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Forum Discussion
GS724Tv4 and QNAP TS-473A cable length estimation wrong
Hi,
Just installed a QNAP TS-473A with two 2.5 GB ports to the Netgear switch.
Doing the cable length check, Neatgear reports a length of 150 - 200 m on both connections (very inconsistent between multiple measurements).
Both cables are shielded CAT6a, of just 1 m!
Is the measurement not capable with 2.5 GB ports? Or with short lengths?
Ron
PS Other measurements seem fair (1 GB and 100 MB ports).
1 Reply
RonfromNL wrote:
Doing the cable length check, Neatgear reports a length of 150 - 200 m on both connections (very inconsistent between multiple measurements).
Look once more: It does estimate a cable length between 0 m and 150...200 m.
On one hand, we need to know that these test methods can't have the possibilities of an x-thousand USD network tester. On the other hand we must be aware that these switch based cable tests are tuned towards a certain cable quality, a GbE Ethernet peer (resp. it's PHY). The more if goes away from the intended design, the wider the estimate is.
From wally brain, a 2.5GbE runs on 156 MHz (Nyquist freq. 100 MHz), a 5 GHz on 312 MHz (Nyquist freq. 100 MHz), a 10 GHz on 500 MHz (Nyquist freq. 400 MHz). This requires the other end PHY to be designed different and more costly. On a side note, several lower cost 10 GbE devices have PHY not supporting 10 MbE Ethernet and 100 MbE Fast Ethernet for this very reason. Beyond the different PHY design tuned for the higher frequencies and data rates, another key factor is that the methods implemented have limitations on extremely short cables.
Last but not least, it's impossibly a measurement - it's an estimation only (for completely linked connections, for open end connections, and for partially broken cables).
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