The History of the Modem
A modem is a device made for sending digital data over a phone line. “Modem” is actually a contraction of the words modulator-demodulator. Modulation is so important for this device because the sending modem must modulate digital data into a form of information compatible with a phone line, whereas the receiving modem demodulates the phone-line-compatible date back into digital data.
For a little perspective, consider that wireless modems convert digital data into radio signals and back; this allows users to be more mobile with their devices so long as they’re within 100 feet of the modem and there aren’t too many walls obstructing the signal.
Modems were first invented in the 1960’s as a way to allow terminals to connect to computers over the phone lines. They allows for a terminal at an off-site office to “dial in” to a large, central computer. Because the 60’s were a time when it made sense to have a time-shared computer, this was a great system through which a business could access its modem (located in a time-share facility) for the time that it was allotted.
When personal computers starting making appearances in the late 1970’s, this system was replaced by bulletin board systems, which still only offered about 300 bps (bits per second). This was faster than anyone could read or type, so it was seen as a useful tool instead of the terrible hindrance that it would be received as today.
Modems that operated at this pace are much easier to understand than today’s extremely fast technology, so let’s start out with those. 300-bps modems are devices that use frequency shift keying (FSK) to transmit digital information over a telephone line. The FSK process involves using different frequencies for different bits. That means that when the originate modem transmits a signal to the computer’s modem, it sends a 1,070-hertz tone to convey a 0 and a 1,270-hertz tone to convey a 1. The computer’s modem is called an answer modem and transmits a 2,025-hertz tone for a 0 and a 2, 225-hertz tone for a 1. The originate and answer modems’ use of different tones allow them to both use the line simultaneously, an ability called full-duplex operation. A modem that can only operate in one direction at a time is known as a half-duplex modem.
Faster modems were made possible by using processes a lot more sophisticated than that of FSK. First they moved to phase-shift keying (PSK), and eventually they moved to quadrature amplitude modulation (QAM). The processes utilize gradual degradation to improve their speeds, meaning that they can test the phone line and fall back to slower speeds if the line cannot handle the modem’s fastest speeds. Therefore the processes do allow for much more information to be crammed into the 3,000 hertz of bandwidth available on a normal voice-grade phone line, but the phone’s bandwidth remains a very limiting factor and only allows for a transfer of 48Kbps.
This prompted engineers to create something called the asymmetric digital subscriber line, a modem named for the fact that it could send data faster in one direction that it could in another. The engineers of the ADSL understood that normal buildings, whether they are homes or businesses, have a dedicated copper wire running between them and the phone company’s nearest location. The wire itself can carry substantially more data than a phone’s voice channel, so if a phone company and a home are equipped with an ADSL modem, the section of copper wire between your house and the phone company can act as a digital high-speed transmission channel. This set up allowed for up to 1 Mbps from the building to the phone company and 8 Mbps from the phone company to the home. The ADSL modem involved the creation of a virtual modem, which was assigned to each 4,000-hertz band of a phone line. The sum total of the 249 virtual modems ended up being the total speed of the pipe.
Today, our modems connect to internet service providers (ISPs) and the ISPs connect us to the internet. The nature of the internet being shared across the internet is so dense that your modem transfers packets of information between you and your ISP as opposed to individual characters. Routing these packets involve the use of Point-to-Point Protocol.