[Asterisk-Users] TDM0xB vs. SIP for FXO

[Rich Adamson]

> I've had issues with the FXO port on the spa3000 - banking apps could
> not hear the DTMF. I've also had problems with phones hooked up to the
> TDM FXS ports where banking apps hear DOUBLE dtmf digits.
> 
> The only mix that seems to work for me is SIP phones / or analog phones
> hooked up to ATA's and TDM / x100P connections to the POTS line.
> 
> Frankly, this situation sucks. I've got half a TDM card that is
> unusable, and half an SPA-3000 that is unusable. The SPA was really
> attractive since it would have allowed for automatic powerfailure mode.
> I dumped my X100P's since the telco tech showed me that it was
> generating almost a direct short across the line according to his meter.
> The TDM card doesn't have that problem. 
> 
> 
> On Wed, Nov 02, 2005 at 11:45:20AM -0500, Rusty Dekema said:
> > Hi,
> > 
> > I am planning to connect my Asterisk PBX to one or two POTS lines, and am
> > wondering if it is better to use a TDM card for this, or one or two SIP
> > devices with FXO ports on them (such as an SPA-3000, Grandstream 488). I am
> > interested in voice quality and reliability of operation and am wondering if
> > one of these options is better than the other in this regard.

I have both a TDM04 and SPA3k in use, and both have some minor issues. The
latest revision (eg, i or j) of the TDM card combined with the latest
zaptel drivers using the KB1 echo can is pretty good; slightly better
then the spa3k. But, the TDM still cannot pass modem signals (eg, fax,
credit card validation).

The echo can in the spa3k tends to be less then acceptable for calls that are
passed directly between the fxs and fxo ports. I've spent a considerable
amount of time over the last year or so with different firmware versions,
etc, trying to find a balance of gain vs echo that is acceptable. However,
if the fxs port always passes audio through asterisk to the fxo port, there
are less echo, etc, issues.

Both the TDM and spa3k are difficult to configure for proper gain settings
and acceptable echo. Nither one has an advantage over the other. Also, the
further you are from the Central Office, the more difficult it will be to
balance audio levels and echo for acceptable use for either approach.