Skip Navigation


ADSL2+ / Max ADSL / up to 24Mbps / up to 8Mbps FAQ

I've heard the hardware needed will be different?

For those people who are still on the older fixed speed products, and using six or seven year old hardware, a hardware upgrade when switching to the up to 8 Mbps and up to 24 Mbps products may be advisable. If you are still using a USB ADSL modem, then ditch it immediately and get something that connects wirelessly or via Ethernet.

If already on an up to 8 Mbps product, then your modem is most likely compatible with ADSL2+, check the modems product speeds, you are looking for support for ADSL2+ or G.992.5.

If you have a wireless modem/router that only supports 802.11b (11 Mbps) wireless, then upgrading to an 802.11g or 802.11n router is recommended. Many providers can supply new hardware that has been tested on their service, but check the cost including delivery against other online shops.

As ADSL2+ pushes what is possible over a telephone closer to the limits, people may find that different hardware performs differently. It is always checking with others on the same service what hardware they have found works best. Sometimes upgrading firmware on a modem/router can improve performance for no cost.

How will I know how fast I can get from an up to 8Mbps or ADSL2+ product?

It is possible to estimate how fast you may get on a Max, Max Premium or LLU product for the downstream line speeds. The BT Wholesale line checker will give an estimate based on a previous measurement of the capacitance of the line.

If you already have an ADSL service, you may have access to your line attenuation and noise margin (SNR Margin) figures, which can be used to provide an estimate of the maximum line speed, which may be more accurate than a simple line length guess. Two main sites exist for this form of calculation Mr Saffron's ADSL/ADSL2+ calculator, and www.dslzoneuk.net. It should be said that the estimators generally give a best case figure, for the line to be stable it may need to run at lower speeds.

If you have no idea about how to get your attenuation and noise margin figures, take a look at www.kitz.co.uk/adsl/frogstats.php which shows how to obtain the stats from the most common hardware. This was written by one of our forum users.

How does ADSL and ADSL2+ work?

When connecting, the ADSL modem splits the upstream and downstream sections of the spectrum into discrete sections known as bins, and will try to use as many as possible. The modem will assign a number of bits to each bin, and a noisy bin will carry less bits than others. This allows the modem to cope with specific frequencies that AM radio stations produce interference on.

The upstream section has less bins than the downstream. ADSL2+ has the potential to use double the number of downstream bins compared to ADSL and ADSL2, essentially it uses frequencies up to 2.2MHz versus the 1.1MHz of ADSL. ADSL2 manages its better performance by clever mathematics to to populates these bins more effeciently with data and better error correction techniques, that help to correct errors in transmission.

Should I be using ADSL2+ or ADSL?

Most broadband providers simply provision a single service, mainly up to 24 Mbps (ADSL2+) and leave the modem to negotiate the best speed.

Some people have found that when modems are left to negotiate speeds that ADSL2+ can actually be slower than ADSL. In cases like this it is usually because the line is a medium to long line, and would generally benefit from being forced to connect using either ADSL2 or ADSL modes.

The reason modems behave like this can be that modem manufacturers have not carried out extension testing on how the UK deploys ADSL2+. Also there can be variable amounts of noise that affect the ADSL2+ frequencies, while leaving ADSL range frequencies to be stable.

What does RADSL stand for?

RADSL stands for Rate Adaptive Digital Subscriber Line. Rate adaption can be applied independently to the upstream and downstream sides of an ADSL connection.

I have an up to 8 Mbps or up to 24 Mbps service, but what download speeds should I be getting?

The download speeds from ADSL and ADSL2+ service are determined by the line sync speed (connection speed shown by your ADSL modem). For those whose service is provided by BT Wholesale (e.g. BT Retail, Plusnet and others) a simple rule applies, if your line sync speed drops to a lower value the download speeds will adjust immediately, but download speeds will only rise if the line sync speed remains stable for between 75 minutes and five days. In most areas where ADSL2+ from BT Wholesale is available this change is now immediate.

