came back...

So out of curiosity I made on both sides the oposite tx off, rx on and again - full speed.

How to hell this can affect speed? I just dont know how does it work because my only explanation in this case is that in this mode router wont generate pause packets, but it seems that this config enabled some buffers.

Can anyone understands and is willing to educate me (or all us others who dont know) what is a difference in those 4 possible setups?

1 - both off
2 - TX flow on, Rx flow off
3 - Tx flow off, Rx flow on
4 - Tx flow on, Rx flow on

Thank you (I really mean that... I dont want to be rude or sarcastic... I just really do want to understand)