[Asterisk-Users] how to debug frame slips?

[Michael Welter]

Joe Presto wrote:
> Hi, I’m running into issues receiving faxes which, from what I have 
> read, may be caused by frame slips.  While I can find many posts saying 
> to investigate it, I can’t find any that describe **how** to debug the 
> problem. Tried searching this list as well to no avail.
> 

Joe Hi,

Boot the Linux Rescue disk and run memtest86.

Boot Linux but don't go into XWindows.

If you're running software RAID, 'cat /proc/mdstat'.  If it's syncing a 
drive then wait till it's done.

Check 'cat /proc/interrupts' for modules sharing the same interrupt 
vector.  Even an unused USB module, when shared with a Digium module, 
will cause havoc.  If you can, you may 'modprobe -r <name>' the shared 
module.  If you can't, try moving the Digium card to different PCI slots 
ion order to find an unshared interrupt vector.  You can also try 
assigning irq numbers in BIOS.

Check 'vmstat 1'.  With a "quiet" system you should see mostly 100% idle 
time.  How many interrupts are you seeing per one second interval?  It 
should be +/- 1000 for the system timer and +/- 1000 for each Digium card.

If you're seeing a lot of activity on vmstat then turn-off unneeded 
services.

Pick-up the handset and listen carefully to the dial tone.  It should be 
pure MF tones.  If you hear any clicks, pops, or strangeness you know 
you have a problem.  Listen to both the TDM card dialtone as well as the 
channel bank dialtone (if you have one).

If you have two FXS lines with fax machines, fax a document directly 
from one to the other.  Don't even start with spandsp until this works 
consistently.  If you have both TDM and T-1 then fax TDM->TDM, TDM->CB, 
CB->TDM, and CB->CB.

After you RxFax a document, open the received .tiff file a tiff viewer 
or your browser (I use Mozilla).  Verify the file contents.

Use TxFax to send the file back to the fax machine.  Did it print correctly?

When fax->fax works correctly, try spandsp.

If you still have problems:

If you're on a channel bank (or PSTN circuit) then look at your T-1 
timing. In the US you should have something like 'span=1,1,0,esf,b8zs' 
in zaptel.conf where the T-1 card is taking its timing from the received 
data stream.  The channel bank should be configured to generate its own 
timing.

If you have IDE drives, try 'hdparm /dev/hdx'.  If 32-bit support is 0 
then try 'hdparm -c1 /dev/hdx' and 'hdparm -c3 /dev/hdx'.  If using_dma 
is 0 then try 'hdparm -d1 /dev/hdx'.  I configured a RAMDISK to 
eliminate the possibility of disk I/O interfering with spandsp.

Try 'lspci -v' and look at the latency timer for your Digium card(s). 
You can set it higher with 'setpci -v -s xx:yy.0 LATENCY=TIMER=ff' (xx 
is the bus number and yy is the slot).

Look at the vmstat output and check for system (not user) spikes every 
three seconds.  If you have spikes then 'modprobe -r wcfxs'--if no more 
spikes then get a T-1 card and channel bank and try it there.

Good luck.
Mike

P.S.  Let's keep this thread going--if anyone else has something then 
please chime in.





-- 
Michael Welter
Introspect Telephony Corp.
Denver, Colorado US
+1.303.674.2575
mike at introspect.com
www.introspect.com