Medición de longitud

[rvalencia87]

Quería consultarles que tan fiable es la medición de longitud de cable que hacen los switches Meraki hacia los AP Meraki. 

Ya que quisiera realizar un reporte anexando la longitud que tiene cada AP desde su puerto en el switch, pero no se que tan confiable sea la medición que realizan los equipos. 

[alemabrahao]

Meraki switches provide cable length estimates for connected devices, including Meraki APs, using Time Domain Reflectometry (TDR).
I consider this more of a baseline test and don't rely on it completely. I think it's still a useful starting point, but certifying the points in this case with the appropriate tool is the best option.

[cmr]

If the connection is good then the length is pretty accurate, I'd say within 2m for cables I have actually measured physically.

[AlexL1]

Hi rvalencia87,

Point 1 - The cable length is determined using TDR (Time Domain Reflectometry):

https://en.wikipedia.org/wiki/Time-domain_reflectometer

It measures the time for a signal to be reflected due to tiny imperfections in the cable termination.  The signal travels at a constant speed, so the length can be calculated.

Point 2 - While this method is widely used in networking equipment, there are factors that can influence the accuracy of the measurements:

• TDR-based measurements are reasonably accurate for estimating cable lengths. They are typically within ±10% of the actual cable length, but this can vary based on several factors.
• The accuracy depends on the quality of the Ethernet cable (e.g., Cat5e, Cat6, Cat6a) and whether the cable meets industry standards.
• External interference, cable bends, or poor-quality terminations can affect the readings.
• Poor or faulty connectors can cause irregular reflections, leading to inaccurate measurements.

Point 3 - Easy test to confirm is by using Fluke tester at both ends of the cable and double check.

• Supplement Meraki's cable length measurements with a professional cable tester for maximum accuracy.
• Use the data as a general guide rather than an exact measurement, especially if the cable runs through complex pathways or includes intermediate devices.

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Additional info:

Cisco Meraki MS switches have per-port cable testing capabilities, which utilize TDR functions to detect faults in metallic cables by sending and observing the responses of electrical pulses. This can be used to eliminate common layer 1 cabling issues by outputting the cable length and testing the status of each cable pair. 

This tool is intended for testing copper twisted-pair cabling as designated under the ANSI/TIA-568 cabling standard. It is not intended for use with fiber-optic cabling, as this requires the use of Digital Optical Monitoring (DOM).

DOM is supported on MS120, MS125, MS130, MS210, MS225, MS250, MS350, MS355, MS410, and MS425. Switches must be running firmware MS 17 or higher. Refer to the Digital Optical Monitoring documentation for more details.

https://documentation.meraki.com/MS/Monitoring_and_Reporting/Using_the_Cable_Test_Live_tool

https://documentation.meraki.com/MS/Monitoring_and_Reporting/Using_the_MS_Live_Tools

Accuracy of Cable Test with MS - The Meraki Community

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