Broadband News

BT publishes details of the forthcoming Max beta trial

After a couple more weeks of speculation and rumour, and some correct facts leaking out, BT has published its Suppliers' Trial Information Note (STIN) for the BT IPstream Home/Office Max and BT Datastream Max beta trials that start at the end of November 2005. The documents can be downloaded from The documents are fairly technical in their nature so will probably appeal most to service provider staff and techies looking for more background.

The key outstanding points are (in no particular order):

  • The beta trial on the IPstream range will cover the Home Max products initially, with Office Max slotting in later.
  • In respect to the Datastream products, the Office Max range will be trialled first, with the Home range Max added at a later date. Which Datastream product you are on will depend largely on the service provider.
  • The trial will start on the 25 exchanges previously mentioned here, this will expand to cover 53 exchanges. The exchanges will be spread across five UK regions, and up to 50,000 users will be supported on the trial. If the trial progresses well coverage may be expanded to allow for a maximum of 150,000 end users.
  • The downstream rate adaption is nominally 288kbps (kilo bit per second) to 8128kbps (DSL line rate), but profile on the DSLAM will allow for downstream speeds as low as 160kbps. If people sync as slow as 160kbps, BT will allow this to be dealt with as a fault, and try to bring the line up to a 288kbps speed.
  • Given the odd sync speeds that seem possible, the original 0.5Mbps steps on the earlier trial appear to not be present. What the new step size in the rate adaption profile is set to, we currently do not know - 128kbps looks likely.
  • RAMBO or Digital Line Management (DLM) is a process that can run automatically or be manually overriden allowing the for the gathering of historical data on a lines performance and stability. The DLM will try to ensure a stable performance profile, basically tuning the maximum speed for a line to the real world performance characteristics rather than estimates.
  • An option called Interleaving will be used by the DLM, to try and provide the fastest possible stable line speeds. Interleaving makes the line more immune to errors, improving throughput but at the expense of latency. Therefore gamers may prefer this was not applied to their line, service providers will have the ability to opt lines out of the interleaving mode. The latency affect is expected to be 20 to 40ms depending on the model of DSLAM at the exchange. This option may prove very useful for those with very long lines.
  • The throughput due to contention/congestion on the Max products looks likely to be managed such that if you had a 2Mbps capable line prior to the Max regrade, you should see roughly equivalent throughputs at peak times. For those with Home 1000 or Home 500 similar throughput levels will may be achieved at peak times. In short this means that while an exchange is uncongested you should see a difference with the Max services, but if an exchange becomes congested download speeds may suffer.

Of course do remember that these details are describing a trial, and thus are open to change, and in particular the final end product if it appears may perform differently.

The news on the interleaving and very low speed rate adaption, does offer some hope to those who have long unstable lines, and possible speed improvements for the small percentage of people who can only use the BT IPstream Home 250 service due to the length of their lines.

Update Friday 11th November: Added the Datastream note.


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