Re: [hylafax-users] T.30 2003/07 spec

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Steve Underwood wrote:

> Hi,
>
> In the July 2003 version of the T.30 spec. a section has been added 
> since the previous version of T.30, which I cannot make sense of.
>
> On page 50, at the end of section 5.3.6.1.6, there is a new chunk 
> describing a length, page number and page information add on for the 
> FIF. However, the format for this seems to be described in isolation 
> from how it is actually used. Can anyone help me understand what the 
> spec actually means.


I think that you mean page 60, not page 50.

It has the usual amount of T.30 feature vagueness.  :-)  Meaning you get 
to look around through the whole recommendation for instances of "double 
side mode" to figure out what they're talking about.  And then you 
really have to observe the feature in action (how the originating ITU 
member uses it) before it really becomes well-defined.

See Table 2/T.30 bits 113 and 114 and notes 66 through 68.

I suspect that those FIF octets discussed on page 60 can only be used 
when "double side mode" is being used (bit 113 or 114 is enabled).  
Notice the very bottom line on page 59.  It's unfortunate that a page 
break occurred where it did.

I suspect that a rare few fax machines actually use this... especially 
the continuous version of it.

Using these extra octets in a post-page or partial-page message without 
bit 113 or 114 being enabled will likely confuse most receivers.

What is still unclear to me is the units of measurement for the "length" 
octet there.  As seems to usually be the case, I suspect that some fax 
machine manufacturer who is a member of the ITU had this "double sided" 
feature that they developed and wanted to be able to call it a 
"standardized" feature rather than a "custom" one.  So this is where 
that came from.  So the trick would be to find some sender that actually 
used this double sided feature to find out how they calculate 
"length"... although I suspect that it is centimeters or 
centimeters/inches based on bit 44 of DIS/DCS.

Lee.


Lee.


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