User's Manual 626 Document #: LTRT-27045
Mediant 1000B Gateway & E-SBC
28.6 Fax Negotiation and Transcoding
The device can allow fax transmissions to traverse transparently without transcoding or it
can handle the fax as follows:
Allow interoperability between different fax machines, supporting fax transcoding if
required.
Restrict usage of specific fax coders to save bandwidth, enhance performance, or
comply with supported coders. These coders include G.711 (A-Law or Mu-Law), VBD
(G.711 A-Law or G.711 Mu-Law), and T38.
Fax configuration is done in the Coder Groups table and IP Profiles table. The Coder
Groups table defines the supported coders, which is assigned to the IP Profile associated
with the SIP entity. The IP Profiles table also defines the negotiation method used between
the incoming and outgoing fax legs, using the following fax-related parameters:
IPProfile_SBCFaxBehavior: defines the offer negotiation method - pass fax
transparently, negotiate fax according to fax settings in IP Profile, or enforce remote
UA to first establish a voice channel before fax negotiation.
IPProfile_SBCFaxCodersGroupName: defines the supported fax coders (from the
Coder Groups table).
IPProfile_SBCFaxOfferMode: determines the fax coders sent in the outgoing SDP
offer.
IPProfile_SBCFaxAnswerMode: determines the fax coders sent in the outgoing SDP
answer.
IPProfile_SBCRemoteRenegotiateOnFaxDetection: You can also configure the device
to detect for faxes (CNG tone) immediately after the establishment of a voice channel
(i.e., after 200 OK) and within a user-defined interval. If detected, it can then handle
the subsequent fax renegotiation by sending re-INVITE messages to both SIP entities
(originating and terminating faxes). For more information, see the parameter in
''Configuring IP Profiles'' on page
393.
Note: The voice-
related coder configuration (Allowed and Extension coders) is
independent of the fax-related coder configuration, with the exception of the G.711
coder. If the G.711 coder is restricted by the Allowed Audio Coders Groups table, it is
not used for fax processing even if it is listed in the Coder Groups table for faxes.
However, support for G.711 coders for voice is not dependent upon which fax coders
are listed in the Coder Groups table.
28.7 Limiting SBC Call Duration
You can configure the maximum allowed call duration (in minutes) per SBC call. If an
established call reaches this user-defined limit, the device terminates the call. The feature
ensures that calls are properly terminated, allowing available resources for new calls. The
following procedure describes how to configure the feature for all calls (globally). To
configure the feature per specific calls, use IP Profiles (IpProfile_SBCMaxCallDuration).
To configure maximum call duration:
1. Open the SBC General Settings page (Setup menu > Signaling & Media tab > SBC
folder > SBC General Settings).
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