Most of today’s broadband users connect to their service provider network using their telephone line, or in some cases, multiple telephone lines.
Because the core of the telephone wire is made of copper, and there are two wires used for each telephone line, we sometimes refer to a telephone line as a ‘copper pair’.
In recent years there have been many developments in broadband technologies that use copper pairs for connecting to the service provider network. In an industry that just loves its acronyms, we may know them as ADSL, ADSL2+, BDSL, SHDSL, EFM, MBE or EoC. But whatever their individual names, we can refer to them collectively as copper-based broadband.
The great thing about copper-based broadband, and the primary reason for its popularity, is that it makes use of physical connections that already exist between the customer premises and the telephone exchange. This makes it one of the cheapest access methods available and an excellent choice for most businesses and consumers in Australia.
How all copper-based broadband works
Whilst each individual type of copper-based broadband has a slightly different implementation that results in a different feature set, ultimately they all rely on the same transmission principles to work.
A signal is transmitted along the telephone line from the telephone exchange that is received by the customer’s modem in their premises. The stronger and clearer the signal received, the more data can be passed from the exchange to the customer.
A signal is transmitted along the telephone line from the customer premises that is received by the telephone exchange equipment. The stronger and clearer the signal received, the more data can be passed from the customer to the exchange.
The exchange equipment and the customer modem negotiate their maximum speed when first connected. This process is sometimes known as ‘training-up’ and the maximum speed is the ‘train-up speed’. The download and upload speeds can train up at different rates.
Distance from the exchange degrades signal The signals degrade and become weaker the longer the copper pair. So the longer the copper pair, the slower the train-up speeds.
For example, an ADSL2+ connection using a copper pair that is 500m long might train up at 20Mbs download, but an ADSL2+ connection using a copper pair that is 4km long might only train up at 4Mbs download.
The signal can also degrade when the copper is of poor quality, gets wet, has been repaired many times or has a poor connection at a kerb-side pit or splice point.
The biggest single factor contributing to poor performance of copper-based broadband is distance from the exchange.
Cross-talk The other issue facing copper-based broadband is one that also faces many other transmission technologies that use aggregation points (such as telephone exchanges) within their network.
The speed at which a device can receive data depends on how loud and clear the signal is that is receives.
The modem at a customer premises is often some distance from the nearest other modem receiving a signal. So there is little chance that the signal being sent down a neighbouring telephone line will interfere with the signal it receives.
The telephone exchange equipment receives signals from sometimes thousands of subscriber connections at once.
Because all of the copper pairs are in close proximity to one another, they actually interfere with one another by creating ‘noise’ on each other’s line. This phenomenon is sometimes called ‘cross talk’.
So it is technically much harder to provide upload bandwidth than download bandwidth. For a telecommunications provider, ‘technically harder’ generally translates to ‘more expensive’.
The Bottom Line Although not an exact science, most of the copper-based broadband technologies ‘hit the wall’ at a line length of around 2.5 to 3kms. This equates, on average, to a line-of-sight distance of around 2 to 2.5Kms from the exchange.
At this distance:
ADSL2+ speeds rarely exceed 8Mbs download and 500Kbs upload
Symmetric copper options rarely exceed 1Mbs or possibly 2Mbs
Customers who need more simply have to seek an alternative solution.
Can’t I just connect to a closer telephone exchange? Unfortunately, no. Telstra is responsible for the copper telephone lines and will only ever run those lines from any given address to one and only one exchange. If you want be closer to an exchange, your only choice is to relocate premises.