DSL is a broadband technology that delivers higher speed data links of up to 24Mbit/s across existing copper wire telephone lines on the "last few kilometres " between the local telephone exchange and the customer premises. It works by using a frequency splitter device to split a traditional voice telephone line into two frequency bands; one narrow one for voice, the other much wider for data, thus creating an DSL enabled line which can be used concurrently for phone conversations and high speed Internet access. The equipment required at the Exchange end of your DSL line is known as a DSLAM (Digital Subscriber Line Access Multiplexer).

There are two categories of DSL

ADSL (Asynchronous Digital Subscriber Line) which has faster download speed than upload, because this is designed for web browsing where most of the data transmission is download.
SDSL (Synchronous Digital Subscriber Line) has the same speed in both directions. This is best for networking computers over VPNs and providing services such as web-site hosting. This type is less common in Australia, but is on offer by some ISPs.
There are three standards of DSL being offered in Australia today, DSL 1, DSL 2 and DSL 2+. Despite their similar names, the two DSL 2 standards are quite different. DSL2 aims to improve the performance and interoperability of the original DSL 1 with longer range and slightly enhanced speed.

Most DSL on offer today in Australia is based on the DSL 1 standard which allows speeds up to 8mbit/sec. Unfortunately, Telstra limits this to a maximum 1.5mbit/sec in its DSLAMs and a range of 4km from an exchange.

DSL2+ offers twice the speed of DSL1 and DSL2, up to 24mbit/sec. Already the major metropolitan areas are being served with high speed DSL2/2+ now, mainly by companies other than Telstra who have their own DSL2+ DSLAM hardware installed in telephone exchanges. As we have seen in the past, and other areas of Australia will struggle to get DSL2+ in the near future, while others even struggle to get an DSL 1 service.

When you purchase DSL from an ISP you will request the speed you want to pay for, but the configuration type is often not clear to you before you buy. It is however important to know if you are to configure your own hardware and software.

Just because the DSL line from the telephone exchange is the responsibility of Telstra, be aware that from the exchange to the Internet is the individual ISPs responsibility and they will use their own inter-network to link into the Internet. Your DSL performance in practice, for example, is much more dependent upon how good the ISPs inter-network and gateways to the Internet are and not on any of the DSL components.

What you need to get connected?

A Telephone Line

It has to be within 5 kilometres of an DSL enabled Telephone Exchange. Most ISPs have a test program where you enter your phone number and it will let you know whether DSL services are available for you. Your line must pass a number of tests before installation can go ahead - Telstra will do these as part of the upgrade at the Exchange.

A DSL Modem or Router

Most ISPs will supply you with a modem or router as part of the installation kit or at additional cost. You can also purchase them through us if you like. Connection equipment can be broken down into 2 basic categories:

• Ethernet, PCI or USB DSL Modem. The easiest way to get online. Just pop in the CD, install the drivers and plug in the modem. These are only suitable for a single PC in a home invironment - WE DO NOT RECOMMEND THEM AS THEY ARE TOO LIMITING FOR THE FUTURE ND HAVE POOR SECURITY.
• Ethernet/Wireless DSL Modem-Router A standalone device which maintains the connection to the Internet for you. Most routers have an Ethernet connection to your local area network and act as a gateway, DNS, DHCP and firewall service. You can use a router to connect multiple computers to the Internet. Make sure you get one with multiple ethernet ports or wireless ethernet built-in.

A Micro-Filter for each Phone Socket

A micro-filter is designed to plug into your phone socket. Its purpose is to separate voice from data and must be connected to each phone socket in your house. If you do not have a telephone, or any device which uses the phone line, a micro-filter isn't required. Most ISPs and retailers sell micro filters.

Finding the right ISP and Plan

Before you choose an ISP's DSL Plan you need to have addressed a number of issues first. Some plans (the cheaper ones usually) may restrict you so that you will not be able to use the DSL connection as you expect to.

Consider these questions :

• How many computers do you want to share the one DSL connection?
• With DSL your computers potentially can be permanently connected to the Internet. This raises the question of the best ways of protecting them from unauthorised Internet intrusion.
• Do you want to host services such as Web-sites and SMTP mail servers that can be accessed from the Internet?
• Do you require a permanent IP address assigned to you or you don't care?

Discussion :

If you want more than one computer to access the DSL connection concurrently, the best solution is to use a modem/router/switch combination unit. There are many of these on the market today and we sell a selection of the best ones. These usually have about 4 Ethernet ports for connecting local PCs or up-linking to another hub/switch to allow many more PCs to connect.

If you are using Windows XP you could use a USB modem and implement Internet Connection Sharing and Internet Connection Firewall to share the access to other computers. We consider this not to be as good from the security perspective as the above hardware solution.

Most modem/routers also provide network address translation (NAT) to shield the PCs from being easily accessed from the Internet (a firewall feature) and by default no TCP/UTP ports are open in the direction from the outside to the inside network. All ports are open from inside to outside, however. What this means is if a communication such as access to a HTTP web site is initiated from inside network, the modem/router will allow the request's response back through the modem/router to the computer that originated the request. Any unsolicited request from outside will be blocked. You can enable specific TCP/UDP ports so that any unsolicited request to that port from outside will be directed to specific local host computer. This enables you to run your own Web-sites or FTP-sites, for example, through the 'firewall'.

If you want to host web-sites or have a SMTP server that receives mail, you really need a permanently assigned IP address. There are ways around this with Internet-based Dynamic-DNS but this adds complexity. If Internet activity is always initiated from the PCs then it is best for security reasons, not to have a fixed IP address.