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Sky: sync rate capped, but downstream margin still 7db.

Mel

ULTIMATE Member
Since Sky upgraded my connection to ADSL2+, I've noticed that although my maximum sync speed seems to be capped, on first syncing the router still obtains a downstream noise margin of about 7db, when I'd expect to often see a DS noise margin a few db higher than that.

I've also noticed that the ADSLCTL command for tweaking the router's noise margin only works as I'd expect if I make a large increase in the target noise margin:-

Raising the target margin to about 12db (170%) will cause my router to sync at a lower rate, but making smaller changes than that to the target margin will result in the router syncing at the normal sync rate and results in changes in the adsl2 framing (and delay etc) instead.


stats with target margin set to 150% (10.5db) - I'd expect the sync rate to be lower than with the default 7db, but it isn't (the 'Max' rate has fallen though)

Code:
Channel: FAST, Upstream rate = 796 Kbps, Downstream rate = 6142 Kbps
Link Power State: L0
Mode:			ADSL2+
Channel:		Fast
Trellis:		U:ON /D:ON
Line Status:		No Defect
Training Status:	Showtime
		Down		Up
SNR (dB):	10.5		11.0
Attn(dB):	50.5		30.6
Pwr(dBm):	11.0		12.8
Max(Kbps):	7736		896
Rate (Kbps):	6142		796
			G.dmt framing
K:		53(0)		25
R:		4		16
S:		1		8
D:		224		8
			ADSL2 framing
MSGc:		72		68
B:		52		24
M:		1		8
T:		3		1
R:		4		16
S:		0.2743		7.7142
L:		1662		224
D:		224		8
			Counters
SF:		6747		6298
SFErr:		0		1
RS:		1579020		55467
RSCorr:		7		0
RSUnCorr:	0		0

HEC:		0		0
OCD:		0		0
LCD:		0		0
Total Cells:	1567701		203297
Data Cells:	337		1312
Drop Cells:	0
Bit Errors:	0		0

ES:		718		1
SES:		0		0
UAS:		70		18
AS:		109

INP:		2.15		2.28
PER:		16.05		17.83
delay:		15.36		15.42
OR:		38.87		33.18


Target margin set to 75% (roughly 5.25db)

Code:
Channel: FAST, Upstream rate = 796 Kbps, Downstream rate = 6142 Kbps
Link Power State: L0
Mode:			ADSL2+
Channel:		Fast
Trellis:		U:ON /D:ON
Line Status:		No Defect
Training Status:	Showtime
		Down		Up
SNR (dB):	5.8		11.5
Attn(dB):	50.5		30.7
Pwr(dBm):	11.5		12.8
Max(Kbps):	9384		896
Rate (Kbps):	6142		796
			G.dmt framing
K:		27(0)		25
R:		10		16
S:		1		8
D:		128		8
			ADSL2 framing
MSGc:		86		68
B:		26		24
M:		1		8
T:		5		1
R:		10		16
S:		0.1396		7.7142
L:		2120		224
D:		384		8
			Counters
SF:		7620		7138
SFErr:		0		1
RS:		3505226		62864
RSCorr:		2813		0
RSUnCorr:	0		0

HEC:		0		0
OCD:		0		0
LCD:		0		0
Total Cells:	1773368		453765
Data Cells:	79		105
Drop Cells:	0
Bit Errors:	0		0

ES:		202		1
SES:		2		0
UAS:		65		21
AS:		122

INP:		7.24		2.28
PER:		16.05		17.83
delay:		13.40		15.42
OR:		45.83		33.18
It's as if there's approx 5db held in reserve.

Maybe adslctl works differently for ADSL2+, but it looks to me that on a SKY LLU connection, a 7db noise margin no longer indicates that you are getting the fastest sync rate for your line!
 
Last edited:

aquiss

ISP Rep
Mel,

Pretty much throw all knowledge you know about ADSL1 out the window when it comes to ADSL2+.

We have a lot of customers on ADSL2+ now, and generally all control measures no longer work. Likewise expect SNR margins to go up, even though conditions have not changed (generally resulting in lower syncs).

One thing we are finding is that we are generally having to educate all our users again, as the expectations are not what the technology intended for many.
 

Mark.J

Administrator
Staff member
ISPreview Team
Your experience mirrors my own Mel but sadly the unlocked Skypass I got doesn't work on my old diagnostics hacked Netgear router so I still haven't been able to play around with this stuff as much as I would have liked. The sky supplied Sagem router also isn’t very good at more advanced tweaks.
 

