Re: [LARTC] TC (HTB) doesn't work well when network is congested?

[Peter Rabbitson <rabbit+list@rabbit.us>]

William Xu wrote:
> Hi,
> 
> I have a server and ten clients in a Gigabit network. The server has 
> 125mbps network bandwidth.
> I want that the server has 40Mbps bandwidth reserved for client 1 (IP 
> 192.168.5.141), and the
> rest bandwidth is for all other clients.
> 
> <snip>
> 
> I ran a test in which all 10 clients send/receive packets to/from the 
> server simultaneously. But
> Client 1 only got 20mbps bandwidth for sending, and 38mpbs for 
> receiving. If I limit the rate of
> both classes 1:1 to 60mbps instead of 125mbps, Client 1 got 39mbps for 
> sending, and 40mbps for
> receiving.
> 
> I am not sure what might cause this. Is it because TC doesn't work well 
> when network is congested?
> Or my script is not right?
> 

No network will be able to operate at its theoretical maximum. In the 
case of a gigabit network you will be lucky to get consistent 120mbps, 
and it heavily depends on the hardware quality, and the number of 
switches in between. So what you are doing is oversaturating the link, 
the ACK packets can not get through, your speed drops due to 
delays/retransmissions. Perform a test with only two systems sending 
stuff to each other to see what is the actual bandwidth you can hope 
for, and use that number instead of 125mbps.
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