Source note · One-way and no-way audio diagnosis
Twilio's trunk troubleshooting page covers the case where the PSTN party hears the PBX user but the PBX user cannot hear the PSTN party. The causes it gives are the PBX putting its LAN IP in the SDP, and a firewall blocking RTP from Twilio. The remedies are to advertise the WAN IP in SDP and to allow RTP from Twilio's published IP ranges and ports.
Checked 2026-09-24
Update the configuration on your PBX so that it puts its WAN IP address in the SDP
- Vendor
- Twilio
- Product
- Elastic SIP Trunking
- Subsystem
- media path
- Deployment
- multi-tenant
- Region
- not restricted
- Release range
- current as of 2026-09-24
- Checked
- 2026-09-24
Sources
- Troubleshooting your Trunk — Twilio · tier 2 current vendor documentation · Heading: The person out on the PSTN can hear the person on your PBX but not vice versa
Cite this note
APA
WarmTransfer. (2026, September 24). One-way and no-way audio diagnosis: source note one-way-audio-twilio-pstn-cannot-hear-pbx. WarmTransfer. https://warmtransfer.net/knowledge/claims/one-way-audio-twilio-pstn-cannot-hear-pbx
BibTeX
@misc{warmtransfer-claim-one-way-audio-twilio-pstn-cannot-hear-pbx,
title = {One-way and no-way audio diagnosis: source note one-way-audio-twilio-pstn-cannot-hear-pbx},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/one-way-audio-twilio-pstn-cannot-hear-pbx},
note = {Source note one-way-audio-twilio-pstn-cannot-hear-pbx, checked 2026-09-24}
}