[e2e] query reg improving TCP performane
query.cdac at gmail.com
Thu Jul 5 23:45:34 PDT 2007
On 7/6/07, V Anil Kumar <anil at cmmacs.ernet.in> wrote:
> 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
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,
that might me the reason. The RTT is obeying the SLA parameters that
defined for this network.
With Thanks and Regards
> On Thu, 5 Jul 2007, query wrote:
> > Hi All,
> > I was doing some Bandwidth measurement test on a 100 mbs link with a
> > 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
> > 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
> > 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
> > 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
> > 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
> > According to many papers that I read , I found that the BDP should
> > 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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