ADSL FACTS

ADSL is the most common type of broadband connection in Australia. It is readily available, easy to install and it uses your existing telephone line which pretty much everybody has so long as it belongs to Telstra.

Optus has their own phone/broadband network and it doesn’t cater for ADSL. The ADSL that Optus and other companies offer utilizes the Telstra network outside the exchanges but 3rd party equipment inside the exchanges.

Problems that can occur

• Your local telephone exchange could be relying on old equipment for each phone line and there are thousands of these unshielded phone lines rubbing against each other and wearing through their thin insulation while straightening the twist in each pair of wires inducing crosstalk.
• Outside there are lots of cable joints in pits or up poles exposed to temperature variations, inclement weather, solar radiation, insect ingress, ageing, and constant access. There are various chemical liquids and gases underground that can also enter and erode the cables between the exchange and your premises.
• Perhaps some dodgy wiring that is damaged, corroding or not connected correctly. Too many phone sockets diluting the signal and lots of filters will not fix this. A monitored alarm or PABX system must be kept separate from any ADSL signal.

If the problem is on your property then it’s no longer the Internet Service provider’s responsibility after the network boundary. You wiring configuration could be telling you the only option is a Central Splitter. This gives your modem a dedicated extension for the sole purpose of internet activities and other phone points their own clean phone signal without the need for further filters.

ADSL or is still a terrific option and with a little perseverance can provide years of trouble free service. Where you have a monitored alarm, PABX or Commander type phone system, multiple phone outlets or other monitored services then a Central Splitter is a must. There’s no getting around it if you want the reliability and the speed you’re paying for.

These situations require a licensed, qualified Technician who can identify and locate potential problems. If any rectifications need to be made you can be assured all activities undertaken and materials used have Australian Standards Approval. Your Technician also warrantees and insures his work giving you piece of mind for the future.

ADSL Modem Signal Levels

The modem’s web page can help you gain an insight to the quality of your ADSL signal. Access to your modem web page could be gained by typing "192.168.100.1" into your browser’s address bar. It may not be this address but something similar. Consult the underneath of your modem, any paraphernalia from the modem or the modem company’s web site.

This look inside the modem interests us because it shows us signal loss measurements. These measurements are expressed in Decibels (dB). We may not be able to do anything to adjust these levels but it’s a good idea to keep a record of them for reference when comparing them later on.

Line signal loss, also referred to as attenuation, is an unfortunate result of 3 characteristics of signals on the phone line.

• Resistance – any cable that carries current will lose signal the further it travels. This is measured in ohms and is known as resistance.
• Capacitance – The phone cables carrying your ADSL are just two wires twisted together, the "Unshielded Twisted Pair". Capacitance is the ratio of the amount of charge on either wire to the potential difference between them. As the frequency increases so the capacitance increases and therefore increasing losses. On the phone network this is measured in microfarads.
• Inductance – As above, if the frequency increases there will be an increasing resistance to current flow on your line.

We can see here if we are to increase the speed of the ADSL signal this requires an increase in higher frequency signals on the phone cabling leading to an increase in signal attenuation and therefore a drop in speed the further it needs to travel. We then need to be closer to the exchange to achieve those theoretical speeds.

Losses are measured for sending and receiving signals and also for noise on the line. The dB scale is logarithmic.

• Downstream Attenuation – This shows us the loss of signal sent from the exchange until it reaches our modem. If this is showing a loss of 30dB then we are receiving 1/1000 of the signal sent out which sounds bad but isn’t.
• Upstream Attenuation – This shows us how much of the signal is lost before the exchange receives our signal. If this is 30db then the exchange is receiving just 1/1000 of the signal sent from our modem.
• SNR – the Signal to Noise Ratio is the difference between the signal being received compared to the noise levels on the line. A level of 30db is also good with anything near 0db is really bad with virtually an impossible internet service.

