Modems 101:

(Modem stands for modulator - demodulator). This discussion is about dialup modems.

There is some confusion as to what the difference is between your connect speed and your throughput rate and what the meaning of "baudrate" is.

The connect speed, which is often displayed by mousing-over the Dialup Networking icon in your Windows System Tray, or as indicated by your ISP's sign-on screen, is only valid at the moment when the connection is established.

Throughput, a variable, is the actual data flow rate, in bits per second at any given moment. It is a fluid measurement that varies depending on instant changes in phone, satellite or cable line conditions, web server loads, the compressibility of the files being uploaded or downloaded and the networking configuration of your operating system and any external modem that feeds the Internet signal to your computer(s).

The term baudrate or baud was used in the past by telegraph companies and by manufacturers of facsimile machines and older dialup fax-data modems, to indicate their maximum data transmission rates. The word "Baud" was named for Jean-Maurice-Emile Baudot, the inventor of the Baudot telegraph code in the late 19th century, and was originally a unit of telegraph signalling speed, set at one Morse code dot per second. What baud really refers to is modulation rate (the MO in MOdem), or the number of times per second that a line changes state. The term baud is sometimes misused to refer to "bits per second" (bps), which is the "data rate". Baudrate coincides with bits per second only for two-level modulation with no framing or stop bits. In modern modem technology one "Baud" may contain many signal bits, using special compression and coding techniques to increase throughput.

Most dialup modems will connect at either 33600 V34, or 56000 V90-92 rates. Older modems, from before 1996, were usually limited to 28800, maximum. These numbers refer to throughput measured in bits per second (bps) and k is a 1000 multiplier; ex: 33.6k = 33600 bits per second, etc. There are 10 bits in each data block sent or received. 2 bits are for control and 8 are for data. Therefore, a baudrate of 40000 represents 5000 data blocks, or bytes per second.

The current field of 56K - V90 - V92 modems are capable of establishing a connection and download rate up to 53000 bits per second (bps). This is due to a limit in the phone equipment, and US and Canadian Federal Communications regulations. ISDN modems are capable of connecting at speeds up to 128000 bps. DSL connections usually range from 384,000, up to about 3 mbps (Megabits per second), varying with your distance from the Central Office or Remote Terminal. Cable modems can reach above 6 mbps, depending on the amount of bandwidth usage in your neighborhood.

With an analog dialup modem, when you sign on to your ISP, your modem will exchange "handshaking" signals with the ISP's modem (the squawks you hear), until it can negotiate the highest possible connect speed for which it is rated. At that point you get signed on, at the indicated connect speed. However, after you settle into your online session you may notice that webpages that should load fairly quickly take a long time to load, or that files take forever to download. In view of what your connection speed reported, you may feel that you are losing a lot of speed somewhere.

During periods of line impairment your modem may downshift in speed, with some modems capable of dropping down to ridiculous speeds in the low thousands, such as 4800 baud. When I was using a dialup ISP my modem was dropping down to that speed, trying to match the line conditions. It took several minutes to load my own webpage, which should take about a half minute, at 40k+ baud. After studying and tweaking the modem settings I was able to connect at 40k and get a relatively steady throughput in the upper 30k's, often hitting at or over 40k baud. I also reduced the number of speed shifts to zero, by limiting the maximum connect speed. My data transfer rate remained fairly steady, allowing pages to load quickly and files to download in realistic, calculatable times.

This is the meaning of the term, "throughput". It refers to your actual transfer of data, either up or down-stream. If your phone line is noisy, or if you have some extension devices connected to the same line, your modem will probably lose throughput, after connecting at an impressive speed. This may be caused by the signals bouncing in the lines, or because of modem-to-modem code chipset mismatches. Chipset mismatches is another complete subject, which we won't get into here. It can have a profound effect on your connection speeds, if your modem and the ISP's modems are fighting each other. Lastly, incorrect settings in the Windows Registry, or in the modem's internal memory, can throttle-down your throughput, making it seem like you have bad lines.

Search Amazon.com for new and used Dialup, DSL, Cable & ISDN modems , or Books about modems & tweaks

Because modern high speed (V90/92) dialup modems have error checking and correction enabled by default, when transmission errors occur the receiving modem will request a re-transmission of the bad data blocks. These are called Block Errors (BLERS), and they cause bottlenecks that slow down your throughput, since your modem must wait for the re-transmission to complete successfully before trying to receive the next data block.

Since bad line conditions impair throughput, you should test the line yourself to see if it is too noisy. Pick up the handset on a telephone near the computer and dial 1. This will stop the dial tone for about 30 seconds. Listen for pops, clicks, or faint voices. If you hear any noise take a (non-electronic) telephone handset (the kind that does not require a power supply adapter) outside to the junction box, and open the Customer Access side of it (if you are able access it). Disconnect the plugin cable for your phone line (takes house wiring out of the equation), and plug the handset into the jack. Try the dial 1 test again. If you don't hear the line noise any more, the problem is in your house wiring. If you still hear it, it's in the phone line. If so, call the phone company and request a service call or line troubleshoot. However, be aware that most phone companies don't guarantee high speed Internet compatibility, but only clear voice transmission quality, which only works out to about 28,000 baud.

If wiring problems beyond your control are causing slow throughput your only recourse may be to reduce the initial connect speed to a level that is compatible with your phone service. This will reduce the bouncing of the signals and re-transmissions required to correct for Block Errors. The "Modem" properties (Win 9x - 2000), or "Phone and Modem" properties (Win XP), inside your Control Panel will have a property sheet where you can input a custom Init string. I have found that by reducing a V90/V92 modem's connect rate, one increment at a time, I am able to find a happy spot, where the throughput reaches its maximum, steady, error-free baudrate. Even though the connect rate may be reduced to under 40000 baud, the lack of Block Error re-transmissions allows everything to download faster. Thus, slower can be faster!

Here is an example of a custom Initiation String I used to use in the modem properties of a UR Robotics V90 Sportster Modem to ensure that X2 is locked out and V90 is locked in, to set a minimum connect speed of 33,333 bps and maximum connect speed of 40,000 bps: S32=34&U21&N26

If you want to learn more about tweaking your modem settings, and the various initialization codes for different brands of modems, I recommend that you read all about the subject, at Modemsite.com.

Windows dialup users can further benefit from another area of adjustment, by means of changing parameters known as MaxMTU, TTL and RWin. These parameters can cause data block fragmentation if they are set too high. There are freeware, shareware and commercial programs that will simplify this process for you, and there is a lot of experimentation required to find the optimum settings. There is a great explanation about tweaking your MTU settings, here. You can also search on Google using the keywords "maxmtu" or "modem tweak."

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