VDSL Performance & Tuning

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393 posts

Ultimate Geek

#667335 4-Aug-2012 01:57

TIS/BG is at 15 Frederick St. You can get the cabinet locations from the cabinet details Excel spreadsheet on the Chorus website (google e.g. cabinet tis/bg location). The locations are NZMG coordinates. You can use an online converter to convert them to NZDG latitude and longitude and then search for that in Google maps.

The VDSL card is installed in the cabinet. The exchange only supports VDSL in a small area around its location at 587 Mount Albert Road.

McGee

200 posts

Master Geek

#667336 4-Aug-2012 02:11

I think that's a power distro / regulator definitely not a cabinet :P

Instinct

41 posts

Geek

#667430 4-Aug-2012 13:06

Thanks all for the replies and advice.

I sure that this must be the cabinet:
https://cdn.geekzone.co.nz/imagessubs/f208f0026cd51998a9299d9d5e956334.jpg

Using google maps this is 600Meters to the top of the driveway. And I would estimate thedrivway at 50 meters.

So around 650 meters in total from the cabinet.

McGee

200 posts

Master Geek

#667433 4-Aug-2012 13:13

Looks like a cabinet.

Another good way to check is to the Chorus SAT tool to see what you should be on then check the markings in the top left corner of the cabinet.

SamF

1578 posts

Uber Geek

Trusted

#667438 4-Aug-2012 13:22

I concur, looks like a cabinet to me!

Based on what you've said I think you should be getting better attenuation & less errors than you are now. Your 20db attenuation figure calculates out to 1.45km, which is obviously not correct. I would wait until your initial 10 day DLM period is up and then speak to snap about getting Chorus back to see where the issue is. AFAIK this should all be covered in the $400 fee and in fact from what I understood, this fee was supposed to cover tests and checks to ensure the line was up to scratch!

SKYMAX

43 posts

Geek

#667597 4-Aug-2012 20:14

Here is an example of today.....
I was having video streaming issues, so had a quick look at the Fritz!Box and found that the SNR had dropped from 12dB to 11dB (due to line conditions changing I guess), and then the error count skyrocketing [remember I have always had a nice low error count].
So I forced a resync, in which it then connected back with 13dB SNR, but didn't clean up the errors completely.

-JASON-

Instinct

41 posts

Geek

#667616 4-Aug-2012 21:09

SamF: I concur, looks like a cabinet to me!

Based on what you've said I think you should be getting better attenuation & less errors than you are now. Your 20db attenuation figure calculates out to 1.45km, which is obviously not correct. I would wait until your initial 10 day DLM period is up and then speak to snap about getting Chorus back to see where the issue is. AFAIK this should all be covered in the $400 fee and in fact from what I understood, this fee was supposed to cover tests and checks to ensure the line was up to scratch!

OK, well I popped out today and on the way home I stopped next to cabinet and can confirm it's the one as listed on the Chorus website mentioned earlier. Although not 100% accurate, I zero'd the odometer in the car and it was showing 0.7 (700 meters) when I parked in the garage. So I have to agree that there may be a problem. It would be good to see other people have similar results who are 700 meters away or more for comparison. I checked the calender and the 10 days is up today. So I'll probably give Snap a call and see if they can investigate, THe tech from Chorus was only in the house about 15-20 min and cut out the old ADSL master filter and installed a $15 VDSL unit from Corys. I believe he checked the line, but it didn't fully work until the next day as changes as to be made at the exchange (I'm assuming as I was keeoing the POTS line).

(I have to say that the Chorus labour charge seems a little high when you consider the Splitter was only $15. I think most lawyers are even cheaper than that! )

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SamF

1578 posts

Uber Geek

Trusted

#667622 4-Aug-2012 21:57

according to my attenuation I'm around 725m from the cabinet but my physical distance by road is 300m. Of course my line may not come to me so directly, but it's probably not that far off. I suppose by that measure your figures are about right, but I've always suspect there are issues with my line so it's probably not a good benchmark. In any case, it certainly can't hurt to get your line checked out!

SKYMAX: ...had a quick look at the Fritz!Box and found that the SNR had dropped from 12dB to 11dB (due to line conditions changing I guess), and then the error count skyrocketing [remember I have always had a nice low error count].
So I forced a resync, in which it then connected back with 13dB SNR, but didn't clean up the errors completely.

I've found that my target SNR fluctuates somewhat; usually between 12 & 11db. I haven't seen it affect anything however. TBH, I'm not sure how a 'target' SNR can fluctuate!? Any ideas Napster?

stevehodge

393 posts

Ultimate Geek

#667636 4-Aug-2012 22:43

SKYMAX: My understanding is that the statistics tab shows the signal to noise ratio margin (SNRM), not the signal to noise ratio (SNR). The margin is essentially an allowance for unexpected higher noise on the line. DLM is trying to configure the line to have an SNRM of 12db. But SNRM doesn't tell you very much of the story - it doesn't tell you how good your line is. As an example compare my statistics tab (below) to the one Instinct posted on the previous page.

