SPEEDING UP BROADBAND AND

MINIMISING DISCONNECTIONS

(in the UK)

Here are a few notes, put together from various sources to help people understand how the broadband process works and how best to achieve maximum throughput. These notes are aimed at people using "traditional telephone lines" as opposed to "cable" in the UK. Many of the points raised will be applicable in other parts of the world

ADSL LINE SIGNAL FIGURES

When an ADSL line is ordered, BT Wholesale perform some checks before activating an ADSL service. If ordering a Max based product, the only check done is whether the service is available on your exchange, and that you've not had your line marked as RED, i.e. 'unsuitable for ADSL' due to a previous failed ADSL activation.

Line Length. Y ou must be within approximately 3.5km to pass for the 2Mbps product, and within approximately 6km for the 1Mbps ADSL products. There is no set limit for a 0.5Mbps service, all but 0.2% of lines should support a 0.5Mbps service

Line Loss. You need a line loss of no more than 43db for the 2Mbps product, 60dB for 1Mbps product. This test is normally a paper exercise based around the records for your line and area, if a border line figure appears they may test it out in the street. No limit exists for 0.5Mbps services, if you are connected to an enabled exchange your line will be enabled and if it does not work an engineer visit will be arranged to try and get you a service

Capacitance. T o pass, this should be below 160nF - for RADSL the figure is believed to be 300nF (nF is nano-farods)

APTS. This test uses special software on the engineers hardware to talk to the DSLAM and measure the attenuation across the actual line. The limits using this kit are 43dB for a 2Mbps service, and 60dB for the 1Mbps service. Currently this is the definitive test, with 0.5Mbps it is a case of so long as your modem will work you can have the service

Woosh Attentuation Test. The woosh test is actually a whole suite of tests, the attenuation measurements are just one subset. This is not used for line qualification anymore, due to the variations caused by the various bits of ADSL hardware people use. The woosh attenuation test looks at the quality of the line across the DSL frequency range and measures how much of the signal reaches your house, the loss should be less than 45db for 2Mbps and 64dB for 1Mbps products. ISPs have the ability via the ECO interface to remotely do this test, but a pass with this test does not guarantee acceptance onto the 1Mbps and 2Mbps limits. Many ADSL modems will display the equivalent of the woosh test, but these can be inaccurate. Some modems can be as much as 20dB, though the majority are within 2-3dB. For those with very long lines, the Signal to Noise ratio (Noise Margin) becomes critical, ideally a figure above 6dB is needed for most ADSL kit to function

SNR is, as its name suggests the ratio of signal (the bit we want) to noise (the bits we don't want). Noise can be introduced by poor quality lines, bad wiring (including extension wiring in the building) etc. The ratio is expressed in decibels (dB) and the higher the number, the better (i.e. if the number is higher, there is much more signal than noise). An average SNR is around 30dB

A low SNR is likely to lead to disconnections if the line is noisy. A high SNR is likely to allow more stability because there is a higher buffer over which noise would have to spike to drop the connection. If the line is not particularly noisy, it is possible to get very high speeds with very low SNRs without dropouts

If the ADSL line is frequently disconnecting, this usually implies a noisy line or that something in the building is interfering with the incoming ADSL signal. Most ADSL modems will pick the most optimum set of speeds and download SN to provide maximum speeds. Changing the modem settings will only alter the speed by trading off SN, so increasing speed will increase dropouts by lowering SN

Generally for ADSL the higher the SNR is the better, but for ADSL2 a high SNR is not normal. ADSL2 should have a SNR of around 6dB unless some sort of stability profile has been added

Loop Attenuation is a measure of the quality of the line from the point of view of how much the signal is impeded. The longer the line, the higher the attenuation will be (hence the 'quieter' the signal). BT will generally not provide an ADSL service if the attentuation is over 55dB. Typical attenuation values from a good working ADSL line are between 30dB and 40dB

Line attenuation is a measure of how much the signal has degraded between the DSLAM, in the exchange, and the modem. So the lower the dB value the better for this measurement

20dB and below is outstanding
20dB-30dB is excellent
30dB-50dB is good
50dB-60dB is poor and may experience connectivity issues
60dB or above is bad and will experience connectivity issues

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HOW TO OBTAIN SNR AND LOOP ATTENUATION FIGURES

Most modem/routers manufacturers allow the user to access this information, usually by entering the web interface address of the modem/router into a web browser. The address will vary depending upon the type of modem/routers. (try 192.168.0.1 as a starting point)

