One-way Audio/No Audio is a common VoIP problem. It is one of the most frequent support questions we receive. There are many possible causes.
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Outdated firmware in routers, VoIP phones, Firewalls, etc. can cause one-way audio. Ensure you have the latest updates for all the devices in the call path.
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Firewall mistakenly blocking RTP, be sure firewalls configured correctly
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Particularly if NAT is involved in the call path, configuration of the various devices may be a problem. Please click here for NAT configuration on Telcobridges devices
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Another reason for one way audio is having your system set to offering unsupported codecs within your other SIP systems.
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Please check the following link for TB supported codecs; Voice Codecs
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Check if the codecs are configured correctly in the SDP; Profile SDP Description
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Just as each side of a call must send RTP within the same codec, each side must also have the same phase timing (or ptime value). Profile SDP Description
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Configured RTP port ranges can cause a problem too. Check FreeSBC and endpoints (Clients, SIP Trunks) are using correct RTP ports. RTP Port Range
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High one-way packet loss. If sufficient packet loss occurs in one direction on a call, that half of the conversion may break down, but not cause the entire call to drop. Packet loss can occur due to a number of reasons:
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High utilization on a link with no QoS.
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Misconfigured interface: Half-duplex or duplex mismatch.
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Underperforming network devices.
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Cabling faults.
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Wrong threshold configuration under SBC Advanced parameter can cause FreeSBC to block RTP-Audio by the firewall due to thresholds. You can see the following error in your call trace;
** Data path error;
-Blocking all packets due to excessive packets/bandwidth from network
Please double check your thresholds configuration from;
Code:
SBC -> Advanced parameters
Please check the following wiki for more troubleshooting steps; FreeSBC Troubleshooting Guide