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OpenVPN phones have intermittent audio loss
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amartin Offline
Junior Member

Posts: 4
Joined: Sep 2015
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Post: #1
OpenVPN phones have intermittent audio loss

I have successfully deployed several SIP-T32G, SIP-T38G, and SIP-T42G Yealink phones at remote locations. These phones use the following OpenVPN config to connect to an OpenVPN server running on my Internet gateway and then to an Asterisk server on my LAN. Some of the time, this works very well - calls are clear and both parties can hear each other. However, at other times the call quality will significantly degrade, so that there are intermittent gaps in the audio from one party or both. I have not experienced these same problems with other phones on the LAN, so I suspect the issue lies in the gateway, remote network, or OpenVPN config. Since this is occurring at several different remote locations, I feel that I can probably rule out the remote network as the culprit, which leaves just the gateway or the OpenVPN config on the phones. I am not showing congestion on the gateway, as it is mostly just used for this purpose. I do not see anything obvious in the syslog of one of the phones.

I have done a Wireshark packet capture and and am seeing some jitter (around 10ms average) and delta (around 100ms average) on the packets, but it is hard to exactly correlate this intermittent loss with the audio problems.

OpenVPN client config:
dev tun
cipher DES-CFB
auth SHA1
resolv-retry infinite
remote <gateway public ip> 1194 udp
ca /phone/config/openvpn/keys/ca.crt
cert /phone/config/openvpn/keys/client1.crt
key /phone/config/openvpn/keys/client1.key
ns-cert-type server

Is wrapping the SIP/RTP traffic inside of an OpenVPN tunnel causing some jitter or latency issues? What else can I do to debugt his prboelm?T
09-10-2015 02:00 AM
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OpenVPN phones have intermittent audio loss - amartin - 09-10-2015 02:00 AM

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