Why the phone line drops out

Most users on the Internet or the BBS have from time to time experienced the line dropping out and losing the session. There can be many reasons for the line dropping out with several easy things that can be fixed at your end. However, determining the cause of the fault can be a long and slow process of elimination. If your line drops out only once or twice a year then don't bother to investigate further as it will probably not be possible to reproduce the results. However, if it is a problem then here are some steps that you can take to try to eliminate the problem.

Line drops out on first call but stays connected on subsequent call
A problem that some users have been reporting is the first dialup always drops within a few seconds, however the next calls are stable. Several users have reported success in fixing the problem using the steps below.

The settings in Outlook Express appear to be the culprit, and generally all was well until users added, and then removed free ISPs configurations. Then the problems started!

To fix this problem, first remove the non-existent ISPs from the accounts by clicking on Tools | Accounts, highlight any ISPs not wanted, and then click on Delete.

To be on the safe side it is suggested that you also uncheck the “Always connect to this account using” by clicking on Tools |  Accounts, Mail tab, Properties, Connection and remove the “Always connect to this account using” tick, even from the default account. If you don’t click on Outlook Express to connect then un-checking this box will not make any difference. Without this tick, you will have to click on the dialler to make the connection and then open Outlook Express.

This may not cure all problems where the line drops out immediately and then is stable, but there is a probability that it may fix some.

Phone line fixes
One very obvious reason for a line drop out if someone in your house picks up another phone that is on the same extension as the modem. Informing other family members not to pick up the phone will fix this problem. Other devices sharing the phone line can also cause drop-outs. Fax machines and security systems are two possible culprits. There are a few phones that periodically send out a signal that interferes with the modem. The Touch Phone 200 is one example. Try unplugging all the other phones before you dial in, in order to determine if they are causing your problem.

Electrical interference caused by household appliances, power tools and transmitting devices can upset modem communication and lead to drop-outs.

Another perhaps less obvious cause is if you have dialled either the Internet or the Intranet number and the line drops due to reaching the expiry of your access time. On the Internet there is no warning and you just get disconnected, however use of the timer advice described elsewhere is there to help you avoid this problem. This disconnection has nothing to do with your hardware.

'Call Waiting' will drop the line if someone tries to ring while you are on the Internet. You can turn off Call Waiting by dialling #43# before making a call and after you have finished your call dial *43# to turn it back on. Although Windows 9x has the facility to automatically disable it by selecting Control Panel, Modems, Dialling Properties, this will not work in Australia. It can be done using a scripting language that allows the phone to be hung up before continuing.

Modem reasons
A modem keeps a record of the errors it gets during a session. You lose points when the signal is bad and then slowly gain points as the signal improves. Once you lose too many points the modem decides that there is no point in continuing and it hangs up. Many dropouts are caused by line noise. Telstra can check this and adjust your line impedance to the correct level if this is required. This is a free service and you just have to ring and request this check. Be sure to tell them that you are using a modem on the line. However, in recent months, probably due to cost cutting, there is a reluctance on their part to do this and they will inform you that their service is only guaranteed to 2,400 bps ( not kpbs) and that you should check your modem. Interestingly enough Telstra's Big Pond Internet service mentions 33.6 kbps service.

Alternatively, your problem could be a marginal modem, a poor phone line or old phone exchange or some incompatibility at the ISP's end in regard to the modems used or a combination.

In order to eliminate the modem as being the culprit you can do several things. Try using your modem at another location and with another computer to isolate if the problem is your modem, or borrow another brand of modem to use at your home and see if the problems go away. If another modem works correctly at your place then you can experiment with the modem's settings or consider selling yours and buying another one.

Before starting, if you have a 28.8 kbps or higher modem and use Windows then you must have a suitable UART (Universal Asynchronous Receiver Transmitter) chip driving the COM port in your computer. If your computer is less than about four ears old then this will almost certainly be the case. With older computer you must ensure that the chip is a 16550. The older UARTs have only a one byte (not kb) buffer which is inadequate in a multitasking environment such as Windows.

