KB 48

What can we do about 'dropped' or 'frozen' modem connections?

Article:48
Created:1999-09-01 16:39:54
Categories:
  General Concepts
  Modems

Question or Symptom

What can we do about 'dropped' or 'frozen' modem connections? SWCP is always disconnecting me. What gives?

Resolution

'Dropped' or 'frozen' modem connections are often a result of one or more factors -- SWCP never intentionally drops it's modem connections, except when they are idle. (see item #1) Here are the most common factors dropped modem connections. One or more of these conditions can cause a dropped or frozen modem connection.

Keep in mind that modems are powerful analog to digital converters, and some modems are great, and some are simply junk. However, with proper configuration, almost any modem can be turned into an adequate performer.

pseudo-problem [1] - Idle Timeout

Idle timeout. SWCP drops connections after 15 minutes of idle time. This timer is reset by ANY network traffic whatsoever. This is for your own protection: you don't want to receive the extra bills for leaving your computer online accidentally overnight, or while away vacationing for 2 weeks. If the idle timer is problem in your situation, there are ways we can arrange to work around this. Usually it's NOT the idle timer which causes true disconnections which actually occur during downloading or other Internet activity.

pseudo-problem [2] - Call Waiting

US West call-waiting. If the phone line your modem has call waiting (clicks when another call comes in), then you must put a "*70," in your dialer configuration. This will disable call waiting for Internet calls, and prevent the clicking noise from causing your modem to drop carrier.

real-problem [1] - Modem Init String

Modem initialization problem. The dialer's modem initialization string tells the modem to do critical things like error correction and flow control. If your PPP dialer says 'standard modem' or 'generic <speed> modem' then it's very likely your dialer is not using an initialization string, or is guessing an inappropriate one. In Windows and MacOS, the fix is as simple as installing the drivers for your modem off CD or floppy that came with the modem, and then making sure that your dialer identifies the modem by brand and name, for instance 'Supra Sonic 56K'. If you don't have a drivers disk for your modem, see if your modem is listed as a known modem type in the modem setup control panel (varies for each operating system). If it's not listed exactly by brand and model, then look in your modem's printed manual for an appropriate 'factory default' initialization string, and enter it into your dialer's extra settings. Here is an example of an initialization string which works for some Rockwell-based modems: AT&F1&D2&K3 . Often modem manuals are available for download from the manufacturers web site. (see URLs below)

real-problem [2] - Line Noise

Severe line noise. POTs (plain old telephone) lines are analog. This means there is always some degree of noise. Environmental sources can put interference on the line: brown outs, lightning strikes, surges, moisture, solar flares, overloaded circuits, crosstalk, etc. can all influence your phone line and thus your modem's ability to maintain a connection. A general rule of thumb is if you can hear the noise, it's definitely a problem for the modem, in fact, modems are much more sensitive to noise than the human ear. Things you can do: if it's audible to you, call the phone company for repair. Otherwise, try removing all other devices from your line including phone handsets, caller ID boxes, answering machines, etc. One device that is out of spec. can disrupt the modem. Lowering the port speed of your dialer down to 19200 might help as well. Finally, sometimes it just pays to wait until the wind or lightning or rain storm is over.

real-problem [3] - Hotel, Office and PBX phones

PBX or office style phone systems. Larger businesses, including hotels, often have these types of phones, the hallmark which is an analog phone jack on the back of a digital console phone. It may just appear as a regular wall jack. This is an analog port which often is limited to 9600 baud or less. Newer systems might offer a maximum of 26.4 or 28.8Kbps. The solution is to lower the port speed of your dialer down to 19200, or demand a POTs, a real phone line, not a multiplexed one, be installed in your office.

real-problem [4] - Out of Date Firmware

Protocol mismatch. Modems communicate using well established protocols for rate, error correction, compression, etc. These v.34, v.34+, X2, K56Flex, V.90, LAPM, V.43bis, and so on. If you have a "56K" modem , this is especially relevant, as there are a lot of protocol mismatches with "56K" modems. It's in your best interest to check the modem manufacturer's web page for updated firmware. Usually this is a flash executable which you can download and will bring your modem up to spec. Even if your computer and modem is "brand new", it doesn't matter-- it still could have shipped with an older firmware revision than is currently available. This is less of an issue for older 14.4 and 28.8 modems.

Recap of above

1) Are you hitting the 15 minute idle timer, or is it really dropping the connection in the middle of a download?

2) Do you have call waiting? If so, disable it with "*70," in your dialer.

3) Does your dialer identify your modem by exact brand/model? If not, select the correct one or enter an appropriate initialization string.

4) Do you have line noise? Try removing all devices from your phone line except for the modem.

5) Are you dialing through a hotel or PBX/office style phone system? This is a severely limiting factor.

6) Have you checked your modem manufacturer's website for updated firmware?

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The SWCP technical support staff would be happy to assist you in determining which of these factors is causing your modem disconnects. They can also assist in selecting modem initialization strings and finding updated modem firmware.

Related URLS

 http://808hi.com/56k/
 http://www.56k.com/