Dial-Up Networking
Remote connectivity has had a huge impact on the world market. Many businesses everywhere use remote connectivity to interconnect sites to a single network. It is also used to connect users to the public Internet and to private corporate networks. The New Connection Wizard in Windows allows you to connect to a wealth of different remote servers or to act as a server, depending on how you answer the questions in the wizard. The New Connection Wizard has replaced the dial-up networking feature in previous versions of Windows such as Windows 9x and ME. The various connections that can be built with the New Connection Wizard in current versions of Windows.
The following list summarizes the options found in the New Connection Wizard that are used to connect to a remote system in one form or another:
- Connect to the Internet This option is used to create a dial-in client that is set up by the wizard asking you questions about your connection to your ISP.
- Connect to the network at my workplace This option is used to create a dial-in client to a RAS server; it also allows you to create a VPN client that connects to a VPN server.
- Set up a home or small office network This option helps you create a small home network by running the Network Setup Wizard.
- Set up an advanced connection This option is used to create a RAS server or a VPN server on Windows 2000 Professional or Windows XP Professional. The RAS and VPN server features that come with these operating systems allow only one concurrent incoming connection.
Modem Configuration Parameters
Modems are data communication devices that are used to pass data through the PSTN from node to node. A modem-the word combines modulator with demodulator -is used to convert a digital signal to an analog format to transmit across the network. It reverses the conversion process on the other end node to receive the data. Typically, the EIA/TIA-232 serial standard is used to connect the modem to a computer.
Modem communication can be of several types: asynchronous, synchronous, or both. In asynchronous communication, all data is sent separately, relying on the node on the other end to translate the bit order. Synchronous communication sends all data in a steady stream and uses a clock signal to interpret the beginning and end of a packet. Most users today employ synchronous communication in the modems that they buy.
Various system parameters must be set up properly to enable a modem to work. These parameters define the system resources for the modem device to use during its operations. Common parameters include serial ports and baud rates. Let's look at these parameters in more detail.
Serial Port
Serial communications send signals across a point-to-point link. Bits are transmitted one after another in a continuous data stream. Serial ports are the typical means for connecting modems to personal computers. They are based on 9-pin (DB-9) and 25-pin (DB-25) connectors commonly known as COM1, COM2, COM3, and COM4. As we mentioned earlier in the tutorial, the computer side of the connection is known as the data terminal equipment (DTE) and the modem is known as the data circuit-terminating equipment (DCE). Various pins are used for different functions inside these connectors. Some are used for transmitting data, others for receiving data, and the remainder for control signals.
You must specify the appropriate serial port settings when you set up a modem. Most modems attempt to use COM1 by default. Each COM port is assigned a specific set of address variables by default when you set up connections. To change the modem COM port after the setup is complete, select Start | Control Panel | Printers And Other Hardware | Phone And Modem Options. Highlight the appropriate modem on the Modem page and click Properties.
Maximum Port Speed
The maximum port speed is defined by the kilobits per second that the modem can support. Maximum rates are defined primarily by the modem hardware; however, the current public telephone network has an upper limit of 56 Kbps through an analog modem. Port speeds are defined by the standards and features available to them.
Note that the terms baud and port speed are not identical. Port speeds define how fast data is traveling; baud measures the signal change per second. With encoding, 2 bits look like 1; therefore, the two terms will not match.
Multiple modem standards exist to define the various features and bandwidths available. Various models provide different standards levels. Before you purchase any modem, you should verify that it fits your current needs and meets the appropriate standard. Table-1 illustrates the standards.
To configure the port speed in Windows XP, select Start | Control Panel | Printers And Other Hardware | Phone And Modem Options. Select your modem from the Modems tab and click Properties. When the properties of the modem appear, click the Modem tab. Select the appropriate port speed from the Maximum Port Speed list.
Unimodem
With Windows operating systems, an additional subsystem is available to simplify dial-up networking. Unimodem provides an easy, centralized mechanism for installing and configuring modems. In installing the modem, the wizard enables you to specify configurations included with Windows or to obtain the configuration from disk. Windows ships with over 600 modem configurations included. The information obtained by this process is then accessible to any other application. Many applications written today that run on Windows specifically request information from this process if a modem is required.
Modem Standards That Define Speeds and FeaturesStandard Feature Se V.22 1200 bps, full duplex V.22bis 2400 bps, full duplex V.32 Asynch/sync, 4800 bps/9600 bps V.32bis Asynch/sync, 14,400 bps V.35 Defines high transfer rates over dedicated circuits V.42 Defines error-checking standards V.42bis Defines modem compression V.34 28,800 bps V.34+ 33,600 bps