Slow faxing

Issue

If a fax connection to a specific destination peer fails, that peer is 'blacklisted' and connection parameters for subsequent calls to the peer are set to minimum functionality.  This leads to all subsequent fax calls to the peer being transmitted at low speed.

Reason for the issue

There is a fallback feature in Dialogic Diva System Release software (present since version 5.3) that will remember the fax number of a peer when there has been a connection failure. Further calls to this fax number will be established with a lower set of features. Specifically, the connection speed is lowered to 9600 bit per second and only MH coding is used (MMR/MR are disabled). 

This feature implements a 'best effort' to communicate with the remote fax machine should there be an interoperability issue (or a line quality issue) that causes a connection to fail.

Disabling the fax fallback feature

This feature cannot be disabled in the registry. The Management Interface must be accessed with 'mantool' using the following command to disable fax fallback on all lines:

1. mantool -w"Config\FAX\Options=200"

If you have multiple Dialogic Diva Media Boards or a Diva 4BRI Media Board and you wish to restrict the scope of the change so that it does not affect all the lines, then you should use a command like the one below. In this case '-c2' disables fax fallback on the second controller only.

1. mantool -w"Config\FAX\Options=200" -c2

How implementation of the fallback function has changed with software version

Before Diva System Release Software version 8.2, Error Correction Mode (ECM) was also disabled for a peer when a connection failed to the peer, in addition to the maximum speed being set to 9600bps and MMR/MR being disabled. From Diva System Release Software version 8.2, ECM is no longer disabled as part of the fallback process because ECM is helpful on the poor quality telephone lines that may be the reason that the earlier connnection attempt failed.
 
Also, in older software the 'blacklist' had 10 entries and used the peer station ID. In Diva System Release Software version 8.2 and higher there are 32 entries and  the phone number is used to identify the blacklisted peer. 

In all versions: when the 'blacklist' is full, old entries are overwritten when new ones are registered; also, the 'blacklist' is reset on reboot of the PC.