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Author Topic: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines  (Read 4132 times)

Chrysalis

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #15 on: October 26, 2017, 11:58:57 PM »

I got no idea why their lines drop kitz, its only 2 friends, not loads to be fair, but it seems vdsl is not as solid as it should be.
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kitz

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #16 on: October 27, 2017, 12:13:06 AM »

I don't know, but if anything it seems like what was the doubler system seems borked.  I think this is one of the things they tweaked after the ASSIA case, because its only since then we started seeing complaints about banding not properly being removed.  The INP part appears to be working as intended.

When they first brought it out we seldom saw complaints about it.  It was only after ASSIA...  then later on with g.inp that things started to go out of balance. 
We've also got the rather strange situation whereby Openreach will attempt to remotely remove a cap, but it never gets done right.   Its only the Engineers resets that seem to work as they should.   :'(

It's like they started with one system and have made too many amendments and something has got broken along the way.   
The original NGA system was built based on banding and INP without Target SNRm.   
Since then something has been changed with banding, the ILQ doubler has been extended. G.INP introduced.  G.INP mk2 introduced..  and now its gone to using various target SNRMs.   
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broadstairs

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #17 on: October 27, 2017, 08:16:08 AM »

I am convinced that there are more issues with DLM and I also suspect there are issues with it on ECI cabinets. Having managed to get my line running without a cap I still see issues with DLM refusing to remove interleaving despite (according to MDWS) my line being green. At its worst my line was left interleaved at 6db SNRM with very low ES and green status for 4 months with zero action by DLM.

Frankly I believe that DLM is not fit for purpose and I also believe it does have significant issues on ECI cabinets. If it cannot work properly with 6db SNRM how the heck can it cope with reducing the SNRM at all.

Stuart
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WWWombat

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #18 on: October 27, 2017, 10:03:26 AM »

On the theory that 3dB should work, and comparison with ADSL2+, where it is successful...

VDSL2 has two problems that DLM seems to not be designed for:
a) SNRM running below target because of DSLAM resets or power cycles
b) SNRM running below target because of crosstalk/takeup increases. Or even one neighbour who turns their modem off daily.

As we all know, running at a lower SNRM invites higher error counts, which can trigger DLM. Running lower SNRM targets makes this more likely than before. Higher takeup makes it more likely too. XdB and high takeup (without vectoring) have fundamentally changed the playing field since the days of 2013. We can no longer trust that a line runs within , say, 1dB of where we set the target. Not over a period longer than a few hours.

DLM patently shouldn't interfere when the running SNRM has badly diverged from the target. XdB requires DLM to be more lenient; probably only triggering a resync as the first response, and then only choosing a further step based on, say, the stats for 12 hours after that resync. Any other statistics are becoming less trustworthy ... such that GIGO rules.
« Last Edit: October 27, 2017, 10:38:04 AM by WWWombat »
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WWWombat

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #19 on: October 27, 2017, 10:32:30 AM »

On the XdB off-switch...

I'm still convinced  that DLM got redesigned (after G.INP fiasco #1)  into 2 layers:
- one operational layer, working as before, each night
- one monitor layer, that set the boundaries that the first layer worked in.

The supervisor would identify external conditions (such as modem type) to determine whether G.INP was a suitable quality-improvement tool, on this line, for day-to-day use.

I then think a lot of new features come with an inhibitory off-switch ... including G.INP and XdB. These switches force the monitor to discount that feature.

When we see a rollout take 3 months+,  turning on N lines per day, I suspect that the underlying DLM process changed on day 1. The slow release is made to happen by turning the off-switch on for a few lines at a time.

In this model, each process has its own history for a line; the operational process changes daily, but the monitor is slower to respond. What we used to see as a reset of DLM can now happen in two ways, depending which histories get cleared.

With this model, I think banding changed ... such that it became part of the monitor layer, and became hard to dislodge. And immune to some DLM resets.

