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.

Voice over IP systems have many methods to leverage DTMF digits depending on the signaling mechanism used. All traditional time division multiplexing (TDM) interfaces on Cisco routers support passing ...