Switching to VoIP

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Chapter 15: What Can Go Wrong?

Dialed digits work to place calls but not to interact with IVR prompts

The network can transmit dialed digits in two ways: in-band and out-of-band. This

problem occurs most often when in-band signaling of digits is used. Because in-band

signaling uses audio (dual-tone multifrequency) signals to represent each dialed digit,

it is possible that the signals can be distorted during encoding, transport, and decod-

ing. If the distortion is significant, IVR systems may not be able to interpret the audio

signals they receive. Sometimes holding down each digit for an extra second or two

can improve the IVR system’s recognition, but not always.

To avoid this issue, configure your SIP endpoints and ATAs to use an out-of-band

DTMF signaling approach such as the SIP INFO method. Generally speaking, the

only time in-band DTMF signaling can be reliably used all the time is on legacy, non-

packet-based voice links.

Callers sound robotic, or they say you do

Like in-band DTMF digits, the human voice can be distorted when many subse-

quent digital/analog conversions or encoding/decoding operations occur. When a

sound stream is encoded digitally, decoded into an analog signal or transcoded, and

then reencoded into a different codec, degradation of the original signal