The SIP Trunk Plus platform supports the following CODECs:
G.711a (PCMA)
G.711u (PCMU)
GSM
Please note that the following CODEC’s are not supported:
G.729
You should therefore ensure that when setting up your SIP trunk, in order to avoid any 'transcoding' issues (refer to 'I Can Make Calls To Some Numbers/Destinations But Not Others'), that you configure your SIP trunk to reflect the above CODEC's. For example, in 3CX, set the 'Assigned Codecs' at shown below:
