[Asterisk-Users] Intermittent Silence

[Andrew Kohlsmith]

First, I would like to commend you on your excellent list post.  Detailed 
without burying people in details and to the point, and not running around 
pointing fingers.

Now for the bad news.

On Wednesday 13 July 2005 15:40, Stuart Lester wrote:
> I am currently experiencing intermittent silences with my asterisk system.
> The symptoms are as follows:

>  * Both for incoming and outgoing calls, I (and other users)
> occasionally experience a brief period of silence.
>  * The silence lasts anywhere from 3 to 10 seconds.
>  * It is not due to silence suppression, because the silences
> generally occur in the middle of sentences.
>  * Silences occur at various times of the day, for calls of various
> lengths, and at different times during calls.
>  * Sliences have occured for incoming and outgoing calls, and
> have affected both people on the VoIP side and the PSTN side.

I had more or less identical symptoms.  I'd tried new motherboards, new cards, 
experimental code, you name it.  We finally broke down and have made only one 
change to our setup, which I'll explain below.

>  * Affected users are connecting to our asterisk system from
> multiple geographic areas, using multiple ISPs, and all seem to have
> reliable and acceptable network connections.

This tells me it is on your side.

Our system looks like this:

Norstar MICS [ PRI ] Asterisk 1 [ SDSL ] Asterisk 2 [ PRI ] Telco

The SDSL loop is just a 4ish-km link between a downtown location and the 
office.  It terminates into a regular old switch (Baystack 350) which also 
carries the internet traffic for a half dozen businesses.  It is not VLANned 
or anything, and the traffic between Asterisk 1 and 2 is over RFC1918 
addresses.

Asterisk 2 can route calls through the telco PRI or through one of a half 
dozen VOIP providers.

The change we made?  We stopped routing calls over the VOIP providers.

As soon as we did that our intermittent silent periods *disappeared*.  We've 
been routing all calls through the telco for the last 45 days or so, and do 
about 25-35000 minutes a month, if I'm not mistaken.

This ruled out:
- Asterisk 1 & 2 (mobo, card, NIC, everything)
- Asterisk jitter buffer code
- the switch
- the SDSL hardware (Megabit Modem 300S) and loop

Our culprit appears to be either the router, the ADSL uplink modem (Sangoma 
S518) or the uplink itself.  I'd like to get another link and do some 
testing.  I'm almost 100% certain it's not the hardware or the router 
(linux).  In fact, we have the link, I just need to get the time to do the 
testing.  My guess is that it's the upstream provider (Ikano), but I can't 
rule out the others yet.

I am sorry I don't have better news for you.  I would suggest trying a couple 
different upstream providers (even just regular ADSL should be good for 
initial testing and it's not expensive to try a few...  I'm looking for a 
more inexpensive T1 provider in my area.

-A.