HOW TO MEASURE BROADBAND SPEED

Determining the true speed of the internet connection isn’t as easy as you may think. Check the attenuation and throughput speed with no other devices connected to the telephone line. Add devices one at a time noting any degregation of speed. Try and reduce the number of phones and equipment connected to the line if you can. There are several, often contradictory, measures of the ADSL connection speed. These include:

Sync speed (or line rate) This is the speed at which the router connects to the local telephone exchange - the theoretical maximum speed the line could achieve in perfect conditions. This is the figure that pops up in the little bubble in the Windows System Tray when the router first connects

Maximum Stable Rate (MSR) After ten days, the ADSL Max connection will be given a Maximum Stable Rate figure. Perversely, this is the lowest stable sync speed the line managed to achieve over that period, during which BT is attempting to find the true speed of the line. ISPs recommend you frequently connect and reconnect during that initial ten-day period so the line can be tested at different times of day

BRAS profile The BRAS profile regulates the maximum throughput received on the connection. BT limits the download speed of data across the ADSL line based on the recorded sync speeds, to help improve stability. This is initally set to 2Mb/sec, but will increase if the line can support higher speeds. The BRAS profile changes only when a stable connection has been made for a period of time, which can be anything between 75 minutes and three days. Sometimes BRAS profiles can get “stuck” at the initial 2Mb/sec speed, artificially constricting the connection

Throughput This is the “true” speed of the connection - taken by measuring the actual rate at which data is downloaded and uploaded. Naturally, this is slower than the sync rate and often well below the mythical “up to 8Mb/sec”. Sites such as www.speedtest.net will accurately determine the actual throughput. It you’re running the router off an extension socket, try performing a speed test and then connect the router to the master socket and run the speed test again to see how much speed is being lost

VARIOUS THINGS TO TRY TO IMPROVE BROADBAND SPEED

ELECTRICAL INTERFERENCE

TV’s, satellite set-top boxes, microwave ovens, Christmas lights etc. can all affect broadband speed by emitting electrical noise due to faulty components and/or power supplies. The bell wire in the telephone wiring (the line that used to make old-fashioned phones ring) acts as an aerial and picks up the electrical noise

Try switching various equipment around the building on/off, one by one, to see if the connection speed is affected. A handy tip is to tune an AM radio to 627KHz and listen for crackling when devices are turned on/off, as this is a sure sign of excessive electrical interference

It can just as easily be neighbour’s equipment that’s slowing the broadband down. Some devices such as faulty TVs can affect broadband speed within a 200m radius!

FIT AN INTERSTITIAL PLATE (iPlate)

BT has been testing a new device that aims to eliminate the electrical interference on the bell wire. Called an Interstitial Plate (or iPlate). This device can make on average, one and a half megs of difference

The £10 iPlate can be installed without the help of an engineer, you simply remove a couple of screws on the front of the master NTE5 telephone socket, insert the plate and retighten the screws. The device is only of real benefit to people who have multiple phone extensions in the building; those who use the master socket alone are unlikely to see any improvement in connection speed

AVOID TELEPHONE EXTENSION WIRING

The experts recommend plugging ADSL equipment into the master NTE5 telephone socket and not on an extension socket. If an extension socket cannot be avoided then make sure the extension wire is no longer than 3m. BT’s broadband checker (www.adslchecker.bt.com/pls/adsl) is reasonably accurate and a good indicator of how badly internal wiring may be affecting the connection if the router is plugged into an extension

WI-Fl TWEAKS

If you suspect that a neighbour’s Wi-Fi may be affecting yours then use a program like NetStumbler (www.netstumbler.com/downloads) to reveal which Wi-Fi channel(s) your neighbour(s) are using. Then either set your router to a different channel or if multiple neighbours, agree which channels to use between you. Be aware that wireless routers may have a weak signals on some channels due to topography etc.

If a Wi-Fi router is plugged into the master socket, as recommended, but now can’t get a decent signal in certain rooms, a booster may be the best option. Also a 5dBi omnidirectional aerial can provide an 80% boost in coverage and performance at a distance. Avoid connecting boosters to surge protectors, as performance can be significantly affected

THE REACTIVE REPAIR TOOL

BT Wholesale offers a service to its broadband providers called the Reactive Repair Tool. With this service, the ISP’s support staff can see a detailed history of a line’s maximum and average speed, faults and uptime over the past fortnight. This is a useful tool for diagnosing hard-to-pin-down problems. Not all ISPs have access to the Reactive Repair Tool, but it’s well worth asking your tech support desk if they do before contemplating more drastic solutions to connection problems

