How Does a Modem Work?
Modem Overview
Analog vs. Digital
Data Compression
Error Correction
Flow Control
UARTs and Data Buffering
Standards and Protocols
Bell/CCITT/ITU-T Standards
Data Transfer Protocols
Fax Standards and Protocols
Modulation Protocols
TCP/IP, SLIP, and PPP
Communications and Software issues
AT Command Sets
COM Port Settings
Data Communications Application Software
IRQ Settings
S Registers
Synchronous vs. Asynchronous Data Transfer
LINKS
LT Win Modem
Modem Help.com