When working with network devices, achieving optimal performance is crucial. This article delves into a specific issue encountered with a DP83869HM-based media converter, exploring the troubleshooting process and eventual resolution. The problem involved achieving a consistent 1 Gb/s data rate when using two media converter boards, highlighting the complexities of gigabit Ethernet and the importance of proper testing methodologies.
A design based on the DP83869EVM evaluation board was developed to function as a media converter, switchable between 100M and 1G speeds. While 100M operation was flawless, and a single board in 1G mode with a looped-back fiber signal worked perfectly, issues arose when using two boards configured as 1G media converters. The data rate would consistently float around 998-999 Mb/s instead of achieving the desired 1 Gb/s.
An EXFO AXS-200/850 Ethernet Test set with an EXFO ETS-1000L Ethernet loopback module was used to generate and analyze Ethernet traffic. The test equipment measured data rate and bit errors. Testing included:
The RFC 2544 test results revealed frame loss and errors when two boards were used, which did not occur when looping back a single board. Common errors observed included:
These errors suggested a potential timing issue or signal degradation when using two boards in series.
Several potential causes were considered:
One area of focus was the clocking circuit. It was noticed that the capacitors used in the crystal oscillator circuit had a higher value (22pF) than recommended for the crystal's load capacitance (9pF). The capacitors were swapped for lower values (20pF, 18pF, 15pF, and 12pF) to optimize the oscillator circuit, as this can affect MDI (Media Dependent Interface) link quality.
The ultimate resolution came with the acquisition of a new EXFO test module: the FTB-8510B Packet Blazer. This module featured dual RJ45 and SFP ports, enabling bidirectional BER and RFC 2544 tests without relying on a loopback module.
With the new setup, the system achieved a stable 1 Gb/s data rate with no errors. This pointed to the loopback module as the likely culprit. The original EXFO ETS-1000L Ethernet loopback module was causing the data rate issues, possibly due to the complexities of the signal on the copper side of gigabit ethernet.
This troubleshooting process highlights several key takeaways:
For more information on Ethernet testing and troubleshooting, consider exploring these resources:
By systematically addressing potential issues and utilizing appropriate testing methodologies, engineers can overcome challenges and achieve the desired performance in their network designs.
