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Between two ZyXELs:

ZyXEL modems will communicate with each other at the highest speed that is 
common to both modems.  This means that the "Plus" (U-1496 B+/E+/S+) and 
rackmount models will communicate with each other at the ZyXEL-specific speed 
of 19.2 kbps.  Non-"Plus" models communicate with each other and with "Plus"/
rackmounts at the ZyXEL-specific speed of 16.8 kbps.  Note that both the
19.2 and the 16.8 kbps speeds are full duplex protocols.

The ZyCellular option is available on ALL ZyXEL modems, and is now capable 
of 14.4 connects using the ZyXEL-specific CELL 14.4 protocol.  Again, both
modems must have the ZyCellular option in order to use the CELL 14.4 protocol.


Between a ZyXEL and a non-ZyXEL modem:

The fastest speed that ZyXEL modems will communicate with non-ZyXEL modems 
is at 14.4 kbps (V.32bis).

The fastest speed that ZyXEL modems will communicate with V.32terbo modems is
at 14.4 kbps (V.32bis).  V.32terbo modems do run at 19.2 kpbs.  The modulation
scheme of V.32terbo modems are separate and distinctly different from the 
ZyXEL 19.2 kbps implementation.  Thus V.32terbo modems are *NOT* compatible
with ZyXEL modems at either the ZyXEL-specific speeds of 16.8 kbps or 19.2
kbps.  (Brent Mosbrook (brentm@zyxel.com) of ZyXEL USA explained that a 
different bit mapping scheme was used in each modem.)

The fastest speed that ZyXEL modems will communicate with USR HST/VHST modems 
is at 2400 baud.  ZyXELs will communicate with a USR Dual Standard (DS) modem 
at 14.4 kbps (V.32bis).

The fastest speed that ZyXEL modems will communicate with V.FC (V.Fast Class)
modems is at 14.4 kbps (V.32bis).