So... with such a model in mind, it is easy to think of multiple inhibitory off-switches existing, some controlled manually (as BS did), and some automatically (such as during a rollout, or by modem detection).
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WWWombat

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #20 on: October 27, 2017, 10:48:59 AM »

On the doubler...

Yes, that mechanism seemed to change ... and in some ways improved. I agree that the Assia case brought many alterations to the party, in a similar timescale to the consequences of the ECI fiascos. And it will have impacted the way line profiles were selected based on line history.

The problem for us is that, while identifying why DLM intervenes is hard, figuring why DLM de-intervenes is hard^2 or worse. Until we can insert a line simulator into a circuit, anyway !
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tubaman

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #21 on: October 27, 2017, 11:12:35 AM »

From a personal perspective Xdb has achieved very little for me.
When I originally got VDSL it was pre G.INP and my line synced at about 35Mbps with a throughput of about 33Mbps.
G.INP then came along and my sync increased to the low 40's with an associated increase in throughput.
Xdb has now put me on a 4dB profile and my sync has increased to 46Mbps.
However, I have seen no increase in throughput as I assume I am now on a retransmission high profile which has pretty much killed any benefit from the increase in sync.
ES have gone from about 100 per day pre XdB to around 250-300 per day now.
 :(
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niemand

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #22 on: October 27, 2017, 02:50:28 PM »

The 3dB margin significantly improved things on my backup BT line. The primary line remains banded and will be ceased in about a month.

I can't say I'm sorry to replace my primary xDSL line with something else either. It's worth remembering that Openreach started deploying this stuff in 2009.
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Chrysalis

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #23 on: October 27, 2017, 10:47:59 PM »

tubaman that sucks if true, DLM should in my opinion if it needs to raise interleaving/retransmission to be stable at a noise margin then it should revert the noise margin and drop interleaving/retransmission back to where it was, so basically if you are correct you now have a higher delay penalty for nothing.
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ejs

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #24 on: October 28, 2017, 06:34:11 AM »

Retransmission high has a higher maximum retransmission delay, but while nothing is being retransmitted, the latency is unaffected.
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Chrysalis

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #25 on: October 28, 2017, 07:22:44 AM »

its still a higher penalty than low retransmission.

ejs am I right that you are of the opinion that max sync speed wins over everything else? as you seem to be in favour of an aggressive xDB DLM.
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ejs

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #26 on: October 28, 2017, 09:40:22 AM »

What do you think the difference in typically latency between retransmission low and retransmission high profiles is?

ejs am I right that you are of the opinion that max sync speed wins over everything else? as you seem to be in favour of an aggressive xDB DLM.

No, and I'm not sure where you got this idea from. I'm pretty sure that whatever the DLM does, people will be complaining about whatever it did. The general consensus will be that the DLM is rubbish, and therefore any details about why it's rubbish, whether they are correct, incorrect or irrelevant, do not matter.
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Chrysalis

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #27 on: October 28, 2017, 02:20:10 PM »

ok thanks for clarifying i asked as you responded to two recent posts i made on it.

i think its ok for people to moan about it as after all its a broadband forum :)

i dont think dlm is completely rubbish but also i dont think its perfect either.

the xDB stuff puts dlm in a weird place as its supposed to be stabilizing poor lines but this applies performance settings instead
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WWWombat

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Re: Openreach Pause Plans to Test XdB Boost on UK ECI FTTC Broadband Lines
« Reply #28 on: November 02, 2017, 08:45:32 PM »

Retransmission high has a higher maximum retransmission delay, but while nothing is being retransmitted, the latency is unaffected.

The extension of this is that, on a line running Retransmission High, there is an expectation for it to be retransmitting more blocks, and perhaps re-re-transmitting a higher proportion too with a higher count of re-re-transmissions.

Those will reduce the effective throughput of the line (the EFTR). Perhaps this is why the IP Profile gets set to a lower percentage - just in case retransmission is severe.
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