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I recently moved over from Plusnet - about a month ago. I was expecting to be seeing something close to the advertised minimum of 76mbs (router has settled on a sync speed of 80mbs - in line with BT's expectations for my property, which is a few metres from the cabinet). On a good day I can touch 40mbs, usually its more like 20mbs. Nothing like the 80mbs sync speed. This has been tested via multiple devices in the home, at different times of day, and both wired and wireless (sat right next to the router for the wireless tests). What can be done? It sounds like congestion upstream from the cabinet. Right now I'm wishing I stayed with Plusnet. Really not impressed with this level of performance. I often have to work from home, and this lumpy connection is really not what I was signing up for. It was supposed to go faster than my previous ISP, not slower!
Update: I had an online chat with a nice guy at Vodafone central. He ran some tests on the line, and 'changed a few things' (no idea what). Router is still saying sync speed is 80mbs, as always, but here I am, 24hrs later, getting speed test results of over 50mbs on WiFi (802.11n), and around 70mbs when I use a wired connection on my crusty old laptop. I'm happy again! Thanks Vodafone.