You'd think his line was much better - consistent 12db SNRM and very few errors compared to mine. But now look at the spectrum tab, which shows the SNR for each carrier:

My line has 40 to 65db at each frequency, Instinct's is much lower. And that is reflected in the number of bits transmitted at each frequency: less than 8 bits at most frequencies for him while I get at least 10 bits at most frequencies. The result is that I'm syncing at 47968 kbits/s and he's syncing at 25600 kbits/s.

So forget about the SNRM and the statistics tab. The important things are the spectrum tab, the line attenuation, and the parameters set by DLM (latency and INP).

stevehodge

393 posts

Ultimate Geek

#667637 4-Aug-2012 22:45

SamF: "I've found that my target SNR fluctuates somewhat; usually between 12 & 11db. I haven't seen it affect anything however. TBH, I'm not sure how a 'target' SNR can fluctuate!? Any ideas Napster?"

I believe it is not the SNR target, it is the SNR margin. The target for the SNR margin is 12db (on an 8b profile), and this is fixed. The actual SNRM may be higher or lower than that. I'd expect if it was much lower then DLM would reconfigure the line.

SamF

1578 posts

Uber Geek

Trusted

#667639 4-Aug-2012 22:50

Yeah, that makes sense Steve, thanks for clearing that up.

I still don't know how this can fluctuate however, AFAICS this is a hard setting!?

What's your current DLM profile?

stevehodge

393 posts

Ultimate Geek

#667647 4-Aug-2012 23:11

SamF: "I still don't know how this can fluctuate however, AFAICS this is a hard setting!?"

The target is a hard setting. But I believe what the Fritz!Box is reporting is not the target, it's the measured SNR margin.

So, just to clarify:
Signal to noise ratio (SNR): how much signal is on the line compared to how much noise. This is shown on the chart on the spectrum tab. It should be between about 20db and 70db. The higher, the better. Higher SNR means more bits can be reliably transmitted and therefore the faster the sync.

Signal to noise ratio margin (SNRM): a measure how much headroom there is on the line, or how much SNR you have kept in reserve, or if you like, how much extra noise could appear without losing the connection (I'm not sure if exactly works out like that, but it gives you an idea). This is what I believe is reported on the DSL and statistics tabs as "Signal-to-noise ratio".

Signal to noise ratio margin target: this is what DLM would like the SNRM to be. The target is 12db for 8b profile connections. I think that if you are not achieving an SNRM of close to 12db then DLM would (eventually) back off the connection parameters. There were instructions posted earlier for modifying this target. If you make the target lower then more data can be transmitted, at the cost of making the connection more sensitive to additional noise.

The important point to take from this is that SNRM does not tell you how good your connection is performance-wise. It's more of a indication of how resilient your connection is to additional noise.

"What's your current DLM profile?"

It's DLM-1. See my post yesterday for the details. It still hasn't resync'd.

SamF

1578 posts

Uber Geek

Trusted

#667651 4-Aug-2012 23:39

Ah, so the SNR Target is the headroom that is being aimed for, and the SNR Margin is the actual headroom available on the line. Now I get it! :)

I also found this post which explains a bit more about SNR margin. The key point I took from it was that the margin is the difference between your current SNR and the SNR required to maintain a stable connection at your current connect speed. So if you have a SNR of 50db and a SNR margin of 12db, you will be using 38db of signal to connect with.

Correlating this to what we're seeing with the 1db SNR margin fluctuations on the Fritz's; when the SNR drops from 12 to 11db, it means that, using the above example figures, your SNR is fluctuating between 50 and 49db.

Sound right based on your knowledge Steve?

EDIT: This has got me thinking; most people's SNR margin only ever drops by 1-2db. Based on that, most of us could probably run on 9 or even 6db margin quite happily! Of course, the higher the sync speed, the more errors are likely, so maybe it's not as clean cut as that. I find that if my sync goes from 37 to 38mbit, my errors go up massively!

stevehodge

393 posts

Ultimate Geek

#667655 4-Aug-2012 23:59

Yeah, that's how I understand it. A drop from 12db to 11 or 10 is nothing to worry about IMHO. So yes a 9 or 6db target margin should probably still be pretty stable for most people. I think someone mentioned that the 17a profile already has a lower target (9db?).

I don't know how accurate this is, but here's my estimate of how much extra performance I might get: Looking at the graphs on the spectrum tab, I seem to get approximately 1 bit for every 5db of SNR. I'm getting an average of about 11 bits. So if I lowered the SNRM target by 5db I might get a 9% (1/11) increase in sync speed (though I'd actually hit the 50Mbps limit for the 8b profile first).

SamF

1578 posts

Uber Geek

Trusted

#667656 5-Aug-2012 00:02

Hmm, could be worth a bit of config hacking to see what happens! :)

You're on DLM-1 at the moment aren't you? The number of errors allowed is much higher than I thought it might have been!

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