[Asterisk-Users] Qs about FXO/FXS cards

[Richard Scobie]

Victor Rini wrote:
> This has been an interesting discussion. I'll chime in with my 
> experience here.
> 
> I have two servers. One with the cheapest motherboard and athlon 
> processor I could find on Newegg.com. The other is a 1999 era 
> motherboard with a Via C3 processor, again a bargain basement special.
> The Athlon system has a decent power supply - 400+ watt, the Via has a 
> very generic PS that came with the case - 300 watt tops.
> 
> On both system I have TDM cards, the Athlon has a 4 port FXS and two 
> x100p's, the Via has a 2 port FXS.
> 
> Both systems are in "production" if you could call it that because they 
> handle little traffic - home/hobby systems.
> 
> I have had no problems at all with the tdm cards or Asterisk. I 
> occassionally lose my network on the Athlon machine - I chalk that up to 
> the fact that I'm currently sharing an IRQ with two ethernet cards and 
> an X100P.
> 
> I'm thinking of ditching the two x100p's in my Athlon machine for a TDM 
> card with FXO modules to free up a slot and hopefully the burdened IRQ. 
> Based on what I'm reading here I probably should think *really hard* 
> about that.

I'd stick with the X100Ps for now. Two of my systems where X100s have 
been replaced by TDM FXOs, have seen a drop in reliability - the well 
noted "FXO fails to respond to either calls from the PSTN or take calls 
from internal phones". Driver reloads and sometimes machine reboots are 
required to restore operation. These are systems seeing small office 
loads - 30 to 70 calls a day. One of these, which only contained 2 
X100s, ran absolutely trouble free for a year and has required 2 reboots 
since switching to a single 4 FXO TDM.

It is interesting to see there have been no posts to this thread from 
small office load users saying, "I am using TDM FXO's and have not had 
any problems at all". All my contact with others in similar situations 
to myself have elicited the same experiences.

Based on the above and following, I'd say the TDM FXO's have issues:

1. The following line in wctdm.c : /* Try to track issues that plague 
slot one FXO's */

2. Digium acknowledge there is a problem and I am currently testing a 
driver modification for them.


Looking at the FXS modules, I too get "Power Alarm " messages on a 
semi-regular basis, although they seem harmless. It is hard to see how 
the power supply is involved - short of a PSU suffering very poor 
regulation.

These messages are created by interrupts generated when power 
dissipation in various transistors external to the ProSLIC, exceed 
programmed limits. To quote from the data sheet:

"This feature protects the external transistors from fault conditions 
and, combined with the loop voltage and current monitors, allows 
diagnosis of the type of fault condition present on the line."

Anyone interested in learning more, should read page 27 of the Si3210/11 
data sheet, which is available from www.silabs.com, after a free 
registration.

Regards,

Richard