The last blog entry covered DTMF relay. This blog entry will focus on Cisco IP Phone and Cisco SIP Trunk DTMF relay support. Cisco’s first generation of IP phones do not support RFC2833 DTMF-Relay.

If you’ve ever wondered about the best way to detect dial and DTMF tones from a phone line, [Debraj] is your man. [Debraj] built a DTMF detector using the Goertzel algorithm. Normally, when w… ...