Refer to the exhibit. Your customers dial in to your company using a local number, and their calls cross the WAN to an IVR system. They are complaining that the IVR system does not always accept their input or may get it wrong. The IVR system has been checked and is working properly. What needs to be added to the dial peer on the incoming H.323 gateway to correct this problem?

A.
no vad

B.
tech-prefix 1#

C.
codec g729ar8 bytes 30

D.
dtmf-relay h245-alphanumeric

Explanation:
DTMF is the tone generated when you press a button on a touch-tone phone. This tone is compressed at one end of a call; when the tone is decompressed at the other end, it can become distorted, depending on the codec used. The DTMF relay feature transports DTMF tones generated after call establishment out-of-band by using either a standard H.323 out-of-band method or a proprietary RTP-based mechanism. For session initiation protocol (SIP) calls, the most appropriate method to transport DTMF tones is Real-Time Transport Protocol named telephony event (RTP-NTE) or session initiation protocol notify (SIP Notify).

When you press a button on the touch-tone phone, a high group frequency is combined with a low group frequency and you can hear a generated tone. Notice that you often dont see the A B C D column in most modern DTMF phones nowadays.

Although DTMF is usually transported accurately when using high-bit-rate voice codecs such as G.711, low-bit-rate codecs such as G.729 and G.723.1 are highly optimized for voice patterns and tend to distort DTMF tones. As a result, interactive voice response (IVR) systems may not correctly recognize the tones. Therefore the IVR sometimes can not recognize the DTMF tones and doesnt accept their input o may get it wrong.

The main advantage of the dtmf-relay command is it sends DTMF tones with greater fidelity than is possible in-band for most low-bandwidth codecs, such as G.729 and G.723.

(Reference: CVoice Student Guide v6.0)