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This article describes how to resolve a situation where SIP calls between branches connected through IPsec have no audio, but calls from branches to the main office (and vice-versa) work fine.
Scope
FortiGate, IPsec.
Solution
SIP calls between branches with no audio, while calls from branches to the main office (and vice-versa) work fine is a common symptom of a VoIP/SIP implementation where direct media is configured on the main office PBX.
Solution 1:
Disable direct media on the PBX configuration in order to have the audio packets flowing via PBX.
Solution 2:
Reconfigure the IPsec phase-2 selectors for all IPsec tunnels towards the Branches so that for each Branch, all of the other branch networks are considered as main office networks.
