Improvements to BT’s Dynamic Line Management

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Ever had a random sync-speed drop that resulted in slow throughput for days? The necessary evil of MaxDSL (otherwise known as the IP Profile) is the throughput cap that BT assign to customers' lines. It's designed to stop packet loss within BT Wholesale's ADSL network and, working alongside our own Maximum Rate for your connection helps to improve end user performance by ensuring the traffic is intelligently managed from end-to-end. The IP Profile and bRAS profile for customer lines react to fluctuations in sync-speed (the speed at which you connect with the telephone exchange). That means that if your connection speed drops - then the IP Profile limit swiftly follows suit. In turn, we then receive an update from BT which updates our own limit for customers' throughput. The net result is a better performing line at lower sync-speeds and therefore better performance in some fault cases. Fluctuations in sync-speed can be caused by a variety of things. Storms, for example, can result in a reduction in sync-speed and you can also affect it by plugging telephone equipment into the line without a microfilter. A line fault could also result in increased noise on the line and therefore a lower sync-speed. The inconvenience occurs, however, when everything returns to normal. That is, everything except your IP Profile. As explained above, it doesn't take much to trigger a decrease of your IP Profile - that all happens smoothly! But currently it can take 3-4 days of a stable sync for it to go back up and that is what BT are now changing the logic of. From 7th August, BT Wholesale are introducing what they call "Adaptive Rate Logic". Essentially, this means more granular management of the sync-speed to IP Profile relationship. Under "Adaptive Rate Logic", raising the IP Profile after a sync blip will be based on the percentage increase monitored. Lines which quickly come back up to normal sync-speed will see the IP Profile lifted within just a few hours in most cases, whilst lines with a sync-speed that increases more slowly will result in a longer wait and thus proven stability of the line before the IP profile follows. BT's briefing to ISPs stated :- "The current Max logic rules mean higher sync rates are required to be sustained for 3 days to invoke an upwards BRAS profile move, irrespective of the degree of line rate change. Adaptive Max Logic will look at the percentage of the line rate increase to determine the period before an upward BRAS profile change is implemented. A small percentage increase in line rate may mean a wait of up to 5 days to change the BRAS profile, but where a larger percentage change occurs, the BRAS profile could change within a very short time (4-6 hours). These timescales are indicative and may vary depending upon the load on our systems. This way any lines that have dropped to an artificially low line rate for any reason ( e.g.. thunderstorm) and revert to a higher line rate soon after may only need to wait a short time for the higher BRAS profile to be invoked." If you wish to find out what your IP Profile is then try a BT Performance Test at http://www.speedtester.bt.com If you think you might be suffering a speed fault, have a read of James's excellent blog post here : http://users.plus.net/QL:8831BC49 Liam Martin PlusNet Comms Team