This is a problem with the way that Avaya has implemented SIP, not a problem with your SIP trunking provider. They do not have the appropriate expertise in the IPO group to understand the RFCs, so they have made errors in their interpretation of the SIP RFCs, one of them being how DTMF volume levels are identified and transmitted. They have implemented DTMF volume backwards, but refuse to admit that they have made an error even though it is very clear that they have! Because of their unwillingness to admit their errors and work with the top SIP providers, customers are limited to a small group of providers, most of whom are either too small (AGN) or too big (AT&T-is there anyone who thinks that AT&T would be a good choice for SIP trunking for their customers?) to be a reasonable option. Also, if you have read any of the forum threads regarding the issues with turning-up any of these providers, you know that Avaya does not have their act together. To add insult to injury, Avaya wants potential SIP trunking providers to pay them $20,000 for the honor of working with them!!! If you have a customer that wants to implement SIP, be very wary of making any commitments of audio quality or even being able to successfully turn-up the service at all because there are too many compatibility issues between Avaya and the SIP RFCs.
