Bob's experience with ADSL2+"I don't think ADSL2+ will be of any advantage in download speeds to most members of our group. In fact it will increase the divide between ourselves and those living close to the exchange." Is Bob's conclusion correct? I hope not. A major telephone exchange in Milton Keynes has just been upgraded to ADSL2+. It doesn't appear to have helped Bob. (He has a long phone line of 5km - like many folk in Milton Keynes.) Here is Bob's account: "Below are my experiences after I was transferred to the 21CN DSLAM. (Please note that I have written this for BB4MK but have forwarded it to John Small and his team at BT who may find some customer feedback useful.)
"The high Line Attenuation (~55dB) and high level of crosstalk generated by the pub opposite my house in Loughton have made this part of Milton Keynes a difficult area to enjoy high speed broadband, so after BT Openreach's sterling efforts to improve my signal level last October and the replacement of my router, I consider myself lucky to have enjoyed a very stable 3 Mbps connection for the last 7 months.
"As part of my ISPs (Andrews and Arnold) planned system upgrade I was moved to the TI 21CN DSLAM on 22nd April and onto ADSL2+ on the 30th April. With 55dB Line Attenuation I realise that any speed improvement with ADSL2+ would be marginal but my stable sync speed on "20CN" was around 3800 kbps so it is just possible that I could achieve the 4000 kbps required for a 3.5 Mbps BRAS which would be a useful upgrade.
"The initial impressions were good as I was connected at about the same down speed as before the upgrade; and the up speed increased from 448 to 800 kbps (my current up speed is 695 kbps).
"What was not initially apparent was that during the upgrade the Target Noise was increased from 6dB to 9dB and when combined with the high levels of crosstalk caused my signal to noise margin to vary between 9 and 12dB on a modem that has been demonstrated to be fully stable down to at least 3dB.
"Today this has been exacerbated when a telephone line fault caused the modem to be reset during high a level of crosstalk and has resulted in my connection speed falling to 3229 kbps and my BRAS to 2.5 Mbps.
"I have spoken to my ISP regarding the target noise level, but have been informed that it is almost impossible to get BT to set it back to 6dB. So it looks like that, for long lines such as ourselves, 21CN ADSL2+ will result in degraded performance. (This, incidentally, has negated all the excellent work that Openreach carried out for me last October.)
"I still have some further testing without interleaving to complete, and have the option to change back to ADSL(Max) (G.DMT Annex A) as well as selectively resetting the modem when the crosstalk generated by the pub opposite is at a minimum, so I may be able to recover a 3 Mbps BRAS. But I don't think ADSL2+ will be of any advantage in download speeds to most members of our group. In fact it will increase the divide between ourselves and those living close to the exchange." Bob, 5th May 2009 Here's an update: Bob has positive news. ADSL2+ does appear to perform better. Future SpeedsBT Wholesale have set the Wholesale Broadband Connect (WBC) date for the exchanges to the 31/03/2009. From the graph of ADSL speeds against distance on this page, 20Mbps should be possible 2km from a telephone exchange. Here's a map of MK - if you live within 2km, there's a good chance of getting 20Mbps from the end of March. (Assuming you ordered ADSL2+) Each disc represents a 2km radius from one of the 6 telephone exchanges. Some discs have "cut outs". These areas are connected to a neighbouring exchange. Don't assume telephone cable are laid in straight lines. They aren't! The routing was determined by the roads that were in place as the city was being built. in the 1970's the telephone network for MK was designed with 2 large exchanges. One in Fishermead, the other in Emerson Valley. But fewer buildings means longer line lengths; that's OK for voice, but not broadband. |  |
"Bradwell Abbey", the exchange covering the centre is one of the biggest in the UK. "That must be good!" I hear you cry. Not really. For ADSL we really need lots of small exchanges so that the phone line length is a short as possible. |