Broadband Related > ADSL Issues
Massive amounts of HEC errors
jon_:
Hi
Bit of background - I live in the sticks, approx 5km from the exchange. I have 2 lines from BT, both with ADSL enabled. Both come in on the same piece of wire on different pairs from the junction point which is at the bottom of my drive.
Up until fairly recently, both were rock solid on a 6dB noise margin (set exchange side). Line one would sync at about 3megs. Line 2 just under 4M. Connection times could be weeks at a time between disconnects. They'd been like this for 3 or 4 months.
Then something changed. I get massive amounts of HEC errors on both lines. The ES count goes up fairly quickly due to the HEC errors. DLM kicks, and both lines get throttled back. Line 1 is currently 2.5M on a 9dB target, Line 2 2.5M on a 15dB target.
Attenuation is around the same on both lines as it's always been. No noise is evident on a quiet line test. Both modems are plugged into the master sockets.
Any suggestions on how to approach this - Uno (my ISP) can request a DLM reset, which results in stable connections that are much quicker, until DLM throttles me back down again. As there's no audible noise present I can't log a voice fault, and obviously don't want to pay for an OR engineer visit!! Unfortunately I can't swap to modems that support a target SNR override as they are Sharedband enabled (bonded DSL connections) :(
Thanks!
Weaver:
Hi jon_
That's fascinating. Background: I have a similar setup, much longer lines 7.3 km times three which are IP-bonded in both directions by my ISP and router working together. A single TCP download goes at triple speed. A single upload is less successful, at something like 70% of triple speed. I get 2600-2800 kbps d/s sync with a d/s attn of ~66dB and a supposed downstream target SNRM of 3dB (actual is 0.6-18dB), upstream sync varies between lines - 400k to 550k at an actual SNRM of 6dB.
Having bored you with that. I now admit that I can't offer too much insight. Questions: are the errors sporadic? - what's time distribution of them? How much can you gather in the way of stats?
I'm wondering about crosstalk - is it possible that you have a new disturber somewhere near you? A neighbour with a new service or one who has changed their kit. Or else a source of non-DSL noise has started up? BT can do an RF noise identification service if they feel like it, but they can't fix it for you as they have no powers to police the noise environment.
Desperation option: If you get sufficiently fed up, you could always talk to Andrews & Arnold and see if you can take advantage of their fix-your-line-or-your-money-back scheme. But realistically if this is an RF noise or crosstalk problem then it may not be a fix-line issue.
I can use any modems I like. I'm ignorant - didn't know anything about Sharedband, to my shame - and didn't understand your point about restricted modem choice. My router knows nothing about modem models, they're just some black boxes that speak PPPoEoE.
jon_:
Thanks Weaver. I remember your setup from some other threads.
The Sharedband setup works in a similar way - my two lines have their own connections, the modems are linked and present a virtual IP to my router behind. I have it set up as a routed connection, you can also present as a NAT address and have the modems act as routers if wanted. The additional firmware on the modems takes care of the aggregation of the links, failover etc, and a server at the ISP takes care of the other end. Single thread downloads go at approx the sum of the two lines, minus some overhead as do uploads. I could add more lines up to a max of approx 20Meg total, but that's dependant on the hardware (TP Link TD-W8968) and it's processing capability, heavier duty routers can support bonding FTTC and faster connections. I don't think Uno support linked PPP sessions, they offer sharedband as their solution for aggregating links.
In terms of stats - the modems are locked down to stop 'fiddling' - I've got a ticket open to gain telnet (& SNMP) access, but it doesn't seem to be working as expected. At the moment all I can get is the stats from the admin page, which don't give a breakdown over time. From my checking, it doesn't seem to be time of day dependant, it's just a percentage of headers have errors, which increments the ES count and annoys DLM.
As far as I am aware nothing round here has changed - but the cable run is long so it could be something further away. Everyone else I know locally seems to also suffer from rubbish connections (if anything worse than mine) and aren't technical so can't offer any insights!
BT/OR are *supposed* to be rolling out FTTH in the next 3 months, so I don't really want to be changing too much as I don't want to get tied into contracts! Worst case I can request to be switched to TT LLU with DLM disabled, which may not fix the HEC errors but will let me stay with a quicker connection, or if it drops much more I'll ditch the aggregated connections and go back to my old Billion router and force it to connect at 6dB!
Weaver:
TT LLU might indeed be a better option with their less obnoxious (or is it non-existent) DLM.
j0hn:
Talktalk have a new DLM, which seems to have done more bad than good. I've no personal experience using it, but I believe it can't be "turned off" like it could before. Early impressions from users on kitz are not good with complaints of previously stable lines having interleaving applied and sync reduced.
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