## Modems

If you are accessing this website right now, then you are almost definitely using a modem! Modem, a combination of the words modulator and demodulator, is a special device used to send data over a phone line to other computers! Most modems are connected to an ISP, or Internet Server Provider, which then connect us to the Internet and to the information superhighway! Because the Internet plays such a major role in our everyday lives, modems are essential devices used by millions of people every day!

So, you might be wondering how modems can connect to and access information from computers throughout the world via the Internet. The idea is to transfer information from one computer to another through the telephone lines. However, there was one problem. Telephone lines were designed to transmit analog information, like voices. Computers, on the other hand, are digital and use the binary system of 0s and 1s.

In order to transfer information between computers via a phone line, the digital information of computers had to be translated into analog information, and then changed back to digital form when reaching its destination. This was done by modems. At one end, modems would modulate the data. This means that they would convert the data from digital form to a series of analog signals. Once the information successfully passed through the phone lines, another modem would demodulate the data- convert the data from analog form back to digital form.

Modulation- the conversion of digital data to a series of analog signals can be accomplished in many ways.

The older modems used a technique called Frequency Shift Keying (FSK). In FSK, digital information was transmitted by having different frequencies represent different bits. For example, a 0 in the binary system would be converted to a 1,070-hertz tone, while a 1 would become the analog signal of a 1,270-hertz tone.

Now, there are new techniques that can be used. These are all much faster than the old FSK technique. One of these techniques is called Phase Shift Keying, or PSK. If you have studied trigonometry in school, imagine a sine graph and a cosine graph. As you know, these two graphs go up and down in curves. If analog and digital signals were visible, this is what they would look like. In PSK, two waveforms (they look like the curved sine and cosine graphs) are compared. When one graph is going upwards, the other is going downwards, and vice versa. Different phases of the waveforms represent different binary digits. When a certain phase of the waveform is shifted over a certain number of degrees (i.e. 90 degrees), it represents a 0, while shifting it over a different number of degrees (i.e. 270 degrees) would represent a 1.

Finally, an even newer technique of modulation is called Quadrature Amplitude Modulation (QAM). This uses the phase shift idea of the PSK, but it also incorporates an idea called Amplitude Modulation, or AM. Remember the sine graph I mentioned above? Well, the wavelengths in the AM technique resemble a sine graph. Where there is the analog signal of a large amplitude sine wave, a 1 is represented. Where there is no sine wave, a 0 is represented.

An important part of modems are serial ports. These serve as connecting devices between computers and their modems. A device called the Universal Asynchronous Receiver/Transmitter (UART) converts bytes into single bits. These chips control the serial port and the computer's bus system. The UART then ships the bits one at a time through the serial port to the modem. This is necessary because PC bus systems can transfer information in blocks of 32 bits, while serial cables can only transfer information one bit at a time.

Modems can come in all sorts of different speeds. The speeds of the modem are usually measured in bits per second (BPS). This is how many bits they can transfer every second. The first modems cold only transfer data at 300 BPS. Then, newer modems developed. Through the mid-80s to early 1991, 1200 BPS, 2400 BPS, and 9600 BPS modems were primarily used. Throughout the early and mid 1990s, 19.2 K bits per second, 28.8 K bits per second, and 363.6 k bits per second modems were in use. In 1998, the 56.6 K bits per second modem was developed.

Now, there is a fairly new type of Internet connection called ISDN. It is much faster than the older modems and is better suited for accessing the Information Superhighway and the World Wide Web. ISDN stands for Integrated Services Digital Network. It can deliver two simultaneous connections and can transfer data completely digitally! Unlike the regular modems, ISDN does not have to transfer data into analog signals and then back to digital form. This makes it much faster, and also it gets rid of all of the little noises you often hear when 56 K modems are working. ISDN can connect to computers throughout the world! Internet access is greatly enhanced through an ISDN connection as compared to regular modems.

There are two major types of ISDN connections. The most common is Basic Rate Interface, or BRI. This is found in many homes and offices. Then, there is the Primary Rate Interface. This is primarily used to make available many applications for remote users.

Now, a new fairly new modem developed in 1999 is becoming popular. It can transfer data at 10 MB per second! ADSL is an acronym for Asymmetric Digital Subscriber Line. Most homes and offices have a special copper wire that is specifically used to connect to their phone company's nearest central office. If both the house and the phone company's office have ADSL modems, then information can be transferred super fast via the copper wire. It can transfer 1 million BPS from your house to the phone company's office, and 8 million BPS from the phone company to your house!

The future will hold even faster and better modems and Internet connections! The Internet will be brought to a whole new level, and all because of modems!

There is a now newer type of modem, called a
Cable Modem