FTTC - Speed Artificially Low by 2.5Mbps... Usually

[#1]

I have had this exact same problem for a number of months now.  Currently from memory my IP profile is also 38,714 but the maximum speeds are clearly restricted to 35Mb.  I did mention this once or twice in other threads but nothing much happened.  I don't like to tempt fate by rebooting the VDSL modem so I just ended forgetting about it. mainly on the basis that 35Mb is far faster than my ADSL used to be!
However it would be good to have that extra 2.5Mb.

James

[#2]

Hi there,
We've got your profile at 40000 but it's currently at 32000 on BTs side of things. Not really much we can do to influence that, might be that resetting the modem and router would bump it up but like you say, it might not. As things stand though it's the only thing that'll make a change at present.

[#3]

Thanks for the reply Matt.
Interesting that the profile of 32,000 is not consistent with the IP profile per the BT speedtester (which is higher) or for that matter the actual speeds I am currently getting (which are also higher then 32,000).  I wonder if the profile has got stuck.  I'll power cycle the modem when I get home and see if that helps.

James

[#4]

Hi,
Sorry this is slightly off topic, but how do you tell what your sync speed is?
Should my router be telling me this? (I'm guessing it doesn't know as it's not making the connection itself)
My FTTC has been installed today. The engineer told my his device was showing my sync speed as 39,998 (or something like that), but my prfile (both BT and PN are around 37Mbps. Yet all my speed test results (the plusnet one, speedtest.net and speedtester.bt.com) all suggest speeds around the 35Mbps mark or lower.
Is there a training period with FTTC? Could this be affecting things?
Thanks.

[#5]

There is a training period, but it seems to be 2 days. I saw an Openreach document that said DLM would be passive for the first 24 hours, unless the line suffers major problems. However, every time my line has been reset to initial conditions, it seems to be 48-60 hours when DLM puts in place its interventions.
On the "vanilla" modem, as given to you by Openreach, you cannot get hold of the sync speed at all - you have to infer it from the IP Profile assigned to your line. The only thing you can do is run a test at http://www.speedtester.bt.com/. This site will display the IP Profile values for your line during the actual download & upload tests, and again in the test report page. I suggest you do this a few times over the first few days, so you can see if DLM makes any changes: You'll never get these 2 days back!
When you have a sync of 40Mbps, you will have an IP profile of 38717. Since the 17a profile was rolled out on some cabinets, we have more frequently seen profile values 2 or 3 less than this. It is assumed that the IP Profile reduces pro-rata in line with any sync reductions, so Sync Rate = 1.0331 * IP Profile.
Another hidden impact of DLM is whether it turns interleaving on - which you won't see from the IP profile. If you have a static IP, you can set up a "BQM" at the "think broadband" website, which produces nice graphs of the ping response times for your line. If not, you will need to perform some manual ping or traceroute commands out to the internet, and see how long it takes to get over to the Plusnet gateway (the first IP address beyond your router in a traceroute).
However, the modem does keep track of the sync rate (and all the other line statistics), and is hobbled from being able to display it to you on a web page or give you access to a telnet shell. To get such access, you need to flash new firmware onto the modem, so it restores access. BT, of course, really don't want you to do this as the modem is part of their service - and in fact could refuse to deal with any faults on your line if you make such a change. Some people have flashed their modem, while some people have bought a spare off ebay, and used that. Take a look here and here (look at the links on the RHS).
One of the most useful aspects of the unlocked modem is that it gives you a lot more information about the use of the frequency bands - and was the main way that people spotted when BT started to roll out the 17a profile (the 17MHz frequency band), and the fact that they re-arranged channels to give more bandwidth to the downstream.

[#6]

@Matt
Further to my pre Christmas post I decided not to resync the VDSL modem as I didn't want to tempt fate.  However today my router decided to reset itself and I ran the BT tester to make sure everything was working.  I then noticed that my IP profile had changed slightly to 38,716 (from 38,714) so the modem must have recently resynced itself.
However my speeds are still exactly the same, i.e. about 2.5Mb slower then I would expect given the IP profile.  They are however quicker then the 32,000 you said it was set at BT's side.  Can you get the profile at BT's side changed from 32,000 to see if that helps?
Thanks

James

[#7]

Hi
Just to add to this - I am experiencing exactly the same problems.  Matt recently increased a stuck PN current line speed, but after this even though BT Speedtest reports an IP profile of 38715 I am capping out on speedtests at 35mbps.
So I too am shy of 2.5mbps (seems ironic, as that's about the max sync my line could hold on ADSLMax - but still - should be available now, line seems very stable).
Hope this adds some weight to the argument that there's an issue on some of the PPP sessions (although I've not managed to get a faster one recently).
Colin

[#8]

Hi,
I've got one possible idea why it might be doing this. Have you noticed any pattern as to whether you disconnect and reconnect the PPP session between resyncing the BT modem? The BTW BRAS profile is calculated whenever you resync and re-auth but I'm wondering if it sees any difference between a PPP drop and a resync. Might be worth experimenting by seeing what happens when it drops just PPP or if it resyncs. Will see if we can think of anything else too but that would be a useful test to start.

[#9]

Hi Dave

I haven't noticed any pattern but I haven't had the full speed for quite a while now albeit for the past couple of months I have just left it alone.
I have tried reconnecting the PPP session in the past but this has done nothing.  I do suspect that the VDSL modem has resynced itself at times and the PPP session has not dropped, basically because my IP profile on the BT speedchecker has changed but there was no PPP reconnect in my routers log.

