snr margin current / snr margin snext

[ddavenport-dcc]

Good Morning.

Does anyone have any information of the above commands when applied to DSL controllers - particularly when applied to GSHDSL WICS? The documentation, to me at least, is a little unclear. I understand thay can provide improved line stability but I am not clear how, or if there are any implications in terms of speed and/or increased CRC errors if these commands are implmented. Any help appreciated! Thanks.

[Giuseppe Larosa]

Hello David,

I've found a reference to a similar command

dsl noise-margin

see

http://www.cisco.com/en/US/docs/ios/bbdsl/command/reference/bba_01.html#wp1013411

the idea is that of instructing the modem to look for a desired signal to noise ratio in negotiating rates with the central office counterpart modem.

instead of executing the auto-adaptive procedure in the standard way the modem looks for negotiating bit rates in the two directions that allow it to respect the added noise margin.

So if the standard search says negotiate a speed if SNR is at least 3 dB adding a margin of 3 dB means look for a speed where the SNR margin is 3+3 = 6 dB.

Clearly this implies that the negotiated speed can be lower than without the noise margin command because the goal on the SNR is increased of x dB.

However, with an increased SNR over time the bit error rate is minimized and link should be more stable.

Errors should be less probable with a better SNR.

Actually depending on the line conditions it may be better to use a lower speed but to have a more stable link.

Hope to help

Giuseppe

[ddavenport-dcc]

Thanks Giuseppe. The command is different but I assume the negotiation process is familiar.

Dave