Types of Access Networks: DSL

There are a number of ways that your end system can access the Internet, let's look at each in detail!

Now that we know what access networks are, let’s look at some common types.

Digital Subscriber Line: DSL

A Digital Subscriber Line or DSL uses the existing groundwork of telephone lines for an Internet connection. DSL connections are generally provided by the same company that provides local wired phone access.

Internet Service Providers

An ISP is just the company that provides end users with an Internet connection. For instance, AT&T and Verizon are ISPs. So the telephone company or telco is the Internet Service Provider or ISP in the case of DSL!

How DSL Works

  • A device on the home user’s end called a DSL modem modulates the digital signals that a computer outputs into high-frequency analog audio signals that are out of the human voice and hearing range.

  • The telephone wire’s frequency spectrum is divided into 3 parts:

    1. A downstream channel (which is used to receive data), in the 50 kHz to 1 MHz frequency range or ‘band’
    2. An upstream channel (used to send data) which takes up the 4 kHz to 50 kHz band
    3. A regular channel used for telephone conversations taking up the 0 to 4kHz range

Did You Know? Modulation - demodulation is where the name MoDem comes from.

For reference, the human hearing range goes from 20 Hz to 20 kHz and the average human voice range goes from 85 Hz to 255 Hz.

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