Question : "All circuits are busy" message received randomly when dialing out from Trixbox 2.8.

We have a server running Trixbox 2.8 / Asterisk 1.6 and when we dial out, we will randomly get a message stating "All circuits are busy now."  This seems to happen randomly and if we redial the same number after receiving this message, the call almost always goes through without a problem.

We have two separate trunks set up using two different methods as posted below.  Both of these trunks have these random failures.  The service provider says they usually see a 503 message on their end, or nothing at all.  I get this message from the Asterisk server: == Everyone is busy/congested at this time (1:0/1/0)

The provider did some more digging and found that the sip headers are sometimes being passed incorrectly.  
Example of incorrect header being sent:
From: <sip:x.x.x.x:5060>;tag=31d8e646+1+0+71f506db
To: <sip:x.x.x.x:5060>;tag=as7e7c519b
Example of correct header being sent:
From: <sip:"CallerID”5555551000@x.x.x.x:5060>;tag=31d8e646+1+0+71f506db
To: <sip:x.x.x.x:5060>;tag=as7e7c519b

The test trunks that we have set up are below as well:

[TEST_TRUNK_1]
disallow=all
allow=ulaw
canreinvite=no
dtmfmode=auto
context=from-trunk
fromdomain=x.x.x.x
host=x.x.x.x
nat=never
insecure=invite
outboundproxy=x.x.x.x
qualify=no
srvlookup=no
type=peer
secret=secretive
username=##########
defaultexpirey=3600

[TEST_TRUNK_2]
host=x.x.x.x
type=peer
dtmfmode=auto

[TEST_TRUNK_2_USER]
host=x.x.x.x
type=peer
dtmfmode=auto

Has anyone else had these problems before?  Is there something I need to change on our system?

Answer : "All circuits are busy" message received randomly when dialing out from Trixbox 2.8.

G729a is the best codec to use to get quality and minimal bandwidth usage...but it requires licenses for each channel.  $10/channel.

GSM codec is what i'm using, and it's quality is "fair"...bandwidth usage is very low...but it requires a little bit more CPU processing to transcode.  No license required.

There's also Speex, which I haven't had a lot of experience with myself...but is also low bandwidth and no license required.

Then there's iLBC, which i've never used either.


.....being that i'm using GSM with no issues, I guess I would recommend that one first.