How we did it

We built a test bed comprising two Enterasys Networks Matrix E1 switches. Each switch had 12 edge Gigabit Ethernet interfaces and 1 backbone 10G-bit/sec interface using 850-nm course wavelength division multiplexing optics. We connected the two switches using the backbone interfaces.

To each of the edge interfaces, we attached the Smartbits traffic generator/analyzers from Spirent Communications equipped with 3201B gigabit Ethernet line cards. We used 24 Smartbits line cards in all - one for each Enterasys edge interface.

We conducted tests both with and without congestion of the 10G-bit/sec backbone. We offered traffic to 10 edge interfaces on each switch in the uncongested tests, and to 12 interfaces on each switch in the congested tests.

We offered traffic at line-rate in all tests. Thus, in the congested case with 12 1G-bit/sec interfaces feeding a single 10G-bit/sec interface, we created a 20% overload.

For all tests, we used a partially meshed pattern. This means all frames we offered to each edge interface were destined for all interfaces on the remote switch, and none were destined for the local switch.

Using Script Automation Interface (SAI), a custom scripting language for the Smartbits, we offered all edge interfaces both 64-byte and 1,518-byte frames - the minimum and maximum sizes allowed in Ethernet. In all tests, we offered traffic for 60 seconds.

We repeated the tests in configurations emulating one host per interface and 250 hosts per interface (240 hosts in the congested case). In all, we emulated up to 5,760 hosts attached to the Enterasys switches, representing the large number of attachments found on backbones of large corporate networks.

Our SAI scripts recorded summary totals for frames sent and received; average latency; latency range; latency range variation; and frames in sequence. On a per-flow basis, we also recorded minimum, maximum and average latency.

Network Test gratefully acknowledges the support of Spirent Communications for this project. Spirent supplied its Smartbits 6000B chassis, 3201B Gigabit Ethernet line cards and a traffic script custom-developed for this project. In addition, Spirent engineers Bob Anderson and Brooks Hickman offered logistical support during the test.

Newman is president of Network Test, an independent benchmarking and network design consultancy in Westlake Village, Calif. He can be reached at dnewman@networktest.com.