Question : DTMF failing across Catalyst 4510

I have a Mitel 3300 IP phone controller and a NuPoint VoIP voicemail server sitting on my server subnet. I can place an IP phone on my DHCP subnet and cannot pass DTMF across to the voicemail server. If I put the phone on the same subnet as the server, DTMF has no issues and the tones work fine. I can also pass tones across our MPLS network to another phone controller that hosts that sites voicemail, but when they call back into my locations voicemail the DTMF tones do not pass across. I am doing all my routing between my local subnets through a Catalyst 4510, IOS 12.2(25). This switch also holds the MPLS routes and routes my traffic to and from edge locations. There is nothing on the 4510 that restricts traffic between subnets on the 4510.

Example subnet: 172.16.63.0  255.255.255.0  gateway is always .1 of the subnet, i.e. 172.16.63.1

All subnets on network are similar to example above.

Thanks in advance

Answer : DTMF failing across Catalyst 4510

If you get audio but no DTMF and you are using INBAND the only thing I can think of is that when you move to a different subnet a different codec is being used. INBAND only really works well if you are using the G711 codec. All the others compress the audio too much and can result in unreliable DTMF detection.

Are you using the SIP protocol for VoIP?

Do you have any firewalls or devices performing NAT between the networks?