DTMF Support
DTMF is the accent generated on a touchtone buzz back keypad digits are pressed.
Gateways accelerate these tones in the RTP beck by default. This absence behavior is fine
when the articulation beck is beatific uncompressed, but problems appear back sending voice
across slower WAN links application compression algorithms, as illustrated in Figure 2-13.
82 Authorized Self-Study Guide: Cisco Articulation over IP (CVOICE)
S0/0/0
256 kbps
S1/0/0
256 kbps
G 729 Codec
Being Used
V V
Figure 2-13 The Need for DTMF Support
During a call, DTMF digits ability be entered to admission IVR systems, such as articulation mail or
automated cyberbanking services. Although DTMF is usually transported accurately when
using high-bit-rate articulation codecs such as G.711, low-bit-rate codecs such as G.729 and
G.723.1 are awful optimized for articulation patterns and tend to alter DTMF tones. As a
result, IVR systems ability not accurately admit the tones.
DTMF broadcast solves the botheration of DTMF baloney by alteration DTMF tones “out
of band,” or abstracted from the RTP articulation stream.