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Single file transfer

These tests were performed using a 1024 MB file for transfer of the hdf5 format. Without any
network modifications or errors induced, the average file transfer time using Pushpull was ~
332.416s which will be used as the reference figure (R1) in the discussion to continue. While
the performance of the tool is evaluated, the capability of tool to deal with network
modifications is studied here. The network was modified using the iproute2 package.

Constant packet delay

A constant packet delay was induced in the network using the following statement

$ tc qdisc add dev eth0 root netem delay 100ms

Image Added

A minimal performance variation is observed for packet delays up to ~200ms, after which there transfer time increases accordingly.
For the packet delays > 800ms transfer stalled and OODT generated the error message after which it continuously re-attempted to download the file:

org.apache.oodt.cas.protocol.exceptions.ProtocolException: Downloads appear to be
hanging . . . aborting wait . . . waited for 15 minutes

Modified TCP window

A single file of 1024MB was downloaded using PushPull using different TCP window sizes.
There is the option to enable/disable TCP window scaling in the configuration file
/etc/sysctl.conf and to set the maximum transfer window under LINUX. The file is then reloaded to update the parameters using

$ sysctl -p

The parameters in /etc/sysctl.conf which were modified are (e.g.):

net.core.rmem_max
net.core.wmem_max
net.core.rmem_default
net.core.wmem_default

A maximum transfer rate of
~20of ~20.1MB/s is achieved for TCP window sizes > 2048 Bytes. The smallest window size found
for PushPull to be in an operational state was 256 Bytes giving an average transfer rate of
~11of ~11.2MB/s.

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