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[guest]

My line is about 1km long and the DMT graph has been unchanged for as long as dmt was available.

So imagine my surprise when the (non-Sky) router emails me to say sync dropped. New profile (Sky do asinine upstream profiles) is 16382/945.

Each night sync increases between 3-4 am (Sky's chosen time to force a resync) and today I'm now on a 3dB margin.

However I know what works on this line - largely as a result of Be letting people play with all the settings in the early days - and 3dB isn't stable enough for me.

I don't like having a 6 year old router (DG834GT) working hard (RSCorr) on an idle line.

So each time Sky DLM adjusts the profile I back it off a bit (4.5dB for now) which seems to result in an increase in sync every night the DLM forces a resync. RCO is about 23Mbps @ 3-4 am so it'll keep going for 10 nights. I am unconvinced that the "3dB DLM module" recognises me backing the margin off so will be interesting to see where we go - currently 4 days into 10 day test period and 20Mbps seems likely even without me meddling.

The Sky DLM system appears to be much improved in the last year or so. For example I could see it backing off the INP levels over 2 days before adjusting target noise margin. I am currently sync'd with near as makes no odds a fastpath connection @ 18.6Mbps. Interleave is 128/8 on a sync of 18618/1164 with a delay of 8ms max (the "gamer" profile). Yes I know the upstream makes no sense, feel free to join the list of people who have explained that to Sky.

Oh and as an aside the new http x1/http x6 tests at TBB are (IMHO) very effective. The x1 test should oscillate a little (TCP/IP stuff) and the x6 test should give max speed reliably. Does what it says on the tin IMO. If one is radically different to the other then your ISP has b/w issues somewhere. Nice but long overdue.

Back off down the rabbit hole - last night brought 19007/1164, wonder what tonight will bring.

[guest]

The answer was "exactly the same" until I rebooted the router. I wasn't aware that using DMT persisted across forced resyncs as I've never seen that happen before. Probably bloody obvious really

Anyway the Sky DLM fairy has brought :

19403/1164 sync, margin 3dB, INP 1.00/1.20, delay 7.84ms with interleaving of 96/8 so I'm getting very close to "fastpath" now. In the real world this equates to a 19ms ping to the first hop and 17.8Mbps on TBB's shiny new http x 6 test.

RSCorr running at about 50/sec on an idle line so getting close to the edge IMHO.

However the interesting part is that you can "subvert" Sky DLM with DMT.

[kitz]

For example I could see it backing off the INP levels over 2 days before adjusting target noise margin.

Do you have any idea of what the (newish) sky DLM is supposed to do and how it works.  Ive seen questions about this, but not being on sky I havent a clue.

[guest]

I haven't bothered looking too closely but there's a 7dB and a 3dB margin now.

The only way of getting a profile over 18Mbps now is to let DLM set it - Sky CST can't set it higher than 18 manually.

The reason for this is because of the number of garbage profiles people were manually applying just to get the customer off the line - IME if you phone Sky between 9am and 5pm you get decent service. Outside those hours you run the risk of getting the Bangalore call centre and frankly you'd be better talking to next-door's cat about any issues

For me DLM kicked in again after about 10 months as the initial training got stuck (twice) at the point where it switches from ADSL2 to 2+ so I reckon the shift to DLM was probably triggered after 6+ months of data got collected. Would probably have kicked in before now if I'd had a successful initial DLM train.

The "old" DLM was pretty damn crude - just like BT's was at first - but this version seems more subtle. My sync speed seems to go up every two days now - got a lot of RSCorr activity which it must be noticing. For example - Day A I go to 19Mbps, Day B I stay there and DLM tweaks INP etc, Day C I go to 19.4Mbps, Day D another tweak of error correction....

The line is impressively stable at 19.4Mbps which I've never managed by tuning using DMT. Even known impulse noise sources (gas valve on boiler/freezer compressor) within the house are having little effect. I get a little burst of RSUnCorr around twilight as you'd expect but we're talking maybe 5 CRC errors at the IP layer over an hour or so.

Very very impressed with this DLM module so far. So impressed in fact I've just stopped messing about with it, in this instance DLM > DMT

[guest]

After I stopped messing with DLM by changing noise margin.....

