BT IP Profile of 77.4Mb are the maximum that BT are limit on it. The Sync rate of 79992k is about right (The crosstalk will drop the max attainable rate only but your line probably stay at 79992k as you are saying u have FTTC over a year now)

Mine is start off attainable rate of 113,000k but now drop to 92,000k but still on sync rate of 79995k. I have FTTC for nearly 5 months now.

I was just worried by the word "congestion", as whenever anyone looking for an ISP sees that they run a mile. It's one of the few times the exact word matters.

Loss of sync speed due to increased takeup on the cabinet is normal (as you know but the poster may not), and affects all ISPs not just BT Wholesale ones. That's what all the talk of vectoring is about.

Keep wondering when vectoring will be implemented on my exchange, seeing as my router is now capable after the recent firmware upgrade. JOOI was that the one that we could opt out of or was that something else, i seem to remember opting out of something, due to my router not being capable at the time.

Does crosstalk affect the frequencies and thus the signal attenuation leading to a lower attainable rate? If the BT profile tracks the sync rate (which I guess can not be higher than the attainable rate) then it's perhaps only the BT profile (and the PN profile) that one should be concerned about in terms of throughput?

Can't remember what my attainable was, but was around 81,000+ now it is 78,512, I have noticed that if I do a IP reconnect about 08:00 I can sync back to 79992, but then a day or so later it will start to drop off until it gets back to 78200, so I'm just letting it stay at that now, seeing as I don't really notice any loss.

Crosstalk affects noise margins, not attenuation. Attenuation is a physical characteristic of the transfer medium and usually constant. Adding more cable/joints/deteriorating joints can change attenuation.

Even fibre optic cable suffers attenuation, just so low that it is ignored normally.

The sync can be a bit higher than the attainable, as the sync speed is fixed between (re)connections but the attainable fluctuates constantly as the noise levels change. (As referred to by MrSaffron).

At a sync, the noise from cross-talk basically causes fewer or zero bits to be assigned to the tones at the frequency of the noise, just as on ADSLx.

In reply to a post by MrSaffron:

Crosstalk affects noise margins, not attenuation. Attenuation is a physical characteristic of the transfer medium and usually constant. Adding more cable/joints/deteriorating joints can change attenuation.

Even fibre optic cable suffers attenuation, just so low that it is ignored normally.

How is attenuation measured, is it measured across the full range of frequencies? Through differing mediums and conditions wont certain frequencies be more attenuated than others? For example ADSL2+ can have a higher attenuation than ADSLMAX (~3dB) possibly due to greater loop loss on the ADSL2+ frequencies?

In reply to a post by RobertoS:

The sync can be a bit higher than the attainable, as the sync speed is fixed between (re)connections but the attainable fluctuates constantly as the noise levels change. (As referred to by MrSaffron).

At a sync, the noise from cross-talk basically causes fewer or zero bits to be assigned to the tones at the frequency of the noise, just as on ADSLx.

OK I follow that: attainable can be variable but on a resync sync speed will be established according to the level of noise affecting the attainable at sync time.

Whilst connected cross talk noise will affect the bits assigned to the tones and not change the signal attenuation - the modem will receive all the signal frequencies, including cross talk noise indicated by a drop in SNRM, and not detect an increase in signal attenuation?

Two main ways in xDSL world

At a fixed frequency e.g. 300KHz or 600KHz or a calculated average across all the tones