Hi Mahmoud
I haven't personally faced this exact scenario, but I've seen similar behaviors when the call path for outbound campaigns is different from the inbound routing.
If inbound calls work correctly with RTP Events (RFC2833) but outbound campaign calls do not, one thing I would verify is whether the carrier or intermediary device (SBC, PBX, or mobile network) is stripping or not properly forwarding the RTP events during the outbound leg.
A few things that might be worth checking:
- SIP signaling and SDP negotiation during the outbound call to confirm that telephone-event is properly negotiated.
- Whether the carrier supports RFC2833 consistently for outbound calls, especially when the call terminates on mobile networks.
- If there is any SBC or media manipulation in the path that could be converting or dropping RTP event payloads.
- Running a PCAP capture on both inbound and outbound scenarios to confirm whether the RTP events are actually being sent by the platform.
Since switching to In-band Audio resolves the issue, it suggests the digits are reaching the far end but the RTP event packets might not be preserved in the outbound media path.
In many cases like this, the root cause ends up being at the carrier or SBC layer, especially with campaign dialing where the call routing can differ from standard inbound calls.
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Kaio Oliveira
GCP - GCQM - GCS - GCA - GCD - GCO - GPE & GPR - GCWM
PS.: I apologize if there are any mistakes in my English; my primary language is Portuguese-Br.
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Original Message:
Sent: 03-20-2026 20:50
From: Mahmoud Alshobaki
Subject: Outbound Campaign not able to detect DTMF
Hi Team,
I have strange issue on the SIP trunk, the media setting for DTMF Method is RTP Events, whenever i made inbound calls i was able to key in any digit and the IVR will be able to detect all digits.
but If i i use the trunk for outbound campaign the DTMF not detected if i receive the call in my cellphone and i start key in the DTMF on my cell phone IVR will not be able to detect the DTMF digits.
I changed the Trunk media setting
DTMF Method to In-band Audio the issue was resolved but it break other IVR application integration so management asked to keep the DTMF Method to RTP Events.
Did anyone face this issue before and is there way to make the outbound DTMF work the DTMF Method is RTP Events??
Thank you.
#API/Integrations
#ConversationalAI(Bots,VirtualAgent,etc.)
#Implementation
#Outbound
#Reporting/Analytics
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Mahmoud Alshobaki
Senior Consultant
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