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Standard User 4M2
(knowledge is power) Tue 16-Jan-18 18:27:25
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G.dmt.bis v ADSL2?


[link to this post]
 
Line has been unstable over Xmas using both ADSL2 and ADSL2+ modulations (Billion 7800N router) so yesterday I tried G.dmt and now the connection is rock solid.

> adsl info --stats
adsl: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 1
Max: Upstream rate = 1312 Kbps, Downstream rate = 10624 Kbps
Channel: INTR, Upstream rate = 1024 Kbps, Downstream rate = 10144 Kbps

Link Power State: L0
Mode: G.DMT
TPS-TC: ATM Mode
Trellis: ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.4 10.0
Attn(dB): 34.0 17.0
Pwr(dBm): 19.8 12.3
G.dmt framing
K: 318(0) 33
R: 12 12
S: 1 4
D: 64 4

It appears from the stats that the connection is interleaved G.dmt.bis rather than interleaved ADSL2 (which I thought were the same, i.e. G.992.3?) The symptoms of the instability using interleaved ADSL2 and interleaved ADSL2+ were high error rates and a reduction in the upstream SNRM from 9dB going to below 6dB which would not recover until a resync. Quiet line tests were OK though.

The connection is TTB partial LLU (SMPF) and now together with using the Billion's G.dmt modulation setting there don't appear to be any issues. Any ideas why G.dmt.bis with almost identical sync rates and interleaving depth to ADSL2 should be better? Possibly not specifically a router fault since with other routers both ADSL2 and ADSL2+ modulations have been unstable...

Edit: with the Billion's G.dmt setting CRC, ES and bit errors, on the upstream, are no longer occurring when there is an incoming phone call.

Edited by 4M2 (Tue 16-Jan-18 19:50:03)

Standard User XRaySpeX
(eat-sleep-adslguide) Sat 20-Jan-18 17:22:52
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
In reply to a post by 4M2:
Any ideas why G.dmt.bis with almost identical sync rates and interleaving depth to ADSL2 should be better?
Cuz you are not on G.DMT despite what the router reports. Max Downstream on G.DMT (G.992.1) is 8 Meg.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC
Standard User 4M2
(knowledge is power) Sat 20-Jan-18 21:58:57
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Re: G.dmt.bis v ADSL2?


[re: XRaySpeX] [link to this post]
 
Thanks for your interest and the reply.

Just guessing but perhaps the Billion router's G.DMT modulation setting is for 20cn exchange kit and hence ADSL MAX - as you say up to 8Mbps downstream (and Annex A 448Kbps upstream.) Yet for some reason with TTB LLU exchange kit the sync (following "xDSL G.994 training") is G.992 a.k.a G.DMT.bis.

The line was unstable over Xmas which I thought might be temporarily due to Xmas lights but after the lights were taken down the instability continued both with ADSL2 and ADSL2+ modulation settings. So I thought I would try the D.GMT setting expecting, as you rightly suggest, ADSL1. However much to my surprise I got a very stable ADSL2 connection.

The PPP link did go down on one occasion shortly before the instability began so I guess it could possibly be an exchange issue rather than a router issue at my end...


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Standard User XRaySpeX
(eat-sleep-adslguide) Sat 20-Jan-18 23:11:24
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
ADSL Max isn't full G.DMT but BT's implementation of it with the upstream limited to 448K or 888K for ADSL MAX Premium (I think it was called) as opposed to G.DMT's true max of about 1.3 Meg, just like ADSL2.

I can't imagine a US router being built for a BT anomaly.

I was once on ADSL1 LLU & got max speeds of 8 / 1+ Meg.

I can't sus out the definition of G.dmt.bis. It's not in those router stats. Where do you see it & why do you think you are on it? Even if it's an offering of the router, the exchange would need to be capable of it. As the stats report G.DMT I would not take it that you were on anything but G.992.1. However that contradicts the speeds reported. Puzzling!

For example my router offers me ADSL2+ Annex M, the double speed upstream, but I can't get it even if I select it as the exchange kit isn't offering it.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC

Edited by XRaySpeX (Sat 20-Jan-18 23:14:18)

Standard User 4M2
(knowledge is power) Sun 21-Jan-18 00:59:20
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Re: G.dmt.bis v ADSL2?