For example, if you connect at 1248Kbps normally, your downloads should be close to 1Mbps, but if you suddenly reconnect at 576Kbps the maximum download speed will drop to 500Kbps. Then if your ADSL modem reconnects again later that day at 1152Kbps the speed wont improve for a variable period of between 75 minutes and five days. For those on the older ADSL service, if the change is significant it will be faster, small one step changes will generally take a couple of days.

A table showing the correlation between line sync speed and the IP profile (sometimes called BRAS Data Rate) is shown below. Some service provider portals will tell you your current IP Profile setting, alternately visit www.speedtester.bt.com and this will test the download speed and also give you your current IP profile value. A warning about the tester site, it does not always work if lots of other people are using it. For the ADSL2+ services there are many more IP Profile steps and they extend to cover connection speeds up to 24 Mbps.

BT Wholesale where it offers ADSL2+ over its 21CN WBC network, has a system that removes the steps totally, with the IP Profile, being set at 88.2% of the connection speed, eg. a 12800 Kbps connection will have a 11289 Kbps IP Profile.

Line sync speed (connection speed)

IP Profile / BRAS Data Rate

from 288Kbps (Kilo bits per second) 0.25Mbps (Mega bits per second)
from 416Kbps 0.35Mbps
from 576Kbps 0.5Mbps
from 864Kbps 0.75Mbps
from 1152Kbps 1Mbps
from 1440Kbps 1.25Mbps
from 1728Kbps 1.5Mbps
from 2016Kbps 1.75Mbps
from 2272Kbps 2Mbps
from 2848Kbps 2.5Mbps
from 3424Kbps 3Mbps
from 4000Kbps 3.5Mbps
from 4544Kbps 4Mbps
from 5120Kbps 4.5Mbps
from 5696Kbps 5Mbps
from 6240Kbps 5.5Mbps
from 6816Kbps 6Mbps
from 7392Kbps 6.5Mbps
from 7968Kbps 7Mbps
8128Kbps 7.15Mbps

What are the myths behind the BT Wholesale Max and WBC products?

A great many myths and legends have grown up around the up to 8 Mbps and up to 24 Mbps services offered by BT Wholesale in the UK. To help people understand some of the truth behind all this BT Wholesale has published a document that can be downloaded in PDF format from here.

The BT Wholesale systems continue to evolve, and for those in areas with ADSL2+ from BT, things are a lot more dynamic.

What is the IP Profile?

Firstly let’s be clear this only applies to people who have an ADSL or ADSL2+ product from a provider using BT Wholesale services (e.g. Orange, BT Total). Some providers use a mixture of wholesale providers, so the simplest way to tell is that BT Wholesale on its ADSL products has two main upstream speeds 448 Kbps and 832 Kbps. There are some exceptions to this since the upstream is rate adaptive and on poorly performing lines may connect at another value, but for most people those two upstream speeds indicate a BT Wholesale Max based service. For those with ADSL2+ the way to tell is whether the BT Speedtester site works.

The IP Profile is a setting that is derived from your downstream connection speed and is used by BT Wholesale to manage the amount of backhaul capacity needed on their network for the millions of people using their service. If you have a 7Mbps IP Profile it is impossible for your connection to download stuff from the internet at faster than 7Mbps (~7000Kilo bits per second, 875KB/sec).

The large difference between connect speed and IP Profile represents the way that traffic is carried over the telephone line in the DSL signal, i.e. the IP data is spread across small ATM packets, thus there is a an overhead for carrying IP (Internet Protocol) traffic of around 10 to 13%. The exact figure varies according to the data being transferred and configuration of the IP stack on the computer. So even without the IP Profile the maximum speed possible from a sync speed of 8128Kbps is around 7250Kbps, the next lowest IP Profile is 7150, so 100Kbps of traffic is wasted.

