DEISA TCP throughput suffers from cross traffic

PTS Case 3

Synopsis

DEISA is a consortium of leading national supercomputing centres that currently deploys and operates a persistent, production quality, distributed supercomputing environment with continental scope (http://www.deidsa.org\). To ensure the ongoing performance of their network connectivity DEISA sites perform single-stream TCP measurements (using iperf) between one another. One set of such tests run between Juelich (DE), IDRIS (FR) and CINECA (IT). While these tests normally run at 900 Mbps throughput, it was seen that this could slow down to ~400 Mbps when an unrelated project performs high-rate (2-3 Gbps) UDP tests between Karlsruhe (DE) and CERN. This was particularly surprising because the cross-traffic was ‘Less then Best Effort’ traffic, and was therefore not expected to compete for bandwidth with the normal, ‘best effort’ DEISA traffic. By the time the PERT investigation had begun the cross traffic itself had stopped, and was not expected to resume anytime soon. This, coupled with a change in G�ANT routing (as the G�ANT network evolved in to the G�ANT2 network) lead to the case being closed.

– Main.TobyRodwell - 29 Jan 2007