FTTC - the "missing" Mbps

[#1]

I'm not sure whether this has been posted before, but here goes. It has been observed by various people that a Plusnet FTTC connection with the maximum BT profile of 38717 (ish - it tends to be 38716 on the 17a profile) does not seem to be capable of sustaining a transfer speed higher than 35Mbps the vast majority of the time, whereas other ISPs manage 37+.
This phenomenon is discussed on http://forums.thinkbroadband.com/plusnet/f/4089092-fttc-speeds-on-full-sync.html but I have seen it mentioned before, especially by WWWombat.
Can anyone from Plusnet offer an explanation for this? Can anyone explain the true meaning of the Plusnet current line speed of "37Mbps" which is the default for FTTC connections with the maximum sync?
Thanks

[#2]

Hi KevinG,
I can see some discussion is already underway about this here http://community.plus.net/forum/index.php/topic,100862.msg861070.html#msg861070 I can also see we've raised this with our suppliers. I'll chase it up now.
I've made an adjustment to the profile on your account. Could you let us know if that's changed anything?

[#3]

I'm only 80yards from the CAB but get a bit less than 35Mbps rather than the Line Speed 37Mbps. 
In November I was getting a transfer rate of 33Mbps and noticed that my Plusnet Line Speed was set at 35Mbs so I was losing 2Mbps then.  Jojo adjusted my Line Speed from 35Mbps to 37Mbps and that increased my transfer speed to 35Mbps. 
Does this 2Mbps loss apply to all Plusnet FTTC customers? 
(There's  been some chat about the missing 2Mbps at thinkbroadband,  The latest thread is here.)

[#4]

Thanks Adam - I'm now seeing 37.5Mbps on speedtest.net so whatever you have done seems to have worked. I notice that my line speed is now set to 20Mb, not 37Mb!

[#5]

OK, what have you done??? Now dropped to 17M!

[#6]

I've had this problem for a long time now.  Going by the number of people that are effected there must be something misconfigured somewhere.

James

[#7]

I now seem to be randomly hopping between 17Mb and 37Mb speed test results, so I would be interested to know what's going on!

[#8]

I've changed the profile, I can't see how it should have dropped things down to 17, sorry that wasn't expected! Can I get you to reboot your modem (to drop and re-auth) the connection please. Come back to me if not and I'll put the profile back to what it was prior to this morning.

[#9]

OK, just got to wait for my 3-year-old to get off the Internet!

[#10]

OK Adam, I've done that and it has completely crippled the connection, now coming in at about 0.25! 

[#11]

I'm watching this with interest from over at the original thread... I can't do much to join in right now, as I'm not where the fibre modem is at the moment, but I might ask to do the same thing later...

Quote from: _Adam_Walker_

Can I get you to reboot your modem (to drop and re-auth) the connection please.

Just a reminder that you could, in re-connecting, accidentally end up on a fast (37.5Mbps) connection anyway, even if it is rare. You might want to try connecting (& testing) a few times, to gain confidence that it has really changed something!

[#12]

Quote from: KevinG

OK Adam, I've done that and it has completely crippled the connection, now coming in at about 0.25!

That very much sounds like one of the "default" management profiles. that is set to 256kbps, I think.
Another reconnect?

[#13]

I thought that too, but how did it happen? Anyway, I've rebooted the router (not the modem this time, it seems to take an inordinate amount of time to re-establish a connection after doing that) and I'm back up to 37.5Mbps on speedtest.net, so all good at this precise moment. I'm happy to let it run for now if it helps and will let you know of any further speed aberrations I get (remembering the 20Mbps evening web throttle).

[#14]

Quote from: WWWombat

Just a reminder that you could, in re-connecting, accidentally end up on a fast (37.5Mbps) connection anyway, even if it is rare. You might want to try connecting (& testing) a few times, to gain confidence that it has really changed something!

Yes, in theory, just that I hadn't had such a connection for as long as I could remember but as soon as Adam did what he did I got one, and although I've had various other anomalies I haven't been back to one of the 2Mb slower connections since, so it looks fairly promising that the cause of the 2Mbps drop is near to being established.

[#15]

Quote from: KevinG

I've rebooted the router (not the modem this time.....) and I'm back up to 37.5Mbps on speedtest.net.

Intriguing - I don't think that rebooting the router should change the synch speed already established at the modem.  Doesn't it just change the ppp session and possibly the gateway? It looks as though the throughput changes are caused by something in the Plusnet system.