Editing Fax (section)

=== Class ===
Computer modems are often designated by a particular fax class, which indicates how much processing is offloaded from the computer's CPU to the fax modem.

* Class 1 (also known as Class 1.0) fax devices do fax data transfer, while the T.4/T.6 data compression and T.30 session management are performed by software on a controlling computer. This is described in ITU-T recommendation T.31.<ref name=peterson2000>{{cite book| first=Kerstin Day | last=Peterson | year=2000| title=Business telecom systems: a guide to choosing the best technologies and services| pages=191–192| publisher=Focal Press| isbn=1578200415| url=https://books.google.com/books?id=W79R0niNU5wC&pg=PA191| access-date=2011-04-02 }}</ref>
* What is commonly known as "Class 2" is an unofficial class of fax devices that perform T.30 session management themselves, but the T.4/T.6 data compression is performed by software on a controlling computer. Implementations of this "class" are based on draft versions of the standard that eventually significantly evolved to become Class&nbsp;2.0.<ref>{{Cite web | url = https://legacy.hylafax.org/site1//Modems/Supra/class2.html | title = Supra Technical Support Bulletin: Class 2 Fax Commands For Supra Faxmodems | date = June 19, 1992 | access-date = March 23, 2019}}</ref> All implementations of "Class 2" are manufacturer-specific.<ref name="Multi-Tech">{{Cite web |date=2017 |title=Fax Developer's Guide: Classes 2 and 2.0/2.1 |url=https://www.multitech.com/documents/publications/manuals/s000239.pdf |url-status=dead |access-date=2019-03-23 |publisher=Multi-Tech Systems|archive-url=https://web.archive.org/web/20200321191129/https://www.multitech.com/documents/publications/manuals/s000239.pdf |archive-date=21 March 2020 }}</ref>
* Class 2.0 is the official ITU-T version of Class&nbsp;2 and is commonly known as Class&nbsp;2.0 to differentiate it from many manufacturer-specific implementations of what is commonly known as "Class&nbsp;2". It uses a different but standardized command set than the various manufacturer-specific implementations of "Class&nbsp;2". The relevant ITU-T recommendation is T.32.<ref name="Multi-Tech"/>
* Class 2.1 is an improvement of Class&nbsp;2.0 that implements faxing over V.34 (33.6&nbsp;kbit/s), which boosts faxing speed from fax classes "2" and 2.0, which are limited to 14.4&nbsp;kbit/s.<ref name="Multi-Tech"/> The relevant ITU-T recommendation is T.32 Amendment&nbsp;1.<ref name="Multi-Tech"/> Class&nbsp;2.1 fax devices are referred to as "super&nbsp;G3".