BT Wholesale is looking to run a trial with service providers, whereby they will have slightly more control over how the BT Central which links the BT Wholesale ATM network to the ISP's network is filled up with users.
Currently a very simple round robin algorithm is used, where as each user logs in they are allocated to the next BT Central for that domain(s). This works reasonably when an ISP has identical size and types of BT Centrals, but if an ISP has 2x155Mbps centrals and a 622Mbps central, there is scope for an imbalance. The trial proposed is to use a 'weighted session allocation', allowing providers to assign a weighting factor. The idea being to allow the ISP to direct more of the log ins to their larger Centrals. At the end of the day this trial if it works, may help to reduce the amount of people who are logging off and on, in an attempt to get onto the quieter BT Central.
Weighted session allocation is not a total solution to problems of one BT Central ending up packed to the limits and another still only 50% utilised. The reason being that no record is kept of each end-users usage, all logins are treated equally, and even if these details were kept there is no way of knowing what usage level a session that has just started will make. Of course it is perfectly possible for a service provider to control the usage level of a users session with other hardware, which will allow them to cope if by some coincidence a cluster of heavy users arrive on one BT Central.
For those desperate to know more on this www.sinet.bt.com has more in STIN 457 which describes this trial.
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