V.92/V.90 (56K) Modem FAQ's
In this FAQ we discuss the two types of modem
modems: They connect to a conventional
phone line like you have in your home.
It may be and internal (ISA or PCI) or
external (Stand-Alone or USB). If you
dialed into your ISP to
read this FAQ, you are using an analogue
modem at your side.
modems: The type of modem used by ISP's
or larger companies for high-density
‘dial-in’ applications. Digital modems
typically 'answer' and are connected
directly into the Telephone Company's
digital network via high-speed digital
connections such as a T1, DS-3, or even
higher Fiber connections. For example,
AOL and MSN use Digital Modems at their side
that you call into. Digital modems,
while primarily answer calls, are usually
capable of originating calls also.
Under what conditions will 56K
analogue modems CONNECT over 33.6Kbps?
when calling into a digital modem
(usually your ISP) and the phone line
connection is of sufficient quality to
support the higher speeds.
Under what conditions will 56K
analogue modems NOT CONNECT at speeds over
modems are answering a call from any
(analogue or digital)
modem, i.e. when calling into another 56K
Will 56Kbps modems really operate at
No. Under the best
conditions, 56K modems top speed in the US
Why? Obtaining 56Kbps
is only possible if the transmit levels
(amplitude) are greater than the levels
allowed on the phone line by the FCC.
Both Rockwell and US Robotics (the first
producers of 56k modems) requested the FCC
allow their modems to transmit at a higher
(louder) level allowing the 56Kbps speed.
They were both turned down.
connection speed and throughput of any modem
depends on the modulation of the signals,
and the quality of that particular
connection. The speed of your
connection may vary from call to call.
factors effecting connection speed for a
given modulation are:
on the phone line (you may not be able
Distance you are from your central
office. The distance may effect
the receive levels of both modems
putting the needed signals close to the
56Kbps modems are
at speeds above 33.6Kbps. Asymmetric
means the upstream speed (the data you send)
is different than the downstream speed (the
data you receive).
V.90’s, your downstream (receive)
maximum speed is 53.3Kbps, and your
upstream (send) maximum speed is
V.92’s, your downstream max is 53.3Kbps,
and upstream is 48Kbps.
My modem is telling me I am
connecting at 57.6Kbps and even higher. - Why?
Modems can report two speed
These speeds are usually,
almost always, different.
DTE Speed is the Data
Equipment speed: This is the speed
setting of the computer COM (communications)
port. This is the port speed between
the local computer port and the local modem.
This speed is set during the installation
process when you install your modem and
modem driver software. You have the
ability to change this setting. Most
modems default to reporting the DTE speed
upon connection i.e. "CONNECT
57600" (or whatever you port speed is set
(COM PORT) speed setting should ALWAYS
be set higher than the maximum capable speed
of the modem. That is, if you have a
33.6K modem, the DTE setting should be
38.4Kbps or 57.6Kbps or higher. If you
have a 56K modem you should make your
setting at 57.6Kbps or 115.2Kbps.
(I recommend 57.6Kbps, but nothing greater
NOTE: If your DTE
setting is lower than the highest
possible modem speed, you are basically
telling your modem to slow down (that is
not a good thing).
DCE speed is the Data
speed. It is the speed between the two
modems. This is the TRUE speed
between the modems. If you are a long
distance from the central office, you will
probably have a lower speed connection, even
lower than 33.6K in some cases.
How can I tell if my modem is
reporting the DTE or DCE speed?
If your modem is reporting
‘CONNECT 57.6’ or
‘CONNECT 115.2’, it is reporting the
DTE (terminal) speed, not the true
connection speed between the modems (i.e.
Here are the standard DTE
speeds. They are defined by the UART
settings and are very specific:
If your modem is reporting
ANY other speed, it is reporting the DCE
speed (speed between the modems). The
DCE speeds are unique to the modulation.
That is, the DCE speed increments for V.92,
V.90, K56Flex, and X2 all vary between
themselves because each design
implementation is different.
(Hint) If you want your
modem to report the real connection
speed, the DCE speed, set the W2
option in your modems’ setup string. (my
personal recommendation)... atw2<cr>
What are the recognized standards
for 56Kbps modulation?
K56Flex by Conexant - (formerly
V.90 standardized by ITU-T (formerly
V.92 standardized by ITU-T (ditto)
K56Flex by Conexant<Rockwell> K56Flex is
practically obsolete now
X2 by 3Com - (formerly USR: US
Robotics) X2 is practiaclly obsolete now
Modems made from Conexant
(Rockwell) chips, support V.92, V.90 and
K56Flex. Modems from 3Com (USR) support
V.92, V.90 and X2 modulations. If two
non-compatible standards attempt to connect to
each other, they will begin connection attempts
at the highest compatible standard. If one
end is not a 56K, they will begin attempting at
the lower speed V.34, which begins at 33.6Kbps
because that was the last unified standard.
For the most part,
K56Flex and X2 are no longer supported, so don't use these standards in your modem
selection consideration. If you feel you
must have a 56k modem, look for a V.90 or V.92
(I personally would look for V.92).
What is V.92?
V.92 is the current ITU-T dial-up modem
modulation specification. V.92 defines
modulation and speeds up to 56Kbps. It
seamlessly supports the older V.90 and is
fully compatible with all lower modem
standards. (56Kbps is the highest data speed
speed available on dial line phone system
because of the telco network sampling rate).
V.92 benefits over
V.92 adds 4 main features to the older V.90
Faster Upstream – up to
48Kbps (PCM Modulation)
Call waiting w/o
disconnect also called MOH (Modem On
better compression for Internet related