What to look for when you cannot connect to a specific modem
Last Updated September 19, 2014
You are making connections over a modem. You are able to connect to all the computers you need to connect to, except one.
There is a long list of things that can cause modems to fail to connect properly with each other. The list includes the following:
Another application or device answering the call
Data rate (maximum speed) set too high on one (or both) modems
Intermediary devices such as phone centers, fax machines, answering machines, surge suppressers, line splitters, com-sharing devices
Non-dedicated or "roll-over" phone lines
Telephone line noise or signal degradation
Incorrect drivers or setup
Interrupt or port addressing conflicts
Another application or device answering the call If you see a black screen with question marks, another application or device, such as a fax application or machine is answering the call. Make sure that pcAnywhere is the only application set to answer calls on the line.
Data Rate This is always the first thing to adjust. Most modern modems are rated to transfer 115,200 bits per second (BPS). In reality, none do and the reasons why are complex. Nonetheless, 115,200 is almost always the default setting for a modem. This setting can result in lost or repeatedly resent data if the receiving computer cannot process the incoming information as quickly as the modem accepts it. Decrease the host's and remote's data rate to 38,400 or lower to help stabilize the connection.
Intermediary Devices If the remote or host modem lines are split, shared, or pass through another device such as a phone center, fax machine, answering machine, surge suppresser, the line signal and voltage may drop enough to prevent pcAnywhere from using it correctly. Using a dedicated line to ensure the best signal quality will resolve this.
Non-dedicated ("roll-over") phone lines If the remote or host modem lines are used with a roll-over system or an internal phone answering system, you may experience problems making a connection. Symantec recommends using a dedicated phone line for the modem.
Line Noise or Degradation Phone lines are "noisy", meaning that external factors create static on the line (this static is not always audible to the human ear). When two modems first connect, you may hear squealing and squawking. This is the modems determining how fast they can reliably communicate over the phone line conditions at that moment. The modems will constantly renegotiate this speed for the duration of the connection even though you won't hear any more squealing. If the lines are too noisy, the modems cannot connect. If the lines suddenly get too noisy, the modems may drop the connection.
While you do not have any control over the phone lines once they leave you home or office, you do have some control over the lines inside. Long lines from the telephone jack in the wall to the modem can pick up lots of noise. The longer the line, the noisier it is likely to be. Replacing a long phone line with a shorter one may allow pcAnywhere to connect. Old telephone lines are subject to the same problems as long ones, so replacing old telephone lines with new ones may also resolve the problem.
Incorrect Drivers or Setup The majority of modern modems are software modems (WinModems, PCI modems) that depend on the software (drivers) written for them to function correctly.. Many initial modem driver releases have problems. As users and developers find problems, new versions of the drivers are released until there is a version that functions correctly. For this reason, always look for the most current version of the drivers for your particular modem. These drivers are usually available for downloading from the web pages of the modem manufacturer. Having the latest driver is particularly important with pcAnywhere because pcAnywhere requires precise and specific functionality from a modem.
Incorrect modem setup will cause similar symptoms as an incorrect driver. When you install a modem to Windows, Windows attempts to match the modem it finds to an existing setup (.inf) file. If it does not find a suitable match, it uses a generic (standard) setup like "Standard modem" or "Standard 56k modem." This is perfectly fine for some modems but not for others. If your modem is a software modem, downloading the current drivers and reinstalling the modem can resolve this problem. However, if you are using an external or an internal hardware modem, you will need to search the manufacturer's web page for an installation file or a downloadable .inf file.
For both drivers and setup files, also be aware that the set that works for Windows 9x may not necessarily work for Windows NT or Windows 2000 - or the other way around.
Cable Problems If either the remote or host modem is external, ensure that the modem cable does not have an adapter attached to it. pcAnywhere requires hardware flow control and adapters are not always configured for this.
Use a cable that does not have a "Y" splitter on it. This kind of cable may function correctly most of the time, but it is something to eliminate if you are having connection problems.
If you have an unusually long modem cable, this can be the source of the problem. Signals over serial cables (such as modem cables) degrade over distance - the maximum length being around 100 ft. before the signal needs to be boosted electronically. Realistically, if your cable is longer than 15 ft., it may be the reason you cannot connect. Try a shorter cable - one that is no longer than eight or nine feet.
Interrupt or Port Addressing Conflicts Although less of a problem than it once was, if your modem shares an interrupt (IRQ) or address with another device, this can cause connections problems with pcAnywhere. Read the document Resolving IRQ/COM port conflicts for details on how to detect and correct this problem.
Modem Incompatibility If all else fails, it may simply be that the remote and host modems are incompatible with each other. This is easy to test. Simply use a different brand modem on the remote or host. If the connection works with the new modem, most likely the original modem was the problem. If so, it may be necessary to permanently switch modems.