Internet Troubleshooting
This section deals with hardware problems that can cause Internet problems. Software problems usually are caused by incorrect configuration of the TCP/IP protocol required by all types of Internet connections. For more information about TCP/IP or other software problems, see Chapter 20.
Diagnosing Problems with a Shared Internet Connection
Although each Internet sharing product has individual configuration issues, the following tips provide general guidelines useful for solving problems with all of them.
Check Your Host Configuration
If your host isn't set up correctly, it can't share its connection with clients. Check the bindings for TCP/IP or other protocols used to create the shared connection. If you are using Microsoft's ICS and two Ethernet cards, you will see entries in the Network configuration on the host computer for each Ethernet card and for the ICS software itself.
Check Your Client Configuration
Make sure your clients have correct TCP/IP, DHCP, and other protocol settings for the host. The ping command can be used to check the Internet connection; try pinging a Web site by opening a Windows command prompt and typing a command, such as ping www.selectsystems.com. If you have a working Internet connection, you should see the IP address for the Web site you specify and the round-trip time (or ping rate) for four signals sent to the Web site. If you get no response or see an error message, you might have a configuration problem with your TCP/IP configuration.
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Because pinging can also be used for denial-of-service (DoS) attacks by hackers on Web sites, some Web sites don't respond to pings. Use ping when your system is working properly to find a Web site that will respond to ping and use that site for troubleshooting as described previously. |
Verify that the host has a working Internet connection that's active before you try to share it. Check the sharing program's documentation to see how guests can dial the host's modem to start a connection if necessary.
Speed Will Drop with Multiple Users
It's normal for the speed of an Internet connection to drop with multiple users, but if you're concerned about the degree of decline, check with the sharing software provider for Registry tweaks and other options to improve performance.
Diagnosing Connection Problems with Signal Lights
Signal lights are found on most external broadband devices, such as cable modems, wireless broadband routers, and DSL modems. The signal lights indicate whether the unit is receiving signals from the computer, sending data to the network, or receiving data from the network and whether the unit can "see" the network—even if no data is currently flowing through the unit.
On many units, the power light also is used to indicate problems. If the light is normally green, for example, a red light might indicate the unit has failed. Other lights flash when data is being sent or received. On cable modem or wireless broadband routers, look for a signal lock light; this light flashes if the unit is trying to lock onto a signal from the cable network or wireless transmitter.
Learn the meaning of the lights on your broadband device to help you diagnose problems; the user manual or vendor's Web site will provide the troubleshooting information you need for the particular broadband device you use.
Analog Modem Fails to Dial
Check line and phone jacks on the modem. Use the line jack to attach the modem to the telephone line. The phone jack takes the same RJ-11 silver cord cable, but it's designed to let you daisy-chain a telephone to your modem, so you need only a single line for modem and telephone use. If you have reversed these cables, you will not get a dial tone. If the cables are attached properly, check the cable for cuts or breaks. The outer jacket used on RJ-11 telephone cables is minimal. If the cable looks bad, replace it. If the modem is external, make sure the RS-232 modem cable is running from the modem to a working serial port on your computer and that it is switched on. Signal lights on the front of the modem can be used to determine whether the modem is on and whether it is responding to dialing commands. If the modem is a PC Card (PCMCIA card), make sure it is fully plugged into the PCMCIA/PC slot. With Windows 9x/Me/2000/XP, you should see a small PCMCIA/PC Card icon on the toolbar. Double-click it to view the cards that are currently connected. If your modem is properly attached, it should be visible. Otherwise, remove it, reinsert it into the PCMCIA/PC Card slot, and see whether the computer detects it.
