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ADSL! What is that?

What does ADSL stand for?

Asymmetric Digital Subscriber Line

What is the difference between ADSL and DSL?

ADSL is a type of DSL where the upstream and downstream speeds differ (hence the "asymmetric" part).

There are many variations of DSL technology for different types of application (HDSL, SDSL, etc).

What is ADSL?

ADSL is a broadband connection technology, which utilises existing copper wired telephone networks.

ADSL uses a wide range of frequencies over an existing telephone line to deliver much higher speeds

than your standard 56k modem (between 10 and 140 times faster).

It is also possible to use your phone while online.

How does it work?

The service makes use of your existing telephone line. It splits the signal into two channels,

one for voice communications and the other for the high-speed data communications.

It makes use of a frequency range not used in normal voice communications:

Voice: 0 - 20 kHz

DSL: 25.875 kHz - 1.104 MHz

Khz	0	20	40	60	80	100	120	140
PSTN	*	*
ISDN	*	*	*	*
ADSL	*	*	*	*	*	*	*	>upto 1.104Mhz

Do I still have to pay BT line rental if I get ADSL?

Yes. BT's telephone billing (line rental and call charges) are unrelated to your ADSL.

You will however not have to make any calls to the Internet, as the ADSL is an always-on connection.

Though there are some exceptions, since there are telephone providers who will pay BT on your behalf, i.e. the telephone line is still BT owned but you can pay for it via a third party.

If you are on a fully unbundled line, then you will not be paying BT any money. Most unbundled providers use shared lines, where BT still provides the telephone service, so rental will continue to be paid to BT.

What can I do with it?

A simple answer to this would be:

Anything you already do with your 56k connection just much faster. However, you can do things that wouldn't be viable on a dial up connection:

Play games with much lower latency.

Multitask - download a file, browse the web, check email at the same time - all still much quicker than using a dial up connection.

Streaming media - You can now watch high quality streaming media on your PC such as music videos, movie trailers, concerts, and even space shuttle launches!

Use VoIP (Voice over IP) and web conferencing

Some users now leave their systems running 24/7 and operate their PC remotely. NB: Users may experience issues using certain services when using NAT on their router.

What does contention mean?

Contention is basically sharing.

If you live in a house with teenage girls then you contend the bathroom with them - which can mean waiting hours to get in.

Your electricity is contended - normally not a problem as there's more than enough to go around however tell that to the residents of California last year who had rolling blackouts due to a lack of generating capacity.

Everything in life is contended - it's an effective way to utilise a shared resource. Regarding ADSL - there are two levels of contention on the BT wholesale network at the moment:

50:1 for the home user (Home 500, Home 1000 etc.)

20:1 for the business user (Business 500, 1000, 2000 etc.)

If you take the worst-case scenario for the home user then that means you're sharing your 500kbs with 49 other people. If you are all downloading at the same time then you'll get 10kbs - about a quarter of the speed of a normal dial-up analogue modem.

In reality, its unlikely BT will allow this to happen. Despite extremely rapid broadband take up during 2003, most users are still able to download and upload at the maximum quoted speed.

I'm not a BT customer - Can I have ADSL?

If the telephone line to your property is actually installed and run by BT then you should be able to have ADSL (subject to survey).

If the telephone line is with a Cable provider (NTL, Telewest) you will need a new telephone line for the adsl to run on

I have a Mac - Can I use ADSL?

Yes. Wires-only customers should buy a modem, which supports the Mac. If you purchase an Ethernet router, you will need a standard network card.(We recommend you chose this option)

We can supply a modem for you (ZyXEL Prestige 630C), These are fully supported by MAC & come with installation instructions for use with a MAC

Which is better, IPStream or DataStream?

Neither IPStream nor DataStream is 'better' necessarily.

These are both BT Wholesale provided services but they deliver the connection to the ISP in a different way.

IPStream is a service where the user traffic is routed longer inside BT's managed network whereas with DataStream, the ISP takes one or more 'virtual path' (VP) circuits to each local exchange so they can manage contention themselves.

Most ISPs use DataStream to deliver services with high contention ratios spread over very small numbers, so often DataStream will deliver worse performance, however technically it is capable of more customised services, including 1:1 contention.

Therefore, you should not choose a service solely because it uses IPStream or DataStream but look into user experiences of the particular service.

DataStream's advantage in the current market is for ultra low cost services, or low contention / un contended services and where Quality of Service (QoS) is needed.

Can I have ADSL on a line with BT RedCare?

Yes.

Since August 2003, the standard RedCare service from BT is available on ADSL lines, although there are some caveats and restrictions.

More information can be found on the BT RedCare web site (http://www.redcare.bt.com/security/products/adsl.htm)

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