[AusNOG] Strange ADSL problem - troubleshooting / diagnosis advice wanted

[John Edwards]

On 12 Sep 2014, at 6:05 pm, Jarrad Mitchell <ausnog at outlook.com.au> wrote:

> I'm not sure if it has been mentioned or not as I just joined, but VDSL2 supports Vectoring, which as I understand it is basically scheduling transmission across the different pairs in say a 100 pair bundle. 

It’s even cooler than that - the DSLAM uses the inherent crosstalk to correct the signal at the far end, by deliberately transmitting in a way that will constructively interfere.

The less appreciated part of the technology is that this calculation can’t be done in parallel. It needs to process the the complete symbol stream of every active port on the DSLAM in real time, in what is a 2^n-1 calculation for n connections in a binder. This also requires at least twice the backplane bandwidth to get the data into the vectoring processor and back into the line card.

> Quote Paul:
> "VDSL2 doesn't really add much functionality to ADSL2 other than the vastly expanded frequency range.”

Perhaps not at the PHY layer, but VDSL2 reboots the model and ends the need for PPPoE/LLC/ATM by defaulting to Packet-Transfer-Mode. While not a new standard, it mitigates the ATM tax we’ve been paying for 15 years on ADSL variants.

John

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