Why Can One Person Hear the Call but the Other Cannot?

One-way audio means a call connects but voice travels in only one direction. The signaling may succeed while the media stream is blocked or misrouted. Common factors include firewall policy, NAT behavior, a VPN path, endpoint settings, or a network change affecting one office or provider.

Compare where the problem occurs

Record the time, calling and called extensions, device type, network location, and whether the issue affects inbound, outbound, internal, or external calls. Compare a wired handset with a softphone or a call from another network, if those are normal supported options. This helps isolate whether the issue follows a device, network, or provider route.

Check the media path carefully

• Review recent firewall, router, VPN, VLAN, and voice-provider changes.
• Confirm the phone system's documented media ports and address handling.
• Check whether SIP helpers or ALG behavior conflicts with the provider's design.
• Capture call logs and timestamps for the service provider.
• Avoid opening broad inbound port ranges without a documented requirement.

Restore and monitor

Test the exact affected call patterns after a change and check both audio directions. Keep a record of the previous network configuration so a failed adjustment can be reversed.

Informatix Systems lists VoIP and business communications among its service areas. A scoped review can map call paths and compare the network configuration with provider requirements. Contact Informatix Systems if one-way audio is affecting business calls.