Introduction:ADSL operates at frequencies in the Medium Wave spectrum. This makes it susceptible to noise pick up, both at radio frequencies and general electrical noise, which in turn can cause your line to become unstable, losing synchronisation with the exchange at frequent intervals, for example. Incidentally, MW signals propagate further after dark, which is why ADSL lines generally become worse at this time. They can also be affected by cross-talk, signals on adjacent pairs of wires interfering with each other.
The Max variant is much more susceptible than ‘vanilla’ ADSL as it is rate-adaptive. Loosely translated, this means that BT’s line management software will push your line to go as fast as it can and still remain stable. This is why there’s a ‘training period’ when you first connect to a Max service.
Note that it’s an urban myth that the speeds established during the training period are set in stone, only one is - the Fault Threshold Rate, which determines whether or not IDNet can raise a speed-related fault on your line with BT. Otherwise, your line is continuously monitored by BT’s Dynamic Line Management (DLM) software, and your throughput (or profile) will alter to match any significant changes in your synchronisation speed.
It’s worth being aware that the DLM has ‘blip’ logic built in, so will generally restore your line speed quite quickly if you get a ‘one off’ low speed connection, but recover to your normal speed soon after. However, if you get a series of disconnections, the DLM will push your profile lower, and it will stay at that level until you have had three days of stable connection at a higher speed.
I should mention at this point that the trigger point for DLM to deem a line as unstable seems to be around 10 disconnections per hour, so don’t manually keep forcing new connections every few minutes to try an achieve better speed, you are more likely to make things worse. It’s also worth mentioning that it’s generally better to remove power from your router/modem before disconnecting it from the phone line. That way, the DSLAM, the network device you connect to at the exchange, gets a ‘last gasp’ disconnection from you, and doesn’t mark it as a sign of instability.
There’s very little you can do to improve the quality of the line from the exchange to your house. Unless there’s a major issue, BT are not going to run new cable for you, and they do not have a universal service obligation for ADSL as they do for voice, so it’s pointless writing to BT or your MP demanding a higher speed.
How you can help yourself:What you can do is to improve the quality of your internal wiring, by which I mean everything after the master socket. Please note that it’s illegal, and potentially dangerous, to work on the wiring on the exchange side of the master socket. If you do, BT can cut your line off without notice.
The absolute first thing to do is to make sure that every device you have connected to your line passes through a filter. That includes all phones, fax machines, Sky boxes and analogue modems. It also includes any alarm systems which connect to the line, but you will probably have to get your alarm company to install a filter in that instance. Note that not all filters are created equal. Personally, I recommend the ADSL Nation
xf-1e, but be prepared to try swapping filters to see if you get an improvement. If you must keep your Sky box connected to the phone line, eg you have a multi-room subscription, I’ve seen reports that using two filters in series can help.
The next thing to do is to make sure that you do not connect your modem or router using a cheap ‘flat’ extension lead of the sort sold by DIY stores. I'm not talking about the cable supplied with the router, but any ordinary telephone extension leads you may use. Flat leads are not constructed from twisted pairs (see below) and so can add to the noise pickup.
Make sure that any extension leads you do have, whether loose or hard-wired, do not run parallel to mains cables, where possible keep them physically separated and if they have to cross, let them cross at right-angles.
Hopefully, you will have what’s known as an NTE5 master socket, like the first illustration below. If you have one of the older style of master sockets, there are still things you can do, so keep reading.
If you do have an NTE5, connect your router to the test socket, which is exposed by removing the faceplate. This disconnects all your internal wiring and leaves you connected directly to the ‘exchange pair’. Note your line stats, and compare them to those you normally get. With vanilla ADSL, you are concerned with the noise margin and whether that increases significantly. With Max, you will be looking for an improved downstream synchronisation speed, with the noise margin remaining the same (that’s how Max works). With Netgear, and many other brands of router, you can automate the gathering of lines stats using the free program Routerstats, available
here.
If you don’t have an NTE5 master socket, then check your figures with everything else in the house disconnected. You’re looking for the same improvements as you would with an NTE5, but the results will not be as clear cut, as you are not disconnecting all your internal wiring.
If your figures do improve, then the chances are that your internal wiring, or devices attached to the line, are adding noise to your line. One of the most common causes of this is the so-called ring, or bell, wire. This wire is a hangover from the days when phones had physical bells, and needed a hefty current to make them ring. Modern phones do not generally need the ring wire, and the current required to ring a bell is generated by micro filters in any case. What the wire does do is act as a big antenna to collect noise and radio signals and, thus, worsen your ADSL connection. The only two wires you need are the exchange pair, which are connected to terminals 2 & 5.
The ring wire is connected on terminal 3 at all sockets, and is usually, but not always, coloured orange/white, you can see it on the second photo below, courtesy of forum member 'Jimbo'.
However, go by the terminal number, not the colour, and wriggle the wire out from terminal 3 at every socket, and then take another look at your figures from the socket where you normally connect. Have they improved? If so, pat yourself on the head as you’ve just mastered the art of getting the most from your line.
If they haven’t, there’s one final thing you can check for. I mentioned previously the use of ‘twisted pairs’. A normal internal phone cable has six wires, which are configured as three twisted pairs. All this means is that, for example, the blue/white and white/blue pair of wires wind around each other in the cable. This twisting acts to reduce noise and interference pick up.
Sometimes, with DIY or builder-installed extensions, you might find a split pair. This occurs if you have, say, the blue/white wire on terminal two, and the green/white on terminal five. Because the wires are not twisted, both of them will also act as antennae and add to your noise levels. Rectify the wiring by swapping one of the wires to its paired colour. Normal BT wiring will use the blue/white and white/blue pair for a single line installation. The photo shows a correctly wired pair, albeit the ring wire is still connected.
If you do find the need to replace any of your wiring, do ensure you use a high-quality cable, designed for the purpose, usually referred to as CW1308.
If nothing here improves your line quality, the chances are it's an issue between you and the exchange. If it's sufficiently bad, contact Customer Services at IDNet. They will be able to test the line and, if the results indicate it necessary, they will arrange for a visit from an ADSL-trained BT engineer. Note, though, that his first act will be to check the signal at the test socket, or the exchange pair if you don't have a test socket. If that signal is OK, but the one on your extensions is not, there will be a fee payable.
Last revision: March 19, 2007.
My thanks to Jupiter for his comments and suggestions.
(C) Rik Bean, 2007