The difference between connection speed and throughput applies to the various LLU (unbundled providers) too, hence why if you connect at 10 Mbps you never see the full 10 Mbps from speedtests. Virgin Media cable connections avoid this due to the different technology used to deliver the service.

Why is my IP Profile a lot lower than my downstream connection speed?

If you for example have a connection speed of 4032Kbps and an IP Profile of just 0.75Mbps, this suggests that at some point within the last five days your modem reconnected to the exchange at a connection speed between 864Kbps and 1151Kbps. The IP Profile will improve given time and prior to August 2007 this was on a fixed 3 day wait period before it improved. As of August 2007 a more flexible system has been implemented where large improvements in the IP Profile may take place with 75 minutes, for example a jump from 135Kbps up to 7.15Mbps should happen quickly, whereas a small increment from 3.5Mbps to 4Mbps may take the full 5 days the current system allows.

In 2011 further improvements took place, meaning the IP Profile changed in real-time for the majority of people using an ADSL2+ (up to 24 Mbps) service from BT Wholesale.

It should be remembered that the IP Profile will lower immediately (within a minute or so) if your downstream connection speed changes and takes into the range for a different IP Profile.

Can I make the IP Profile change faster?

Some people advise using tricks to make your modem sync very slow and then quickly let it sync faster again, the problem with this is that if you get it wrong you could end up on an even lower IP Profile than you started with.

Why can't the IP Profile be set to a higher value than my downstream connection speed?

This is not desirable because if this was done the BT Wholesale network would try to feed you data faster than your ADSL line would manage, this data would be then buffered and after a short while packets may be thrown away (dropped), resulting in lost data and having to request data again. Another effect of this is that it makes the network hardware busier and may impact on how well the network can handle all the data from other people.

How can I find out what my IP Profile is?

A number of broadband providers expose the setting on their customer portal as the BRAS Data Rate or IP Profile. So you can login and see what the current value is and how it has changed. Broadband providers get informed of each change to the IP Profile so in theory if a provider stores this information it should be available to help desk staff. NOTE: In some providers only second line support may have the ability to see the information.

For those that cannot get the IP Profile from their ISP see this FAQ entry for information on the using the BT Wholesale Speedtester.

I think my IP Profile is stuck, what can I do?

Remember that it takes up to five days of being connected at a downstream connection speed that justifies an increased IP Profile now, so don't assume it is stuck until the five days is up. Make sure your ADSL modem has not reconnected at a slower speed when you were not watching, some modems log all the connection attempts making it easier to check this.

Some broadband providers (e.g. Plusnet) mirror the IP Profile from BT Wholesale, and if their system is not informed of an update, your internet speeds can be slow, even if the BT speed tester suggests they should be fast. In that case be sure to point out the disparity to your provider.

If after five days it is still stuck, raise this issue with your broadband provider, if this does not get the problem resolved then try emailing andrew@thinkbroadband.com who may be able to help.

I have always connected at 8128Kbps, but never see downloads faster than 2Mbps?

There is a situation where a line that is very stable when it gets converted to MAX does not trigger an update to the IP Profile. If you have been like this for more than ten days and the broadband provider has failed to resolve it then email andrew@thinkbroadband.com who may be able to help.

Remember to check what speeds you get at off peak times such as around breakfast time, to ensure it is not congestion on the BT Wholesale network, broadband provider or just the internet in general.

I've heard removing the ring wire can improve my connection, how do I do this?

The ring wire (sometimes called bell wire) is a hang-over from old telephones that needed the telephone line to generate the bell ringing signal on a third wire. Modern telephones generally do not need this third wire, and its presence creates an imbalance in the telephone wiring and can cause rate adaptive ADSL connections to connect slower than would otherwise be expected.

If you have already fitted an NTE5 ADSL faceplate then removing the ring wire will not make any difference. It should be noted that any improvements will be immediately apparent if you look at the connection speeds reported by your ADSL modem after it has restarted. Actual download speeds on a Max product will take some time to improve due to the delay in the IP Profile improving which is between 75 minutes and five days.