I ended up with a sync of just over 20Mbps on a 3dB margin with 96/8 interleave up/down and a 5.66ms delay.

Apart from twilight when there's a few RSUnCorr (5 CRC or so at IP layer) I end up with a maximum of one CRC error per 3GB of data transfer at IP layer.

I'm quite stunned to be frank about this. A stable 20Mbps on a 21dB line is about as good as it gets. Shame the line goes 100 metres away from the exchange before heading back from the PCP as it'd max out the line otherwise.

+1 to whoever did this DLM module. Its the dogs wossnames

[guest]

Just to add to this, if you use PPPoA rather than MER then you can relog and will likely get switched to another tunnel (and will get a different IP address).

I go into home gateways in Birmingham and yesterday I relogged and ended up with only 3-5Mbps of throughput @ 10 am. Made note of home gateway (br0) and relogged again. Got br1 which was a bit quicker (10Mbps); relogged a third time and got br4 which runs at line-speed (so I get 17Mbps or so). I didn't resync at all so all this is at the IP layer, not ATM.

So if you happen to be on Sky ADSL and use your own router then you should be aware that not all tunnels are equally balanced - in fact it reminds me of the "good tunnel, bad tunnel" which used to happen with BT's 34Mbps managed gateways a decade or more ago.

Probably worth a shot if your exchange seems to be running a bit hot.

[kitz]

Thanks rizla for your observations.. meant to say so earlier.
The reason Im interested is that my dad is one of those that liked to turn the router off at night...  hes now been told he shouldnt!

But the other week after a power surge from a faulty toaster.. he now seems to be stuck on a stupidly low sync of about just 1.5Mbps that wont seem to shift.   Ive left it like that for a couple of weeks since he only checks mail and browses the odd amazon site so doesnt really notice and I wondered if the DLM will ever shift to anything more on its own accord..  but so far it hasnt. 

 I guess Im going to have to do the sky phone call for him sometime

[guest]

There seems to be someone around these forums who knows a fair bit about the new DLM - such as it samples data twice a day and now has the g.INP module management on at least some exchanges.

Very impressed how this works on an old DG834GT router (c2008 IIRC).

Code: [Select]

                Down            Up
SNR (dB):       3.1             8.7
Attn(dB):       21.5            14.3
Pwr(dBm):       18.3            12.3
Max(Kbps):      22900           1329
Rate (Kbps):    19508           1168
                        G.dmt framing
K:              143(0)          18
R:              14              12
S:              1               8
D:              96              8
                        ADSL2 framing
MSGc:           63              13
B:              142             17
M:              1               8
T:              4               7
R:              14              12
S:              0.2341          3.9122
L:              5364            319
D:              96              8
                        Counters
SF:             6893971         6961227
SFErr:          7               3
RS:             1902736252              2160842
RSCorr:         1139853         1540
RSUnCorr:       58              0

HEC:            6               100
OCD:            0               0
LCD:            0               0
Total Cells:    829857590               1554285967
Data Cells:     31427807                118395833
Drop Cells:     0
Bit Errors:     0               5385

ES:             6               2
SES:            0               0
UAS:            35              653
AS:             111381

INP:            1.00            1.20
PER:            16.15           16.26
delay:          5.61            7.82
OR:             34.16           9.34

Bitswap:        9168            17

That's stats on the line up for 30 hours, probably between 5-10GB transfer - depends on how much younger daughter has streamed (perma-streams stuff in background).

Not too shabby on a ~1km line which is 220m over* your mapping line length estimator kitz, not too shabby at all. Edit - sync will vary by as much as 1Mbps if you time the sync right. It'll hold 20Mbps fine but the 834GT will be working hard at that rate on RSCorr, never mind anything else. 19.5Mbps seems about right heading into summer and increased daylight hours, we'll see.

*Ah it now shows correct distance of 1.1km rather than 900m or whatever, I assume that's updated BT plant record visibility showing cab location?

[guest]

The reason Im interested is that my dad is one of those that liked to turn the router off at night...  hes now been told he shouldnt!

I dunno about "shouldn't" but Sky will love him to bits right now for IP address pool rebalancing - they're desperate for IPv4 addresses prior to 02/Be purchase completion when they will start reclaiming all the /28 and /29 subnets assigned to individuals. When RevK over at AAISP says he'd "hope" they could always provide a single IPv4 address free of charge with an ADSL/line circuit you know things are getting seriously tight.

