What is ADSL


DSL or xDSL, introduced in 1987, is a family of technologies that provide for digital data transmission using the normal telephone line. DSL originally stood for Digital Subscriber Loop, although in recent years it is more commnly known as Digital Subscriber Line.

Typically, the download speed of consumer DSL services ranges from 256 kilobits per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, distance from the exchange, line conditions and hardware implemented. Typically, upload speed is lower than download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to download speed for Symmetric Digital Subscriber Line (SDSL).

ADSL and very high speed DSL (VDSL), typically work by dividing the frequencies used in a single phone line into two primary 'bands'. The DLS data is carried over the high frequency band (25 kHz and above) whereas the voice is carried over the lower frequency band (4 kHz and below). To seperate out the signals, a DSL filter needs to be installed at each point where a telephone is connected. This filters out the high frequencies from the phone, so that the phone only sends or receives the lower frequencies (the human voice), creating two independent 'bands'. This is how the DSL modem and the phone can simultaneously use the same phone line without interfering with each other. Failure to install the correct filters will result in your DSL connection being disconnected and you may also hear additional "noise" during your telephone call.

Just to explain the difference between Download and Upload, when you, for example, receive an eMail, you are Downloading the message from your eMail provider. When you send an eMail you are Uploading the message to your eMail provider. For most purposes, it is better to have a higher Download speed than your Upload speed.

When you look at ADSL plans, you will notice that in addition to the Upload and Download speeds, a Data allowance is often specified. For example, a 512kbps / 128 kbps connection may limit you to 5Gb (Giga Bytes) of data. The amount of data you use will depend on what it is you use your internet connect for. Downloading Music, Pictures and Videos will use much more of your data allowance that general browsing and eMail use (See Download Usage Guide for more details). The other thing to be aware of is that some ISP's (Internet Service Provider) will count your Downloaded data while others also count your Upload data. From a VoIP perspective, you need to be aware that your Upload and Download usage will be pretty much the same so try and avoid providers that charge you for your Upload data as well.


ADSL fact sheet

What is ADSL?

Asymmetric digital subscriber line (ADSL) is a broadband technology offering high speed internet access. 'Asymmetric' means data is transmitted 'downstream' to the customer faster than it is sent 'upstream' to the service provider. This meets the data needs of most internet users, that is, users typically download substantially more data than they upload.

What are the advantages of ADSL?

ADSL offers high data rates, allowing fast file transfers and internet downloads. The downstream/upstream data rates of ADSL are typically 256/64 kilobits per second (kbit/s), 512/128 kbit/s or 1500/256 kbit/s depending on pricing plans. ADSL is an 'always on' service, that is, you will be connected to the internet whenever your modem is on. ADSL uses the copper telephone lines that currently carry your voice traffic to deliver broadband internet, yet you can make a telephone call and be browsing the internet or receiving an email simultaneously, with no interruption to either service.

This means that there is:

  • no need for an additional phone line;
  • no need to dial-up the ISP; and
  • no connection drop-outs as may be experienced with a dial-up modem.

A customer can also have different service providers for their telephone and ADSL internet access services.

Can I get ADSL?

The availability of ADSL is dependent on a number of factors, including the area in which you live, the quality of your existing phone line and the distance to your nearest telephone exchange.

To provide ADSL services, a customer's local exchange must be 'ADSL enabled'. To confirm that your local exchange is ADSL enabled, contact your ADSL service provider.

ADSL services also require an 'unconditioned' telephone line. Unconditioned means the telephone line that provides your current telephone service is continuous all the way back to the local exchange. In addition, the telephone line must not have any network conditioning devices or components that might modify its inherent electrical characteristics attached. If other network devices or components are attached, you will not be able to access ADSL services.

The distance to the local exchange will also affect the availability of an ADSL service. In general, the maximum range for DSL without repeaters is 5.5 km (16,000 ft). As distance decreases toward the telephone company office, the data rate increases. Another factor is the gauge of the copper wire. The heavier 24 gauge wire carries the same data rate farther than 26 gauge wire. If you live beyond the 5.5 km range, you may still be able to have DSL if your phone company has extended the local loop with optical fiber cable.

To confirm that you are able to receive ADSL internet access services, contact your ISP.

What equipment do I need to connect via ADSL?

If you are not connected to the internet, or currently connect via a dial-up modem, you may need additional equipment and software to connect using ADSL.

You may need all or some of the following:

  • an ADSL modem;
  • an in-line or micro filter for each installed telephony device, up to 3 devices;
  • a central filter (master splitter) if you have more than 3 telephony devices installed (if you need a central filter it will need to be installed by a registered cabler (see ACMA Fact Sheet Telephone cabling in your home); and
  • installation software.

Check your hardware and software requirements with your ISP and get an estimate of the total cost for a broadband connection.

Who installs and supplies ADSL?

If you are an experienced computer and internet user, you may find you are able to install the required devices yourself. Alternatively, your ISP may be able to arrange an installation for you. Be sure to check out our Recommended Products and Services Page for ISP options available.

ACMA has fact sheets on various topics.

Please note: this infomation is intended as a guide only and should not be relied on as legal advice or regarded as a substitute for legal advice in individual cases.

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