Powerful demo of PHY devices

The UNH Interoperability Lab participated in a demonstration with the Ethernet Alliance of physical-layer interoperability. In preparation, staff and student engineers tested two 10GBase-T PHYs.

Martin Rowe, Senior Technical Editor -- Test & Measurement World, 8/1/2007

DEVICE UNDER TEST

Physical-layer interface (PHY) ICs embedded into network-interface cards (NICs), Ethernet switches, and test equipment. The PHY devices provide a 10GBase-T (10-Gbps) interface from the equipment to Ethernet networks.

Test for physical-layer interoperability between equipment. Construct a pair of test networks, one each for equipment connected with each PHY IC. Test for interoperability among equipment on each network and then connect the two networks and perform interoperability testing between the two PHY ICs.

• Agilent Technologies: Ethernet cable tester. www.tm.agilent.com.
• Fluke Networks: Ethernet cable tester. www.flukenetworks.com.
• Fulcrum Microsystems: Ethernet switch. www.fulcrummicro.com.
• Ixia: data generator. www.ixiacom.com.
• LeCroy: digital oscilloscope. www.lecroy.com.
• The Mathworks: technical computing software. www.mathworks.com.
• SMC Networks: Ethernet switch. www.smc.com.
• Spirent Communications: data generator. www.spirentcom.com.

The University of New Hampshire Interoperability Lab (UNH-IOL, www.iol.unh.edu) participated in a May 2007 demonstration with the Ethernet Alliance (www.ethernetalliance.org) of physical-layer interoperability. In preparation for the demo, staff engineers and students led by UNH-IOL 10 Gigabit Ethernet Consortium manager Jeff Lapak tested two 10GBase-T PHY ICs for interoperability.

The test bed consisted of two independent networks that were later connected. Each network used servers containing NICs, an Ethernet switch, and a data generator, all of which contained a 10GBase-T PHY from the same source (PHY-A and PHY-B in the figure).

Two networks, each with equipment containing PHY-A or PHY-B ICs, let engineers perform interoperability tests.

Engineers started by connecting two servers with the same PHY over a 5-ft, Cat-6A cable to verify that the identical PHYs would communicate. This test consisted of each server sending a “ping” signal to the other.

With communication established, the engineers connected the servers and a data generator to an Ethernet switch, with all equipment in each network using the same PHY. This configuration used 100-ft Cat-6A cables. Engineers used cable testers to measure insertion loss, return loss, and crosstalk of the cables.

The engineers set the data generator to loopback mode, so it received its own transmissions through the switch. The servers then sent 100-Gbps data streams to each other through the switch.

Because the PHYs in each network were early revisions, engineers from each PHY manufacturer were on hand to make firmware changes following a test. “This process takes about two days,” noted Lapak.

With interoperability established, UNH-IOL engineers tested the cables for interference. While the servers loaded the network, the data generator sent traffic to itself though the switch and counted packet errors. “We consider the test a success if the data generator counts less than one error per hour,” said Lapak. The engineers repeated the interference tests with cables from three manufacturers (Panduit, Siemon, and Systimax).

In the final test, engineers connected the two networks so they could demonstrate whether PHY-A and PHY-B equipment could communicate. Communication initially failed, so the engineers used an oscilloscope to verify that each PHY complied with 10GBase-T Ethernet standards. They measured jitter, power, rise time, and clock frequency.

A UNH-IOL-developed Ethernet auto-negotiation test tool monitored the negotiation process, looking for violations from the standards. Once engineers from Solarflare and Teranetics modified their respective firmware, UNH-IOL engineers turn to the PHYs’ built-in diagnostics to complete the test.

Just because communications devices meet industry standards doesn’t guarantee they will work with compliant devices from other sources. Interoperability tests let engineers verify that devices will behave as expected.