James

[#10]

Hi Dave,
I've tried:
- just dropping PPP in the router GUI;
- power-cycling the router;
- pulling the DSL cable from the modem, waiting, then re-attaching, waiting for resync, and waiting for router to re-establish PPP itself;
- power-cycling the modem
- power-cycling both the modem & router, manually restoring router 30s after modem;
- power-cycling both modem & router together
None of these have resulted in getting a "fast" connection in a consistent way.
Dropping PPP in the GUI seems to be the least effective - or rather, I've tried it the most times with negative results - but it has worked once. Pulling the DSL cable has also worked once (triggering a resync, but leaving the router to automatically re-auth PPP).
The most effective thing actually seems to be the occasions when the link resyncs are triggered by something at the cabinet end - but you have little control over that. I'm pretty sure that both times this happened in November - first when 17a was turned on, and later when interleaving was added by DLM - I ended up with "fast" sessions without any intervention from myself.
We've just completed the house move, with FTTC now up & running. Unfortunately, I haven't yet managed to get a "fast" session here at all yet - and that includes the automatic disconnection that happened last night as part of Jojo's regrade. This line also has a profile of 38717, but is shorter and seems to be better quality in terms of max speed & error rates.
Edit: Don't confuse sync & profile.

[#11]

Quote from: JEB

because my IP profile on the BT speedchecker has changed but there was no PPP reconnect in my routers log.

I also wonder about this part. I remember Openreach's documents ask that ISP's have a pretty low PPP timeout for just such an eventuality, but I've seen the router behave in both ways after a modem resync - sometimes a new session needs to be established, and sometimes it works without a new session.

[#12]

Interesting that you have the problem at two different premises connected to two different cabinets.  That would indicate to me that the issue is linked to certain user accounts, well either that or there is a widespread issue but in that case I would guess lots more people would be moaning!
James

[#13]

Hi all, I have been following this thread with great interest.  In my case I have a Static IP, my FTTC has always synced at 40 meg (I have unlocked the BT modem, just don't tell BT - I will flash the original firmware back onto it if I ever need to get an engineer out) both on the old 8c and on the 17a .  All my speedtests (mybroadbandspeed and speedtest.net) consistently give slightly below 35Mb/s during unmanaged periods (yes, about 2.5Mb/s below the PN profile which has always been 37).  I guess that the static IP means I 'always get the same connection' and will never see the benefit of download speeds at or above 35Mb/s?
I also have very low FEC & HEC counts so I'm not loosing speed through resending of data.

[#14]

Hi WWWombat,

Quote from: WWWombat

I also wonder about this part. I remember Openreach's documents ask that ISP's have a pretty low PPP timeout for just such an eventuality, but I've seen the router behave in both ways after a modem resync - sometimes a new session needs to be established, and sometimes it works without a new session.

I think you may be referring to BT's SIN 498 document ( http://www.sinet.bt.com/498v3p2.pdf ) that states:-
“2.1.6 Downstream shaping
The CP is expected to shape the downstream traffic to match the actual VDSL2 line rate in order to avoid excessive traffic loss.
CPs should be aware that the mechanism for reporting the downstream and upstream line rates relies on a line re-train causing the CP, or the CPE, to initiate a new PPP session or a new DHCP request.
The success of this is down to the CP's choice of timers used around PPP / DHCP handling.
If the PPP/DHCP survives a re-train, then the CP will be unaware of any change in the line rate and will not be able to shape appropriately.
The line re-train time for VDSL2 can be anywhere between 10 and 60 seconds, with typical values in the 20-30 second range.
As DHCP typically uses lease timeouts in the order of days rather than seconds, CPs intending to use DHCP are advised to consider the impact of downstream line rate changes on their service and any strategies they could adopt if they wish to shape downstream traffic.”

My own connection re-syncs “on the fly” quite regularly, usually following a very high & sudden burst of various errors, particularly RSUNCorr errors.
These re-syncs are usually very quick (16 seconds or so in duration), & as the dynamically allocated IP address does not change, they are not seen in Plusnet’s Radius logs, or in the router’s logs.
They are however detected in my own ongoing stats logs (harvested every minute,  24/7), & also in the HG612 modem’s logs.
However, the BT IP Profile does usually change instantly (upward or downward), with throughput speeds adjusting accordingly.
Very rarely, the IP profile “sticks” until the next re-sync.
I have been communicating with Plusnet’s Alex R over the last few months (regarding my reduced FTTC speeds) & he is now aware of this phenomenon.

FWIW, I have noticed that a user’s BT IP Profile / BRAS rate is usually around 96.8% of sync rate, & in my case, DS throughput is usually around 97% of my IP Profile / BRAS Rate.
e.g. With a sync speed of 39999 k, the IP Profile is around 38719 k, with a DS throughput of around 37557 k.
EDIT: Please see the attached graphs for my connection over a 40 day period.
Plusnet were initially unaware of many of these re-syncs & were originally of the impression that my connection was very stable, maintaining a connection for many days at a time.
Please also note that the blank spaces in some of the plots are purely down to the fact that I wasn't collecting those particular stats at that time.

Paul.

[#15]

@walker23
Our connection is static IP too, so the faster sessions should be available to you too.