I have been weighing the pros and cons of internal card FXO gateways like the Wildcard TDM400P and external FXO gateways like the Sipura SPA-3000, Grandstream HT-488, and the ever growing list of companies that are starting to make them.
Can anyone comment on them on these points:
Audio quality: Is the audio quality the same for the TDM400P compared to the SPA-3000 or other gateways?
Power failover: My main beef about the TDM400P is that it has no power failover capability to connect the FXS port to the FXO when the power is off while the external gateways do. Can you recommend external boxes that connect to the TDM400P to do this kind of relay switching?
Pass-through Fax/T.38 Fax: The TDM400P has the great benefit of having a developmental fax engine and T.38 through SpanDSP while some external gateways will support both pass-through and T.38 and others will support only pass-through. Unfortunately, the SPA-3000 does not support T.38.
Scalability: The Wildcard family scales from FXO lines to T1/E1 while the low cost external gateways only offer FXO lines. (Of course the higher end gateways scale up as well.) You also have a spaghetti of power cords when you set up more than a couple of FXO lines.
Adjustible FXO impedance: The TDM400P seems to have adjustible impedance from the country setting of the Zaptel driver. I have only seen the SPA-3000 support adjustible impedance settings for external gateways. This is important to match the impedance standards of different countries and possibly variations with PSTN lines (?) otherwise you will get echo.
To me, the closest thing to a best solution would be for Digium to release a board that includes FXS-to-FXO power failover.