An Investigation into Transport Protocols and Data Transport ...

3.2. Network Monitoring 45
Internet environment. The hosts were equipped with Gigabit NIC cards and
the network path consisted of 15 hops as shown in Figure D.1 with a path
bottleneck capacity of 622Mbit/sec. The machines were chosen to give a representative
transfer rates achievable by real physics users wishing to transfer
data from CERN, in Switzerland, to Rutherford Appleton Laboratory, in
England, UK.
In order to generate UDP throughput traffic, UDPMon [HJ] was used and
configured to a inter-packet wait time of zero seconds (i.e. back-to-back
packets). For the TCP traffic, iperf [TQD + 03] was used to simulate the
transfer of data and appropriate provisions for a large socket buffer size was
used with a sufficiently large socket buffer size of 8MB at both ends (See
Section 5.1.1).
Tests were run over an entire week, with randomised start times. UDP
flows were conducted with 1,000 full sized packets and TCP was ran for 30
seconds. These values were found to be sufficiently long to reach steady state.
3.2.3 Results
Figure 3.1 shows the results of the tests and shows that whilst UDP was
able to achieve almost line rate with a mean throughput of 493Mbit/sec,
TCP was only able to achieve about half of that with a mean throughput of
195Mbit/sec. Therefore, there is a clear discrepancy in the performance at
the transport protocol layer.
Hardware performance bottlenecks between the two end-hosts can be assumed
to be negligible due to the successful transmission of UDP packets at
high speeds.
Similar tests to CERN from Manchester showed only marginal improve-