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Some computer BIOSes had this feature where they would analyze the plugged in Ethernet cable using this signal reflection to determine if there is a break in th

Some computer BIOSes had this feature where they would analyze the plugged in Ethernet cable using this signal reflection to determine if there is a break in the cable, and would tell you approximately where (in meters).

cricalix 3y ago
Still common in the networking world; as an example, Ciena optical gear can do Optical Time Domain Reflectometer(try) (OTDR) periodically to measure the length of the physical circuit, and the nature of the test also reveals where cables are joined based on reflections. It's also how you measure where a break is, at which point you dig out the geo-coords for the path the cable takes to work out where someone just ran an optical cable finder (backhoe/JCB digger/whatever you call it where you are).
dboreham 3y ago
The feature is in the Ethernet NIC, not the BIOS. It's been present in pretty much all hardware implementations since the 1980s. There's a fun story of TDR on "thick-wire" Ethernet being used to characterize nuclear detonations[1] [1] https://web.archive.org/web/20160507110751/http://www.csd.uwo.ca/staff/magi/personal/humour/Computer_Folklore/How%20do%20you%20measure%20nuclear%20warhead%20yield%3F.html https://web.archive.org/web/20160507110751/http://www.csd.uw...
kjs3 3y ago
In the thin-coax ethernet days, pretty standard tool in the bag was a Fluke[1] portable Time Domain Reflexomter to do this. Much more precise than the NIC based measurements. Very useful for finding exactly where someones 'cable management' ended up nailing through the coax, or where someone ignored bend radius limits when installing. [1] Other vendors made them...I just always had a Fluke