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odd loss of 9mbit downstream rate

gyre
Grafter
Posts: 271
Registered: 19-11-2007

odd loss of 9mbit downstream rate

Folks,
I'm at a loss to explain this.  I need your help Smiley
I've been syncing at a downstream rate of 74-75mbit/s for over a year.  (It only dropped below that when g.inp kicked in, but I switched to a 8800nl and all was well again.)
I have very low error rates.  No errored seconds.  A few hundred rs correctable errors per day.
A few days ago, I noticed my downstream snr had dropped from 6.4 to 4.6.  I've never seen this behaviour before, so I rebooted the router.
Now, my downstream rate is always in the 66mbit/s ballpark.  Still the same number of low errors.  Still the same downstream snr of 6.4.  Still the same downstream attenuation of 14.6.  Same ping.  Same interleaver depth of 8 and 1 with g.inp enabled.
I've turned the modem off for over 30 mins and disconnected it, but no change when I powered back on.
I'm at a loss to know why I've suddenly lost around 9mbit/s in downstream rate.
Any ideas?
Thanks!
-- gyre --
7 REPLIES
elfish
Grafter
Posts: 235
Registered: 22-02-2009

Re: odd loss of 9mbit downstream rate

It is hard to pin down the exact reason, but it could be an increase of FTTC uptake on your cab, resulting in more users and thus more crosstalk. What modem are you using?
If G.INP has been applied to the downstream, then I wouldn't of thought interleaving would be applied as well (to the downstream), perhaps interleaving has been applied to the upstream, but the G.INP fix that has been rolled out, applies G.INP to the down and some error correction to the up (not interleaved), unless your upstream is unstable.
Some stats would be great, if you could post them.
gyre
Grafter
Posts: 271
Registered: 19-11-2007

Re: odd loss of 9mbit downstream rate

I'm using a Billion 8800NL.  g.inp has been applied to the downstream.  Stats included below.
I've been monitoring the router stats several times a day for the last few months.  This wasn't a slow degradation.  One minute I have 75mbit/s.  I could reboot 5 times and I'd still have 75mbit/s as long as the DLM didn't kick in Smiley
However, after noticing the unusual 4.6 snr margin, I rebooted and have been stuck on 66mbit/s since.
-- gyre --
elfish
Grafter
Posts: 235
Registered: 22-02-2009

Re: odd loss of 9mbit downstream rate

Have you been re-sync'ing more than once?
DLM may of intervened if you have rebooted your CPE multiple times. Try to minimise reboots (none at all if you can resist), preferably early in the morning.
I would wait until DLM deems fit, and re-sync's, hopefully then you will gain your sync speed back.
If your speeds do not increase over time, I would try a new filter, if no increase, it will most likely be down to interference/crosstalk.
englishrick
Grafter
Posts: 463
Registered: 14-02-2013

Re: odd loss of 9mbit downstream rate

Crosstalk so they say, I have had the same problem, Gone from 77.43Mb/s to 66Mb/s.... Funny how all of us with this problem have dropped down to the same Downstream.!!!!!!!!!!
Pendragon
Rising Star
Posts: 425
Thanks: 3
Fixes: 1
Registered: 07-04-2007

Re: odd loss of 9mbit downstream rate

Can I join the group, I had the G.inp ‘problem’ and changed to a Billion 8800NL and everything was fine, around 73 to 77 down for months, then last week around 8 in the morning a re-sync.
No reason just an out of the blue re-sync and speed dropped to 68 down (from the BT tester site) although the Billion still reports a download speed of 78584 but a connection max speed of 72399  Huh.
I have some before and after stats if anyone would like them but they don't seem much help.
Regards P.
Plusnet Help Team
Plusnet Help Team
Posts: 5,056
Thanks: 445
Fixes: 161
Registered: 01-01-2012

Re: odd loss of 9mbit downstream rate

@gyre
I've run a few tests and I can't see any issues I'm afraid. As others have mentioned it could well be crosstalk that's caused this.
@Pendragon
I'm not sure why your getting results of 68mbps as your profile on ours and BT's end is set around 75mbps. Is this still ongoing?
If this post resolved your issue please click the 'This fixed my problem' button
 Matthew Wheeler
 Plusnet Help Team
Pendragon
Rising Star
Posts: 425
Thanks: 3
Fixes: 1
Registered: 07-04-2007

Re: odd loss of 9mbit downstream rate

Morning Matthew,
Just done a BT speed test and everything seems almost back to normal today (72.09 down and 16.09 up), it might have been nothing more than local congestion at our local cabinet.
The speed drop was right after the re-sync and we have had no others since then to put the speed back so it must have been local.
I might get a ‘crosstalk’ drop on Thursday as our new neighbours are having their phone connected and broadband as well, I would expect them to go for FTTC as they have two boys with Xboxes (that should screw our download speed  Roll eyes).
Just bad luck with the BT test is seems, so please ignore, regards Pendragon.