CABLE MODEM FACTS

Cable internet is available on that big black cable you’ve seen sometimes strung between the power poles or coming internet into your Foxtel Set Top Box. It’s limited in availability to the major cities and not in all suburbs. This broadband cable carries signals for the internet and Pay TV. The Optus cable also has the ability to provide phone services though not in the same sense as the Telstra cabling in the street. But the final result at the phone socket is the same.

Optus had a world breaking technology and Bigpond has also upgraded their cable technology in recent years to provide serious competition with reliability, ease of connection and speed. Speeds achievable are now are up to 35 Megabits per /sec whereas originally 10 years ago we thought up to 1 Meg was "dreams come true".

Are there any problems?

Sure there are problems. When it comes to getting a connection the sales people tell you it’s not available "in your street" or "your suburb doesn’t exist". It’s mind boggling when I’m looking at a cable service at the same time I’m told it’s not there. But you’ll get that when you apply for ADSL and "you’re too far from the exchange".

But seriously, while problems are very few and you may never experience them, you most likely will not be able to resolve them. Hopefully it’s just a small matter of restarting your modem and computer in the order where your modem must be online before switching on your router and then your computer.

If it’s not that simple or is constantly reoccurring and you’re sure it’s not your equipment then a technician visit from your Internet Service Provider is necessary. You can open up your modem web page and attempt to analyse the signal levels but this won’t tell you whether water has got into network in the street, dirty or corroded connectors, or other network issues.

Cable Modem Signal Levels

If you’ve explored your modem’s web pages then you would have noticed the signal status page where you will see the "Downstream" and "Upstream" tables.

These signals should not be compared to those for ADSL.

A downstream "e;SNR" (signal to noise ratio) is also displayed.

• Downstream Channel - A downstream level shown as dBmV shows the strength of the downstream signal your modem is receiving. This is supposed to be between -15 and +15dBmV however closer to zero would be ideal.
• Upstream Channel - The upstream level also shown as dBmV shows the strength of the signal your modem is sending back to your ISP. This needs to be less than 55dBmV and the lower this level is the better.
• SNT - The downstream Signal to Noise Ratio shows the strength of your signal to your modem compared to noise corrupting your signal on the cable. So if the noise on the cable increases then the ratio decreases. A SNR over 30dBmV should indicate reliability as opposed to a noisier signal towards 20dBmv showing up as an intermittent connection.

Modem speed does not necessarily mean there is a fault waiting to rectified. Users in a neighbourhood may share only a single coaxial cable so the service can become sluggish if many people are using the service at the same time. This is why you’ll notice internet speeds on early weekend mornings are particularly quick.

The Good News

Apart from the rarely ever occurring problem it’s all good news. A coaxial cable provides protection of signals from external electromagnetic interference which effectively keeps signals clean along the length of the cable. There is some signal loss but this is periodically restored through amplifiers placed regularly along the cable. On overhead cables this can be seen a rather large shoebox looking thing with cooling fins around it.

There are other issues beyond the everyday user would consider but these we leave for forums to provide input through public opinions.

The lead-in cable to the premises needs to be kept reasonably short, preferably less than 50 meters as some signal loss calculations would need to be noted to ensure a premium service. One particular Internet Service Provider offers amplifiers in extraordinary situations whereas the opposition would rather throw it in the too hard basket.

Broadband Problems Summary

Because there are so many variables in an imperfect world we cannot say what sort of figures you should expect to see for losses. Sales people quote us theoretical figures which is fine if you happen to exist in a drawing on paper. But if you’re realistic then you’ll know this, as a previous Prime Minister once said, "Life wasn’t meant to be easy".

There is little you can do to avoid signal losses except to look after what cabling and connections you’ve got by keeping them clean and free from moisture and damage.

Your Internet Service Provider will hopefully look after the network outside. Chances are if you are experiencing problems and you’re pretty sure it’s not you then others are also having problems and this will show up with their phone complaints. Network faults usually effect a number of users and are resolved fairly quickly.