Does BT Vision Reserve Bandwidth?

macman

I've got a friend whose BT 'Unlimited' Broadband is running much slower than her line test would indicate. The BT checker says she should be getting around 4.5Mbps download. But speedtest.net shows under 2MBps.
I've got her to check both using wireless and ethernet and the result is the same. I haven't seen the set up, but she says she is subscribed to BT Vision. Am I right in thinking that BT Vision reserves part of the bandwidth in order to download the on-demand services? If so, does this reduce the linespeed all the time, or only when BT Vision is being used?
There are no other line problems that would account for the slow speed.
I've not encountered BT Vision before, so any advice would be appreciated.

kwikbreaks

I can't give a definitive answer but my belief is that BT will ringfence 2Mbps for your connection while BTVision is in use.

Unfortunately I also think that they didn't increase their total capacity so that means as more and more sign up for and use BT Vision the general broadband will suffer as the available bandwidth gets squeezed. That of course applies to any BT Retail adsl connection whether or not you have subscribed to BT Vision.

macman

Thanks, does the definition of 'in use' mean actively downloading? Or if you have the BT Vision service connected will it ring fence 24/7 anyway?
Those figures do fit, as she should be getting 4MBps+ and is only getting just under 2MBps.

kwikbreaks

I don't know for sure but my belief is that if you are watching a stream it will ensure that you get the bandwidth to do that without it dropping frames etc.

This would be done by special hardware in their data centre (lookup QOS, deep packet inspection, and traffic shaping if you are interested).

It wouldn't reserve bandwidth as such except that if you were downloading something at the same time that would be slowed down to ensure the guaranteed streaming rate was maintained.

The reason you are seeing slower speeds is because some of the available bandwidth is being reserved for other customers so your non-BT Vision usage suffers additional contention.