[cisco-voip] NM-HDA FXO ports ground line during reboot

[Dan Lanciani]

I noticed that when I reload the router phone lines connected to FXO
ports on NM-HDA cards go busy until the router comes back up.  Closer
investigation revealed that one side of the line is being grounded as
if the port were trying to busyout a ground-start trunk.  (These are
regular loop-start lines and the FXO ports work fine with them when
the router is up.)  I tried two different NM-HDA cards in two different
routers (3640, 3660) with 12.4 and 12.4T IOS releases; all behave the
same.

This effect is disturbing because it means my lines would be out of service
if the router ever fails to come back up.  I played with various configuration
options but I couldn't find any way to disable this feature(?).  Getting a
little frustrated I physically modified the NM-HDA FXO card by unsoldering
and lifting the pins of the solid state relays that are used to apply ground
to the lines.  This "solves" the problem but of course the cards will no
longer support ground-start lines and my SMD soldering capabilities aren't
that great, so I'd prefer a software solution.  Also, should the code get
clever and (assuming this is indeed a feature) try to busyout the line
correctly for a loop-start I'll be back where I started.

Has anyone encountered this on NM-HDA cards or any other FXO interface?

				Dan Lanciani
				ddl at danlan.*com