What SNR Margin should I Expect?

Hi All,

I recently returned to a FTTC broadband connection after an 18 month tribulation with VM.
Prior to that I was with Sky on FTTC using the Sky provided router.

I'll ask my question first and provide my setup details at the end of the post.

Although my connection achieves 80/20 it does this with a downstream SNR margin of 6dB (sometimes slightly less)
What seems strange to me is that my Max Downstream rate is shown as ~100,000kbps which suggests significant headroom.
I get 5ms to bbc.co.uk so I guess I'm on Fastpath.

My question is:- does VDSL use the highest possible frequencies it can which have a lower SNR so that more distant connections can get good rate on lower frequencies?

When I was on Sky my downstream SNR margin was showing as 18dB.

Here's my setup...
A TD-W9970 in bridge mode connected to a TP-Link AX20.
The W9970 is connected directly to the master socket with no POTS phone services or extensions.
The W9970 is set to the required VLAN 101 so the PPPoE link to the AX20 is untagged.
I use OneStream which seems to be Vodafone for all intents.
I'm about 250m from my cabinet which is in the local exchange compound.
The cabinet is Huawei 96 and has multiple extension pods to both the DSLAM cabinet and the PCP.
These extensions have been added since I was with Sky.

It is syncing at 80/20 …. that is the max you can get . DLM doesn’t need to tweak it down, as it runs stable at 6snr. It’s doing what I would expect it to.

You're synced at the highest rate you can get, and 6dB is a very healthy margin. There's nothing more you need to try and achieve.

For comparison, here are my own FTTC line stats (Plusnet, cabinet about 700m away):
• Max DSLAM throughput: 55,000 / 15,000 kbit/s
• Attainable throughput: 47,876 / 9,058 kbit/s
• Current throughput: 47,876 / 9,058 kbit/s
• SNR margin: 6 dB down / 5 dB up
• Line attenuation: 24 dB down / 37 dB up
• Approx. line length: 750 m
• Latency: < 1 ms both ways
• Profile: 17a
• G.INP: On downstream / Off upstream
• Bitswap: On both directions

My line is G.Fast, so the attenuation looks odd. Am about 100/110m from the cab.

uptime:12 days,01 Hours27 Mins51 Secs
Data rate:49.216 Mbps / 329.045 Mbps
Maximum data rate:62.991 Mbps / 398.424 Mbps
Full Fibre (FTTP) Mode:On
Noise margin:12.7 / 7.9
Line attenuation:0.0 / 28.6
Signal attenuation:0.0 / 28.6
VLAN id:101
Upstream error control:Off
Downstream error control:Off


Loads of spare shown on the max data rate.

Your stats are totally irrelevant for FTTC/SOGEA products.
Not sure what the OP is expecting 80/20 is the best you can get and a perfectly good SNRM.

In reply to a post by Realalemadrid:

Your stats are totally irrelevant for FTTC/SOGEA products.
Not sure what the OP is expecting 80/20 is the best you can get and a perfectly good SNRM.

Eh? The stats are very relevant for FTTC/SoGEA. Just not relevant for a line which gets the bullseye with 80/20.

In reply to a post by DFScale:

In reply to a post by Realalemadrid:

Your stats are totally irrelevant for FTTC/SOGEA products.
Not sure what the OP is expecting 80/20 is the best you can get and a perfectly good SNRM.

Eh? The stats are very relevant for FTTC/SoGEA. Just not relevant for a line which gets the bullseye with 80/20.

My question wasn't about why I don't get better that 80mbs but why my margin is only 6dB given my max rate shows a lot of headroom.

Given my line is quite short (it has 4.5dB attenuation) I assume it can use a significant proportion of the higher frequencies but at a lower margin.
I'm wondering if the DSLAM will use the higher frequencies where it can in preference to the lower frequencies to reduce crosstalk on these lower frequencies thus helping longer lines.
Does the DSLAM use frequencies that have a margin around 6dB in preference to those with a higher margin?

I'm also sure I read something about cabinets that are in an exchange compound (i.e. exchange only lines) not using the ADSL frequencies, or at least at a lower power.

In reply to a post by Eeeps:

My question wasn't about why I don't get better that 80mbs but why my margin is only 6dB given my max rate shows a lot of headroom.

You're at max sync, so the DLM doesn't need to make any adjustments. Should you get a lot of disconnections your margin could be increased, but as you say you have a 4.5dB attenuation, its likely you will have no issues.

I'm wondering if the DSLAM will use the higher frequencies where it can in preference to the lower frequencies to reduce crosstalk on these lower frequencies thus helping longer lines.

At max sync I don't think the DLM will do anything to your line.

Don't understand your comment. Please tell me in what way Zarjaz's G.Fast stats are relevant for FTTC/SOGEA. I don't believe they are.