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Author Topic: Poor downstream sync speed  (Read 245 times)

tsh854

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Poor downstream sync speed
« on: September 26, 2018, 01:10:26 PM »

Hi,

I've moved home and had FTTC (Zen 80/20) activated 2 weeks ago but my downstream sync (50.8) is much lower than predicted for line length (Range A 80 - 66.8, Range B 80 - 59).

I'm 300m from the cabinet (drop line comes via poles from cabinet so I can easily see the route and measure it), these are my current line stats:
                            Receive Direction   Send Direction
Max. DSLAM throughput   kbit/s  80000   20000
Min. DSLAM throughput   kbit/s  128     128
Attainable throughput   kbit/s  51057   20828
Current throughput      kbit/s  50827   20000
Seamless rate adaptation        off     off
          
Latency                         fast   fast
Impulse Noise Protection (INP)  0      0
G.INP                           off    off
          
Signal-to-noise ratio   dB      7      6
Bitswap                         on   on
Line attenuation        dB      15     16
          
Profile   17a      
G.Vector                        off    off
          
Carrier record                  A43    A43


BT checker, and spectrum images attached.


I've checked (and fixed) the wiring in the house, and tried through the filtered face plate, and direct via test socket with new microfilter, but this is the best I've managed to get.  I've also done a quite line test and can't hear any noise.

Any ideas where to go next?  Do I just live with it, or is it worth raising as a fault with Zen?
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dee.jay

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Re: Poor downstream sync speed
« Reply #1 on: September 26, 2018, 01:14:07 PM »

Are you on the same cabinet as before? Or was this a big distance move?

I know Blackwood - I grew up in Tredegar :)
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Sky FTTC 69/17 @ 3dB SNR - HG612
AAISP FTTC 67/16 @ 3dB SNR - HG612
Routed by pfSense on VMware ESX 6.0
~600M Huawei cabinet

tsh854

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Re: Poor downstream sync speed
« Reply #2 on: September 26, 2018, 01:22:45 PM »

Diolch dee.jay!

Different cabinet & different exchange - I've moved about 2 miles, previously was on Newbridge exchange.
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Weaver

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Re: Poor downstream sync speed
« Reply #3 on: September 26, 2018, 01:24:55 PM »

Talk to Zen. It is below one handback threshold and above another - see
http://www.ispreview.co.uk/index.php/2017/01/bt-wholesale-broadband-checker-adds-downstream-handback-threshold.html
http://forums.thinkbroadband.com/fibre/4524970-downstream-handback-threshold.html?fpart=all

Ask Zen what the MGALS is for the line. It may be that OR just got the original estimate way way wrong and there’s a lot of interference coming from somewhere or a lot of crosstalk. There is no G.INP and no G.VECTOR so everything is pointing towards rubbish performance compared to what it could be like with a good green cab and good modem at your end.
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tsh854

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Re: Poor downstream sync speed
« Reply #4 on: September 27, 2018, 11:56:58 AM »

This is Zen's reply:

Quote
I can understand the frustration in not being able to reach the higher estimates of your line. Unfortunately these estimates are given to us by BT and also confirmed at the point of sale via Zen. With your sync rate being 50mbps and the lowest ever seen being 44mbps, this does not qualify for us to raise it as a fault to BT as they will just reject it back advising it is within their estimates for the line and their handback rate.

Unfortunately with you having done all the troubleshooting steps we would ask of you, there is nothing more I can suggest. I have also checked our side for any changes we can potentially make but found the line is not capped in any way and is on the best profile for this line.

 >:(
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dee.jay

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Re: Poor downstream sync speed
« Reply #5 on: September 27, 2018, 12:02:02 PM »

I'm amazed you only get 50Mb with only 300m distance, I get ~68Mb on 2 lines at double that distance!

Looks like you may be on an ECI cabinet looking at the original stats output.

What also puzzles me is that your 50.3 sync is lower than the handback? At least when considering the "Clean" ranges.
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Sky FTTC 69/17 @ 3dB SNR - HG612
AAISP FTTC 67/16 @ 3dB SNR - HG612
Routed by pfSense on VMware ESX 6.0
~600M Huawei cabinet

j0hn

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Re: Poor downstream sync speed
« Reply #6 on: September 27, 2018, 12:38:12 PM »

What estimates did Zen quote you.
They will have given you a range, and a minimum guaranteed rate.
Usually this is sent on your order email.

For 15dB attenuation the sync is quite low.
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Weaver

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Re: Poor downstream sync speed
« Reply #7 on: September 27, 2018, 01:53:54 PM »

Ask them what the actual numbers are, as this doesn’t sound quite right. But a very decent reply though, explaining how it usually is with OR or BTW.

And your downstream sync rate is more than 16 times higher than mine so not to worry too much. If it is too slow you can always nail two or more lines together with IP bonding given a suitable good ISP and router.

[Moderator edited to merge two successive posts, within minutes of each other, into one.]
« Last Edit: September 27, 2018, 03:49:28 PM by burakkucat »
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