Anybody has weird results from the MS cable test?
It seems to me that if the end devices are "Meraki MR" devices, it seems to be always accurately (did not measure actual length but reported length looks reasonable to me). If end devices are PC (mainly Intel NUC), also the case.
However, I am getting wrong figures if the end device are Sonos AMP and Dahua NVR. Eg have a Dahua NVR which is in the same rack connected via a 2m patch cable, but cable test reported it as 19m (1Gfdx and all 4 pairs OK).
Anybody having this issues?
Yes, I have had "weird" and inconsistent results as well. I don't consider it much more than a base line test and don't completely trust it. That said, I think it is still a useful starting point, but I would not take the results and tell a cable contractor they need to go fix their cable necessarily without closer inspection.
The cable length is determined using TDR (Time Domain Reflectometry):
It measures the time for a signal to be reflected due to tiny imperfections in the cable termination. The signal travells at a constant speed, so the length can be calculated.
If you find that a particular kind of device is constantly mis-reporting length it may also be that the device is messing with the impedance of the cable solution as well.
On MS120-8P and MS120-24P switches i see that wire pair 4 is not tested on ports that are in 100FDX mode.
I have found the cable test tool pretty useful. I understand the slight inaccuracies of TDR, true testing really needs a device on both ends. But this tool makes for a great quick analysis.
I am curious about a result I am seeing. One of the pairs shows "XXX" I couldn't find a document referencing the different results of the feature.