Tips for troubleshooting problematic
Check the Line for Noise
First you need to get rid of the dialtone so you can really listen to the line. Dial a
number, any number but obviously one which is valid for your area, so that you
do not get the dialtone replaced by a busy signal. The easiest and most common
across all areas is "1". Is your dialtone gone? Now listen and really concentrate
while you are doing so because you are only going to get 30 seconds before
it times out and gets replaced by a busy signal again.
This is the first major step to checking if you have a good line for a
modem or not. Is it quiet? No pops, bangs, crackles, creaking, or faint voices in
the background from other people's conversations? All or any of these noises
will cause you a probley on a high speed modem link.
Just what are these noises? Well, it can be something as simple as a loose
screw on a connector block somewhere between you and the exchange, or water
getting into one of the Telco's cable ducts and the waterproofing (around
the cable joints) has started to break down. You could have a bad connection
in the house somewhere, and not necessarily on the line extension that's feeding
your modem. Other people's conversation's (called "crosstalk") are not so easy
to pin down, and are usually more likely to be further "into the system" before
the source becomes apparent.
Let's presume you have one of these noises. Next you need to check the
phone itself. If you have a spare phone, take it and plug it into the same
socket and the check for noise again.
Now let's assume your happy with the perceived "quietness" of the line.
Now you move to the modem. How can you check to see if the modem has a bad
socket or plug associated with it? Well, it all depends what kind of
computer you have. If you have a phone hooked into the other modem plug so you can
still use the line when you are not on your modem, you can enter into a terminal
screen (hyperterminal, SmartTerm, ZTerm, Qmodem, Procomm - or if you are on a
mac, you can use a terminal window, like the one in FreePPP).
Inside of your terminal screen, enter "atz", then hit enter. This resets
your modem. Now type "atx0d1" and hit enter. You should hear your modem pick up
and dial one number. Pick up the phone you have hooked into the modem, and
listen for about 20 seconds and see if you can hear anything. If you did hear
some crackling from that, it may just be the connections with the modem. The
leads on the connections may have become a little tarnished. A good ink
eraser should take care of that.
Initial Connect Speed Issues
Help! My 56K modem connects at 33.6 or less!
THE EASY ANSWERS
Treat this as a troubleshooting matrix. Go through all of these steps, and
you will have a better than 90% chance of solving your problems with slow connects.
Make sure you're calling the right number.
If this is a Rockwell-based k56Flex modem, issue an ATI3 command in a
terminal program. If the version is 0.5 something, you should upgrade. If
the version is 1.0 something, you should try adding S202=32 to your init
If this is a Lucent-based K56flex modem, issue an ATI3 command in a
terminal program. The firmware version should be at least 1.0 or greater.
It's always a good idea to check with the modem manufacturer to see if
there is a newer firmware available. Many people's problems have
disappeared once they installed a new version of the firmware. DO NOT
SKIP THIS STEP. Check to see if the manufacturer offers a newer driver.
Try disconnecting additional telephony devices (fax, phones, answering
machines) from the phone line. This is a basic and useful step in modem
THE HARD ANSWERS
Multiple A/D conversions
The most likely reason is that your phone line has multiple analog/digital
conversions, which prevents the use of 56K technology. This interrupts the
process of the single digital to analog pathway.
Office PBX systems generally create an extra A/D conversion. How do you
know if you're on a PBX? If you have to dial a number (usually 9 in the U.S.)
to dial an outside line, you're on a PBX. If your phone has it's own extension, you're on a
PBX. The solution in that case is to plug the modem into a direct outside
line. The office fax machine is usually dialed into a direct outside line, so
The phone lines outside of your building may have equipment that
introduces extra A/D conversions. Non-integrated SLCs (subscriber line concentrators)
are one source. If that's the case, there's little you can do except to call
the phone company and complain. Before you get your hopes up, be aware that the
phone company is generally not sympathetic, and only guarantees speeds of 9600
baud or so (the exact answer will vary from telco to telco). It is worth a
shot, though, and some people have managed to get their phone company to fix their
The best defense against these problems is to borrow a k56Flex modem for
testing before you buy. The second-best defense is to buy your k56Flex
modem from a store or catalog that offers a money back guarantee.
I'm connecting at 38400, 57600, or 112500. Or am I?
No. Those speeds are computer-to-modem speeds (AKA DTE speeds or port
speeds) that you set in your software. What you want to know is the
modem-to-modem speed (AKA connect speed or DCE speed).