About bloody time too.

[snadge]

joining the thread

want too keep up to date with your findings...as always

[guest]

Right its all change again. Sky appear to have reorganised the network so there's a lot more regional gateways (at least 254).

They appear to be all in the subnet 2.120.8 and have PTRs starting 0278. For example my gateway is 02780842.bb.sky.com and I do not appear to be able to get another gateway by relogging.

I'm speculating that this is connected to the recent "half-speed" issues many Sky "Fibre" customers have suffered for the last 9 months. Further speculation on my part is that this is connected to Sky having to support CHAP rather than MER on these connections - I think there was probably a fair few gateways running too many concurrent PPP sessions and running into cpu issues.

Will be interesting to see if this is the end of being forced to use MER on some ADSL connections, I'd think so as one of the reasons for using MER in the first place was to avoid overloading specific segments of the core network by distributing gateway loading.

We'll see.

[snadge]

All interesting stuff keep it coming...  I'm just worried about o2/be coming over...

Sent from my Sony Xperia Miro on Tapatalk

[Stop It]

Hey all

I've been lurking a bit here after moving to Sky ADSL and this thread has interested me as I've had DLM play with my line and wanted to share my experiences.

I moved to Sky ADSL in January and the DLM process at the time took my line (Using the provided SR101 modem) all the way to around 20mbit with 3db SNRM before settling for just under 19mb down/1.2mb up on my line. This was on an attenuation of 18.5db on the downstream and 11.5db on the upstream.

I was happy with this, but my pings (At 30+ to sky.com and the BBC) were not the best, so when there was a thread on the official Sky forum saying that it could still be requested, I did so. This turned out to basically be just a DLM reset and again the line tried 20mb with a 3db SNRM, it reverted to the same speed again, but now with average pings of 24-25. Job done, I thought.

However, recently, my modem has been reseting overnight as per another DLM run. Initially, it kept the speed/SNR the same each time, sticking to 6db SNRM and around 18.-19mb depending on how the line looked at at the time. A couple of days ago however, my line reset again and set to 20mb, this time with 6db SNRM, and it seemed to unlock the upstream SNRM which was locked at 8.8 to over 10db. The pings were the same as before, but the downstream was a bit faster. Last night saw another reset to the stats below, re-locking the upstream SNRM. I wish I could see more detailed router stats because I would love to see what DLM has done to hit my line at the very nearest to 20mb it can get (Looks like a line cap) where before DLM would try the same speed but with a 3db SNRM and reverted because of errors on the line.

Any ideas or thoughts welcome.


Port   Status   TxPkts   RxPkts   Collision Pkts   Tx b/s   Rx b/s   Up Time
WAN   PPPoA   64729   90866   0              32             0           09:02:13
LAN   Up           12772   20697   0                   102           102           09:03:39
WLAN   Up           125305   80051   0                   51964   5122           09:03:13
Broadband Link           Downstream   Upstream
Connection Speed   19999 kbps   1205 kbps
Line Attenuation           18.5 dB   11.5 dB
Noise Margin            6.1 dB   8.8 dB

[guest]

Its probably set g.INP now which reduces overheads somewhat on routers which support it (SR101 does). Snadge has had something similar happen in the last day or so.

I don't use a Sky router (not having them push more dodgy f/w updates at me thanks) so I probably don't get the maximum speed I can although it does run at 3dB happily enough.

[guest]

The flip-side to all this good stuff in the DLM module is that once DLM has tweaked your line to the max, if you then mess about with noise margins that might be enough to convince DLM that your line isn't stable.

I've stopped using DMT for anything other than "stat-staring". I don't mess about with the line at all for the simple reason I know I can't keep this line stable at 20Mbps on a 3dB margin. I messed about with stuff like that years ago and I know that with the tools (easily) available to me I could just about manage 18Mbps stable. Sky DLM manages 19.5-20Mbps stable so why bother messing around?

NB - by "stable" I mean doesn't desync even with major local impulse noise (CFL blowing is pretty noisy) & doesn't have any measureable packet loss due to errors.