DSL Basics: How Does a DSL Modem Work & How Do You Connect It

A Basic Review

To understand how the DSL modem works, let’s review a little about how DSL works in general. First, the signals that come to you are split into hundreds of sections, some upstream and some downstream, with lower frequencies reserved for voice transmission. These lower frequencies are allowed through by the use of low-pass filters that you plug into you’re your phone jack. Your phone then plugs into the filters and allows only the voice frequencies through.

The other frequencies are used by your computer, which plugs into the line by using an unfiltered phone jack and a DSL modem. The modem is the connection point between your computer and the telephone line, and connects either by USB or Ethernet.

What Does Modem Really Mean?

“Modem” is a compression of two other words that describe what the equipment does. It stands for “modulator-demodulator,” and acts as a translator between telephone line and your computer and back again (wireless modems translate the language into radio signals or incoming data from radio signals).

A Closer Look at the DSL Modem

The DSL modem uses the ability of the telephone’s copper wire to transmit millions of bits per second. Because the line is split into voice, downstream, and upstream data motion, it can travel in both directions at the same time as well as allow you to talk on the phone.

The Splitting Process

The splitting is done one of two ways. CAP, or the carrierless amplitude phase method splits the bandwidth into three parts. The voice occupies the lower frequencies in this split, and the upstream and downstream data transmission ride the other two sections. Around 1996, the discreet multitone method began to take favor. The DMT divides the available frequencies into hundreds of separate sections of 3 to 4 frequencies. As a result, there are many separate upstream and downstream channels.

Connecting Your Modem

Connecting your modem will depend on its brand and whether or not it’s wireless. Basically, you will take these steps to plug in your DSL modem:

• Plug in low-pass filters into phone jacks, but not the one you will plug the modem into
• Connect to computer using Ethernet wire or USB
• Connect power to modem
• Turn equipment on, and open internet with browser

Registering Your Modem Unit

Here you may have to register your product online and wait for acknowledgement in some way; then you will be able to connect to the rest of the internet. You also may have to install software at some point, and the instructions that came with the modem should tell you.