2901 FXS SCCP gateway with analog phone connected back to the home office using DMVPN over a Cellular connection.
When playing or receiving calls on analog phone the call connects but there is one way audio. The analog phone can receive audio but not send. The one way audio condition only occurs when the call is between the analog phone on the FXS and any phone or gateway at the home office. Calls made from IP phones connected to the LAN side of the router are fine. Other analog phones connected to the other FXS ports have 2 way audio as well.
PCM captures verify that the analog phone is sending audio to the FXS card. Show voice rtp packets command verify that PCM is getting turned into UDP data stream. But the UDP data stream never leaves the router out the DMVPN tunnel. Packet captures at the home office DMVPN router verify that no RTP traffic is coming from the remote site.
Routing is correct because I can ping the home office phones and or gateway from the remote site router.
If I take the cellular connection out of the picture and connect the remote site using DSL or Cable Modem the call is fine. It is only over the cellular connection where the outbound audio is lost. Is there some special routing required to send voice RTP streams through a cellular DMVPN connection?
