[e2e] query reg improving TCP performane

[V Anil Kumar]

Hi,

What are the buffer sizes configured at the interface level on
intermediate routers? Are they also set to the BDP of the link? Also, what
is the buffer management scheme (RED or FIFO) on the intermediate routers?
These parameters will also have an impact on the end-to-end throughput.

The configuration you attached shows that you could improve the throughput
from 55 mbps to 95 mbps by decreasing the buffer size from 921600 to
175636. While your text says that you achieved 95 mbps by increasing the
buffer size.

Any idea why a dedicated 100 mbps link gives an RTT of 70 msec. under no 
load condition? 


Anil
  
 On Thu, 5 Jul 2007, query  wrote:

> Hi All,
> 
>   I was doing some Bandwidth measurement test on a 100 mbs link with a RTT
> of about 70ms.
>   Based on that, I calculated the BDP as follows.
> 
>           BDP = Bandwidth * RTT
>               = 13107200 bytes * .07 secs
>               = 896 Kbytes
>               = 900 Kbyes (approx)
>               = 921600 bytes
> 
> 
>    After that I adjusted the TCP window size as follows:
> 
>            /proc/sys/net/core/rmem_max  921600
>            /proc/sys/net/core/wmem_max  921600
>            /proc/sys/net/ipv4/tcp_rmem      4096    87380   921600
>            /proc/sys/net/ipv4/tcp_wmem      4096    87380   921600
> 
>    These adjustmenst I had done on a Linux host with 2.6.15 kernel. The
> congestion
>    control algorithm , it is using BIC
> 
>    The same window adjustments I had performed on the other hand on a Linux
> host
>    with kernel 2.6.9 . It is also using BIC for congestion control.
> 
>    The Bandwidth Performnce test I am doing using iperf , a highly popular
> public
>    domain tool for measuring TCP & UDP Bandwidth Performance .
> 
>    With the default Linux 2.6 TCP window settings , I was getting a
> throughput of
>    nearly 10mbs which is very low for a 100 mbs link.
> 
>    So , I performed the above TCP adjustmets and I found the throughput to
> be around
>    55 mbs which is a significant improvement . But that is not fully
> utilsing the link
>    as it is a dedicated link and there was no other traffic.
>    This , I proved with the next experiment where I reached a link
> utilisation of
>    little more than 95 mbs . That is very much O.K for a 100mbs link.
> 
>    I did the following adjustments. I increased the above calculated BDP by
> nearly
>    half of the value . The TCP settings now look like this.
> 
>            /proc/sys/net/core/rmem_max  175636
>            /proc/sys/net/core/wmem_max  175636
>            /proc/sys/net/ipv4/tcp_rmem      4096    87380   175636
>            /proc/sys/net/ipv4/tcp_wmem      4096    87380   175636
> 
>     After these settings , I find the link utilisation to be nearly 95 mbs.
> 
>     According to many papers that I read , I found that the BDP should be
> equal
>     to the product of Bandwidth * RTT .
>     I had done that , but the link utilisation is only 50%. But when I
> increased
>     to a much higher value , the link utilisation is nearly around 95 %.
> 
>     I am confused regarding my findings.Please clarify me so that I can
> perform
>     the experiment correctly.
> 
>     With Thanks in Advance
>