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56K Modem Troubleshooting Guide

Initial Connect Speed Issues

Help! My 56K modem connects at 33.6 or less!

Even if I don't connect at 56K, I'm guaranteed 33.6, right?

I'm connecting at 38400, 57600, or 115200. Or am I?

How can I get my modem to report the true connect speed?

What are typical connect speeds for 56K modems?

Is initial connect speed all it's cracked up to be?

What's the command for connection speed and stats on my K56flex?

What's the command for connection speed and stats on my USR?

What's a good way to test actual modem performance? (FTP)

Help! My 56K modem connects at 33.6 or less!

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.


We hate to ask, but you did check the obvious things, right?

  • Make sure that you and your Internet service provider use the same 56K protocols. 56K requires that both ends have 56K modems, and they both have to use the same kind of 56K technology (x2, K56flex, or V.90). Despite what you may have heard, V.90 is not the same as x2 or K56flex. It is a third and distinct 56K protocol. Your ISP will be able to tell you which protocol they use.
  • Some Internet service providers have separate phone numbers for 56K. Make sure you're calling the right number.


Things that are easy to try even if you don't know much about computers. Don't skip this section, because these fixes often work.

  • If there is a telephone, answering machine, etc., plugged into the back of the modem, unplug it from the back of the modem. The modem is supposed to ignore devices plugged into it when it is online, but that is not always the case.
  • Try disconnecting additional telephony devices (fax, phones, answering machines, alarm systems, etc.) from the phone line, even if they're in a different room. I've heard from readers whose connect speed jumped 10K when they unplugged a fax machine or cordless phone in another room.
  • Also try running the phone line directly from the back of the modem to the wall, without passing through surge suppressors, splitters, phone line extenders, etc. This is a basic and useful step in modem troubleshooting.


These require slightly more computer skill. If you don't know how to use a terminal program, click on the links for help.

  • DO NOT SKIP THIS NEXT STEP. It's always a good idea to check the firmware page to see if there is a more recent firmware version available. Many people's problems have disappeared once they installed a new version of the firmware.
  • Visit the inits and drivers page to see if there is an init string or better yet a driver for your modem. If there is, download and install it. The inits and drivers page includes installation instructions.
  • If your modem supports more than one 56K protocol, you may want to tell it which protocol (V.90, x2, or K56flex) it should use. The commands are listed on the interoperability page.
  • It's possible there is an incompatibility between your modem and your ISP's modems. You might try dialing into some other local ISPs. You don't have to join or do anything after you connect: just see how fast you can connect to their modems.
  • If this is a Rockwell-based K56flex modem, issue an ATI3 command in a terminal program. If the version number includes the letters "DSP", click here. If the version is 0.5 something, and your Internet service provider uses K56flex Livingston Portmasters, click here. If the version is 1.0 something, you should try adding S202=32 to your init string.
  • If this is a Lucent-based K56flex modem, issue an ATI3 command in a terminal program. The firmware version should be at least 4.06, and higher versions are better. Click here for more information.


I was hoping it wouldn't come to this, but it may not be your modem or inside phone lines at all.

It may be that the phone lines in your immediate neighborhood don't support 56K

As explained in the Basics section of the 56K Primer, multiple digital/analog conversions will prevent the use of 56K technology and limit your modem to V.34 speeds (a maximum of 33.6K).

"It's not my phone lines. I know they support 56K"

OK, how do you know your phone lines support 56K? 3Com's line test is not guaranteed. It can tell you that your phone line supports 56K when in fact it doesn't, and vice versa. Don't put all of your faith in it. If you must use the test line, 3Com recommends calling it multiple times (ten times, say). On some calls it may say your line supports 56K and on other calls it may say the opposite.

The fact that your modem can connect at 56K speeds to a long distance number is no guarantee that the same is true of local numbers, and vice versa. Long distance calls may be routed through telephone circuits which are significantly better or significantly worse than the local circuits used to connect to your ISP.

How to find out for sure if your phone lines support 56K

This is the only reliable way I know of to test your phone lines: borrow a known good 56K modem and try it with your phone lines. By "known good 56K modem," I mean a modem that has connected at speeds higher than 33.6. Remember that connects speeds of 38400, 57600, and 115200 aren't true connect speeds, so they don't count.

If it's an internal modem, have your friend bring the whole computer to your house. In fact, it's easier that way, because his computer will already be configured for his modem. Let him use your monitor, keyboard, and mouse so he won't have to cart them over to your house.

If you can only borrow the modem, be sure to get the disks that came with the modem so you can install the drivers for that modem. You'll have to install the modem and drivers. Be sure to select the modem in your dialing software (such as Windows 95 Dial-Up Networking or Apple's PPP for Open Transport). Instructions are on the Inits and Drivers page.

