Traditional modem standards assume that there is an analogue connection
to the PSTN at both ends and that upstream and
downstream data requirements are symmetrical.
Analogue transmissions are limited to 35
Kbps in a 4-kHz channel (Shannon’s theory), and limited further
by noise and distortion on the line.
Most applications (particularly for
Internet access) require asymmetric access with much larger downstream requirements
than upstream.
V.90 modems were approved in February 1998 to achieve
significantly higher data rates (up to 56 Kbps) because upstream
data is sent by analogue transmission while downstream data is
transmitted in digital format.
V.90 modems are also known as V.PCM
modems and replace the temporary K56flex modems.
The analogue upstream conforms
to V.34 and the digital downstream is PCM.
Manufacturers of V.90 Modem
Brands
of V.90 Modem include:
ActionTec.
Products from ActionTec include and V.90
Modem
Banksia.
Products from Banksia include and V.90 Modem
Best
Data.
Products from Best Data include and V.90 Modem
Boca
Research.
Products from Boca Research include and V.90 Modem
Compaq.
Products from Compaq include and V.90 Modem
Diamond Multimedia.
Products
from Diamond Multimedia include and V.90 Modem
Digicom Systems.
Products
from Digicom Systems include and V.90 Modem
E-Tech.
Products from
E-Tech include and V.90 Modem
Global Village.
Products from Global
Village include and V.90 Modem