The term Modem stands for MOdulator/DEModulator. A modem is a device used to access the Internet. It allows communication between computers over a telephone line, by converting (modulating) electronic signals (a binary form) into audio tones (sound) when passing through a telephone line, and vice versa (demodulation).




To be able to communicate with one another, modems should comply with standard communication protocols such as CCITT, an acronym for the Consultative Committee for International Telephone and Telegraph (an official standard, now known as ITU). The standards define the format of the message and the speed of its transmission. Some modems, which communicate at slow transmission speed have built-in support for common protocols.




Types of modem

A modem can be either internal or external. When internal or onboard, it is in the form of a circuit board with telephone jacks at the back, which will be inserted into a vacant internal slot (PCI or ISA) in the computer. Usually less expensive, an internal modem receives power via the computer’s power supply.

An external modem, on the other hand, is a separate device plugged into a vacant serial port at the back of the computer. It has its own power supply and indicator lights, which show the status of the connection. External modems are more expensive than onboards.



Modem characteristics

Modems have the following distinguishable characteristics aside from the different transmission protocols they support:

Bits-per-second: Bits-per-second (bps) is the unit of measurement used to describe the transmission speed of a modem. Modems vary in transmission speed capability.

Fax Capability: Modems with this feature can receive and send fax messages (fax modems).

Voice/data: Modems can switch between data and voice modes. To support the voice mode, a built-in speaker and microphone should be used.

Simultaneous Voice and Data (SVD): A modem that can handle voice and data calls simultaneously. It is usually used when playing games over the Internet and enables players to talk to with one another.

Speakerphone: When used with a microphone and headset, it can be used as a regular telephone.

Auto-answer: A modem with an auto-answer feature allows the computer to receive calls even if the user is not present. This feature is a necessity for fax modems.

Data compression: When a modem can compress large data files, it sends data faster. With small files, a little value is added because it cannot be further decompressed. The compression standard for modems is V.42bis.

Flash memory: Flash memory is a feature available only to some modems. With this feature, the existing communication protocol supported by the modem can be updated easily.


Modem speed

Modem speed is measured in bits-per-second (bps). It is supported by different communications protocols and duplex modes (half or full).

The first modems could transmit data at a speed of 300 bps, from the Bell 103 standard. Currently, a modem is capable of running at a speed of 56,000 bps (ITU V.90 standard) or even faster (64,000 bps). Please see the following table for more information about modem transmission speeds.

The speed at which data will be received depends on the transmission speed of the modem used to send it. Data transmitted at 2,400 bps will be received at 2,400 bps regardless of the speed of the receiving modem.<!-- / message -->