Click image for larger version

The image above shows a standard BT Master Socket with the removable faceplate lifted off. There are four wires connected; the blue pair to pins two and five, and the orange pair to pins three and four. The ring wire is the wire on pin three, i.e. orange wire with a white strip. It should be pointed out that old wiring may use just four solid colours and the wires will not be twisted together, in which case rewiring the telephone extensions in the property to use modern twisted pair phone cables is worthwhile; www.adslnation.com stocks suitable cable. If you have two or more telephone extensions, you will find multiple wires connected to pin three.

To disconnect the ring wire(s) lift the wire away from the metal conductor as shown below:


Click image for larger version

Removing the wire on pin 3 on the other sockets around your property may help, but generally will have no effect. As with any changes make sure your telephones and ADSL still work and if not return your wiring to its previous state, to test the phones fully you need to make an incoming call to check they still ring.

NOTES:Where possible do not cut the ring wires, but lift them out of the connector, cutting them may leave you with too short a wire to reconnect when you move out of the property. If refitting a wire to connectors like those in the sockets, an IDC Krone tool must be used which can be purchased at stores that sell telephone extension kits (such as DIY stores) and also online.

This procedure of removing the ring wire is also useful if you do not have an identifiable master socket in the property.

Why does my attenuation change when I use ADSL2+?

The attenuation figure displayed for downstream on ADSL and ADSL2+ services can vary, when switching between ADSL and ADSL2+ modes. Generally you should see the number increase by 3dB (a doubling due to the logarithmic scale).

This does not mean your line is performing worse, or an upgrade has degraded the line. The attenuation for the downstream bins below 1.1MHz remains identical, the change arises as you are now including the attenuation on the signal between 1.1MHz and 2.2MHz.

An additional factor is that the way some modems calculate the attenuation will vary, leading to an old and trusted devices giving different figures compared to a new modem.

Which ADSL2+ service will be fastest?

It is almost impossible to predict which provider will give the best performance, particularly at peak times as what speeds you get from the internet are governed by all the other users on a provider.

In terms of connection speed, this should be more consistent between providers, assuming that they all use the same target noise margin.

The standard target noise margin is 6dB, and this figure is what the modem uses when trying to negotiate a connection speed, i.e. it calculates the highest speed possible that will give a 6dB noise margin once connected.

BT Wholesale on some ADSL2+ exchanges, will allow a lower 3dB target margin for stable lines, which can add anything from 0.2 Mbps to 1 Mbps to your connection speed.

TalkTalk and Cable and Wireless generally default to a figure of 9dB for the target. With TalkTalk if you feel your connection is stable, you can get this lowered by posting in the TalkTalk Members forum.

The target noise margin on Sky varies, according to how stable their system assesses your line to be, their fastest speeds can be obtained by requesting a change to the gamer profile.

Be Broadband allows its customers to tweak the target noise margin and other parameters of their ADSL2+ via the customer portal, giving people full control.

I have ADSL2+ from Sky but my router always connects at 4 Mbps?

Sky has a dynamic line management system (DLM) that attempts to assess what speed a line is capable of when you first join. It operates very differently to how BT Wholesale run their system.

The default speed is 4 Mbps, even on lines that with other providers managed 10 Mbps or more. If a line looks like it will run faster, then the Sky systems progressively run the line faster over a period of a few days, until it finds what it thinks is the best speed.

If the speed stays stuck at 4 Mbps for over a week, and your modem reports a downstream noise margin of more than 9dB then contact Sky support.

For those whose line will not run at 4 Mbps, the system immediately trys slower speeds until the modem will connect - this takes as little as 30 seconds.

Some people who had a line that was unstable for the first few days of service with Sky have reported that speeds are sometimes capped, in which case report this to Sky support and request that they allow the DLM to be reset.

Why does the noise margin vary so much?

The noise margin is a dynamic value, and most modems update the display of it every few seconds. A variation of plus or minus 1dB is normal.

