[Asterisk-Users] Intermittent Silence

[Stuart Lester]

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.
	* Silences have occured for devices from multiple manufacturers 
(Currently we are using Polycom IP 300, IP 500, and Grandstream 101).
	* 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.
	* All users are connecting to the asterisk system via SIP.
	* Multiple "carriers" have been used, and the issue seems to not 
be related to any particular carrier.
	* Call load doesn't appear to be an issue, as the silences have 
occured when the call in question was the only one on the system.

The current asterisk system configuration is as follows:
	* 1.2 GHz Pentium Celeron 512 GB RAM, Linux 2.4.21
	* 10 SIP devices connected
	* Connected to Carriers via IAX
	* Using uLaw codec
	* Using asterisk HEAD, built on June 28th
	* Running ztdummy
	* Server is not firewalled.

I have tried, to no avail, to find a solution for this issue, and I am 
having no luck.  The issue is perplexing, and quite bothersome to our 
users.  Could anyone suggest any solutions, tests or anything?  At this 
point, I'm getting frantic, and any help would be appreciated.

Stuart