KEEP THE ROUTER UP-TO-DATE

The type of ADSL router can make a huge difference to the actual speed of the connection. It’s critical that the modem/router is kept up-to-date with the latest firmware. It may also be a good idea to consider upgrading hardware every time the connection is upgraded

REPLACE THE ADSL FILTERS

ADSL filters are a surprisingly common point of failure for home broadband connections. These devices separate the low-end frequencies required for voice calls from the high-end frequencies needed for the ADSL connection. However, many poorly made filters given out by some lSPs are prone to fail, leading to excessive noise interfering with the speed of the connection

Check that there is a filter fitted to every socket where there is telephone equipment attached (telephones, Sky boxes, fax machines etc.). The filter should plug directly into the wall socket. If there is a two-way splitter coming off the wall socket, make sure the filter is plugged in before the splitter

A tell-tale sign that a filter is faulty is noise on the line when making voice calls. Zen Internet provides a comprehensive guide to testing ADSL filters at www.zensupport.co.uk/knowledgebase/article.aspx?id=10012, but it essentially involves plugging each filter into the master socket in turn to eliminate the faulty unit

The ADSL nation website (www.adslnation.com/support/filters.php) provides a detailed example of what is inside a filter

Alternatively, filters can be replaced with an ADSL faceplate like the iPlate, previously mentioned. This is fit over the master NTE5 telephone socket, and provides separate voice and ADSL connectors, instead of the single connector. It also does away with the need to fit dedicated filters on extensions, meaning equipment can be plugged in as normal. Clarity (www.clarity.it/telecoms/adsl_faceplate.htm) has decidedly no-nonsense advice on fitting and buying these devices

AR7 CHIPSET ROUTERS

ADSL routers with AR7 chipsets may keep dropping the connection every few minutes because the chipset has a problem dealing with electrical noise on the line. A list of some of the models containing the AR7 chipset can be found at www.linux-mips.org/wiki/AR7

Some manufacturers, such as Netgear, have released firmware updates (kbserver.netgear.com/release_notes/d103272.asp) that have reportedly solved the problem. Check the router’s software interface to see if there are any firmware upgrades available. Alternatively, borrow a non-AR7 router to see if that improves the reliability of the connection, before investing in new equipment

FINE-TUNE MTU SETTINGS

When a PC requests data from some websites, they use Path MTU Discovery to check what size packets to send back to the computer. If the site can’t check what size packets to send, it reverts to the default of 1500, but if any of the gateways or routers along the path have a smaller MTU the data packet will be dropped

The MTU settings can be tweaked on both the PC and the router, but the same figure must be used on both. www.kitz.co.uk/adsl/MTU.htm provides a clear guide on how to adjust these. Both Kitz and Zen Internet recommend adjusting the MTU down to 1458. Zen’s MTU support page (www.zen.co.uk/support/tools.aspx) says values of 1418, 1468 and 1430 have also worked well. The free SG TCP Optimizer (www.speedguide.net/downloads.php) will determine the optimal MTU and other settings for XP machine. Backup the Registry first!

INTERLEAVING

Asking the ISP to switch on interleaving might improve the performance of the connection

Excessive noise on a line can cause packets of data sent over the connection to corrupt, leading the router to re-request the data, which affects the overall data throughput. Interleaving takes those data packets and hacks them into smaller pieces, leaving the router to reassemble them. BT can apply interleaving to lines, which can significantly improve stability and speed by correcting errors that would normally cause a loss of sync and reduction in speed

The downside is that latency is sacrificed, which may be seen as a problem for some online games. BT also claims interleaving can reduce the maximum throughput of the line, although anecdotal evidence on internet forums suggests many people find their connections still achieve the same speeds after interleaving is applied. If you’re suffering from an erratic connection, talk to your ISP to see if it can switch on interleaving on the line

GOING FURTHER

If the modem/router keeps randomly disconnecting then there is a way of telling the modem to instruct the DSLAM equipment at the exchange to trade off speed for SNR. This is pretty cutting edge and to-date I'm only aware of one modem (Netgear DG834GT) that is capable of being instructed to do this. There are a couple of firmware re-writes available on the web that can be uploaded into this modem which then allow many parameters, not generally available to the end user, to be tweeked!

I've successfully tried the UberGT Project software and found that it solved a disconnection problem completely

Its actually quite easy to alter these parameters from the command prompt but a program such as the one above is required to keep the settings through a modem/router re-boot

LINKS

Davey Winder’s round up of broadband diagnostic tools

Find out if your exchange offers cable, LLU and when it will be ready for BT’s next-gen 21CN network

Reliability of the AR7 chipset in ADSL modems