asterisk users - Nov 2008 - Calls drop after a couple of minutes.

I have been encountering a rather hard to debug problem for the last
couple of months:

* Calls are setup fine.
* After a couple of minutes, two way audio becomes one-way and the
remote or local party drops out of the call.

Setup:

* Nokia E71i sip on NAT'd network (multihomed linux box)
* Remote asterisk 1.4.21 on Ubuntu on public network
* using a Finera/Betamax provider to route calls to PSTN.

I initially thought it may be a NAT problem and have checked everything
on the NAT gateway/firewall.  I see no rejected packets hitting the
firewall logs.

I'm really at a loss as to what could be causing the calls to drop out
for one party so regularly.

Any clues where I could look further to debug this would be most useful.


local firewall:

modprobe ip_conntrack_sip ports=5060
modprobe ip_nat_sip
# probably not needed since everything is forwarded:
$IPTABLES -A FORWARD -s $INTERNAL_NET -d $ANYWHERE -p udp --dport 5060
-j accept-log # sip

remote Asterisk server:

$MODPROBE ip_conntrack
$MODPROBE ip_conntrack_sip ports=5060
$IPTABLES -A INPUT -s $ANYWHERE -d $PUBLIC_ADDR  -p udp --dport 5060 -j
accept-log # voip
$IPTABLES -A OUTPUT -s $PUBLIC_ADDR -d $ANYWHERE  -p udp --sport 5060 -j
accept-log # voip
$IPTABLES -A OUTPUT -s $PUBLIC_ADDR -d $ANYWHERE  -p udp --dport 5060 -j
accept-log # voip
$IPTABLES -A INPUT -s $ANYWHERE -d $PUBLIC_ADDR  -p udp --dport
10000:20000 -j accept-log # voip
$IPTABLES -A OUTPUT -s $PUBLIC_ADDR -d $ANYWHERE  -p udp --sport
10000:20000 -j accept-log # voip

sip.conf:

[101]
callerid=Simon Tennant
type=friend
username=101
secret=xxxxxx
host=dynamic
reinvite=no
canreinvite=no
mailbox=101
context=from-internal
nat=yes
port=5060
qualify=yes
insecure=very
disallow=all
allow=alaw

also sip.conf

[justvoip.com]
type=peer
host=sip.justvoip.com
fromdomain=sip.justvoip.com
progressinband=yes
disallow=all
allow=alaw              ; only alaw works with sip1...
nat=no
canreinvite=no
qualify=yes
insecure=port,invite
username=imagi-justvoip
fromuser=00491785450880
secret=xxxxxxxxxxxx
registerattempts=0 ; keep trying to register (normally times out after
10 attempts)
context=from-external

from rtp.conf

rtpstart=19000
rtpend=20000





-- 
Simon Tennant _____________________________________________

fixed: .uk +44 20 7043 6756          .de +49 89 420 955 854
  mob: .uk +44 78 5335 6047          .de +49 17 8545 0880
 xmpp: simon at buddycloud.com