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t.38
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H.323 and H.404
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M.16 and M.204
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k.30 and k.38
EXPLANATION
The T.38 fax relay standard was devised in 1998 as a way to
permit faxes to be transported across IP networks between existing Group
3 (G3) fax terminals. T.4 and related fax standards were published by
the ITU in 1980, before the rise of the Internet. In the late 1990s,
VoIP, or Voice over IP, began to gain ground as an alternative to the
conventional Public Switched Telephone Network. However, because most
VoIP systems are optimized
(through their use of aggressive lossy
bandwidth-saving compression) for voice rather than data calls,
conventional fax machines worked poorly or not at all on them due to the
network impairments such as delay, jitter, packet loss, and so on.
Thus, some way of transmitting fax over IP was needed.
SOURCE
https://www.3cx.com/pbx/foip/