cancel
Showing results for 
Search instead for 
Did you mean: 

Increasing SNR lowering sync on 40/20 contract

sjptd
Grafter
Posts: 467
Registered: 01-09-2014

Increasing SNR lowering sync on 40/20 contract

PlusNet 40/20 contract is unusual in that they contract with Openreach for 80/20 and then reduce download to 40 on the PlusNet side.  The VDSL modem connection to the cabinet uses the fastest sync that DLM will allow it.  There is always a risk that intermittent noise will cause errors on the line, and if you are unlucky can even cause DLM to introduce interleaving.
This risk can be considerably reduced by a more conservative sync speed with associated higher SNR, and without compromising on actual speed.  I have been looking into this on and off since moving to PlusNet, and have finally cracked it; with lots of help at http://forums.thinkbroadband.com/plusnet/f/4385538-fascicle-plusnet-traffic-shaping-again.html
You need an unlocked HG612.  telnet to it (probably telnet 192.168.1.1, user admin, password admin) end enter sh to go into the BusyBox shell.  (If you don't know how to do this anyway, don't try.)
Then enter the command
xdslcmd start  --up --maxDataRate 50000 25000 75000
If your sync was previously above 50000 this will give you a lower sync rate and higher downstream SNR: my downstream SNR is now 14.5db.
As I expected, speedtests are unchanged. http://www.thinkbroadband.com/speedtest/results.html
BT wholesale showing 48.4/20 profile, 38.25/17.38 speedtests.
I expect my error rates to go down, and feel pretty sure I will only get interleaved if something quite bad happens.
This will only last until the next time the modem resyncs.  If you add the command
xdslcmd configure --maxDataRate 50000 25000 75000
I think (?) it will last until the next modem reboot/restart.
You could probably get away with --maxDataRate 40000 20000 60000,
especially if your MAX sync is nearer to 40000, but I thought a little 'headroom' wouldn't do any harm.

                Down            Up
max:            75080          22355
path:          49999          19999
SNR (dB):        14.5            7.1
R:              16              16
N:              254            254
I:              254            127
INP:            0.00            0.00
D:              1              1
delay:          0              0