Your <-DTE Speed-> Your <-DCE Speed->
Computer Modem Modem
How can I get my modem to report the true connect speed?
You can force most modems to report the true connect speed by adding a
command to your init string. For Rockwell-based 28.8 and K56flex units,
command is W2.
If your dialing software uses settings files, make sure you have the right
settings file, which will usually include an init string with the correct command.
For instance, you would need to the correct .inf file for Windows 95 Dial-Up
Networking, or the correct CCL file for Apple's PPP for Open Transport.
These may have been included on a disk with the modem.
What are typical connect speeds for k56Flex modems?
As with 33.6 modems, your results will depend heavily on your phone lines.
Typically, 38-48K for k56Flex modems are good. Some people are getting
better results, some are getting worse.
Is initial connect speed all it's cracked up to be?
Initial connect speed is a convenient benchmark, but it can be deceiving.
V.34 and 56K modems can and do shift their speeds up and down during the course
of the call to respond to changing line conditions. Some modems connect
very aggressively at high speeds, but are then forced to lower their speed to a
more stable level. Others may connect conservatively and upshift.
The best test is to download a compressed file with FTP. For help with
getting accurate results, see the section below on FTP.
What's the command for connection speed and stats on my K56flex?
Lucent-based K56flex modems
After disconnecting, issue an ATI11 command in your terminal program (such
as HyperTerminal or Telix for Windows, or ZTerm for Macintosh).
Rockwell-based K56flex modems
After disconnecting, issue an AT&V1 command in your terminal program (such
as HyperTerminal or Telix for Windows, or ZTerm for Macintosh). These are
some example results. TX is the transmit (upload) speed. RX is the receive
TERMINATION REASON.......... LOCAL REQUEST
LAST TX data rate........... 31200 BPS
HIGHEST TX data rate........ 31200 BPS
LAST RX data rate........... 46000 BPS
HIGHEST RX data rate........ 50000 BPS
Error correction PROTOCOL... LAPM
Data COMPRESSION............ V42Bis
Line QUALITY................ 127
Receive LEVEL............... 014
Highest SPX Receive State... 00
Highest SPX Transmit State.. 00
EQM Sum Value............... 00A2
RBS Pattern detected........ 00
Data Rate Dropped in kbps... 00
Digital Pad Detected........ None
What's a good way to test actual modem performance?
If done correctly, file downloads are a good way to test modem performance. The
trick is to make sure you're really testing the modem's raw transfer rate,
and not some other factor that you're not aware of. Here are some guidelines for
1. USE AN FTP PROGRAM
Web browsers often lie about download rates. FTP is more reliable. Note
that some FTP programs reports download speeds in Kilobits per second (Kbps),
while others use Kilobytes per second (KBps). To convert, multiply
Kilobytes per second by 10 (eight bits plus the start bit and stop bit). A valid
alternative to FTP is a terminal program that supports Zmodem.
2. DOWNLOAD A PRE-COMPRESSED .ZIP OR .SIT FILE
If the file you download isn't compressed, hardware data compression in
the modem will kick in, leading to erroneous results. Different file types compress to
different degrees, so if you download a Microsoft Word file and I download a
QuickTime movie, there's no way to compare the results. Use .zip
(PKZip/WinZip) or .sit (StuffIt) files for your tests. Some file formats
(GIF, JPEG, QuickTime, etc.) offer some compression, but can sometimes be compressed
further by hardware protocols.
3. DOWNLOAD A FILE THAT'S AT LEAST 200K
A file size of at least 200K will minimize the effects of TCP/IP slow
4. DOWNLOAD FROM YOUR LOCAL FTP SERVER OR UNIX DIRECTORY
A local server is one that's on your system, not on the other side of the
If you download a file from across the Internet, you're testing Edgenet's
connectivity to the Internet just as much as you are testing your modem.
