Refer to the exhibit. Users report that when they dial to Cisco Unity Connection from an external network, they cannot enter any digits. Assuming only in-band DTMF is supported, what is a reason for t

The correct answer is D. No DTMF is negotiated.. The root cause is that no DTMF method is negotiated in the SDP exchange. For in-band DTMF to work over SIP, the SDP must include a negotiated codec that supports it (e.g., G.711 carries DTMF tones in-band). If the SDP does not advertise or negotiate any DTMF capability - and out-

Signaling and Media Protocols

Question

Refer to the exhibit. Users report that when they dial to Cisco Unity Connection from an external network, they cannot enter any digits. Assuming only in-band DTMF is supported, what is a reason for this malfunction?

Options

AThe negotiated RTP port is outside of the range described by RFC, so inband DTMFs do not work.
BThere is SIP Delayed Offer. DTMF is supported only in Early Offer.
CThe rtpmarp:0 value for the negotiated codec is marking DTMF as inactive.
DNo DTMF is negotiated.

How the community answered

(22 responses)

A
5% (1)
C
5% (1)
D
91% (20)

Explanation

The root cause is that no DTMF method is negotiated in the SDP exchange. For in-band DTMF to work over SIP, the SDP must include a negotiated codec that supports it (e.g., G.711 carries DTMF tones in-band). If the SDP does not advertise or negotiate any DTMF capability - and out-of-band methods like RFC 2833 (telephone-event) are not present either - the Unity Connection voicemail system will never receive the digit signals. Option A is incorrect because RFC port ranges don't affect DTMF delivery. Option B is incorrect because Delayed Offer vs. Early Offer does not inherently block DTMF. Option C is incorrect because 'rtpmap:0' refers to PCMU/G.711, not DTMF inactivity.

Topics

#DTMF#Media Negotiation#SIP#Cisco Unity Connection

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