Line quality

I'm once again looking for assistance from all your collective ADSL expertise.

I've recently had to replace my long-serving Linksys router as its progressive failure was manifesting itself as increasingly intrusive phone line noise. I'm now getting good service from a modem and separate router (both D-Link, new), but the speeds are somewhat lower than results I was getting a year or two ago. I'm wondering if the failing router has caused the DSLAM to rack the profile up to 15 dB (this assumes that my understanding of these things is correct), but before requesting a reset from my ISP (Talktalk Business), I've been running BQM to check for any other problems.

A typical result is available here

http://www.thinkbroadband.com/ping/share/0c8697c3b5c...

and the latency, at around 50ms, seems high to me. Is this within aceptable limits? For comparison, at a second property about 100m away, the latency is around 30ms, and both should be on the same cabinet.

The line stats are:

Downstream: Sync 3072 Kbps, Attn 47.0 dB, SNR 15.0 dB
Upstream: 704, 25.0, 15.0

Typical TBB speed check results are now consistently around 2.6 - 2.7 Mbps download, 0.6 - 0.68 Mpbs upstream (bits/s); as an example, Iplayer will usually function, but at times is so erratic as to be unusable. I used to get around 4 Mbps download.

(For comparison, the other property, notionally 100 m further from the cabinet, has a downstream sync of 10850 Kbps, attn of 38 dB, at 6 dB SNR.)

I'm sure I should be getting significantly better speeds, but do I just ask my ISP to reduce the SNR, or do you think I have grounds to ask them to get the line investigated, with the usual caveats about charges if 'nothing' is found? I'm concerned that just resetting the SNR will lead to the DSLAM racking it up again.

Further info: The exchange is WWPNZ, Cabinet 1 (Newlyn): straightline distance cab to exc is about 1700m, which at first sight does not fit with the downstream attenuation which is more in line with 3500m. I've been told in the past that the line distance is around 2000m, which seems a little optimistic, although by no means unlikely. However, it is quite possible that the line is actually routed via another cabinet, and I understand that there is some old aluminium cabling to be contended with. (I've used the OR checker which shows cab 1, but I do know that in these parts at least, it is not reliable in that respect.)

Thanks in advance for any comments and assistance you can provide.

Edited by Mygri (Tue 30-Dec-14 17:29:25)

You need to check the line stats immediately after a resync to check your default margin. I wouldn't expect a line with the ring wire isolated to show a swing betweeh 6dB and 15dB though so I'd guess you may well have an elevated target margin - badly performing routers that can't hold sync can do that. I had a supposed good Draytek years back which I'd had on a fixed speed service that caused me problems when I got VDSL.

Thanks for your response.

I got the stats with a Netgear DGND4000 router, and I won't have an opportunity to do such a test for a day or two; Netgear units generally have a fairly good reputation for holding onto difficult lines. All the checks I've done so far suggest the line performance is reasonably consistent, it's just slowwww.... The latency is perhaps my initial concern. I can easily request a reset to a 6 dB target, but if the latency is indicating other problems, then I'd like to try and get that fixed.

I'll report back when I've had a chance to run the test.

The badly performing router I was talking about was the one you said you had to replace. Incidentally noise on voice would normally indicate a problem with the filters or sometimes an "hr dis" fault on the line (bad joint). As you seem to be happy with that since the replacement router though I'm assuming it must have been a fault with the original router.

Latency would not normally indicate a line or router fault.

In reply to a post by Mygri:

The exchange is WWPNZ, Cabinet 1 (Newlyn): straightline distance cab to exc is about 1700m, which at first sight does not fit with the downstream attenuation which is more in line with 3500m.

You do mean WWPENZ Penzance?

The cab and its distance is irrelevant to ADSL. It's the line length to exchange that matters. You can start worrying about the cab when you get fibre.

You should be syncing at about 6-7 Meg @ 6dB NM. Ask TTB to do a reset.

The sync speed of 3 Meg shows that the sync-time NM was well above 6dB and most probably the 15 dB it is showing now. So it probably hasn't drifted much.

Hi again,

Thanks for the clarification - yes, replacing the router solved the noise problem, and I had also done several filter swaps to be absolutely sure that they weren't the problem. Reasurring to know that latency isn't normally indicative of a line problem.

I'll be on to my ISP for an SNR reset tomorrow...

Thanks again

Hi XraySpex,

Thanks for your response. Penzance - yes! I agree that line length to the exchange is the thing that matters for ADSL, but in this case we are about 25 m from the cabinet, which does not add much; I should have been clearer about that.

With respect to fibre, I propably won't be worrying about distance to the cabinet as we are due for FTTP ), when they get round to installing it.

The speed calculators I've used are in line with your estimate, so I'll be on to TTB tomorrow for an SNR reset as you suggest.

Thanks again

Hi again,

Hmmm... not sure I understand, but as I indicated in my response to your earlier reply, I'm going to see what resetting the SNR does tomorrow,

Thanks again.

I was replying to:

In reply to a post by kwikbreaks:

check the line stats immediately after a resync to check your default margin. I wouldn't expect a line with the ring wire isolated to show a swing between 6dB and 15dB

and showing there has not been such a swing by demonstrating that the sync-time NM was about 15dB anyway.