InterceptRadio.com Forums

Not that the the title of this post means anything, but I have a CRAP ton of questions regarding the various modem standards in regards to fax machines.
I know all the other standards. But the use of v.34 made me question the standards table.
During transmission of a v.34 fax, theres a *second* standard that is used in the middle of transmission, which is used after the main v.34 datastream, and is used before the entire transmission is done.

Here are the questions...
Is it an ECM scheme?
Is it HDLC?
Is it a vectorized format of v.22 that transmits the image in a unique format that I never heard of before? It has a REALLY cool sound and I CANNOT for the life of me understand the techincal information behind it.
Is it a completely different modem standard?
Is it the other fax machine receving the image data when the v.34 stream is sent?

WHAT IS IT???
Somebody PLEASE tell me.