A/UX: Ethernet TDR Test Results, "Shorts" (8/94)


If you run a Time Domain Reflectometry (TDR) test on a thin Ethernet network, all the A/UX systems (and only the A/UX systems) may appear as what seem to be shorts -- whether the systems are powered on or off.

Since the systems appear to be shorts even when powered off, the problem is almost definitely not A/UX-specific.

When a thin Ethernet was tested with Macintosh II or IIx (with the systems both powered on and powered off) the Macintoshes did not appear as shorts during any of Apple's TDR tests -- however, the TDR did show minor disturbances for each of the EtherTalk cards on the network.

Although these disturbances are within specifications when compared to other types of Ethernet connections, they might be interpreted as shorts. Since the network is otherwise operational, the problem described above may be due to the interpretation of the TDR results or to the TDR itself having been improperly configured.

If the TDR sees disturbances other than what appear to be shorts, it is not reporting shorts. Try deliberately shorting one of the connections (temporarily) to see exactly what a short looks like, and how it affects the TDR display.


Article Change History:
23 Aug 1994 - Reviewed and updated.

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Published Date: Feb 18, 2012