Softphone works on LAN but one way audio on hotspot

Scenario

A remote user on mobile hotspot can connect calls, but only one party hears audio.

Recommended Resolution Path

1. Inspect NAT traversal, STUN/TURN behavior, and UDP blocking on the hotspot path.
2. Compare codec negotiation and whether media is trying to use a blocked IP range.
3. Test with VPN off and on if policy allows to isolate path differences.
4. If only one carrier path fails, document that constraint for field staff.

Technician Notes

Document what changed, what confirmed the fix, and whether the issue points to a broader standards gap worth addressing for the client.