SIP Links Configuring a SIP Trunk The "Codecs/Channels" Tab
The "Codecs/Channels" Tab
The following settings can be made:
Here you can define the type of compression to be used on this connection.
If the Codec priority "Prefer Quality“ is selected, the Codecs are provided in the sequence G.722, G.711a, G.711µ, G.729 or Fax over IP. Specify the filter(s) you want:
* Voice, highest bandwidth (G.722)
HD quality
* Voice, high bandwidth (G.711a, G.711µ)
The voice data is slightly compressed. This keeps the packet delay time in the LAN (Local Area Network) to a minimum. A voice connection requires approximately 64kbits/s.
* Voice, low bandwidth (G.729)
High compression. A voice connection requires approximately 24kbits/s.
* Fax over IP
In this case, the special fax protocol T.38 is used, which takes the set-up of the IP network into consideration. A fax connection using T.38 requires approximately 20kbits/s.
If the Codec priority "Prefer low bandwidth" is selected, the Codecs sequence changes to G.729, G.722, G.711a, G.711µ, Fax over IP. The aim here is to use as little bandwidth as possible. Here too, specify the filter(s).
Click on ”Next>”.
If there are several voice codecs selected, SwyxServer will filter voice data according to the current settings. The communicating sides will have to decide which voice codec to use.
It won't be written in the change log, if a Codec was activated or deactivated. See also Change log.
Action on fax receipt
If the T.38 protocol is negotiated for the establishment of a fax connection between the devices involved, certain variants of this negotiation may possibly not be supported by some IP adapters. Use the following filter options to establish compatibility with such devices.
* Remove T.38 codec from initial invite
Some IP adapters cannot correctly interpret an initial connection request which includes T.38 as well as voice Codecs.
If this option is set, SwyxServer removes T.38 from the initial connection request. The fax devices first set up a voice connection and then switch to the fax protocol T.38 because of the fax tone (CED tone, 2100Hz).
* Prohibit T.38 reinvite by sender
The receiving fax device switches to T.38 after detecting the fax tone (CED tone, 2100Hz). Alternatively, the switch to T.38 can be carried out by the sending fax device.
Some IP adapters don't support switching by the sender.
If this option is set, SwyxServer suppresses a switch to T.38 by the sender.
If the receiving side involves a combined phone/fax device (fax switch), a fax data transmission is impossible when the option "Prohibit T.38 reinvite by sender" is activated.
The filter options can only be set when the Codec "Fax over IP (T.38...)" is activated.