[re: XRaySpeX] [link to this post]
 
Sorry I neglected to mention that the router's system log reported "...Line 0: ADSL G.992 Started" which was the connection. Yet the stats report G.DMT although the sync speeds, interleaving, attenuations and SRNM's are virtually the same as the stats that were reported on ADSL2. Since the sync speeds etc. are virtually the same as the previous ADSL2 connection I've interpreted the current connection as G.DMT.bis. The big difference is the stability factor.

There isn't a way to select G.DMT.bis nor G.DMT.bisplus from the router's GUI, only the G.DMT setting is available. Alternatively I can select ADSL2 or ADSL2+ modulations, both of which appear to be currently unstable. It seems that by selecting G.DMT from the router's GUI I'm automatically getting some form of different ADSL2 connection than I did previously.

As I mentioned before I don't think there is a fault with the router since other routers when set to either ADSL2 or ADSL2+ also report instability, However i haven't tried an ADSL1 setting with them.

Edited by 4M2 (Sun 21-Jan-18 01:08:12)

Standard User XRaySpeX
(eat-sleep-adslguide) Sun 21-Jan-18 01:26:01
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
But where are you getting the terms G.DMT.bis , G.DMT.bisplus from?

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC
Standard User 4M2
(knowledge is power) Sun 21-Jan-18 01:31:30
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Re: G.dmt.bis v ADSL2?


[re: XRaySpeX] [link to this post]
 
http://www.kitz.co.uk/adsl/adsl_technology.htm
Standard User XRaySpeX
(eat-sleep-adslguide) Sun 21-Jan-18 03:40:56
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
Ah, they are just other terms for ADSL2 & ADSL2+ respectively.

You are running on ADSL2 with a max of 12 Meg Down. Dunno why your router's calling it G.DMT.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC
Standard User 4M2
(knowledge is power) Sun 21-Jan-18 06:26:38
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Re: G.dmt.bis v ADSL2?


[re: XRaySpeX] [link to this post]
 
Well the router calling it G.DMT seems to have solved the issues smile What is particularly noticeable now is the lack of errors on the upstream, e.g. previously incoming phone calls would cause CRC, ES, SES and bit errors on the upstream. Quiet line tests were always OK though. Additionally, at other times, weird things happened on the upstream such as very high FEC rates which were higher than downstream FEC's, the upstream attenuation reducing to 11dB (from 17dB) whilst the downstream attenuation remained at 34dB and the upstream SNRM reducing to less than 6dB (from 9dB) and not recovering until a resync.

Makes me think there is an issue at the exchange, perhaps something to do with partial LLU (SMPF) - the line is now absolutely fine using the router's G.DMT setting, sync speed is adequate for my needs and throughput has been invariably very good.

I don't really want to get a SFI engineer to visit since with the ADSL2 and ADSL2+ settings it did look like a devilish intermittent fault that happened at random times...however there is something odd going on and it would be interesting to know what it is.
Standard User XRaySpeX
(eat-sleep-adslguide) Sun 21-Jan-18 07:15:01
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
It's all a coincidence or a matter of timing!

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC
Administrator MrSaffron
(staff) Sun 21-Jan-18 10:00:11
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Technical correction....


[re: XRaySpeX] [link to this post]
 
There is no such thing as a variation of G.DMT for BT.

The 448 and 888 Kbps limits are not part of the standard, but simply one of the many configuration options available in the DSLAM and any G.DMT compliant microcode will handle this.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User 4M2
(knowledge is power) Sun 21-Jan-18 17:45:31
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Re: Technical correction....


[re: MrSaffron] [link to this post]
 
if there is a faulty filter at the exchange end could selecting G.DMT modulation at my end somehow use a different non-faulty filter at the exchange? Possibly something to do with partial LLU?
Standard User witchunt
(committed) Sun 21-Jan-18 18:03:04
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Re: Technical correction....


[re: 4M2] [link to this post]
 
No, the filters are either in DSLAM port or hard wired to it.
Administrator MrSaffron
(staff) Sun 21-Jan-18 18:23:26
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Re: Technical correction....


