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How to tweak SIP Invite SDP header to negotiate Echo Cancellation and Silence Suppression

Article ID: 952
Last updated: 22 Mar, 2024

Applies to:

Imagicle Digital Fax rel. 2023.Spring.1 and above


How to improve G.711 pass-through FoIP negotiation, to grant more interoperability 


If the remote fax recipient (or the FoIP network) can’t negotiate T.38, Digital Fax falls-back to G.711, with a default handshake setup. This is sometimes causing some interop problems.

From 2023.Spring.1 release, it is possible to adjust two parameters, pretty important for proper G.711 negotiation:

  • Silence suppression
  • Echo cancellation

Please edit the following setting file: C:\Program Files (x86)\StonevoiceAS\Apps\StoneFax\Server\System\Stonefax.ini

and add the following lines under [Settings] parameters:

  • EnableT38SilenceSuppression=  0 ⇒ off     1 ⇒ on
  • EnableT38EchoCancellation=  0 ⇒ off     1 ⇒ on

By default, both settings are not set within the SIP INVITE header.

Note: Please bear in mind that Imagicle Digital Fax VoIP engine does NOT supported above media attributes. They are just used to improve handshake, but actually both options are disabled on Imagicle UCX Suite side.

Once above settings are applied, please restart Digital Fax service. In a cluster, please restart the service in all nodes.

Article ID: 952
Last updated: 22 Mar, 2024
Revision: 3
Views: 143
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