This document is declared to be in the public domain and may be freely distributed.
Credit to the Author and to Tulsa Computer Society is requested on republishing.
When the first version of Golden Rules of Modems appeared in 1994, the changeover from 2,400 bps to 14,400 bps was in full swing. The official protocol for 28,800 bps had not been released, though there were several speculative designs on the market from different manufacturers who tried to anticipate the V.34 specifications.
Since that first edition, the protocol for 28,800 has been released as V.34, and all major manufacturers are now producing that type of modem. The second guesses as to what V.34 would be like have about disappeared, and few if any of them were fully compatible with the true V.34 Protocol.
I have acquired a new 28,800 bps modem and have had the opportunity to install and test it and several others. To date I have mixed emotions about their performance. Theoretically they should be able to send and receive twice as fast as a 14,400 bps modem. Since a well tuned 14,400 can transmit at above 1,600 characters per second, you might reasonably expect a 28,800 to send at about 3,000 characters per second or better. In actual operation they will not consistently achieve that speed. There are at least two possible explanations. The biggest factor is telephone line quality and the other is computer speed limitations on one or the other end of the line.
My recommendation however, is that if you plan to spend a great deal of time on the Internet or any other paid service using a graphical interface you will need all the speed you can get, so you would be well advised to get 28,800 bps.
On the subject of modem programs, I have several recommendations. For a brand new user, or even for an experienced user having setup problems with a new modem, I strongly recommend Banana Com, a very clever shareware program which installs itself and finds and sets up the modem and all its parameters. It is available on many popular BBS's around the country. The latest version currently released is V1.5. It is by far the easiest modem program to install and operate that I have ever seen. I wish to thank Linda Hargraves of Access America BBS for finding this little jewel and bringing it to my attention.
If you advance to the point where you want more bells and whistles in a DOS modem program, I would recommend QModem Test Drive V4.6 as a shareware starter. It has a script programming language, and many upload and download protocols, plus many other features. If you use Windows 3.1 or 3.11 and would like a strong modem program to work in those environments, I suggest Procomm Plus for Windows V2.11. It has been my mainstay until I moved to Windows 95. Qmodem Pro for Win 95 was released long before Procomm plus for Win 95 so I acquired Qmodem Pro 95, which I am using currently with excellent results and no plans to change. It is a true 32 bit multi-threaded multi-tasking communications program, and will upload or download in the background while you do other things in the foreground.
Regardless of which one you choose good luck with your modem.
Constraints:
1. A computer will not tolerate two of any COM port, such as two COM1 ports.
2. Two active devices may not share the same interrupt request (IRQ). Unfortunately COM1 and COM3 are both normally on IRQ 4, while COM2 and COM4 are on IRQ 3.
3. Serial Ports (also called Com Ports) should be configured sequentially. Com 1, 2, and 3, NOT Com 1, 2, and 4. Non sequential ports (Com 1, 2, & 4) will not work reliably under Windows or OS/2, however they will work sometimes under DOS. This configuration is not recommended, but depending on your situation it may or may not work.
2. Caution - before removing or installing any cards or other components in your computer, turn off power to the computer!
3. Study your modem handbook and see if your modem will allow configuration as com3 IRQ5. If it will, study your terminal program (modem program) documentation and see if it will allow configuration as com3 IRQ5. If both are OK, change switches or jumpers on your modem to com3 IRQ5 and install the modem. Again run MSD and see if you have three com ports. If so, proceed to step 7. If not recheck your jumper settings.
4. If either the modem or terminal program will not accept configuration as com3 IRQ5, remove your I/O card, study the I/O card booklet and disable com2. This means move jumpers on the card. Simply unplugging the flat ribbon cable will not disable the com2 port.
5. Reinstall the I/O card and again run MSD.EXE. You should now have only one com port. If you have more than one you did not correctly disable com2 and you must try again until MSD tells you that there is only one com port.
6. Configure your modem as com2, IRQ3 and install it. Run MSD and see if you have two com ports again. If you do proceed to step 7, if not remove your modem and double check the jumper configuration.
