Asymmetry in throughput using bbftp

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File transfers from Stanford to SLAC

Our first test transfered data from a SLAC machine, evagore.slac.stanford.edu, to a Stanford machine, loggy.slac.stanford.edu, using the standard bbftp binary.

The SLAC machine is a Sun Ultra 5/10 with a single processor UltraSPARC-IIi 333MHz, with network connection via a 100 mbps/full duplex Ethernet link. The Stanford machine has also a single processor Pentium II (Klamath) 300MHz. The operating system of the two machines is:

• evagore.slac.stanford.edu: SunOS 5.7
• loggy.stanford.edu: Linux 2.2.16

The parameters of the transfer are the defaults for bbftp:
number of streams = 1
window size = 256K

The results obtained indicated an asymmetry:  

Stanford to SLAC (mbps)	SLAC to Stanford (mbps)
42.4 +/- 6.7	21.2 +/- 2.6

We were quite puzzled by the observed asymmetry in trasnfer rate, and we concluded that this was likely due to the different operating systems.
Further analysis have indeed shown that on Linux platform the window sizes cannot be correclty tuned.

File transfers from Stanford to UK

As a second test, we transfered data on the link Stanford University - Darsbury Lab, over the Internet2 backbone, where the marked packets can be observed.
The Stanford machine is the same of the previous test, while the machine in the UK is:

• rtlin1.dl.ac.uk: Linux 2.2.14, with a single processor Pentium 75 - 200 MHz

1 stream

10 streams

20 streams

File transfers SLAC - UK

As a third test, we transfered data on the link from SLAC - Darsbury Lab, in order to verify that the differences we have observed are indeed due to the different operating systems.
The machine used to trasfer data are the same as in the previous test, evagore and rtlin1.
The results of data transfer with different windowsizes and different number of streams are obtained using bbftp, clearly show how the window size change does not have any impact in the transfer rate to a LINUX machine, while there are some variations with the Sun operating system at the receiving end.
We checked looking at the SYN packets ecahnged between the two systems, that the windowsizes (send and receive) on the Linux box cannot be modified from the default of 32KB. On the other end, the receiving windowsize on the Sun machine can be modified and this leads to different perfomances expecially with one single stream.

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