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Standard User j0hn83
(member) Fri 03-Feb-17 12:06:21
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: Realalemadrid] [link to this post]
 
Modems shouldn't assume any target SNRM. It should actually use the set target. As seen with Williams line. Maybe, maybe the likes of a home hub made specifically for BT could do something like that, but it goes against how it's designed to work. You can't trust stats from most GUI's though, and I wouldn't trust stats from any modern they behaved in that way. Any Broadcom based or any half decent modem that works as it should, doesn't have target snrm hard coded anywhere. Using such stats to work out of you're on this trial is as helpful as peeing into the wind.
Standard User Realalemadrid
(regular) Fri 03-Feb-17 16:34:41
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: j0hn83] [link to this post]
 
You're still not getting it. No one has suggested that the modem sets or assumes a value for the target SNRM. That is defined by DLM and the DSLAM and was normally 6dB until the trial of lower values started. The hard coded value is only used for the attainable rate calculation.
Administrator MrSaffron
(staff) Fri 03-Feb-17 17:41:45
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: Realalemadrid] [link to this post]
 
I'm glad someone gets it...

Using a hard coded figure for this calculation is logical too, as it helps you see if your performance is poor due to a bad SNR environment too.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.


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Standard User j0hn83
(member) Fri 03-Feb-17 22:39:41
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: Realalemadrid] [link to this post]
 
I know that's what you meant. I'm disagreeing with the fact the attainable is hard coded to a 6dB target. Again, as clearly seen on Williams line. His attainable is increasing as the target snrm is lowered. That's exactly as it should be, and how it is on any decent modem working as it should. I regard all Broadcom based chipsets in this category.

If a modem is using a hard coded 6dB to work out attainable, it's not working as it should, or it is designed specifically for the U.K. market on a ridiculous assumption it will always be 6dB.

In my opinion any modem that works in this way (incorrectly) shouldn't be trusted as to wether it's part of this particular trial. Doing so is as useful as peeing into the wind. "My sync has gone up and my downstream snr is 3dB" does not mean they are in the trial, especially on an exchange not on the list published. That was my original point. Using a decent modem (Broadcom for 1) and comparing the attainable is a sure way to work it out. Monitoring the stats at the time of sync would also confirm it. Again, best done with something like a Broadcom modem, that gives proper stats.

We can agree to disagree though. Opinions are like ****holes, everyone has 1, including me ;D
No offence meant, just putting my point across.
Standard User RobertoS
(elder) Fri 03-Feb-17 23:53:07
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: j0hn83] [link to this post]
 
OK, let's take you through it. Assuming no faults on the line and SRA is not in operation. A few scenarios.

If you have a sync-time margin of 6db we can safely assume you are not on the trial, as if you were that would simply demonstrate your line is not good enough. How is the max attainable calculated, in particular what figures are used and where do they come from?

If following that sync the SNRM falls to 4dB, what happens to actual and attainable? If the SNRM rises to 8dB, what happens to actual and attainable?

Now say you have a sync-time margin of 3dB. How is the max attainable calculated, in particular what figures are used and where do they come from? Then as above, what happens with a 2dB move in either direction, assuming a drop to 1dB does not break the connection.

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - AAISP Home::1 80/20. Sync 54999/14466Kbps @ 600m. BQMs - IPv4 & IPv6
Administrator MrSaffron
(staff) Sat 04-Feb-17 00:29:00
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: RobertoS] [link to this post]
 
Another way

1. Line syncs to a 6dB target margin and attainable sync and actual are very close
2. DLM forces a 9dB target margin, so we now expect the attainable to still be very close to the actual, or still reflect the previous figures when it was 6dB

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User j0hn83
(member) Sat 04-Feb-17 00:42:49
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: RobertoS] [link to this post]
 
In reply to a post by RobertoS:
If you have a sync-time margin of 6db we can safely assume you are not on the trial, as if you were that would simply demonstrate your line is not good enough. How is the max attainable calculated, in particular what figures are used and where do they come from?
From the DSLAM/DLM, 6dB is used
In reply to a post by RobertoS:
If following that sync the SNRM falls to 4dB, what happens to actual and attainable?
It falls, still based on a 6dB target, due to the extra noise on the line, or other factors that made the SNRM fall.
In reply to a post by RobertoS:
Now say you have a sync-time margin of 3dB. How is the max attainable calculated, in particular what figures are used and where do they come from?
Again, from the DSLAM/DLM. If the attainable was hard coded at 6dB to the firmware of the modem then the attainable would not change if the line synced with a 3dB SNRM. The example I used was Williams line. He definitely had a lower SNRM target. At the time of sync his attainable went up with his sync. It went up each time the SNRM target went down.
In reply to a post by RobertoS:
Then as above, what happens with a 2dB move in either direction, assuming a drop to 1dB does not break the connection
The attainable would drop as the actual SNRM drops.

Simply, if the attainable was hard coded to 6dB, it would NOT change with a change of target to 3dB. But it DOES change. It SHOULD change.
Not every country/ISP uses a 6dB SNRM target. The point being made to me previously was that with some modems the attainable was fixed to a 6dB SNRM target. Are you now arguing that's always the case?
Standard User j0hn83
(member) Sat 04-Feb-17 00:48:11
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
Another way

1. Line syncs to a 6dB target margin and attainable sync and actual are very close
2. DLM forces a 9dB target margin, so we now expect the attainable to still be very close to the actual, or still reflect the previous figures when it was 6dB
The fact they remain the same is because the modem uses the newer 9dB to work out the attainable. If the attainable was still being worked out from a 6dB target but the line had an actual target of 9dB, the sync and attainable would no longer be close.
Administrator MrSaffron
(staff) Sat 04-Feb-17 00:51:47
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: j0hn83] [link to this post]
 
So why when people sync with a 9dB target do we see modems reporting attainable much higher than the sync?

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User RobertoS
(elder) Sat 04-Feb-17 01:17:56
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: MrSaffron] [link to this post]
 
Which if I remember tomorrow, (hmmm - later today LOL), I can show on my line with the telnet stats. Currently on iPad so can't. My sync-time margin is as near as dammit 9dB, sync 54999, attainable fluctuating around the mid 65Mbps area as SNRM 0.3dB or so.

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - AAISP Home::1 80/20. Sync 54999/14466Kbps @ 600m. BQMs - IPv4 & IPv6
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