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Some PC Card modems do not use a standard RJ-11 cable because the card is too thin. Instead, they use a connection called a dongle, which runs from the PC Card to the telephone. If this proprietary cable is damaged, your modem is useless. You should purchase a spare from the modem vendor and carry it with you. And if you find the dongle is too short to reach the data jacks in a hotel room, buy a coupler from your local RadioShack or telephone-parts department and attach a standard RJ-11 cable to your dongle via the coupler. Dongles are also used with some PC Card network cards for the same reason; the RJ-45 twisted-pair cable connector is too wide to attach to a standard PC Card. To avoid using dongles, look for a network or modem card that has a standard RJ-11 or RJ-45 connection built in to it. |
Make sure your modem has been properly configured by your OS. With Windows 9x/Me/2000, use the Modems control panel to view and test your modem configuration (with Windows XP, you can use the Modem Troubleshooter). Select your modem and click the Diagnostics tab. This displays the COM (serial) ports in your computer. Select the COM port used by the modem, and click the More Info tab. This sends test signals to your modem. A properly working modem responds with information about the port and modem. If you get a Couldn't Open Port error message, your modem isn't connected properly. It might be in use already by a program running in the background, or there might be an IRQ or I/O port address conflict with another card in your computer. Whether you have a modem installed, every COM port that is working will display its IRQ, I/O port address, and UART chip type when you run Diagnostics. The UART type should be 16550 or above for use with any modern modem.
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You can also test your modem response by setting up a HyperTerminal session (discussed earlier) to send the modem commands. If the modem fails to respond, this is another indication of a problem with the modem-PC connection. |
Computer Locks Up After Installing or Using Internal Modem, Terminal Adapter, or Network Card
The usual cause of lockups after you install an internal card is an IRQ conflict. Internal analog modems that use ISA slots typically cause the "curse of the shared IRQ," especially if a serial mouse is also used. PC Card and PCI modems can share IRQs safely, and USB mice use the same IRQ as the USB port itself. For more information about shared IRQs with ISA modems and serial mice, see the Technical Reference section on the DVD packaged with this book.
Computer Can't Detect External Modem
Make sure the modem has been connected to the computer with the correct type of cable. For external modems that use an RS-232 serial port, you might need a separate RS-232 modem cable, which has a 9-pin connector on one end (to connect to the computer) and a 25-pin connector on the other end (to connect to the modem). Some external modems have an integrated modem cable. Because RS-232 is a very flexible standard encompassing many pinouts, be sure the cable is constructed according to the following diagram: |
3 | TX data | 2 | 2 | RX data | 3 | 7 | RTS | 4 | 8 | CTS | 5 | 6 | DSR | 6 | 5 | SIG GND | 7 | 1 | CXR | 8 | 4 | DTR | 20 | 9 | RI | 22 |
If you purchase an RS-232 modem cable prebuilt at a store, you'll have a cable that works with your PC and your modem. However, you can use the preceding chart to build your own cable or, by using a cable tester, determine whether an existing RS-232 cable in your office is actually made for modems or some other device. Make sure the COM (serial) port or USB port to which the modem is connected to is working. The Windows 9x/Me/2000/XP diagnostics test listed earlier can be useful in testing the serial port, but third-party testing programs such as AMIDIAG have more thorough methods for testing the system's COM ports. These programs can use loopback plugs to test the serial ports. The loopback plug loops signals that would be sent to the modem or other serial device back to the serial port. These programs normally work best when run from the MS-DOS prompt. Some diagnostics include a loopback plug to test serial ports. Loopback plugs may vary in design depending on the vendor. To ensure that the USB port is working, check the Device Manager in Windows; a working USB port is listed as a USB Root hub and a PCI to USB Universal Host Controller in the Universal Serial Bus device category. Any external USB hubs also are listed in the same category. If this category is not listed and the ports are physically present on the computer, make sure you are using Windows 98/Me/2000/XP (only a few late versions of Windows 95 have USB support). If you are, be sure the USB ports are enabled in the system BIOS. Check the power cord and power switch.
Using Your Modem Sound to Diagnose Your Modem
If you listen to your modem when it makes a connection, you might have realized that different types of modems make distinctive connection sounds and that different connection speeds also make distinctive sounds.
The various types of 56Kbps modems have distinctly different handshakes of tones, buzzes, and warbles as they negotiate speeds with the ISP's modem. Learning what your modem sounds like when it makes a 56Kbps connection and when it settles for a V.34-speed connection can help you determine when you should hang up and try to connect at a faster speed.
The Modemsite's troubleshooting section has a number of sound samples of various modems during the handshaking process. Use RealPlayer to play the samples, available at www.modemsite.com/56k/trouble.asp (click the Handshakes link).
Compare these sound samples to your own modem; be sure you adjust the speaker volume for your modem so you can hear it during the call.
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