We are using a Cisco IAD 2431-16FXS with a 4-port FXO card in the VWIC slot.
We are attempting to cross-connect or "nail up" a modem call from one of the FXS ports to a FXO port that is in turn connected to the PSTN. We can dial consistently, but are getting very poor connect speeds, topping out at 16.8k.
For debugging purposes, if we plug the modem directly into the same phone line that's on the FXO port, we get consistent 50.6k connects.
Any advice on why connection from FXS to FXO would cause such a quality loss? Any ideas on how to rectify it?