2.1.2. Fax or Modem Transmission and Detection 
The “FMoIP“ (Fax/Modem over IP) feature is used for the transmission of
fax and modem signals over the IP network.
The FMoIP feature provides the following functionality:
- DMC (Direct Media Connect) for fax/modem calls. This results in a maximum of one IP hop (2 IP/TDM conversions) for fax/modem connections within a local HiPath 4000/OpenScape 4000 network. DMC is supported for HG 3500 / HG 3575. This is the major improvement in comparison with the last version, where a switch back to master call was performed after tone detection.
- The DMC endpoints HG 3500 and HG 3575 support G.711 F/M.
- T.38
IMPORTANT:
When connecting a fax adapter to a HG 3500 (SIP subscriber),
DMC must be deactivated for this device (only then is T.38 transmission
possible). If you want nonetheless to connect DMC for this device, the
codec must be set to G.711 (fax transmission with G.711, not T.38).
IMPORTANT:
T.38 configuration/usage requires end-to-end DMC
between OpenScape 4000 gateways (minimized IP hops) because of timing
requirements according to T.38 standard. In case of multiple IP hops
the fax transmission could fail with some fax machines. Negative list
of affected fax machines can be found in the Release Notes.
IMPORTANT:
In earlier versions only four T.38 connections
were possible per DSP. From HiPath 4000 V6 R2 this limitation is removed
and up to 60 T.38 parallel calls are supported and possible on STMI boards
and 120 on vSTMI boards.
-
For more information on which scenarios are supported please refer to document “T.38 Fax”, Chapter 2, “Feature Description”.
- RFC2833 and RFC2198 for fax/modem tones are supported for HG 3500/75 to transfer the fax/modem signals over IP.
- Enhanced DSP tone detection (incl. tone information transfer based
on RFC2833/RFC2198) for HG 3500/75 boards. Supported tones:
- call initiation tones CNG and CT (calling side)
- call answer tones ANS(CED), /ANS, ANSam, /ANSam (called side)
Restrictions
- When DMC is not able to reduce the number of IP hops for a connection to one IP hop, there will still be a certain risk of broken fax or modem connections because of the resulting delay, even though a G.711 channel optimized for analog data is chosen.
- Fax/Modem call: only supports basic call, no support for supplementary services initiated on basis of an existing connection, such as consultation call. Support of basic call includes forwarded calls (CFU).
- Due to the variety of the available modem and fax types on the market, there is no guarantee that all FMoIP scenarios will work with 100% reliability. The different behaviors of the modem and fax types (e.g. tolerance) and the typical IP conditions (jitter, delay etc.) can result in failed FMoIP scenarios.
- Clear Channel has to be disabled via AMO configuration because there is no RFC2833/RFC2198 tone detection for Clear Channel. Each fax/modem call should be configured as a regular voice call (G.711, G.729, ...).