Codecs Help

To establish an IP voice communication, call participants have to use the same codec. When establishing a communication line, this codec is negotiated. If the caller does not find an appropriate codec, the communication does not take place. To allow communication with all IP callers, it is helpful to support as many codecs as possible. In this case, all codecs that the system offers should be enabled in the Codecs table. On the other hand, some codecs require quite a high transfer rate of up to 64 kBit/s. If you definitely do not want to use these codecs, make sure they are disabled in the Codecs table.

The Codecs table lists the regular voice and video codecs, as well as HD (High Density) codecs supported by the Quadro. Each table entry is assigned a checkbox that is used to manipulate the entry, for example to disable, to move it up or down, etc.

The table entries in bold type indicate codecs enabled for the selected extension/attendant. The enabled codecs participate in codec negotiation at the call setup. The order of the enabled codecs is very important. Each codec in the table has a higher priority than the codecs below it, and a lower priority than the codecs above it. A codec placed at the top of the table is used as the preferred codec. When establishing a call, the system will try this codec first. If the remote party does not support the preferred codec, the following codecs will be tried out strictly in the order given in the Codecs table.

• Enable/Disable enables or disables the selected codec. Disabled codecs do not participate in codec negotiation, i.e. they will never be used to for call setup. At least one codec must be enabled; otherwise voice communication with an extension/attendant will be impossible.
  Note: HD codecs are adjustable only for IP lines.
• Select all selects all entries in the table.
• Inverse Selection performs an inverse selection of the selected entries. Clicking this button when no entry is selected will select all entries
• Move up moves the selected codec one level up, increasing the codec's priority.
• Move down moves the selected codec one level down, decreasing the codec's priority.
• Make preferred moves the selected codec to the top of the table, setting its priority to the highest. Clicking the Make preferred button when a disabled codec is selected will first enable the codec and then move it to the top.

The following settings are available for user extensions and attendants only:

Out of Band DTMF Transport enables the DTMF code transmission in parallel with the voice stream. Destination received the DTMF code will play it locally if it supports the feature too. This helps avoid DTMFs loss in case of heavy traffic. The feature is valuable for all codecs but it is especially recommended for low bit rate codecs, such as G.729, G.726/16, etc.

Enable T.38 FAX enables the T.38 codec support for the FAX transmission from/to the FAX machine/modem in case if that FAX machine/modem is connected to FXS line attached to target extension. It also enables the T.38 codec support of FAX transmission for incoming unified FAX messages (fax to mailbox) and remote IP devices connected to Epygi unit via routing rules which using the target extension user settings (UES).

Enable Pass Through FAX enables the G.711 codec support for the FAX transmission from/to the FAX machine/modem in case if that FAX machine/modem is connected to FXS line attached to target extension. It also enables the G.711 codec support for incoming unified FAX messages (fax to mailbox) and IP devices connected to the attached IP line.

If both of the above checkboxes are enabled, the T.38 codec will be used as a preferred codec for FAX transmission. If it is not supported by the peer, the G.711 codec will be used instead. For virtual extensions, the incoming FAX can only be stored in the extension's voice mailbox. To allow FAX to be stored in the voice mailbox, the extension's user should not answer the incoming calls, so that they are forwarded to the voice mailbox.

Note: If both of the above checkboxes are disabled, no FAX transmission to the peer's voice mailbox will be possible.

Enable Pass Through Modem checkbox is available for the Auto Attendant and the extensions attached to the FXS lines only. This checkbox enables the modem tone detection and the G.711 codec support for the data transmission from/to the modem attached to the line. During data transmission, Silence Suppression and Echo Cancellation are automatically disabled on the line.

Note: If the extension/attendant is intended to accept modem connections, disable the Enable T.38 FAX checkbox to allow the system to identify the modem tones correctly. Otherwise, the modem connection may fail.

Force Self Codecs Preference for Inbound Calls enables the usage of your own preferred codecs (if available on both peers).

Secure RTP Settings are used to configure secure voice over IP communication on the Quadro. The SRTP Policy drop down list is used to select the secure IP connection policy. For IP phones, the following options are available:

• Make and accept only secure calls - only the secure calls will be generated and accepted.
• Make and accept only unsecure calls - only the unsecure calls will be generated and accepted.
• Try to establish secure calls, accept anything - system will try first to establish secure call, but will fallback to unsecure call if party doesn't accept secure calls; both secure and unsecure incoming calls will be accepted, as requested by remote party, with the preference given to establishing secure call.
• Make unsecure calls, accept anything - system will establish unsecure outgoing calls, but both secure and unsecure incoming calls will be accepted as requested by remote party.

For Auto Attendant, the following options are available:

• Accept only secure calls - only the secure calls will be accepted.
• Accept only unsecure calls - only the unsecure calls will accepted.
• Accept anything - both secure and unsecure incoming calls will be accepted.

For bandwidth used by secure calls, see here.