Mel

ULTIMATE Member
The main reason I think the sync rate is capped, is while on adsl (gdmt) I used to see quite a variance in sync rate especially depending on whether I rebooted the router during the day or the night (and even on which router I used), and although I still see the same drop in noise margin in the evening, rebooting the router when the currently reported noise margin is either well below or above the default 7db target noise margin doesn't affect the sync rate, but does bring the noise margin back to 7db :shrug:

Another thing I find slightly odd is the very high value of "D" which I believe is supposed to indicate interleave depth. I know I'm on fast path so I guess it isn't relevant to my connection, but a reported value of 64 seem more typical whether on interleave or fast path, but mine's typically 384 unless I raise the target margin by a few db to the point where the sync starts to drop, in which case it does drop to 64.

I've been meaning to experiment to see if adjusting target margin affects pings...
 
Last edited:

Mel

ULTIMATE Member
I've been meaning to experiment to see if adjusting target margin affects pings...

Target noise margin reduced to 25% (still same sync rate)

C:\Users\mel>ping bbc.co.uk

Pinging bbc.co.uk [212.58.254.252] with 32 bytes of data:
Reply from 212.58.254.252: bytes=32 time=37ms TTL=248
Reply from 212.58.254.252: bytes=32 time=37ms TTL=248
Reply from 212.58.254.252: bytes=32 time=36ms TTL=248
Reply from 212.58.254.252: bytes=32 time=37ms TTL=248

Ping statistics for 212.58.254.252:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 36ms, Maximum = 37ms, Average = 36ms

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

Default 7db target margin


C:\Users\mel>ping bbc.co.uk

Pinging bbc.co.uk [212.58.254.252] with 32 bytes of data:
Reply from 212.58.254.252: bytes=32 time=39ms TTL=248
Reply from 212.58.254.252: bytes=32 time=38ms TTL=248
Reply from 212.58.254.252: bytes=32 time=38ms TTL=248
Reply from 212.58.254.252: bytes=32 time=38ms TTL=248

Ping statistics for 212.58.254.252:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 38ms, Maximum = 39ms, Average = 38ms

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\


Target noise margin increased to 160%

C:\Users\mel>ping bbc.co.uk

Pinging bbc.co.uk [212.58.254.252] with 32 bytes of data:
Reply from 212.58.254.252: bytes=32 time=41ms TTL=248
Reply from 212.58.254.252: bytes=32 time=41ms TTL=248
Reply from 212.58.254.252: bytes=32 time=40ms TTL=248
Reply from 212.58.254.252: bytes=32 time=40ms TTL=248

Ping statistics for 212.58.254.252:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 40ms, Maximum = 41ms, Average = 40ms

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\


So it looks like the answer is it does!
 

Mark.J

Administrator
Staff member
ISPreview Team
Mel did you have the Sagem or NetGear router?
 

Mel

ULTIMATE Member
I have the v1 Sky router - a white netgear DG834GT with sky firmware.

Are you still having problems getting a working password from your sagem?
 

Mark.J

Administrator
Staff member
ISPreview Team
I got the password but now I'd like to find a way of forcing the Sagem's noise margin to be more static as the same variability you had is still causing problems for me. Sky seem to have locked the router done, while with your NetGear you can at least tweak its advanced settings.

Failing that I'll just need to wipe my newer NetGear, add all the firewall rules back in manually (will take a good couple of hours) and get it working that way. I wanted to avoid that though but there doesn't seem to be any way with the Sagem of tweaking the margin :( .

I can reduce the problem by reconnecting until the margin is high and then leaving it connected but at peak times the problem will still occur.
 

Mel

ULTIMATE Member
I gather they've locked the Sagem's firmware down better than either of the two sky Netgears, and don't seem to have complied with the terms of their GNU licence that require them to make the source available (After looking at parts of the Sky netgear dg934g source, I was pretty certain that if I had one, I could hack my way in :D).

If you want to retain a Netgear's firewall settings after wiping it - backing up its settings before and after, then inserting the firewall rules section from the before netgear.cfg into the post wipe netgear.cfg and restoring that would quite possibly work, although I don't suppose the same trick would work to transfer settings from the Sagem - unless they've based them on the same source.

I must admit before Sky's dlm, I used to have to raise the Sky router's noise margin if it was re-synced durring the day, or the connection would become unstable later in the day as the noise margin tailed away - although if I used my DG834N, it would sync at a higher rate and usually retain it throughout the day - better chipset / adsl driver I guess, shame the router itself wasn't at-all reliable.
 
Last edited:

Mark.J

Administrator
Staff member
ISPreview Team
Ah good point, the CFG seems editable so I'll give that a try.
 

Mark.J

Administrator
Staff member
ISPreview Team
Reset the NetGear and it worked, though the problem came back when I tried to re-add my Firewall rules from the modified CFG. It turned out to be an obscure service rule I'd added that was causing the problems, though quite why I cannot fathom as it merely opened a port for the game ‘Company of Heroes’.

Still, connection pauses have been noticeably rare since I switch back to my faithful NetGear, which is good at handling such problems. I still see the margin dropping but it doesn’t always result in a disconnection. Now at least I should be able to Telnet my way in and have a play.
 
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