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| Support: Modem | Phone Line Problems | ||
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▪ Phone Line Problems ▪ Modem Problems ▪ Modem Initial Strings ▪ 56k Flex Guide V90 |
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One very
obvious reason for a line drop out if someone in your house picks up another
phone that is on the same extension (like a double-adapter) as the modem.
Informing other family members not to pick up the phone will fix this
problem. Most people will assume that call waiting is not available to their phone number, however Telstra enabled call waiting in all of their Exchanges in early 1997 and is enabled by default when a new phone line is installed by a Telstra technician. Call Waiting Call Waiting will cause your connection to VISP to drop out if someone tries to ring while you are on the Internet. Use these numbers to toggle call waiting on and off. Status Dial OFF: #43# ON: *43# If you received, from Telstra, a Touch Phone 200 when your phone line was installed and you have one connected to the same phone number somewhere else in the house, this could be causing the problem as well. The Telstra Touchphone 200 will draw some electricity from the phone line every ten to twenty minutes to keep the numbers that are programmed into the 'speed-dial' buttons (the Touchphone will even do this if there are no numbers programmed - redial). The amount of current they draw is enough to disrupt your internet connection. Try unplugging all the other phones in the house before you dial in, in order to determine if they are causing your problem. Faxes are a big culprit as well. Most faxes are used to being on their very own phone line for incoming and outgoing calls and will send a current along the line to detect if the line is in tact (some faxes will inform you if there is no line attached). If you are connecting to VISP using your fax line, it is recommended that you remove your fax from the line also. Why do I keep getting disconnected?!?! The definitive guide to helping you solve the reason why you keep getting disconnected. These pages have been created to help making the reason why you're getting disconnected from VISP easier to solve. The VISP Help Desk have decided to rack their brains for every reason they can come up with, and they can all be found here. There are many reasons why you can get disconnected ranging from troubled phone lines to modem serial cables. The VISP Help Desk have seen (and heard) it all. We've included tips and tricks on each of the following 'categories' of disconnection problems: Modem Problems Most modems will keep a record of all of the errors they receive whilst in each session. It's like a scoreboard. 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 the line. 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. VISP has referred a number of clients to this service, 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 or take the issue up with your Internet Service Provider (us!). So be assertive that you would like your phone line's impedance checked. Alternatively, your problem could be a marginal modem, poor phone line or old phone exchange or some incompatibility at the ISP's end in regard to the modems used or a combination. All of VISP's modems use a Rockwell chipsets, so most modems out there should communicate with ours just fine. The VISP Help Desk employ as many troubleshooting techniques as possible to eliminate your modem as the culprit for causing your disconnection's, however there are a few things that you need to try yourself. Using your modem at a friend's house and with another computer to isolate if the problem is your modem is one way, borrowing another brand of modem to use at your home and see if the problems go away is another. If a different modem works fine at your place then you can experiment with the modem's settings or consider selling yours and buying another one. Some modem drivers can tend to cause problems as well, and we have noticed that by changing the driver to the Windows 95 Standard driver, some problems tend to go away. Click here for instructions on how to add a new modem driver and try connecting using that. 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 three years old then this will almost certainly be the case. With older computers 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. Why the phone line drops out The following is an article that was written by George Skarbek, who wrote the article from neither the ISP's, or the communications companies point of view. A subscript of this was published in the "Melbourne Age" - 22/07/97. Most users on the Internet or the BBS have 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 her e are some steps that you can take to try to eliminate the problem. Phone line 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. 'Call Waiting' will drop the line if someone tries to ring while you are on the Internet. You can turn off Call Waiting by dialing #43# before making a call and after you have finished your call dial *43# to turn it back on. Although Windows 95 has the facility to automatically disable it by selecting Control Panel, Modems, Dialing 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. 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. 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. 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, 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 three years 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 speed supported by the communications port. Windows selects a conservative default speed so that slower computers do not lose data during 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 communication s rate as different modems use different commands. This command is hardware specific to your type of modem and you must consult your 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 95 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 modering, 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 S91and 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 ad just 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: -22.1dBm TOO SOFT Error rate: 2 bits/100,000 Excellent Line noise level: -53.6dBm Good Sending speed: 14400 bits/sec V.17 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 HyperTerm or Terminal which come with Windows 95 and Windows 3.1 respectively and are found under Accessories. Spend some time on this BBS in order to determine if the fault still occurs. You 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, or use another modem. The choice will depend on your level of frustration and the amount of money that you wish to spend. 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. |
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