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Mediatrix 4104 247
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H A P T E R
16
Fax Transmission
This chapter describes how to perform fax transmissions in clear channel and T.38 with the Mediatrix 4104.
You can also set some of these parameters via the web interface, as described in “Voice & Fax Codecs” on
page 77 .
Introduction
The Mediatrix 4104 handles G3 fax transmissions at speeds up to 14.4 kbps. Automatic fax mode detection
is standard on all lines. Real-Time Fax Over UDP with the T.38 protocol stack is also available.
The quality of T.38 fax transmissions depends upon the system configuration, type of call control system used,
type of Mediatrix units deployed, as well as the model of fax machines used. Should some of these conditions
be unsatisfactory, performance of T.38 fax transmissions may vary and be reduced below expectations.
A fax call works much like a regular voice call, with the following differences:
1. The fax codec may be re-negotiated by using a re-INVITE.
2. The goal of the re-INVITE is to allow both user agents to agree on a fax codec, which is either:
a. Clear channel (PCMU/PCMA or G.726) without Echo Cancellation nor Silence Suppression
(automatically disabled).
b. T.38.
3. Upon fax termination, if the call is not BYE, the previous voice codec is recovered with another re-
INVITE.
All lines of the Mediatrix 4104 can simultaneously use the same codec (for instance, T.38), or a mix of any of
the supported codecs. Set and enable these codecs for
each line.
Fax Calling Tone Detection
You can enable the fax calling tone (CNG tone) detection.

To enable fax calling tone detection:
1. In the dataIfMIB , set the dataIfCngToneDetectionEnable variable to enable .
Upon recognition of the CNG tone, the Mediatrix 4104 switches the communication from voice
mode to fax mode and the CNG is transferred by using the preferred fax codec.
This option allows for quicker fax detection, but it also increases the risk of false detection.
If you do not want the Mediatrix 4104 to detect the fax calling tone, set the variable to disable . In
this case, the CNG tone does not trigger a transition from voice to data and the CNG is transferred
in the voice channel.
With this option, faxes are detected later, but the risk of false detection is reduced.