5. DOWNLOAD DURING OFF PEAK HOURS
To eliminate congestion issues, download early in the morning or late at
Interoperability: 33.6, K56flex 1.0 and 1.1
Understanding the version numbers
The 1.0 and 1.1 terminology is a little confusing, because it does not
match the firmware version numbers. To determine your modem's K56flex version, type
"ATI3" in a terminal program and press the enter key. Here's how to match
the ATI3 response to the K56flex version:
ATI3 result K56flex version
- - - - - - - - - - - - - - - - - - - - -
less than 1.0 1.0
1.0 or greater 1.1
The actual result will look something like "V0.519DHY-K56_DLS". The
"V0.519" is the version number in this case, indicating that this is K56flex 1.0
The modem manufacturer will need to issue a firmware update to upgrade
your modem to K56flex 1.1. Until then, you'll be limited to V.34 speeds (up to
You can easily tell if you're dialing a K56flex 1.1 modem because of the
extra tone at the beginning of the connection sequence. You will need
to turn on your modem speaker to hear the sound, or you can simply call
Edgenet with a telephone and listen for the sound.
If you have a k56Flex modem but you're dialing into a V.34 modem bank,
your modem will still try to negotiate a k56Flex connection, even though it's
impossible. You may want to use one of the commands below to tell the
modem to not attempt a k56Flex connection.
How can I disable K56flex?
For Rockwell-based K56flex modems, add +MS=11,0 to the end of your modem
For Lucent-based K56flex modems, add S38=0 to the
end of your init string.
Known Problems with Specific Modems
Poor connects with 1.00x K56flex firmware
Symptom: When you issue an ATI3 command in a terminal program, the modem
reports 1.00x firmware (1.003, 1.009, etc.). The modem fails to connect at
high speeds. Prior to the firmware update, the modem connected at higher
Try adding S202=32 to your init string. This has been very effective for
many readers. Once this string has been added, many K56flex modems show much
What does this command do? According to Zoom technical support:
The command disables dual pcm detection. i.e. it won't
look for how many analog to digital connections are on
your phone line. This is a bug in 1.0x code. It was fixed
in 1.1 maybe 1.09 but I'm not sure.
Poor connects with early Lucent LT Winmodem firmware
Early versions of the Lucent LT Winmodem firmware had problems connecting
at K56flex speeds. Here is a rundown of Lucent LT Winmodem firmware versions
to separate the good from the bad (taken from Lucent):
Well, basically anything before 4.06 had little to no
chance of getting K56flex connections. 4.06 was the first
"decent" version of drivers that gave about 42K
connections. 4.15 or 4.16 increased the performance by
about 4K, and 4.21 gave about 2K higher.
The only "bad" release I know of is 4.20, which had some
fax problems. Other than that, everything's looking pretty
Note that many companies currently do not have updates.
Firmware, init strings, and drivers
Many disconnect problems can be solved by loading a more recent version of
the firmware. Contact your modem manufacturer.
Likewise, having the correct modem init string or driver installed is
Too many devices on the phone line
It's possible to have too many devices on your phone lines or extension.
Try unplugging extra phones, fax machines, and answering machines to see if
the disconnects stop.
Lowering connect speed with K56flex
Some k56Flex owners have found that they can reduce disconnects by setting
a limit on the initial connect speed. The commands for controlling maximum
connect speed are different for Rockwell-based and Lucent-based K56flex
On Rockwell-based K56flex modems
If you normally get disconnected when you connect at 48000, you might try
If that didn't work, you would try:
and so on, reducing the maximum connect speed by 2000 each time.
Experiment with different numbers to see if lower numbers result in fewer
On Lucent-based K56flex modems
The S38 command can be used to control the maximum connect speed. The
values between 2 and 14 set the maximum speed between 32K and 56K. So, if
you normally get disconnected when you connect at 48000, you would try:
to set the maximum connect speed to 46000. If you still get disconnected, you
S38=8 (for 44000)
S38=7 (for 42000)
and so on.
External PC modems
Older PCs may have weak UARTs that are not capable of high speed
communications. As a result, you may get frequent dropped connections
and/or poor modem performance due to resent packets.
To test this, try lowering your connect speed to 38400 or even 19200. If
the dropped connections cease, a slow UART may be the problem. A replacement
serial port card should fix the problem.
For use with a 56K modem, you want at least 16550 UART. Internal 56K
modems should include a 16550 or higher UART on the card.
The Macintosh uses an 8-pin serial port, rather than the 9- or 25-pin port
on most other computers. As a result, Mac modem cables handle DTR differently, and
DTR is often used as a disconnect signal.
The classic symptom of unwanted DTR disconnect on the Mac is getting
knocked offline when receiving a large stream of data. This may happen
during a download, or when issuing a dir command in a command-line FTP program.
To disable DTR hangup, add &D0 (zero) to the end of your init string.
For Macintosh technical support questions, call Mad Macs in Pittsfield at (413) 445-5858.