Bad voice quality with two foneBRIDGE devices

Asterisk Asterisk Support
1

Hi all,

We have a problem with our VoIP setup and maybe someone has encounter similar problem and hopefully was able to solve it.
Our setup contains an Asterisk 11.7 machine with 2 E1 trunks, one of them to PSTN and the other to a Panasonic TDA-600 PABX.
The E1 interfaces are supplied through 2 Redfone’s foneBRIDGE2 TDMoE devices.
First, we’ve encountered problems to make them work with DAHDI 2.6, supplied together with Asterisk 11.7. The problem was that DAHDI couldn’t manage two TDMoE trunks in the same time due to a bug in 2.6 version.
The use of DAHDI 2.9.1 solved the problem.

The problem is now the audio quality, not very low but enough to affect fax transmission between the analog extensions of Panasonic and PSTN.
We’ve suspected some E1 configuration issues but we’ve performed an extensive test with a specialized analyser and no problems were detected.
We’ve replaced the 2 TDMoE devices with a dual E1 DIGIUM board and everything was ok, the voice quality was perfect and the faxes were working fine.
This is, of course, not a solution because we have to use the two foneBRIDGES.
Can anyone encountered a similar situation? Any hint, ideas?
Thank you very much!

Here are the main configuration files:

/etc/asterisk/chan_dahdi.conf

;Automatically Generated chan_dahdi.conf configuration file
;Generator Version 0.3.4

[trunkgroups]
;
[channels]
usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
canpark=yes
cancallforward=yes
callreturn=yes
echocancel=no
echocancelwhenbridged=no
relaxdtmf=yes
rxgain=0.0
txgain=0.0
pridialplan=unknown
prilocaldialplan=private

callgroup=1
pickupgroup=1

group=0
context=from-pstn
switchtype=euroisdn
signalling=pri_cpe
callerid=301601
channel => 1-15, 17-31

group=1
context=from-pstn
switchtype=euroisdn
signalling=pri_net
channel => 32-46, 48-62

/etc/dahdi/system.conf

[code]
##Automatically Generated dahdi configuration file
##Generator Version 0.3.4

RTc

dynamic=ethmf,eth0/00:50:c2:65:dd:78/0,31,0

Panasonic

dynamic=ethmf,eth0/00:50:c2:65:dd:7b/0,31,1

bchan=1-15,17-31
dchan=16
bchan=32-46,48-62
dchan=47
alaw=1-62

loadzone=us
defaultzone=us[/code]

2
  1. are tdm devices connected to the server through dedicated server’s NIC? tdm creates 1000 frames per second flow. so if there is some pulsing traffic on the server, it can delay the tdm frames.
  2. poor or long tdm cable?
  3. i had a sound quality issue with wrongly set E1 crc4. for example when it is swithed on, but must be swithed off.
3

Hi elphssp,

thank you for your answer.

  1. Actually they’re connected through gigabit ethernet cards, but in separate VLAN, so we don’t mix traffic from other devices. Anyway, I will try to put the server and the tdm’s devices on one dedicated fast ethernet switch.
  2. No, I don’t think that’s the case. The very same cables used in a Digium Dual E1 card (PCI card in a different Asterisk installation) works just fine. Like I said, we’ve done extensively tests with an E1 analyser tool and it seems to be no problems at this level.
  3. Actually, this may be an issue, AFAIR the Panasonic has CRC4 enabled on it’s E1 card … I’ll double check this.
    I’m thinking still at the DAHDI software for beeing responsible … but have no proof for this assertion.

Thanks again,

Dan

4

I hope something of this will be useful.