Broadband News

BT Wholesale Release Contention and Packet Fragmentation Briefing

BT Wholesale have released a briefing today which outlines a number of issues which are currently in focus. Primarily, these areas include contention and packet fragmentation, both of which can significantly affect the overall experience for end users.

BT state clearly that the IPStream products (those used for ADSL) are contended services. They have been designed so that end users share a finite amount of bandwidth available across the network. As many of our readers are aware, contention for the IPStream 500 and Home 500 services is stated to be 50:1, and Office 500/1000/2000 is 20:1. BT claim that the ratios enforced are based upon experience and continual network monitoring. The most interesting mention is that the sharing of bandwidth for typical applications such as web browsing should be "virtually transparent" and doesn't significantly impact upon the end user experience.

Due to the "bursty" nature of web browsing, the aggregate network usage tends to average out over time, which is good news for web browsing, but may impact speed for the downloading of files or streaming media. To date, we have seen relatively few signs of contention around the country which may suggest that BT are reluctant to compromise on performance especially as competition is rising in the areas of cable and wireless technology.

The briefing continues by confirming that the Maximum Transmission Unit (MTU) size should be no larger than 1458 bytes (as recently announced). For the majority of Internet users, changing such settings is an unrealistic task to undertake and resultantly, BT has plans underway to eliminate fragmentation from the network by the end of May 2003. This target date will be achieved through a "phased set of programmes commencing in mid January 2003" and will involve extensive upgrades to both software and hardware network components. Testing and trials will be completed before the full deployment date and customers are expected to see incremental improvements as time proceeds.


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