On Mon, 2012-10-01 at 09:39 +0100, Mark Rogers wrote: > Our main office ADSL connection has always been slow but seems to be getting > worse. We're with O2 which at one point got us up to the giddying heights of > ~4Mbps but now we're struggling to get 2Mbps sync speed. > > Looking at the router (Vigor 2830) we seem to be syncing at 1Mbps upstream > which seems odd if we can't get more than twice than downstream, unless I'm > interpreting the figures incorrectly: > > ADSL Information ( ADSL Firmware Version: 232201_A) > ATM Statistics > TX Cells 38462411 > RX Cells 211479088 > TX CRC errs 0 > RX CRC errs 71 > > ADSL Status > Mode ADSL2+(G.992.5) > State SHOWTIME > Up Speed 1012989 > Down Speed 2032803 > SNR Margin 10 > Loop Att. 60
The last one is the killer - loop attenuation of 60 dB implies 4 to 6 km of wire from you to the exchange. That's above the original 55 dB limit for supplying 512k broadband but things have moved on a bit - at the time 45 dB was the limit for a 2M fixed speed service. I guess the first question is whether 60 dB is reasonable for the location, or reflects a signal loss due to a fault - my attenuation went from 34-38 up to over 60 recently and dial tone failed, they fixed the dial tone (I guess one leg of the pair disconnected) but the attenuation is now in the 40s. I'm assuming FTTC "superfast broadband" isn't available in your location, which would reduce the copper loop length to the distance to the cabinet rather than the exchange. If the 60 is for real and the best available your only hope is to reduce the SNR margin and trade for some extra speed and possibly reduced stability. I don't know what O2's stance on this is, but the exchange kit could bet set to 6 dB and give you maybe a meg or so extra. 3 dB is also possible. If O2 won't play there are some routers that allow you to tweak the SNR margin down from the target, don't know if your will do that - "SNR tweaks" in a search engine perhaps. The high ratio of upstream to downstream speed just reflects the use of lower frequencies for the upstream - they're attenuated less so haven't fallen off the cliff edge yet whereas the downstream speed is a long way off its peak on account of loss of high frequency bands with distance. Phil _______________________________________________ Peterboro mailing list Peterboro@mailman.lug.org.uk https://mailman.lug.org.uk/mailman/listinfo/peterboro
