What is an ADSL Modem?


What is an ADSL modem? That’s a great question. However, in order to give you a better understanding, I have to first tell you what ADSL is. No long-winded introduction here — let’s jump right into it.

A Little History of Modem Usage

Before we get into what an ADSL modem is and what a DSL modem is, let’s take a step back a few years. Back when I was walking to school through 10 feet of snow barefoot (uphill both ways, mind you), we were using phone lines to log onto the Internet. We used a modem. These were the pieces of equipment that made those annoying noises when you first connected. If you’ve ever heard a fax machine, you know what I mean when I call the tones annoying.

As I mentioned in my article on modems, the word modem is an abbreviation for MODulate-DEMulate. Modulate and demodulate are just fancy terms for converting a digital signal to an analog signal and back. This was required because the phone systems back then (late ’80s and early ’90s) were all analog but computers by this time had moved up to being digital devices.

Now, in the parlance of the phone company, the phone line serving your house (or business) is called a subscriber line, because you subscribe to their services. Originally, you had an Analog Subscriber Line (ASL). Because the equipment in the various phone company locations — central offices and regional offices, to name a couple — was all analog, the modem was required to convert the data being sent to and from your computer into a format the computers on both ends could understand. Hence, the modem. Consider it a type of “universal translator.”

Enter the ADSL Modem

But what’s that got to do with ADSL modem, Mike? Your DSL modem is simply another type of modem, somewhat similar to those I used to use. However, they’re capable of sending and receiving data at a much higher rate. There’s another difference, though. This difference is something we “original netizens” screamed about for a number of years — an event called “getting bounced or bumped.”

“Getting bumped” happened if someone picked up one of the phone extensions in the house, or if an incoming call came in and you had “Call Waiting” (and you hadn’t set the proper command strings during the initial dialup phase to ignore incoming calls).

We hated that! We’d be in the middle of a nice chat or downloading something and all of a sudden — poof! — our Internet connection was lost and the phone was ringing.

The ADSL modem did away with all that. We no longer had to remember complicated strings of modem commands in order to stay online. We could also talk on the phone and surf the web at the same time. What was even better was that those wonderful engineers had also figured out a way to increase the speed at which our Internet connections worked. This speed increase wasn’t much to begin with, maybe a little under double what the fastest analog modems were capable of but the fact we could surf the web without worrying about being knocked offline by someone calling in or someone wanting to call out was wonderful.

What Does ADSL Mean?

ADSL is an abbreviation for Asynchronous (or Asymmetric) Digital Subscriber Line. Remember that above I said your phone line is considered by the phone company to be a “subscriber line” and that the older phone service was considered Analog Subscriber Line. ADSL is just another type — a digital type — of phone subscriber line.

I also mentioned above that the DSL modem converts the signals coming and going to and from your computer back and forth between analog and digital signals, just at a much higher speed than previous modems. The DSL modem also separates voice service and Internet service using what’s known as a microfilter. This allows, like I mentioned, simultaneous use of the net and the phone to make calls on the same line.

I’ve seen some pretty hard to understand definitions for what asynchronous means. Those definitions are much too technical for us, though. Suffice it to say that asynchronous/asymmetric means that data can only be sent in one direction at a time. Radio is a type of asymmetric or asynchronous communication — only one person on the circuit can speak at a time otherwise all that’s heard is gibberish.

With an ADSL modem, the computers at either end send signals at the beginning and end of a transmission to inform the modem at the opposite end that it is either starting or finishing a data transmission. These are known as start and stop bits.

If you’re thinking about buying a new ADSL modem, here are several of the best modems at Amazon that you might want to check out.

Photo Credit: PC Actual