Remote Access Connection Configuration Requirements
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Remote access requires two basic components: a remote computer (typically a laptop) and a remote access system on the network (typically a computer or device running special software called the Remote Access Server). The remote computer connects to the remote access server and then operates just as it would if it were a workstation on the network.
| Note | The most common remote access connection (and, therefore, the one that the Network+ exam tests you on) is a dial-up connection over a regular analog phone line. This section covers only one type of remote access configuration; however, each NOS (network operating system) has many options for remote access to your network. Check your NOS documentation for these options. |
Hardware Requirements
The device most commonly used to connect computers over a public analog phone line is a modem (a contraction of MOdulator/DEModulator). A sending modem converts digital signals from the computer into analog signals that can be transmitted over telephone lines and other analog media. On the receiving end, the modem changes the analog signals back to digital signals. Because telephone lines can be found almost everywhere, this method of remote communication is readily available to everyone with access to a phone line.
Modems change the digital ones and zeros into analog signals that can be transmitted over telephone lines. The pattern of these analog signals encodes the data for transmission to the receiving computer. The receiving modem then takes the analog signals and turns them back into ones and zeros. This method is slower than a completely digital transmission, but data can travel over longer distances with fewer errors.
A modem can be either internal or external. The key difference between the two is the amount of configuration required. You must configure internal modems with an IRQ and an I/O address, as well as a virtual COM port address, to ensure that they function properly. External modems simply hook to a serial port and don’t require nearly as much configuration.
Configuring an Internal Modem
Internal modems are on expansion cards that fit into a computer’s expansion bus. To that end, the modem you install must be designed to work in the type of expansion bus slot in that computer. Configuring an internal modem is much like configuring any other hardware device. You must set the IRQ, I/O address, and virtual COM port so that they don’t conflict with other devices.
The only one of these configuration parameters that you haven’t seen before is the virtual COM port. A virtual COM port is a logical designation given by the operating system for a serial port. A computer can have only two physical serial ports, but it can have as many as four logical ports. Each physical port must be associated with a logical port so that the operating system can use it. The same is true for modems (since they are, in fact, serial devices). You must set a modem to use a COM port that is not being used by any other device.
| Note | You usually configure the IRQ, I/O addresses, and virtual COM port automatically with Plug and Play. Jumpers, DIP switches, or software programs can be used on legacy devices. See Chapter 6, “Network Installation and Upgrades,” for information on configuring expansion cards. |
Each COM port shares an IRQ address with another port. COM 1 and COM 3 share IRQ 4, and COM 2 and COM 4 share IRQ 3. If two devices are set to different COM ports (COM 1 and COM 3, for example) but have the same IRQ, the modem may not function properly. It is usually best to set an internal modem to COM 4, because COM 1 is most likely to be in use, while COM 2 (which shares the IRQ with COM 4) is less likely to be used. Table 7.1 lists the virtual COM ports, their associated IRQs, and default I/O addresses. Note which COM ports share IRQ addresses.
| Port | IRQ | I/O |
|---|---|---|
| COM 1 | 4 | 3F8 |
| COM 2 | 3 | 2F8 |
| COM 3 | 4 | 3E8 |
| COM 4 | 3 | 2E8 |
Configuring an External Modem
Although almost all modems used today are internal, there are some situations when external modems may be more appropriate (such as modem pools). Also, some people prefer external modems because they can see the modem’s status lights. Most internal modems use software status lights, which don’t work if the hardware or software is failing. When using external modems, you have two considerations: available serial ports and the UART type.
Available Serial Ports
With the large number of external serial expansion devices available— including modems, cameras, and printers—a spare serial port is often not available, and so you have to purchase an internal modem. A technology called the Universal Serial Bus (USB) is now available on almost all new computers. The USB allows up to 127 devices (including modems) to be chained off of a single serial port. This technology will eventually eliminate the current need for multiple serial ports on a computer.
UART Type
UART stands for Universal Asynchronous Receiver-Transmitter and is the chip that manages serial communications. Each set of serial ports shares a UART. The type of UART chip determines the maximum port speed that a particular serial port can handle. There are two main types: the 8250 and 16550 series. The primary difference between them is the capacity of the port buffers. Internal modems have built-in, high-speed UART chips, so this isn’t an issue with internal modems.
The 8250 chips have 8-bit buffers that are limited to a maximum speed of 9600bps and are typically found in PCs manufactured before 1986 (before the IBM AT).
Starting with the IBM AT, computers have the faster 16450 and 16550 UARTs. These chips use 16-bit buffers and transmit data at a maximum speed of 115,200bps. Any modem faster than 9600bps that will be connected to a PC for remote access requires the use of 16550 UARTs in the PC to get the maximum possible speed. Otherwise, connection speed will be limited to the fastest output speed of the 8250 UART, 9600bps.
Software Requirements
When configuring a workstation for remote access, you must configure the software to recognize the modem in addition to configuring the hardware. In Windows 95/98, you do so using Device Manager (choose Start Ø Settings Ø Control Panel Ø System to open the System Properties dialog box, and click the Device Manager tab). Additionally, you must configure the software to initiate and maintain the connection. This means configuring the dialer software (the client software that uses a local modem to dial the remote access server) and the network protocols that the communications will use, including TCP/IP (Transmission Control Protocol/Internet Protocol), IPX (Internet Packet eXchange), PPP (Point-to-Point Protocol), and PPTP (Point-to-Point Tunneling Protocol). Even if the hardware is configured properly, the software may not initiate a connection.
| Tip | You can configure remote access from Windows 95/98/NT workstations using the built-in Dial-Up Networking software. |
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