The "Codecs/Channels" Tab

help | 19 SIP Gateway Links | Configuring a SIP Gateway Trunk | The "Codecs/Channels" Tab

The following settings can be made:

Codecs

Here you can define the type of compression to be used on this connection.

Specify which Codecs should be permitted for this trunk.

Voice, low bandwidth (G.729)

High compression. A voice connection requires approximately 24 kbits/s.

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 64 kbits/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 20 kbits/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 Change log.

Action on fax receipt

When a fax connection is set up, the T.38 protocol is negotiated between the two devices involved. Certain variants of this negotiation may 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.

Channels

Specify how many channels (connections) should be routed simultaneously via this trunk and forwarded from there to the public network. You can also determine how many outgoing and/or ingoing connections are established at most.

The maximum number is determined by the gateway used.

If channels were added or removed, you will find these changes in the change log.