# T.37 and TIFF-S

T.37 describes an end-to-end fax session, using e-mail as the transport. The ITU-T document for a T.37 session completely describes the format and addressing conventions required to transport a fax using e-mail protocols as the transport over the internet to a G3 device. Part of the ITU-T defines TIFF-S, the file format used for fax over e-mail.

TIFF-S is a subset of the commonly used TIFF-F file format. TIFF-S has the following page characteristics across all pages:

- 1D encoding

- LOW resolution

- A4 page width

TIFF-S also specifies the physical layout of the TIFF file. No optional TIFF fields are allowed when writing TIFF tag data, to ensure that minimal black and white fax transmission occurs.