[asterisk-users] DAHDI phantom pickup when ringing

[Jonathan Hunter]

Hi,

I've been experiencing trouble with my DAHDI channels for some time and have
finally decided to try and resolve the issue.

Essentially, the problem I am having is that when a call comes in, and my
DAHDI phones therefore ring, Asterisk thinks that one of the handsets has
picked up to answer the incoming call - whereas in actual fact it is still
on hook. The call then gets instantly dropped (the phone is on-hook, after
all), and the caller has to redial.

Sample log (this is an incoming call from SIP/5555, that was "phantom
answered" by DAHDI/7. There is no time delay between the 'answered' line and
the 'hungup' line):

    -- DAHDI/5-1 is ringing
    -- DAHDI/3-1 is ringing
    -- DAHDI/7-1 is ringing
    -- DAHDI/2-1 is ringing
    -- DAHDI/4-1 is ringing
    -- DAHDI/6-1 is ringing
    -- DAHDI/7-1 answered SIP/5555-0000011f
    -- Hanging up on 'DAHDI/6-1'
    -- Hungup 'DAHDI/6-1'
    -- Hanging up on 'DAHDI/4-1'
    -- Hungup 'DAHDI/4-1'
    -- Hanging up on 'DAHDI/2-1'
    -- Hungup 'DAHDI/2-1'
    -- Hanging up on 'DAHDI/5-1'
    -- Hungup 'DAHDI/5-1'
    -- Hanging up on 'DAHDI/3-1'
    -- Hungup 'DAHDI/3-1'
    -- Hanging up on 'DAHDI/1-1'
    -- Hungup 'DAHDI/1-1'
    -- Hanging up on 'DAHDI/7-1'
    -- Hungup 'DAHDI/7-1'
  == Spawn extension (macro-stdexten, s, 3) exited non-zero on
'SIP/5555-0000011f'

I'm using a PhonicEQ E100P card in my Asterisk box, paired with a Zhone
Zplex 10 channel bank - this has worked perfectly for years in all other
respects.

My first thought was that it was a hardware issue, related to short line
length perhaps (cable runs are over Cat5 structured cabling, anywhere from
5-30m long), or possibly due to my use of "PABX Master" phone adapters with
ring capacitors, instead of plain adapters. (This is probably UK specific -
the adapters look like this:
http://www.cablecity.co.uk/product_info.php?products_id=439 )

However I did swap out the PABX Master adapters for plain ones, and this
made no difference at all. I haven't got much control over the cable length,
either. The issue seems to manifest itself mostly on a couple of channels (5
and 7), which have quite different cable lengths - and I did also try a
different telephone handset on channel 5 (this has the shortest cable
length). No difference.

My next angle of attack was the software - I dug around in the dahdi source
code to try and find timeouts to adjust, so that it wouldn't be quite so
quick to think that I had picked up the phone. However I didn't have any
luck with that, either. There is a 'debounce' parameter which is great in
theory, but only worked when I hung up the phone - it had no impact on
picking it up in the first place.

So I'm throwing the question open to the amassed wisdom of [asterisk-users].
Can anybody perhaps point me in the right direction of what I can try next?

Thank you!

Jonathan
-- 
"If we knew what it was we were doing, it would not be called research,
would it?"
      - Albert Einstein


Software versions:
dahdi-linux-2.3.0.1
Asterisk SVN-trunk-r280559M (built on 2010-07-30 00:09:55 UTC)

Config snippets:

/etc/asterisk/chan_dahdi.conf:
[channels]
; Have tried this, but it only affects going ON hook, not going OFF hook
; debounce=1000
rxgain=0.0
txgain=0.0
group=1
callgroup=1
pickupgroup=1
immediate=no
signalling=auto
--- most of the channels look like this---
mailbox=****
callerid=******* <****>
context=******
accountcode=***
callgroup=1
pickupgroup=1,2
channel=>5

/etc/dahdi/system.conf:
loadzone=uk
loadzone = us
defaultzone=uk
# T1 interface with channel bank
span=1,0,0,esf,b8zs
fxoks=1-24
# T100p plugged into BT line
fxsks=25
# 2010-08-18 No echo canceller is now loaded by default
echocanceller=mg2,1-25
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