[hylafax-users] fax batching

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

I just was reminded by another HylaFAX administrator that fax batching 
(faxq support, faxsend capability was added in 4.2.0 without any way to 
queue a batch) was included in 4.2.1, and that reminded me that I 
wanted to make a few comments about it to everyone so that there was a 
general awareness of how fax batching works.

Fax batching is the sending of two or more different fax jobs to the 
same destination in one call.

When a modem becomes available for faxq to allocate a job to it faxq 
will go through the rest of the queue looking for other jobs to the 
same destination.  It will then "batch" all of these jobs together, 
provided that there is not a job of a higher priority to a different 
destination that should precede the additional jobs.  Then faxq will 
invoke faxsend for the entire batch of jobs.

Batching was done this way primarily because it was the most 
straight-forward approach with the way that faxq and faxsend currently 
function together.  There really wasn't a feasible way to get faxq to 
send another job to faxsend after faxsend had already been invoked.  
Likewise, there really wasn't an easy way to get faxsend to "look back" 
into the queue for other jobs, because faxq does not prepare them until 
it is ready to allocate the job to a modem.

I think that this is okay, though.  One of the nice things that this 
does is that it provides a limit to how many jobs can be batched 
together: it is limited to the number in the queue at the time.  This 
prevents a modem from being tied up indefinitely while faxing an 
infinite set of batched jobs.  The downside to this, of course, is that 
if multiple jobs are submitted to hfaxd in rapid succession that they 
will only be batched after faxq can no longer allocate modems to them 
as they come in (so that when a modem does become available they all 
then are already in the queue).  The workaround to this is to send them 
all with a set time-to-send that will occur after all of them are 
already in the queue.  In any case, I don't expect this to be too much 
of an annoyance.  Fax batching was mainly intended for busy outbound 
servers where all of the outbound modems are regularly in-use and many 
jobs frequently are sent to the same destination as others.  Most of 
the rest of the community will likely never notice that fax batching 
exists.

In the fax protocol fax documents are "batched" (tied together) by the 
EOM signal, which tells the receiver that "one document has ended and 
that another one is coming".  This usage of the EOM signal is 
consistent with the T.30 specification and is consistent with how many 
other fax products work.  Unfortunately, there were some typos in some 
of the older revisions of the T.30 recommendation that caused some 
issues with the compatibility of the EOM signal with various fax 
equipment (for the curious, this is another one of the shortcomings in 
some older USR Class 2.0 firmware).  For this reason there is an "info" 
setting called "supportsBatching" (see 'man hylafax-info').  If, for 
some reason, we encounter a problem when trying to send batched faxes 
to a destination and the problem appears to be a result of batching, 
then batching to that destination will be disabled via the 
supportsBatching info entry for that destination, and no further calls 
to that destination will be batched.

As I don't administer any servers where fax batching is really used 
much (I don't run any servers as I described above), I would certainly 
appreciate feedback on how well or how poorly fax batching support 
works for you.

Lee.

____________________ HylaFAX(tm) Users Mailing List _______________________
 To subscribe/unsubscribe, click http://lists.hylafax.org/cgi-bin/lsg2.cgi
On UNIX: mail -s unsubscribe hylafax-users-request@xxxxxxxxxxx < /dev/null
 *To learn about commercial HylaFAX(tm) support, mail sales@xxxxxxxxx*