[asterisk-users] Asterisk 1.4 and g723

[Phil French]

I am setting up Asterisk for use in a low bandwidth environment.  As
bandwidth is precious and our ATA's support it, the decision was made to
use the g723 codec.  I have been working on this for a few days and have
not been successful.  The issue that I am having is garbled noise at the
client on calls whose RTP streams are terminated by Asterisk system.
This is the case for all the dialplan applications I have tested except
for Echo.  The critical application for us is Voicemail.  When a call to
voicemail extension is initiated the Asterisk console does not indicate
any error.  Packet captures indicate the call is active and streaming
g723 data.  Everything seems well but is not.  The audio at the client
is unrecognizable.  One thing that I have noticed is that the bitrates
in the upstream and downstream direction differ.  From Asterisk to ATA
the g723 bitrate switches between 5.3 kb/s and 6.3 kb/s.  From ATA to
Asterisk the bitrate is a constant 6.3 kb/s.  I don't think this is a
problem but seems odd.  As a comparison I captured packets from a call
to the echo application and found that the bitrate was 6.3 kb/s in both
upstream and downstream packets.  Additionally, all prompts are g723
format.  Voicemail is saved as g723sf.  As a parrallel task a co-worker
has gotten 1.2 to work with g723.  However we require 1.4 for t.38
pass-through.

The end-to-end system is illustrated below.

                      [Asterisk]
                       /     \
                     ip       ip
                     /         \
  [PSTN]--pri--[GATEWAY]--ip--[ATA]<--2pr-->[Phone]

System details
 -Asterisk server version 1.4 - compiled from source - Fedora Core 6
-Gateway - Cisco 2811  -ATA - Linksys 2102

I would appreciate any advice or suggestions.  It should be noted that
the calls to the PSTN through the gateway and calls between ATA's are
working fine.  

Regards,

Phil French

Phil French
Systems Engineer
-------------------------------
CapRock Communications
4400 S. Sam Houston Parkway E.
Houston, Texas 77048
Office: 832 668 2643
pfrench at caprock.com
www.caprock.com
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