[re: 4M2] [link to this post]
 
ADSL is known for being for more stable on some lines, simple explanation is that ADSL2 packs more bits into the same spectrum and in some scenarios this can make lines more unstable, even though ADSL2 does have more error correction ability.

ADSL2+ adds more frequencies on top of the changes from ADSL2, but as these are in the 1.1 to 2.2 MHz space this only is of help for shorter lines.

Beyond the changes above, some firmware for routers may simply be more debugged for ADSL, or ADSL2 or ADSL2+ without a lot of investigation impossible to say with any confidence, so users finding what works best for them in their particular set of conditions is the best way forward. The DLM systems that do exist try to automate a lot of this so that for the majority of the public there is no need for long discussions on the topic

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User 4M2
(knowledge is power) Sun 21-Jan-18 18:38:55
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Re: Technical correction....


[re: witchunt] [link to this post]
 
So something must be causing problems with the frequencies when I select ADSL2 or ADSL2+ modulations from the router but not when I select G.DMT. As I mentioned previously using the Billion router's G.DMT setting (6 days ago) the stats are virtually the same as with ADSL2, although on the upstream there is an interleaving depth of 64 4 rather than 64 8, now no FEC's on the upstream, and an upstream sync of 1024Kbps rather than the fixed (?) TTB 1022Kbps.
Standard User flippery
(experienced) Mon 22-Jan-18 10:56:09
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
Interesting.
I have similar 7800N on partial LLU. With comparable Attenuation. No errors reported.
If I only use G.DMT the speeds are 890 up 7780 down.
With ADSL2 and ADSL2+ only then down increases to 12100.
Do you have both G.DMT and ADSL2 ticked on your unit.
My ISP was reporting Errors on Up and increased SRN for both to 12.0 hence 7800N purchase.
Standard User 4M2
(knowledge is power) Mon 22-Jan-18 16:12:41
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Re: G.dmt.bis v ADSL2?


[re: flippery] [link to this post]
 
I just have G,DMT ticked.

If I have both G.DMT and ADSL2 ticked then the router will sync using ADSL2. Also if I have G.DMT, ADSL2 and ADSL2+ ticked then the router will use the ADSL2+ modulation.

Previously instead of increasing the SNRM values with ADSL2+, due to high error rates, I chose to use ADSL2 with a forced downstream SNRM of 3dB (upstream remained at the default 9dB) and got a sync rate only slightly slower than ADSL2+ with a SNRM of 6dB. This I did in agreement with my ISP nearly one year ago.

However instability began just before Xmas so I reset the downstream ADSL2 SNRM to 6dB but unfortunately there was no improvement. Now I'm using the G.DMT setting with a downstream SNRM of 6dB and the line is performing really well smile

Edit: looks like you are syncing with interleaved ADSL1 when using the 7800N's G.DMT setting.

Edited by 4M2 (Mon 22-Jan-18 16:36:31)

Standard User flippery
(experienced) Tue 23-Jan-18 11:03:37
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
Thanks
Now I understand why speed difference on G.DMT setting
Standard User 4M2
(knowledge is power) Tue 13-Feb-18 19:40:20
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Re: G.dmt.bis v ADSL2?


[re: flippery] [link to this post]
 
Thought you might be interested to know that after a while errors started to increase with the Billion's DMT setting so I am now using the ADSL2+ setting with PhyR checked on the upstream and downstream. Seems to holding the connection really well with a downstream sync of ~11.5Mbps, 6dB SNRM and an attenuation of 37dB.
Standard User flippery
(experienced) Tue 13-Feb-18 19:57:56
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Re: G.dmt.bis v ADSL2?


[re: 4M2] [link to this post]
 
Similar to what I get on 36dB attenuation with ADSL2+. Never tried .biz route.
Do you ever get random wifi disconnections with your 7800N? I get these sometimes 3 or 4 in a day. Then maybe a week with none.
Standard User 4M2
(knowledge is power) Tue 13-Feb-18 20:50:26
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Re: G.dmt.bis v ADSL2?


[re: flippery] [link to this post]
 
Sorry I don't use wifi - wireless is turned off and no antennas fitted. However I have set-up wireless security just in case, after a reboot, the router might default to wireless mode.
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