thinQmaster Virtual testing partner Adaptive practice exams that find your weak spots and drill them. Every answer explained. From $69
Enroll

thinQmaster

Find your exam

Five questions free, before you decide.

Step 1 · choose a vendor

In one of our camps? Your practice exams come with the tuition — they are on your study page already.

Collaboration, Voice & AV · Intermediate

One-Way Audio

A call fault where only one party can hear the other, usually caused by routing, NAT, firewall or SDP address problems.

Definition

One-way audio occurs when RTP flows in one direction but not the other. Typical causes include missing return routes to the phone subnet, NAT or ALG rewriting SDP incorrectly, firewalls blocking the UDP media range, wrong bind interface on a gateway or CUBE, and asymmetric routing through stateful devices. Troubleshoot by comparing SDP addresses with actual packet captures.

Example

A gateway sources RTP from its loopback but the remote site has no route to that loopback, so the far side hears nothing.

Exam tip

On Cisco gateways, check voice-class sip bind control and bind media to a routable interface when one-way audio appears.

Related terms