RFC 2159 (rfc2159) - Page 3 of 7
A MIME Body Part for FAX
Alternative Format: Original Text Document
RFC 2159 MIME Body Part for FAX January 1998
It is possible (but misleading) to view the representation of these
values as single-bit flags. They correspond to the following bits of
the T.30 control string and X.400 G3FacsimileParameters:
Parameter T.30 bit X.400 bit
page-length=A4 no bit set
page-length=B4 19 21
page-length=Unlimited 20 20
page-width=A4 no bit set
page-width=A3 18 22
page-width=B4 17 23
encoding=1-dimensional no bit set
encoding=2-dimensional 16 8
encoding=Uncompressed 26 30
resolution=Coarse no bit set
resolution=Fine 15 9
The reason for the different bit numbers is that X.400 counts bits in
an octet from the MSB down to the LSB, while T.30 uses the opposite
numbering scheme.
If any bit but these are set in the Device Control String, the DCS
parameter should be supplied.
2.2. Content Encoding
X.400 defines the g3-facsimile data stream as a SEQUENCE of BIT
STRINGs. Each BIT STRING is a page of facsimile image data, encoded
as defined by Recommendation T.4. The following content encoding is
reversible between MIME and X.400 and ensures that page breaks are
honored in the MIME representation.
An EOL is defined as a bit sequence of
000000000001 (eleven zeroes and a one).
Each page of the message is delimited by a sequence of six (6) EOLs
that MUST start on a byte boundary. The image bit stream is padded
with zeroes as needed to achieve this alignment.
Searching for the boundary is a matter of searching for the byte
sequence (HEX) 00 10 01 00 10 01 00 10 01, which cannot occur inside
the image.
Alvestrand Standards Track