An Investigation into Transport Protocols and Data Transport ...

3.2. Network Monitoring 47
1
0.8
Bottleneck (fraction)
0.6
0.4
0.2
Network
Sender
Recveiver
0
0 50 100 150 200 250 300
Throughput (mbit/sec)
Figure 3.2: Bottleneck limits of TCP WAN transfers between CERN and RAL as
reported by Web100.
only lost when the network queues overflow, the consistent high throughput
of the UDP packets suggest that the average queue occupancy is low. Given
this information, it is expected that TCP should also be able to sustain high
throughput (on average).
To investigate the details of TCP transfers, all TCP results were passively
monitored using the Web100 [MHR03] framework in order to determine the
possible bottlenecks on the system. Web100 implements a facility whereby
the performance of TCP can be determined to be bottlenecked by either the
receiver, the sender or by the path in between. These variables are presented
in a ‘triage’ whereby the fraction between the three bottlenecks are logged.
Web100 is a Linux kernel patch that enables the in-depth logging of TCP
parameters. Figure 3.2 shows the result of the Web100 triage [MHR03] for
numerous network transfers (including those not presented in Figure 3.1) for
the network path shown in Figure D.1. The triage determines the bottleneck
associated with each transfer in terms of a ratio between the network, the
sender, and the receiver.