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Getting the most out of your 56K modem connection
By Greg Shultz, The Windows Wizard
If you live in an area of the country where neither DSL nor cable modems are available, you're still relying on your trusty 56K modem to connect to the Net. While 56K modems are a lot faster than their 33.6K predecessors, they really don't allow you to connect at 56K. That's because FCC regulations limit the 56K modems to a maximum connection speed of 53 Kbps. Unfortunately, the story gets worse when you add the fact that a speed of 53 Kbps is only possible if there is just one analog phone switch between your modem and the local phone company's office. If your connection goes through more than one analog switch, which is very likely, your modem's connection speed drops. This means that most people using a 56K modem typically get a connection speed of somewhere between 45 Kbps and 50 Kbps. As you can see, there is little that you can do to boost the connection speed between your modem and your ISP beyond what you're already getting.
However, the connection speed between your modem and your ISP only represents one half of the picture. The other half represents the connection speed between your modem and your computer. Most folks don't realize that this can be the source of a big bottleneck. Fortunately, there is something you can do alleviate this bottleneck and boost the connection speed between your modem and your computer. Doing so will ultimately boost your overall connection speed.
In this article, I'll show you how to tweak a few settings that will optimize the connection between your modem and your computer. As I do, I'll pass along some additional Wizardly tips that will help you get the most out of your connection to the Net.
Understanding the COM Port
As you may know, Windows uses the COM port to transfer data back and forth between your computer and your modem. This means that regardless of how fast your modem connects to the outside world, it must transfer information to your computer though the COM port.
If you have an internal modem, the board contains its own COM port that it adds to your computer. Chances are good that an internal modem's COM port is already set to optimal values.
If you have an external modem, the modem is connected via a cable to the COM port built into your computer, which is also known as the serial port. You'll discover that these Windows default settings are less than optimal.
Wizard Note: There are two types of 56K modems on the market today-WinModems and conventional modems. WinModems do not have built-in controllers and just provide the connection and translation to the phone line-your computer's CPU does the real work. The main advantage of leaving out the controller is that it makes WinModems extremely cheap-you can get your hands on a WinModem for $50 or less. The main disadvantage of this scheme is that your modem's performance will suffer when the CPU is busy processing a big operation.
You'll definitely get better performance with a conventional modem because it has its own built-in controller that's specifically designed for handling telecommunications. Of course, you'll pay a bit more for a conventional modem, but in the end, you'll have a much better online experience.
Tweaking the COM Port
You can tweak the COM port settings from within Device Manager, which you can access by right clicking on My Computer and selecting the appropriate tab. Then, scroll through the list and double-click the Ports branch. Now, double-click the communications port to which your external modem is attached. At this point, select the Port Settings tab to access its settings.
As you can see, the default value for the Bits Per Second setting is 9600, which controls the rate at which data can flow through the port. As you can imagine a setting of 9600 is fairly slow and represents a big bottleneck. To crank up the rate at which data can flow through the port, choose a value of 115200. Keep in mind that while you can select higher values than 115200, doing so won't offer any additional benefit, as the highest speed that the chip running the COM port can handle is 115K.
You should leave the default values for the Data Bits, Parity, and Stop bits settings as they are. These values represent standard settings and will work fine for all your communications needs.
Wizard Links: If you have a WinModem or if you have an older modem and decide that you want to upgrade to a conventional 56K modem, you'll want some assistance in selecting the best modem for your money. Fortunately, the folks over at computershopper.com have put together an excellent guide called How To Buy Modems. You'll also want to investigate PC Magazine's modem roundup called The Ultimate Modem. In addition, you should visit Help & How-To's Modems page.
Investigating Flow Control
Towards the bottom of the Port Settings tab is the Flow Control setting. This setting has three values that you can use to determine how data flows from the modem to the COM port. In this type of communication system, the modem keeps sending data to the COM port until the COM port is full and tells the modem to stop. The COM port then processes the data and passes it on to the CPU. At this point, the COM port lets the modem know that it's ready to accept more data and the process starts all over again.