Other possible modem fixes
Try setting your modem for a lower speed. (Some older exchanges just can't cope with high speed modems.) If you have a 28.8 kbps modem select 14.4 or 20 kbps and then work up if this speed works. Note that this is the line speed which is the speed the modem is using to communicate to another modem and NOT the speed that your computer talks to the modem. The data terminal speed, set from Windows is limited by the CPU speed of the computer and the peed supported by the communications port. Windows selects a conservative default speed so that slower computers do not lose data uring transfers. The data terminal speed should be 57.6 kbps for 28.8 or 33.6 kbps modems. Unfortunately I cannot give the AT codes to set the slower communications rate as different modems use different commands. This command is hardware specific to your type of modem and you must consult your modem manual. Reading the modem's technical manual is no fun and very many manuals do not have the full explanations so you may have to consult your supplier and hope that they have the technical knowledge. If you are using Windows 9x then these extra commands should be entered from Control Panel | Modems | Properties | Connection | Advanced | Extra Settings. Tick Record a log file and view that file after your session to ensure that you have connected at the correct speed. In some cases limiting a 28. 8 kbps modem to never connect faster then 24,000 bps will reduce the bit error rate and prevent drop outs.

Look at setup strings
Determining whether the setup string is correct requires a reasonable level of expertise. AT&F&C1&K3 is a fairly standard initialisation string which works for most modems, but yours may require additional AT commands to actually function properly. You should be using hardware flow control. This is normally set as the default. If you are using Windows 95 select Control Panel | Modems | Diagnostics | Connection |, Advanced.

One not often considered modem command is the %Ex. This is used to select the compromise equaliser that best matches the existing line characteristics. It is usually set to %E=0, by default, which is the automatic selection. If excessive errors appear, try setting %E=3 which is for poor line conditions.

On some modems, having the Data Compression on may lead to loss of carrier. Try disabling modem compression and error correction in your modem initialisation string. Try switching off Data Compression. You can normally do this by adding %C0\N0 to your modem's initialisation string. On some modems this will not work and you will have to consult your modem manual or supplier for the correct string.

Delving deeper
Some modems have their transmit power set too high. The "correct" power levels vary in different countries and even then, the power level should be lower the closer you are to your exchange. The transmit power setting can have more bearing on faxing rather than for modems, but it is worth investigating. In Australia you should use numbers around -15dBm. Surprisingly, the new digital exchanges are less tolerant than the old ones in this respect and if the signal is too loud, they just chop off part of the signal and this can lead to the line dropping out. Many modems use the S91 and S92 registers, some modems use S61. Not all modems can alter this setting. Again you will have to delve deep into the technical reference to find out how to adjust your hardware.

One very good way to find out your transmission level, line noise level and error rate is to use Telstra's Testfax service. For 25 cents, from anywhere in Australia, you can obtain comprehensive diagnostics within one minute. Simply ensure that your fax software has the Fax ID (CSID) set to Telstra standards ie 61 3 1234 5678 then send a single page fax to 1 300 368 999. A return fax will be faxed to you within one minute (make sure that you have automatic receive enabled). An example of part of such a fax is show below.

Transmission Level (dBm)
Did you know that 85% of fax transmission problems are caused by transmission level being set incorrectly? The Transmission level is the calculated signal level arriving at your local exchange. Telstra recommends the fax machine be adjusted for a transmission level of -17.0 to -19.0 dBm as the optimum range.

I believe that the power setting for fax machines and modems differ, and the range for the modem should be in the -15 to -17 range. The less negative the number is, the greater the transmission power.

Further tests
If none of the above suggestions isolate your problem, you may need to test whether the problem is with the ISP end. Dial into a BBS (Bulletin Board Service) if you do not have a second ISP to determine where the problem lies. Use a communications program such as HyperTerminal in Windows 95/98 or Terminal in Windows 3.1  and are found under Accessories. Spend some time on this BBS in order to determine if the fault still occurs. For Melbourne users try the PC User BBS on 9699 6611. Country or interstate members can get a list of BBS numbers from the Internet by using a search engine such as www.hotbot.com and searching two words: BBS and your city. Then select one that interests you from that list. If the problem goes away, then it could be the telephone exchange at the ISP end (assuming the BBS is in another location) or their modems not being fully compatible with yours.

In this case, if you have tried several initialisation strings, your options are limited. You can endure the line drop outs, use another modem or use another ISP. The choice will depend on your level of frustration and the amount of money that you wish to spend. If you do decide to change to another ISP, pick one that offers a number of free hours of use before you pay for a full annual subscription in case you experience the same problems with the new service.

Finally, some modems are poor quality and never work very well in certain conditions. This is not much consolation for someone who bought a real cheap modem (note that many very cheap modems work well) but it can happen.

[This information is heavily based on an article by George Skarbek and we are grateful for his permission to use it.]