If you see variations of 3dB or more, then the cause is most likely due to random noise, example sources can be a plasma TV, fluorescent lights, electric trains, essentially anything that would produce noise when listening to an AM radio station.

Generally noise margins are lower at night, because there is more noise once the sun has set due to the way AM radio waves can propogate further once the sun has set.

My modem is showing a noise margin of -1dB, how is it still connected?

Some ADSL modems will actually manage to provide a connection even when in theory you should get no data over the connection. The -1dB noise margin may reflect very bad noise for some frequencies, but there still be a few bits of the ADSL signal that are able to be used.

Generally if an ADSL modem sees a noise margin this low, it will disconnect and reconnect automatically, avoiding the frequencies that caused the problem. Sometimes if you are getting a very poor connection, you can find switching the router off and on after checking the problem is a very low noise margin will give you better speeds.

The Huawei HG532 supplied by TalkTalk is an example of a router that will hold the connection even though the number noise margin is low and the number of errors is so high that webpages and video are intermittent. This may explain why many TalkTalk customers complain of low speeds, if they do not realise switching the modem off and on can help sometimes.

How can my noise margin be as large as 2147483647 dB?

Sometimes router web interfaces do not display negative numbers correctly, thus 2147483647 is actually a reading of -1dB.

My modem shows an attenuation of 63.5dB, but when I tried my friends if showed 70dB, which is right?

Most ADSL and ADSL2+ modem/routers have limits on the size of the downstream and upstream attenuation figures.

For downstream most routers only display a maximum attenuation of 63dB (or 63.5dB). On the upstream side the limit is usually 31dB or 31.5dB.

This means if you see these figures, then your attenuation is likely to be higher, and on a line that is perhaps 10km long it may be as high as 80dB.

Should my upstream attenuation be higher than my downstream attenuation?

As a general rule, downstream attenuation is roughly double that of the upstream attenuation e.g. downstream attenuation 48dB, upstream attenuation 26dB.

If a modem is showing the upstream attenuation higher than downstream, it is usually down to the web page displaying numbers in the wrong column.

I am in my training period, can I switch off my modem?

One of the myths for the up to 8 Mbps and up to 24 Mbps services is that you should not switch off your modem.

Switching off a modem overnight, or if going away for a few days will not cause any problems with the training systems some providers use. The only time it may cause problems is if you switch the modem off and on multiple times in a short period, e.g. ten or more times in an hour.

How fast will a telephone line of a certain length be?

If you have an ADSL or ADSL2+ service already, then the best estimate is by using the current data from the modem. If you only know the line length, in terms of actual cable distance between your property and the telephone exchange the table below may help.

Line Length (km)AttenuationEst. ADSL SpeedEst. ADSL2+ speed% UK lines shorter than this
0.5km 6dB 8128 Kbps 24576 Kbps 1.5%
1km 12dB 8128 Kbps 20700 Kbps 5%
1.5km 15dB 7900 Kbps 20000 Kbps 11%
2km 24dB 7350 Kbps 17500 Kbps 18%
2.5km 30dB 7000 Kbps 14500 Kbps 27.5%
3km 36dB 6300 Kbps 11500 Kbps 37.5%
3.5km 42dB 5300 Kbps 8200 Kbps 57.5%
4km 48dB 4200 Kbps 5600 Kbps 66%
4.5km 54dB 3200 Kbps 3400 Kbps 73%
5km 60dB 1900 Kbps 2250 Kbps 85%
5.5km 66dB 1100 Kbps 1600 Kbps 90.5%
6km 72dB 576 Kbps 800 Kbps 94%

The speeds above are estimates based on a mixture of sources, which ranges from manufacturer estimates, to actual real-world feedback. The line length distribution is taken from Ofcom UK telephone line data.

If you have obtained a distance estimate from the exchange to the property by using a straight line on a map (radial distance) a rough line length can be estimated by multiplying the radial distance by 1.4.