[Asterisk-Users] Snom clients deregistering

[Richard Watson]

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Hi all,

I have a server currently running Asterisk 1.0.7 placed out in the wild
(i.e. not behind NAT).

I have groups of sip clients all behind various NAT firewalls (mainly
adsl routers).

Up to now I've mainly used Sipuras and not had any serious problems.
Recently I've been experimenting with Snom phones and I have encountered
 problems where the Snoms register fine initially but after a while
(which could be anything from 2minutes to 45 minutes) they lose their
registration. Sample snom configuration in sip.conf follows:

[888120]
type=friend
username=888120
mailbox=888120
canreinvite=no
nat=yes
secret=secret
host=dynamic
qualify=yes
context=sipdemo
subscribecontext=sipdemo

I've experimented with several different adsl routers and was surprised
at the difference this can make, however the problem is still there to a
greater or lesser extent.

I've also tried using a Stun server following recommendation here:

http://www.asteriskguru.com/tutorials/sip_nat_oneway_or_no_audio_asterisk.html

Again this makes a difference, but doesn't entirely solve the problem -
there are still occasions where the Snom is unreachable or unknown.

The implication seems to be that if asterisk does not send keepalives
often enough then the way through the nat is lost.

I've also tried lowering the expiry time of the asterisk sessions (in
increments down to 30 seconds) in the hope that it would result in more
activity and keep the firewall open, but it didn't help.

Another strange factor is using the BLF on snoms - the situation seems
to be worse with those enabled, but that might not be relevant.

So I guess I have a few questions:

1) Has anyone had this happen before and what, if any, was the solution?

2) How do I increase the frequency with which asterisk sends keepalives?

3) Does SER handle this better - would placing this outside the NAT help
handle connections from inside?

4) Do newer versions of asterisk handle this better?

5) Any other suggestions?

TIA.

- --
Richard Watson
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