DTE rate - Set this as high as possible.
Usually 115,200 bps on recent PCs (even using
Windows 3.1). 230,400 bps will likely become the
norm on newer PCs. If nothing happens when you 'log
on' change the setting to a slower rate and try
Compression - Make sure that compression
is used on your connections.
Error Control - Make sure your modem is
set to LAPM (V.42) error control rather than MNP
which is around 20% slower.
Modem Line Rate - Force your modem to
connect at a lower speed (2400 or 4800 bps less)
if it retrains (pauses transmission and re-negotiates
the connection) often or your calls break down
frequently. Many modems, by default,
disconnect after a certain number of re-transmits
of a data block. A stable connection at a
lower speed can often give more data throughput
than an unstable connection. Check your modem's
handbook to find out how to set the maximum line
Using FTP - Probably the best way to test
you modem's actual speed is to download a
compressed file, a ZIP file for example, from
your ISP's server using an FTP program, such as
CuteFTP. If possible, you should dial directly
into your ISP's server rather than dialling into
a Point-Of-Presence (POP). This call may cost
more than dialling into a POP, but, it avoids
possible congestion on the link between the POP
and the server.
Recording log files - If you are using
Windows 95/98 you could record
The modemlog.txt file logs interaction between
your PC and your modem while your connection is
being set-up and disconnected. From this file you
can determine at what speed you modem connects,
and what type, if any, of error correction is
used, and if compression is enabled. Look out for
a connection string such as "CONNECT 28800
LAPM COMPRESSED", which confirms that error
correction and compression are used.
A connection string containing "38400",
"57600", "115200" or "230400"
indicates the DTE speed (port speed), and
suggests that the modem has not been set-up
The ppplog.txt file logs Point-to-point protocol
activity, and records instances of errors such as
CRC errors, overrun errors and incomplete packets.
You can use a Modemlog
File Viewer and a Ppplog
File Viewer to monitor and trouble-shoot your
System Monitor - The Windows 95/98 System Monitor can be used
to measure data throughput on your modem. The
utility (Start | Programs | Accessories | System
Tools | System Monitor), is useful for indicating
the peak data throughput. In Windows 95, you must
be on-line before you can add your modem to the
items list in System Monitor. The version of DUN
with Windows 98
Initialisation String - If you are not
sure that you have the correct INF file for your
modem you could set-up your modem as a Standard
28800 bps modem. The initialisation string for
this type of modem is ATE0V1. Alternatively, add &F
to the extra settings part of the Advanced
Connection Settings window. For most modems, this
re-loads the factory settings, cancelling the
Dial-Up Networking setting changes. Default
settings for most recent modems are suitable for
Internet connections, but, you could also refer
to the user manual of the modem, and add other
commands to the extra settings part of the
Advanced Connection Settings window.
Link diagnostics - Some modems monitor a
connection and store information about the link
operations, such as the last rate before
disconnection, disconnection reason and number of
retrains. This information can be helpful in
isolating the source of problems. Examples are 3Com/U.S.Robotics'
ATI6 and ATI11, Rockwell's AT&V1 and
MultiTech's ATL8. After an Internet connection
use any terminal emulation program such as
Windows 95's HyperTerminal or Windows 3.1's
Terminal to check your modems diagnostics
information. Note: In Windows 95/98, it may be necessary to
change a setting in your system registry to
prevent Dial-Up Networking from resetting your
You can also dial your ISP's access number using
a terminal program, enter three pluses (+ three
times in quick succession), wait one second for
an OK response, enter ati6 and press the
This example demonstates link diagnostics on a 3Com/U.S.Robotics
~ÿ}#À!}!}!} }9}"}&} }*} } }#}%Â#
}9}"}&} }*} } }#}%Â#€}%}&} }<^3}
U.S. Robotics 56K Message Link Diagnostics...
Chars sent 3 Chars Received 219
Chars lost 0
Octets sent 3 Octets Received 146
Blocks sent 3 Blocks Received 7
Blocks resent 0
Retrains Requested 0 Retrains Granted 0
Line Reversals 0 Blers 0
Link Timeouts 0 Link Naks 0
Data Compression V42BIS 2048/32
Current Call 00:00:10
The strange characters above
are associated with setting up protocols, and the
three pluses won't be echoed back to you. Instead
of hanging-up using the ath command, you
can re-enter ati6 repeatedly, although
your ISP's modem may disconnect you after a
couple of minutes.
