Specifications

Engineering Guidelines
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• For most applications, the default values of 3 for the low speed portion of the Fax call and
1 for the high speed portion should be fine.
• Error Correction Mode (ECM) should be enabled if this capability is supported and enabled
on both Fax machines.
• Non Standard Facilities (NSF) capabilities. Whether or not to enable this capability requires
experimentation.
What happens if there are insufficient DSP resources or T.38 licenses?
• If DSP resources are not available for a T.38 call a generic DSP resource exhaustion alarm
will be raised and the call will be handled as G.711 pass through.
• If the 3300 has not been provisioned with enough T.38 licenses, an incoming Fax call will
be handled as G.711 pass through.
Are there fax speed restrictions?
• V.17 at 14,400 bps is the fastest speed supported by the T.38 solution.
• A V.34 fax machine attempting a call should renegotiate to V.17. The call will then be
processed as a T.38 call; however, the V.34 machine must transmit a 'CNG' tone so that
the 3300 can switch to T.38.
• If a V.34 fax machine attempts a call and does not renegotiate to V.17, the call will be
processed as a G.711 pass through, however the success of the call cannot be guaranteed.
Bandwidth Management
• Mitel's Bandwidth Management solution will keep track of the Bandwidth consumed by Fax
calls and Call Admission Control decisions will be made according to the system's
configuration.
• As a rule of thumb the System Administrator may want to limit the bandwidth used by Fax
calls to the same amount of bandwidth used by voice calls. For example, if zoning rules
dictate that calls between two points should use G.729 compression, which uses 8000 bps
of bandwidth, then the Administrator may want to limit Fax calls between these two points
to 7200 bps.
• Inter-zone Fax Profile 1 by default will set Fax bandwidth usage to 14.4 kbps.
Minimum network requirements
The following tables indicate the minimum network requirements for various T.38 Fax calls,
Voice and G.711 Pass Through are provided for reference.