7. Start your modem program and set it up to match your configuration from the previous steps, then type "AT" and press Enter. Your modem should respond "OK". If it does, use and enjoy your modem. If it does not respond properly, recheck the steps above.
One of the above will work in almost every case. The configuring or setup process referred to is accomplished by moving little jumpers around on jumper block pins on either the modem or on the I/O card. It is not difficult but requires careful study of your modem booklet and/or your I/O card booklet.
2. 16450 UART chips on your IO card can only handle 19,200 bps modem communications.
3. 16550 UART chips can handle up to 115,200 bps depending on computer and modem. Most modern internal high speed modems come with a 16550 UART.
4. When in your communications program in terminal mode, you must be able to type "AT" and get a response "OK" from your modem - every time! This should occur even without a telephone line connected to your modem.
5. Modems are like computers in some respects. When they are turned off they lose the active configuration, and when turned back on they must restore an operating configuration into active ram. ATZ as an initialization string will restore whatever you have saved in NVRAM.
6. File transfer problems are often caused by a software or setup problem. If your modem dials and connects but will not transfer files, check your communications program setup.
7. If you are running a Windows communications program, it is important to have your ports set at the proper speed in that program AND in the Windows control panel under ports.
| V.32 | Full duplex CCITT (International Consultative Committee for Telephone and Telegraph, recently replaced by ITU) modulation standard for 9,600 bps. |
| V.32bis | An upgrade to 14,400 bps (became available in early 1991). (Bis is second.) |
| V.34 | Full duplex ITU (Replaced CCITT) modulation standard for 28,800 bps released in 1995 |
| V.42 | CCITT error correction and 2:1 data compression standard for 9600 bps. 2:1 at 9,600 bps equals 19,200 bps (only on uncompressed data!) V.42 can also strip the start and stop bits and get an additional effective 20 % increase in speed. |
| V.42bis | The same with a 4:1 data compression which equals 38,400 bps at a nominal 9,600 bps (again only on uncompressed data). |
| CCITT | International Telephone and Telegraph Consultative Committee (Recently replaced by ITU.) |
| BPS | Bits Per Second |
| LAPM | Link Access Procedure for Modems. An error control protocol incorporated in V.42. |
| ARQ | Automatic Repeat Request. A general term for error control protocols which feature automatic retransmission of defective blocks of data. |
| DCE | Data Communications Equipment. Technical term for a modem. |
| DTE | Data Terminal Equipment. Technical term for your computer when used in communications |
| HST | (High Speed Technology) is US Robotics' proprietary system for 9,600 bps, developed in 1984, improved to 14,400 bps in 1989 and further advanced to 16,800 in 1992. It could only talk to other USR HST modems at this speed. Non-USR modems with V.32/V.42 could talk to each other at 14,400 bps but not to HST. US Robotics HST Dual Standard which incorporated V.42 bis, V.32, (V.32 bis was included after early 1991.) could talk to both at any speed available at the time. |
| MNP | (Microcom Networking Protocol) levels 1-4 are methods of error correction in which two connected modems verify the integrity of the data transmitted. |
| MNP5 | (Microcom Networking Protocol) Data compression. Since most BBS's have their files compressed in ZIP or some other format, MNP5 can actually slow down the process by attempting to compress the file further. Therefore BBS's leave MNP5 turned off, and so should the BBS callers. |
| CPS | Characters Per Second |
| UART | Universal Asychronous Receiver Transmitter |
| 2400 | 14400 | 28800 | |
| Max CPS Raw data rate | 240/235 | 1440/1400 | 2880/2800 |
| Max CPS with V.42 stripping stop and start bits. | 300/270 | 1800/1700 | 3600/3400 |
| Parameter Name | 2400 Setting | 14.4/28.8k Setting | Comment |
| CTS/RTS | off | on | Hardware Flow Control |
| Xoff/Xon | on | off | Software Flow Control |
| Auto Baud | on | off | |
| Locked Baud | off | on | |
| DTE to DCE Rate | Same (2,400) | Higher | (19,200/38,400 or more) |