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VoIP Troubleshooting 101 – One-way Audio March 26, 2010

Posted by TelUS Consulting Services in VoIP catagory.

Identifying and Resolving One-Way Voice Issues

This section describes some of the possible ways a condition known as one-way voice can occur. This is a situation where the IP Phone users might be able to hear voice traffic in one direction but not the other.

Gateway Route Not Present

Whether dynamic routing is used or static routing is used, the lack of the proper route to the default subnet gateway can cause the one-way voice issue to occur. Check for the presence of this needed route, open a connection to the MRP, and do a show ip route or similar command.

MRP Configuration Missing the voice RTP Send/Recieve Command

Typically the IOS command voice rtp send-recv is needed within the MRP to allow voice traffic to pass both ways. The voice rtp send-recv command is used to establish a two-way voice path when the Real-Time Transport Protocol (RTP) channel is opened. By default, the voice path is connected in only the backward direction when the RTP channel is opened. Enabling voice rtp send-recv allows the voice path to be established in both the

backward and forward directions and, as a global command, affects all VoIP calls when enabled.

Other Potential Causes of One-Way Voice

The following are other situations that can also show up as one-way voice:

A bad phone load could have bad TCP libraries.

IP routing (static or dynamic) has not been defined on the MRPs.

our next installment of VoIP Troubleshooting will be on Latency

Joe Buck, N.C.E.

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