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Author Topic: Sync speed difference between RJ11 cables.  (Read 3311 times)

Iam_TJ

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Re: Sync speed difference between RJ11 cables.
« Reply #75 on: August 23, 2017, 03:40:23 PM »

I have VDSL on the end of a (high quality) 2km copper line to the farm here. Typical sync/actual hovers around or just under 10Mbps/1.1Mbps with a Zyxel VMG8924-B10A. With the Openreach supplied HG612 it was around 8Mbps/1Mbps. G.INP is operational.

The router is very close to the master socket (in trunking just below the ceiling) so this weekend I replaced the ~2m long flat cable with a 30cm cable. It seems to have increased the sync rate by 0.5Mbps but that could just be environmental factors so I'll be watching the line stats.

I didn't bother with shielded or twisted-pair cables for such a short run but I am testing if wrapping the cable with tin-foil will stop GCHQ from listening in, err, aliens zapping the line with First Contact signals, err, interference from the mass of other equipment in the data cabinet
which is next to it - we have to eak out every last bit here. literally!

On a side-note I also asked Zen (the ISP) if it's possible to have the target SNR lowered to 3db but they tell me they have no control over the targets. Openreach did announce that 3-6db targets would be set in the DLM (Dynamic Line Management) from March 2017. Not sure if that's been activated for the cabinet here as yet though since I understand activation across the country might not be completed before September.

I'm actively considering paying a household 750m away across the fields to host a VDSL line or even FTTPoD and 5.8GHz point-to-point wireless link because they're less than 20m from a cabinet. Seems like the only way for us to ever get anywhere close to the advertised speeds.
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Dray

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Re: Sync speed difference between RJ11 cables.
« Reply #76 on: August 23, 2017, 03:49:45 PM »

What is the attenuation?
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Iam_TJ

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  • Posts: 86
Re: Sync speed difference between RJ11 cables.
« Reply #77 on: August 23, 2017, 06:22:55 PM »

What is the attenuation?
I assume that was aimed at me?
Code: [Select]
~ # xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    1
Last initialization procedure status:   0
Max:    Upstream rate = 1153 Kbps, Downstream rate = 11262 Kbps
Bearer: 0, Upstream rate = 1153 Kbps, Downstream rate = 10960 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State:       L0
Mode:                   VDSL2 Annex B
VDSL2 Profile:          Profile 17a
TPS-TC:                 PTM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        6.6             6.4
Attn(dB):        34.0            0.0
Pwr(dBm):        8.1             10.4
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GigabitEthernet

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Re: Sync speed difference between RJ11 cables.
« Reply #78 on: August 24, 2017, 07:49:42 PM »

My line went down today and didn't sync up. The Cat5e cable I got from eBay (white, the non "troublesome connections" one), doesn't sync on my line anymore. I did notice it struggling when I swapped it over yesterday: I had to plug it in a couple of times.

Back to the 0.5m Tandy cable and all is well again.
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Iam_TJ

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  • Posts: 86
Re: Sync speed difference between RJ11 cables.
« Reply #80 on: August 26, 2017, 01:16:16 PM »

I've just replaced the 30cm flat cable with a 30cm twisted-pair.

I checked it with my cable-tester before connecting it and all looked good. Once plugged in however, the link would not establish. The VMG8924 xDSL LED would flash (yellow = VDSL) rapidly then switch off.

After plugging/unplugging several times I checked it on my cable-tester once again and found that the pair on 3 and 4 (blue and blue/white in this case) were shorted together. Some tugging at the cable to pull it tight has temporarily sorted that out but I'll replace the cable later on (shop-bought cable).

The modem is now sync-ing about 100Kbps faster on the incoming (Down) side.

Code: [Select]
xdslctl info --show

xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 1153 Kbps, Downstream rate = 11407 Kbps
Bearer: 0, Upstream rate = 1153 Kbps, Downstream rate = 11088 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Link Power State:       L0
Mode:                   VDSL2 Annex B
VDSL2 Profile:          Profile 17a
TPS-TC:                 PTM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        6.7             6.4
Attn(dB):        34.0            0.0
Pwr(dBm):        8.2             10.4

So it looks like the combination of going from 200cm to 30cm gained 500Kbps and then going to twisted-pair has added another 100Kbps, so about a 7% improvement.
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