DSL modem chipset issue comes to the fore
The Register is claiming an exclusive on the reliability of an ADSL modem chipset that is in use around the world. Our forum has had information on this topic pre-dating The Register article, and there is frequent discussion with regards the reliability of many different pieces of ADSL kit in our DSL Hardware forum.
It needs to be said that one of the problems with ADSL around the world is its use of the AM radio band frequency range, which makes it subject to potential interference from AM radio. Many other electrical sources (e.g. low voltage lights, heating pumps and speakers) can also cause impulse interference that affects stability. This is one reason for rate adaptive ADSL, so that during periods of noise, an ADSL modem will disconnect and re-negotiate a speed that can be sustained, and is less susceptible to the interference. One thing many people are not aware of is that the time of day is a big factor in the reliability, since during the hours of darkness the interference mentioned above can often be worse. As the nights draw in, people who have had lines that were stable for 6 months may find things become more unreliable.
An ADSL modem disconnecting once or twice a day is probably acceptable to 99% of ADSL users, but when it happens more often, plenty of people have found by using an ADSL faceplate at their BT master socket the effects of noise can be diminished. This is hardly a unique situation to the UK and our old copper network is probably of similar age and quality to that of other countries that use ADSL.
The AR7 problem highlighted appears to be more to do with frequent re-syncs in a short period of time with the modem refusing to connect at a slower, more sensible, speed. With the BT Wholesale Max product, this can result in an increase in the target noise margin, i.e. sacrifice speed for stability.
What is not obvious for those quickly reading up on this issue, is that different modems using the AR7 chipset can actually perform very differently on the same telephone line. We have a number of AR7 based devices and the Netgear DG834G does disconnect a number of times in the evening on a noisy line, while a Solwise SAR-600E and 600EW appear to be highly stable. The line in question is not of the best quality, and it has two master sockets and a star configuration which can mean transient noise can have a great effect on stability.
In summary, some people are seeing issues with some AR7 based kit, but until we have a lot more information, it is hard to draw any firm conclusion. If you have hardware that appears to disconnect a lot, the first thing to do is ensure it is not the telephone wiring in your property before running out to buy a new ADSL modem or router. This can be done by testing your ADSL hardware in the test socket of your BT Master socket. If this is more stable then your extension wiring is having a negative effect on the line. To access the test socket, you must have a new-style split faceplate known as a NTE5. Unscrew the two screws that hold the lower face plate on to the rear, and carefully remove this portion, avoiding disturbance to any wiring connected to it. You should reveal a second socket on the right hand side of the portion still attached attached to the wall, as pictured. This is the test socket.
Click image for a larger version
If you are sure your home wiring is not the issue and things remain unstable, a good course is to borrow some hardware from a friend for a few hours to see if that works better on your line, thus avoiding buying what may be another lemon device. A number of people who have had problems have found that SpeedTouch devices appear to run reliably.
We look forward to more information surfacing over time on this issue. Investigation may reveal that only one particularly DSLAM exhibits the problems with the AR7 chipset, or that a firmware upgrade could tweak performance to an acceptable level. When looking at ADSL hardware over the years we have found things like firmware upgrades can drastically alter how hardware behaves, so those happy to carry out their own upgrades may want to try this to see if it makes any changes.