Modems are one of the most common ways for computers to connect to each other. Satellite systems are used to connect WANs across the globe. Multiplexers are a key component of WAN technology. Transmissions can be asynchronous or synchronous.
The term modem comes from the two primary tasks it performs: modulation and demodulation.
In many ways, a modem is like a language translator between the analog and digital components.
Modems have several sets of standards:
V series
Hayes-compatible (AT command set)
PC Cards
V series Standards that cover today’s modems, with speeds up to 56 Kbps.
Hayes-Compatible Standards The set of transmission signals, commands, used originally by Hayes modems for exchanging status information, such as readiness to send or receive.
PC Card standards Standards developed for personal computer cards and intended for laptop users that target a broad range of devices, including modems. Developments in the past few decades enabled modem speeds to transmit at 56 Kbps.
However, the 56K transmissions can occur downstream. The upstream, or outgoing transmission from the modem, is limited to 45 Kbps.
There are several different types of modems available:
Cable modems
ISDN modems
DSL modems
cable modem A modem that uses a cable television connection to get transmission rates that are faster than a dial-up connection.