The modem "knows" the achievable data rate on a line by virtue of successfully transmitting/receiving at that rate. I think the rate is established during the "training" state which takes place when a modem is restarted or sync is lost.
My Netgear DG834G can sync higher on a better line. The reported max rate is what it can achieve currently on the current line. On a good line it must be capable of meeting the fastest sync for the ADSL2+ standard it claims to support.
Which modem are you using?
tommy45 (fountain of knowledge)
Tue 22-Feb-11 14:37:05
Re: difference between ADSL info MaxRate and CurrRate ?
It;s your routers interpretation of what the max speed is, this also changes frequently, i currently have an upstream sync slightly higher that the max rate, it's based on the current SNR level and other factors such as error rates, the values displayed are theoretical limits my downstream shows values of 21169 Kbps
with a sync of 18145 Kbps on a 3db snr
I don't think that ADSL modem can know about the max rate that the line can support.
my idea is that maxrate is about the max rate that the modem can support
for example if a modem is ITU G.992.1 Annex A ===> UpstreamMaxRate = 1.3 Mbit/s , DownstreamMaxRate =12.0 Mbit/s
I want to confirm or infirm this
Those max speeds you quoted are capped values , ADSL2+ Annex A can support speeds of at least 24mbits down (advertised as upto 24mb )and 1.6mbits up, but most isp's cap it to 1.3-1.4mbits for technical reasons
Basically, they mean taking into account perfect conditions and disregarding BRAS, the maximum your line can possibloy sync at. Of course your actual sync will be lower, but the best lines should only be about 15% lower. My one at home is about 82% downstream and 86% upstream.