Once his modem is at your house, call his ISP. How fast is the connection? You can also try calling your ISP, if your ISP and your friend's modem use the same 56K protocol (x2, K56flex, or V.90).

More about multiple digital/analog conversions, and what to do about them

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 its 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 try that.

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 re-route the lines.

Even if I don't connect at 56K, I'm guaranteed 33.6, right?

No. In fact, even if you and your ISP were using 33.6 modems, you still wouldn't be guaranteed 33.6 connects. Few people get 33.6 connects. A large number get 28800 or 31200 connects, but many people only connect at 26400, 24000, or even slower. The phone lines in some areas simply can't support higher speeds.

If you'd like to try improving the speed, make sure you have the latest firmware and drivers/settings files. Also, try passing the phone line directly from the back of the modem to the phone outlet on the wall. Passing the phone line through surge protectors, phones, answering machines, etc., has sometimes been responsible for slow connects.

Again, though, your phone lines may simply not support higher speeds.

I'm connecting at 38400, 57600, or 115200. 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->  Remote
Computer                 Modem                 Modem

How can I get my modem to report the true connect speed?

For Windows 95 Dial-Up Networking and Apple's PPP for Open Transport

You must install the correct drivers for your modem. 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. The drivers interpret the result code from the connection and translate it into a connect speed. Without the driver, you won't get an accurate connect speed. These may have been included on a disk with the modem. If not, check the 56K.COM Inits and Drivers page, which has links to downloadable drivers and instructions for installing the drivers.

If you have the correct driver/settings file and you still don't get the true connect speed, add one of the init strings below to your init string.

For other programs that do not use driver files

According to 3Com/U.S. Robotics, any init string that includes AT&F1 should report the true connect speed.

For most Rockwell-based 28.8 and K56flex units, the command is W2. (For Rockwell-based PCI modems, the command is MR=2.) However, several commands can override W2, including the S95 commands and the &Q commands. If W2 doesn't have the desired effect, you might try adding S95=0 or S95=1 to the init string.


What are typical connect speeds for 56K modems?

As with 33.6 modems, your results will depend heavily on your phone lines. To see what kind of performance other people are getting, see the performance survey. Typically, 42-46K for K56flex and anywhere from 44-52K for x2 is good performance. 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.

Rockwell-based K56flex modems

After disconnecting, issue an AT&V1 command in your terminal program. These are some example results. TX is the transmit (upload) speed. RX is the receive (download) speed.


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 the command for connection speed and stats on my USR?

After disconnecting, issue an ATI6 and ATI11 in your terminal program. These are some example results. Note that the ATI6 Speed line shows the highest download/upload connect speeds. The ATI11 command shows the number of upshifts and downshifts for receive (RX) and send (TX).


Chars sent                  580      Chars Received            49642
Chars lost                    0
Octets sent                 360      Octets Received           26533
Blocks sent                 191      Blocks Received             805
Blocks resent                 0
Retrains Requested            0      Retrains Granted              0
Line Reversals                0      Blers                         1
Link Timeouts                 0      Link Naks                     0
Data Compression       V42BIS 2048/32
Equalization           Long
Fallback               Enabled
Protocol               LAPM SREJ 128/15
Speed                  46666/31200
Last Call              00:04:34
Disconnect Reason is Escape code


USRobotics Courier V.Everything Link Diagnostics...
Modulation               x2/V.34+
Carrier Freq    ( Hz )   NONE/1920
Symbol Rate              8000/3200
Trellis Code             NONE/64S-4D
Nonlinear Encoding       NONE/ON
Precoding                NONE/OFF
Shaping                  OFF/ON
Preemphasis Index        NONE/0
Recv/Xmit Level (-dBm)   15.7/12.2
SNR             ( dB )   61.5
Near Echo Loss  ( dB )   10.2
Far Echo Loss   ( dB )
Roundtrip Delay (msec)   26
Timing Offset   ( ppm)   -1406
Carrier Offset  ( ppm)   68
RX Upshifts              0
RX Downshifts            1
TX Speedshifts           0
x2 Status                0000; 0000-0000-0001-0000-0000-0000; 00,00 0031;03

What's a good way to test actual modem performance? (FTP downloads)

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 download testing:

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). (V.42 error correction strips out the start bit and stop bit, but adds other overhead, so multiplying by nine may be more accurate.) A valid alternative to FTP is a terminal program that supports Zmodem.

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.

A file size of at least 200K will minimize the effects of TCP/IP slow start.

A local server is one that's on your system, not on the other side of the Internet. If you download a file from across the Internet, you're testing your ISP's connectivity to the Internet just as much as you're testing your modem.

Most ISPs have FTP sites at ftp.ispname.com. If you're on AOL, for instance, go to ftp.aol.com to download files. There will usually be a directory called pub that contains downloadable files.

To eliminate congestion issues, download early in the morning or late at night. 


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