[e2e] query reg improving TCP performane

[query]

On 7/6/07, V Anil Kumar <anil at cmmacs.ernet.in> wrote:
>
>
> 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 network is not under my administration .
So , I will
   probably ask my  metwork provider to give me the result.


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.


   Sorry, that was a typo . It should have been  1756366. (nearly 1.7 MB ).


Any idea why a dedicated 100 mbps link gives an RTT of 70 msec. under no
> load condition?
>
>   The two end points are very far away. It is more than 3000 kms . So,
> probably

      that might me the reason. The RTT  is obeying the SLA parameters that
was
      defined for this network.


With Thanks and Regards
 zaman





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
> >
>
>
>
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