Line Diagnostics - Using a Communications
program, such as Windows Terminal or
HyperTerminal, dial your ISP's access number.
When you get the CONNECTED message type +++
(three pluses). The modem should respond with OK.
Type AT%L and press the enter key. Next
type AT%Q and press the enter key.
If all goes well (and your modem supports these
commands) your screen should look something like
The line level reading is in -dBm,
where 018 is -18dBm. If you have a short line you
should expect to get between -13dBm and -16dBm.
Longer lines will give readings between -17dBm
and -60dBm, although most modems quote -43dBm as
the minimum required level. A level of -30dBm may
sustain a 28.8Kbps connection, but, 14.4Kbps
could be as high as possible from a -35dBm
The line quality reading represents the number of
re-transmissions the modem has performed over a
specific period of time. The lower this figure is
the better, although at speeds above 9600bps you
probably won't get zero, even on a good line,
since the number of transmissions goes up as the
speed goes up. I normally measure between 40 and
60 on a known good line at 33,600bps. If the
quality figure goes too high (99 on some modems)
the modem retrains and may re-connect at a lower
speed which should have a better quality figure.
Your modem's speaker - It is not uncommon
to have a line fault or synchronisation problems
in the telephone exchange or switching centre.
This can cause your modem to retrain repeatedly,
and in extreme instances, force the connection to
dis-connect. By adding m2 to the extra
settings part of the Advanced Connection Settings
window, your speaker remains on for the duration
of the connection. The sound should remain
constant, with retrains, if they occur, being
easily recognisable. Typically, a retrain causes
an interruption in data flow lasting around 8
You can download 10
second samples of a normal connection and a connection
with a retrain.
Both Microsoft ADPCM WAV files are 55KBytes,
and the expected download time for each
file is less than 20 seconds at 28,800bps.
A complete swap - Temporarily swap your
computer and modem with another computer and
modem that doesn't have connection problems. If
the other computer uses the same ISP and dials
into the same point-of-presence, this should help
prove that the problem lies with the line (or
internal wiring), or with the computer and modem.
Common problems - Some modems have two
sockets, one for the line and the other for a
telephone, but, many recent modems just have one
socket (less manufacturing costs), and use a
special adapter which plugs into the telephone
wall socket or modem socket. If the adapter is
not used, the line is, effectively, short-circuited
once the cable is plugged into the modem. A
workaround is to re-terminate the telephone plug
using only the inside pair of wires, but, ideally,
the proper adapter should be used.
CRC errors, as recorded in the Point-to-Point Protocol
log file PPPLOG.TXT, are errors found in the PPP packets.
Put simply, as you download data, the data is broken-up
into blocks of data, up to 1500 bytes in size. A
mathematical calculation is applied to the data in a
block and a checksum is derived. This checksum is sent
along with the data in the PPP packet. At the receiving
end the same calculation is applied to the block and
compared to the checksum. If the checksums don't match
then an error is recorded and the packet must be resent.This
method of data verification is said to be 99.95% reliable.
Ideally, your PPPLOG.TXT file should not record any
CRC errors. If the line is noisy, but error control is
used by the modems, all packets should eventually be
delivered intact. Alternatively, if error control is not
being used by the modems, occurrences of line noise will
cause CRC errors which will be recorded in the PPPLOG.TXT.
Overrun errors, which are also recorded in the PPPLOG.TXT
file, will also be recorded as CRC errors since the CRC
checksums from incomplete packets will not match.
I recently had a problem that I only
experienced with Internet Explorer while downloading JPG
graphic files. An apparent pause during downloads seemed
to coincide with CRC errors recorded in the Point-to-Point
Protocol log file. Click here
for more details.
The bandwidth that your Internet Service Provider
offers can greatly affect your speed. An ISP may have one
or more T1 (1.544Mbps) or E1 (2.048Mbps) to the back-bone
of the Internet, but this is of little use if they only
feed your POP (Point-of-Presence) with a 64Kbps data line
and you are not the only user on-line. When you are
connected to your POP you ultimately share bandwidth with
all other users connected to the POP a that time. So,
even if two users' modems connect to their ISP's modems
at 56Kbps, if the POP is served by a 64Kbps data line,
they both share this 64K bandwidth. If dialling directly
into the server, rather than going through a POP,
or going through the POP at quiet times of the day, is
much faster there
may be not enough bandwidth to that POP.