BT Wholesale Max service round-up
Wednesday 21 June 2006 09:31:00 by
The BT Wholesale Max and Max Premium products have been out in the wild now for a couple of months, and the experience is perhaps best summed up as a variable one. Plenty of people have had no
real problems and are enjoying what is mainly a free speed boost, but some are seeing things like a line that resyncs many times in a day, or download speeds slower than they previous had. This
news item is going to address some of these issues, provide hints and tips, and also give a little more background on the service, that maybe not all providers are passing on.
Our glossary we published covering some of the basic terms is worth reading, and can be found here. Perhaps the
most common cause for confusion when people are posting on our forums is when posting download speeds, and the difference between bits and Bytes is mixed up. As a general rule, a capital B means
Bytes, e.g. KB/sec is Kilo Bytes per second, and a small b means bits, Kbps is Kilo bits per second. The conversion between bits and Bytes is fairly simple, as one Byte contains eight bits (there
are some exceptions in communications, but for dicussion on broadband download speeds, 1 Byte is 8 bits). Now onto some of points recently raised with service providers.
- In terms of the ADSL hardware used, not all hardware is created equal, for example a USB ADSL modem may connect to the ADSL line, but the USB bus or the modems drivers may not handle a full
line speed of 8128Kbps, this often only shows up as slow speedtest results. Also posters on our forums are indicating that some ADSL
hardware is more likely to be stable and not drop the line constantly, whereas other hardware will drop the line at the first hint of a noise margin change. Selecting ADSL hardware for a fully
rate adaptive ADSL line, should in theory be easy, as rate adaption is used world-wide, but alas the software in ADSL modems can be very variable, so its worth seeing if others are having
problems with specific hardware. There are some ADSL modems that actually allow the end-user to tweak the connection, by setting a higher target noise margin.
TWEAKING, what many may not realise is that with previous tweaking, or maybe even the default settings on their computer, they may be limiting themselves to lower speeds than the
hardware and provider can manage. The key point is that the Receive Window (RWIN) in the TCP stack needs to set at a size that will provide an optimum experience depending on the latency
between your computer and the most common sites you use. As an example if you tweaked your old 0.5Mbps to a RWIN of 6400, then under Max and assuming a 50ms latency, the maximum throughput is
likely to be around 1Mbps even if synced at 8128kbps, the highest BRAS Data Rate of 7.15Mbps is set and there is no congestion in the networks. Sites such as www.netmonitor.org/tools (UK based), and www.broadbandreports.com/tweaks (US based) provide tweak tests and lots of information and tools to tweak the best performance out of a computer.
- If you are connected to a very small provider, there is a small chance that the connection between service provider and BT Wholesale, called the BT Central may be a bottleneck. Some niche
providers may still have 0.5Mbps, 1Mbps, 2Mbps or 4Mbps BT Centrals, and even on the large 10Mbps, 34Mbps & 155Mbps Centrals the data delivery is done in two paths, i.e. 2 x 5Mbps pipes, so a
user on an ISP with a 10Mbps BT Central will not see a full 8Mbps ever, in fact the maximum IP rate would be around 3.8Mbps if they were the only user on the pipe.
- Internal telephone extension wiring, with the large margins built into the previous fixed rate broadband products this was of little concern apart from on very long lines, but with Max
exploiting the capabilities of the copper line fully, poor internal extension wiring and layouts can cause havoc. For example running untwisted extension wiring behind a monitor can create lots
of noise pick-up and make a Max line resync a lot, or simply run a lot slower than estimates suggested. If you are not sure whether your telephone wiring is an issue, then ask in our BT Wholesale forum, where you may find other similar posts, or people who can help in explaining what to
do. The subject of improving the telephone wiring can be lengthy, but the results can be surprising, returning a flaky Max service to a nice fast stable line. It is possible to pay for a BT
engineer to visit and resolve your extension wiring, but its worth doing the basic checks like disconnecting your many extensions and using the test socket located under the Master socket
- Not all ADSL microfilters are created equal, and price is not always a guide to quality. You may have had your microfilters for some years and they've worked well, but if you have an unstable
Max service it is worth reviewing the ones you have. Remember also that all devices connected to the telephone line need a microfilter, so make sure your Sky and Freeview boxes are using a
microfilter if they are connected to the phone line.
- Don't confuse the various speeds you are seeing, for example if connecting to a router via Ethernet, in Windows the task bar icons may well show 100Mbps as the connection speed, this is just
the speed to your router, not some super fast DSL service. The line sync speed reported by your ADSL modem, covers the amount of ATM packets that can be sent, the actual throughput over the
Internet is less, generally 10-13% less, as overheads in the protocols need to be allowed for. The table we published in April 2006, shows the best BRAS Data Rate for various line sync speeds, which represents the best download speeds you should see, if everything else is perfect. Of course congestion
can give you slower speeds, and this can happen at many points between you and the various speed testers.
- BT Wholesale speedtester, it is normal for people to be directed to the BT Wholesale speedtest if they are having speed problems, but BT has announced it has had a problem with its tester,
which meant that many people may have seen a maximum speed test of 3.5Mbps, even if their line was capable of much more. This will be fixed, and hopefully we will let people know when this is
- Congestion, some are reporting seeing more congestion and different behaviours now that Max is in use by many thousands and thousands of people. Congestion has been around since the inception
of ADSL, but often it was not visible, or at such a low level that people did not say anything. As individuals get lines that are running faster and faster people need to be aware that since
prices have not shot up, that providers and BT Wholesale are not always throwing a lot more capacity into the equation. This means at peak times the relative reduction in speed may be greater
compared to maximum line rates that were seen a few months ago. Add to this mix the rapid rate of new users to ADSL services, changing usage patterns and it is almost impossible to say for sure
if congestion is worse now than 3 months ago.
- Some myths to do with contention and how BT Wholesale manage the link between the exchanges and where the ISP takes control have arisen. One common one is that all IPstream traffic now uses a
single link (virtual path - VP), this may be the case on some exchanges, but multiple virtual paths are still used, and may contain a mixture of IPstream products, i.e. a Home 500 connection may
be on the same path as a Max product. BT Wholesale does apply a weighting scheme so that at peak times, those paying for Max Premium should get more packets than those on Max, who in turn get
more packets than for example Home 500 users. One possible side-effect of the weighting system seen sometimes now, is that people at busy times of the day may see traffic going up and down in
speed in steps, as the BT systems adjust to the peak loads. Of course on top of this there is whatever traffic controls your provider uses or does not use.
- To give some idea of the spread of speeds people are seeing with Max products in May 2006, we have collated the results from December 2005 when the Max product was relatively rare as it was
still in the trial stages, and results from May 2006 to show how things have changed.
Click image to view a larger copy
The two lines represent the averaged trend in downstream and upstream speeds. The plots allow you to see the variation in results between peak (which seems to be around 8pm) and off-peak. The
results for individual lines are going to vary greatly of course, but the plots give some idea of the changes to the UK broadband landscape, and how average or not your own speedtest results
are. The scatter plots include users still on 0.5Mbps, 1Mbps and 2Mbps services, plotting just Max users would probably give a higher trendline.