The flow control system is designed to prevent a problem known as data overrun, in which the receiving device is overrun with data faster than it can process it. The default setting Xon/Xoff is a software method of flow control. In this method, two special characters (Xon and Xoff) are used to control the flow of data between the modem and the COM port. The Xoff character, which stands for transmit off, is used to tell the modem to stop transmitting. When the COM port is ready to receive data again, it sends the Xon character, which stands for transmit on.
The next setting is Hardware, which uses a wire in the cable to signal when to start and stop sending data. As you can imagine, hardware flow control is much faster than the Xon/Xoff method because it doesn't have the overhead necessary to manage the software commands.
Keep in mind that not all modems support hardware flow control. Check your modem's manual to find out what type of flow control is recommended. If you do use hardware flow control, make sure you have a good quality modem cable.
Wizard Tip: To boost the performance of your overall telecommunications sessions, you can configure your modem to dial faster. To do so, you will need to add a special command to the modem's initialization string. This command is the ATS11=50 command and sets the length of each touch-tone pulse to 50 milliseconds-the fastest most phone systems can handle.
To do so, open Control Panel, double-click on the Modems icon, select your modem, click on the Properties button. Then, select the Connection tab, click on the Advanced button, and type S11=50 in the Extra Settings text box.
Two things to keep in mind: First, you don't have to type the AT part of the command as it already exists in the modem's initialization string. Second, if you already have commands in the Extra Settings text box, simply separate the new command from the existing commands with a space.
Examining the FIFO Buffers
The next part of the COM port system that you'll want to investigate are the FIFO buffer settings, which are designed to take advantage of the FIFO buffering system built into COM port's UART chip. The UART chip is the brain behind the COM port.
The FIFO buffering system is designed to work with and enhance the basic operations of the flow control system. Basically, the FIFO system allows the UART chip to continue to receive data and store it in a buffer while the CPU is busy. Since data is going both ways through the UART, the FIFO system actually has two buffers. The Receive Buffer stores data coming in from the COM Port and the Transmit Buffer stores data heading out to the COM port.
To investigate the FIFO settings, click the Advanced button at the bottom of the on the Port Settings tab. You'll then see the Advanced Port Settings dialog box.
Normally the default settings are fine. However, you may want to experiment with adjusting the settings if you believe that your system is experiencing data overruns. Examples of such situations are excessive errors during file transfers, poor overall performance, or jerky multitasking during file transfers.
Wizard Tip: Have you ever noticed that downloading files from the Net seems to take forever? Have you ever been disconnected in the middle of a download? If you answered yes to either of these questions, you'll want to investigate a shareware program called Download Accelerator Plus. This program uses multithreading algorithm that allows it to more efficiently download big files. It can also resume an aborted download right where it left off.
Guidelines for Adjusting The Receive And Transmit Buffers
When you do adjust the Receive Buffer and Transmit Buffer settings, you should keep the following guidelines in mind:
The Receive Buffer slider allows you to set the size of the buffer to values of 1, 4, 8, and 14 bytes. The default is 8 bytes, which should be sufficient for most situations. When you increase the value to 14 bytes, of course the buffer can hold more data. However, this can cause an overrun situation and data could get lost. When you decrease the setting, the receive buffer holds less data and will fill up faster. This causes the UART to communicate with the CPU more often, which, in turn, slows down the UART's ability to accept incoming data.
The Transmit Buffer slider allows you to set the size of the buffer to values of 1, 6, 11, and 16 bytes. The default is 16 bytes, which should be optimal for most systems. However, if you're experiencing problems uploading files, decrease the size of the buffer. When you do, the UART communicates with the CPU more often, which slows down the rate at which data is sent to the transmit buffer. On the other hand, when the buffer is set to the default, the UART communicates with the CPU less and the system's performance improves during uploads.
Greg Shultz is a Senior Editor with Element
K Journals. He writes the monthly tips and techniques journals, Inside
Microsoft Windows 98, Inside
Microsoft Windows 95 and Windows
Professional. You can reach Greg at The_Windows_Wizard@hotmail.com.
