FXS/FXO cards vs. adapters - reliability, quality and echo?

Asterisk Asterisk Support
1

I am considering how to deal with one FXO for a legacy # we need to keep for a while (planning digital all the way), and 5 FXS for analog phones we currently need to keep (Polycom conference phones, Fax & Cordless). Cost is a consideration here, but cheap isn’t good if the functionality isn’t there.

Would you recommend PCI cards or Ethernet to IAX adapters for our FXO & FXSs? Would there be a difference in quality, echo or reliability? I see the expandable cards Digium makes have echo cancellation (still unclear if I’d need it), but the more basic PCI cards don’t. Further, it’s difficult to find a real understanding of why you might use cards vs. adapters. Also, if the devices don’t feature echo cancellation, is that a problem (searching yields why you might have echos, but not whether you need this cancelling. I have to admit that I’m leaning toward adapters because it means we can just unplug a FXS and move it somewhere we have Ethernet. Can anyone help here? Thanks!

2

First, the echo cancellers are hardware echo cancellers- there is a chip on the board which deals w/ echo. Asterisk has software echo cancellation for the cards that don’t have echo canceller chips. I’ve never had a problem with it. (Although, cheap X100 clone cards often present a hard-to-fix echo).

As for the rest, personally I like cards because there is less to configure- you configure the card in zaptel, and the extensions in Asterisk. With ATAs, you have to configure the extensions in zaptel, the SIP link in sip.conf and on the device, and the line on the device. Cards let you skip the SIP step. At the very least I’d use cards for the FXO interfaces, as they don’t move. For the fax i’d definately recommend an interface card as you can get a much more reliable transmission that way. Cordless and conference can go either way.

Hope that helps!

3

Ok, so in that case, get cards if you can and it’s ok to get non-hardware echo cancelling cards, right? Thanks!

4

yuppers. Good luck!