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2012-05-13

A+: Internet connectivity and dial-up modems

One of the best reasons to create a network of any size is to provide access to the Internet. 
Properly used, the term modem (modulator-demodulator) refers only to a device that connects to the telephone line and performs digital-to-analog or analog-to-digital conversions. However, other types of Internet connections such as satellite, wireless, DSL, and cable Internet also use the term modem, although they work with purely digital data; the proper term is codec (coder-decoder). When used by itself here, however, modem refers only to dial-up (telephone) modems.

Dial-Up Modems and Internet Connectivity

Until the late nineties, dial-up networking (DUN) had been the most common way for home and small businesses to connect to the Internet. Dial-up connections are often referred to as analog connections because the device used to make the connection is an analog modem, which connects to the Internet through an ordinary telephone line. Every time you connect to the Internet with a dial-up modem, you are making a network connection.

There have been various standards for analog modems used to make dial-up connections. Before the advent of so-called “56K” standards, the fastest dial-up connection possible was 33.6Kbps. Virtually all modems in recent systems or available for purchase support either the ITU v.90 or v.92 standards.

Although v.90 and v.92 modems are all designed to perform downloading at up to 56Kbps, FCC (Federal Communications Commission) regulations limit actual download speed to 53Kbps. Speeds greater than 33.6Kbps apply only to downloads from ISPs (Internet service providers) and their special modems. If you make a direct connection between two PCs, the fastest speed you can have in either direction is just 33.6Kbps (if both modems can run at least that fast).

Dial-Up Modem Technologies and Types

A modem sending data modulates digital computer data into analog data suitable for transmission over telephone lines to the receiving modem, which demodulates the analog data back into computer form. Modems share two characteristics with serial ports:
• Both use serial communication to send and receive information.
• Both often require adjustment of transmission speed and other options.
In fact, most external modems require a serial port to connect them to the computer; some external modems use the USB port instead.

Modems come in five types: add-on card, external, PC Card, motherboard-integrated, and mini-PCI card. Add-on card modems for desktop computers fit into a PCI expansion slot. External modems plug into a serial or USB port. PCMCIA (PC Card) modems are sometimes built in a combo design that also incorporates a 10/100 Ethernet network adapter. Many desktop computers have integrated modems, as do many notebook computers. However, some notebook computers that appear to have built-in modems actually use modems that use the mini-PCI form factor and can be removed and replaced with another unit.

Add-on card dial-up modems for desktop machines

Although some high-end add-on card and PC Card modems have a hardware UART (universal asynchronous receiver transmitter) or UART-equivalent chip, most recent models use a programmable digital signal processor (DSP) instead. Modems with a DSP perform similarly to UART-based modems, but can easily be reprogrammed with firmware and driver updates as needed. 

Low-cost add-on card and PC Card modems often use HSP (host signal processing) instead of a UART or DSP. HSP modems are sometimes referred to as Winmodems or soft modems because Windows and the computer’s processor perform the modulation, slowing down performance. HSP modems might not work with some older versions of Windows or non-Windows operating systems.

PC Card or PCMCIA dial-up modems


A typical PC Card modem can require a dongle, a proprietary cable that attaches to one end of the PC Card to enable the modem to plug into a standard telephone jack or telephone line. If the dongle is lost or damaged, the modem can’t be used until the dongle is replaced. 

Some PC Card modems use an integrated or pop-out RJ-11 jack instead of a dongle (it’s one less thing to lose or break as you travel). 

External serial port and USB attached dial up modems

External modems, must be connected to a serial or USB port. Serial port versions require an external power source (USB modems are usually powered by the USB port or hub), but the portability and front-panel status lights of either type of external modem make them better for business use in the minds of many users. 

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