To those of you familiar with the SIP signalling protocol or any other VoIP protocol for all that matter, you are most probably familiar with the issue of traversing DTMF (Dual Tone Multi Frequency) tones correctly over a VoIP link. The main issue is that there is no one standard for doing this. While in the old days of H323, most gateways were utilizing inband signalling (that means sending the tones as part of the media stream), in modern day systems and protocols (such as SIP), most of the time vendor conform to either rfc2833, in-band or SIP-INFO.Continue reading