• The Bell 103, which was the first commercial computer modem, is an AT&T standard for American Telephone and Telegraph.
• These modems were designed to hold a telephone's receiver in a cradle with wire connections running from the cradle to the computer.
• It allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 300 bits per second.
• Each station uses different audio frequency pairs.

The Bell 103 modems use protocols during data exchange. Bell 103 protocols are as follows:

• Microcom Networking Protocol (MNP) Levels 1-4: Deployed in the 1980s as an industry standard due to high demand.
• MNP Level 5: This protocol incorporates the first four MNP levels with a data compression process.
• V.42: This protocol are internationally recognized for data compression and error control.
• Although the Bell 103 modem is rarely used in modern computing, the Bell 103 encoding scheme is still used by devices known as Bell 103 or compatible Bell 103 modems.
• Bell 103 can either originate or answer calls and can be used with a direct connection or by acoustic coupler.