How To Check Your Maximum Line Speed

Tue 2nd Jun 2015 - 3:46pm : General

Telkom might be busy rolling out 20Mbps and 40Mbps VDSL in certain areas, but most of the landline internet users in South Africa still use the older ADSL technology. By design, ADSL is capable of up to, roughly, 24Mbps, but the implementation Telkom has rolled out only allows for a maximum speed of 10Mbps.

A few months ago Telkom announced that it would upgrade the default line speeds for users on packages lower than 10Mbps. Those with 1Mbps (or slower) lines were bumped to 2Mbps. Those on 2Mbps saw speeds boosted to 4Mbps. And those who already had 4Mbps lines at home got free upgrade to 10Mbps.

It’s not as easy as that, though. ADSL, being a copper line technology, relies heavily on the quality of the cabling that supports it. Some people complained that they didn’t even get the 1- or 2Mbps lines they were paying for, and wondered how Telkom were going to offer the faster speeds. The short answer is: the speeds probably won’t get faster without some changes. The longer answer is that Telkom would need to uproot existing copper infrastructure to make sure those users got the best possible signal through the cabling. Telkom, of course, also has a disclaimer: it doesn’t guarantee speeds, and its products are advertised as “Speeds of up to xx Mbps”.

To help you obtain and understand the maximum speed your ADSL line is capable of, we’ve got the guide below. There are some exceptions, and we’ll explain them along the way, but hopefully you’ll leave here more informed – and with a hope that newer technology gets rolled out in your area, rather than hoping the old stuff gets fixed.

1) The official line

First thing’s first: check what Telkom says your maximum supported line speed is. Fortunately this can be done instantly, online, by using the ADSL Checker tool on the Telkom website.

Telkom’s DSL speed checker lets you know what to expect.

There’s method to the madness here. This tool will immediately let you know if you should get your hopes up for a faster line. It checks Telkom’s systems for whether or not your phone line and area support speeds higher than 4Mbps or 10Mbps. If you’ve heard of Telkom rolling out 10, 20, or 40Mbps lines in your area, this will let you know if you will be able to upgrade to one of those.

2) The tech specs

If Telkom’s site says the maximum speed in your area is higher than your current line speed, you’re in luck, and could potentially upgrade to a faster line. However, just because Telkom says your area supports 10Mbps, and your line is only 4Mbps, doesn’t necessarily mean your line will support 10Mbps. Your ADSL line, a piece of copper that runs from your house to Telkom’s equipment, has certain properties and one of those is its attenuation – or the reduction of its signal strength, as it gets longer.

Believe it or not, these numbers are actually useful to end users.

To get the statistics for your line’s attenuation, log into your ADSL modem/router’s web interface. Simply open your web browser and type in an address like, or This address will vary depending on the make of your equipment, so to get the exact address just consult the documentation that came with your modem. Once you’ve logged in to the web interface you can navigate to the section that give you the specific details for your ADSL line – jot down the downstream attenuation as well as the signal-to-noise ratio (SNR). These figures are measured in decibels, so will likely have a dB notation next to them.

3) The interpretation

Once you’ve got the attenuation and SNR figures, you can load up the tool on this website. This calculator lets you plug in the attenuation of your line, and gives you the distance from the exchange. It’s important to note that this distance isn’t from your house to the exchange but rather the distance of the cabling.

The longer the cable, the higher the attenuation. And this is one of the main things that determines the maximum possible speed of your line. This is because, just like mobile wireless connections – where speed is determined by signal, and signal is affected by external factors – ADSL speeds are determined by signal and interference. Copper lines might be more reliable, but they’re still subject to the laws of physics and electricity. In this case, the longer the copper, the slower the speeds. And the older the copper, the less reliable the connections. It’s for this reason that Telkom should be rolling out newer technology capable of higher speeds, rather than fixing ageing copper infrastructure that’ll only be good for 10Mbps.

Plug in your line’s attenuation, and get a theoretical speed.

The calculator gives you a speed that is closer to what your line is physically capable of. Even then, it’s a best-case scenario. Your attenuation gives you an idea of what the line is capable of, based on distance from the exchange, but it is also important to consider the noise on the line.

When Telkom turns up the speed on your line, it means sending more power through the circuit. And this power introduces noise. At some point the noise starts overpowering the signal (ie: a low signal-to-noise ratio), and your modem loses sync, then connects at a lower speed that has a better SNR.

If your line has a SNR of more than 12 or 13 decibels, it means that your line can reliably support higher speeds. Once you’ve found out that Telkom supports higher speeds in your area, you can use the calculator here to check whether your line (or rather the distance from the exchange) can support those higher speeds. And then you use the SNR on your line to judge if the higher speed will be reliable.

A 4Mbps line with a SNR of 13dB could have the power turned up to achieve 10Mbps, but depending on the distance from the exchange and the condition of the copper, it could drop the SNR to 8dB, or lower. If you have a quality modem, it’ll be able to deal with this. Cheaper modems might not – and your internet connection will be fast, but may reset often.

It’s also entirely likely that the copper in your area is of poor quality, and even though you live very near to the exchange (with a corresponding low attenuation), the line won’t reliably support higher speeds.

4) Other considerations

If your line has a low attenuation and high signal-to-noise ratio, congratulations – it’s extremely likely that it supports higher speeds. Go ahead and phone Telkom (or your ISP, if it is the one managing your line) and request an upgrade. Just remember that your higher line speed will probably also mean that your ISP data account needs to be upgraded, though this usually only applies to uncapped customers.

If your line isn’t eligible for an upgrade, you can still use this information to troubleshoot problems. As mentioned above, if you live physically close to a Telkom exchange (and have a low (sub-30dB) attenuation, but your SNR is high, you could complain about the quality of the copper in the area. This can come down to things like interference from electrical fences or poor drainage – it’s been reported that ADSL lines can be affected by lots of groundwater after heavy rains.

Source: Christo van Gemert via

What kind of issues have you had in the past? Let us know in the comments below.



Brad Daniels

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