FTTC/VDSL2 Line Errors

I've had FTTC/VDSL2 installed for 13 months now but it was only yesterday that I got hold of a spare modem and unlocked it enabling me to access my line stats.

Since then I've kept a "log" of the number of errors -

http://img.photobucket.com/albums/v427/griff_90/fcd7...

NOTE - Between 00.10AM and 11.05AM NO DEVICE was connected to the internet at all. The only traffic was the TBB Quality Monitor pinging my router.

Are these errors a cause for concern?

Are these errors a cause for concern?

Yes and No

Yes in the sense that it looks as though you have a noisy line and the number of errors and the fact that you're not quite syncing at the full 40Mbps despite a short line are manifestations of this.

No in the sense that they're probably not affecting throughput (have you measured this?) There is error correction built in to DSL and TCP is designed to withstand a bit of packet loss (although it interprets it as congested networks and slows down if it's too bad).

All DSL lines have some errors. Some are quite good, some less so - when I had ADSL I was only just able to get 3Mbps by tweaking my SNRM right down to 3dB and the error figures were truly frightening but actual packet loss was generally less than 0.3% and throughput ran at the max for the sync speed.

I wouldn't worry too much.

Throughput seems fine as far as that is concerned and generally I'm pleased with the line speed even if my IP Profile is a little lower than it should be.

My concern over the errors is really two fold.

A, There seems to be a lot of packet loss recorded by my TBB QM. Pick any day at random over the last 9 months and I can produce that days graph with packet loss indicated all day long.

If I play an online game in the evening every now and then there a massive lag spike/connection error presumably as the packets are dropped. It only lasts about 1-2 seconds at the most but it happens every few minutes.

B, It is my understanding (maybe incorrectly) that the DLM takes these errors into account when setting things such as the interleaving level on the line. I used to have less than 10ms latency but the level of interleaving has been slowly increasing which I'm guessing is due to the errors recording and dropped packets.

Edited by griff_90 (Fri 09-Sep-11 11:54:10)

How much packet loss is there? On any of the TBB graphs i've seen there is usually a little bit recorded in red at the top and this appears to be normal.

My Broadband Ping

My Broadband Ping

My Broadband Ping

A few days at random. The last is from 8th July (I just chose it based on the date in your signature)

I just disconnected the modem and reconnected it.

I then sat watching the status page update every few seconds and was pleasantly surprised to see no errors at all. That was until after about 8 minutes 16,000 CRC errors suddenly appeared

Unless its actually affecting the connection throughput speed, don't worry about it. CRC errors are to be expected on any xDSL service, even short lines will have some. Same with HEC errors. It doesn't necessarily mean there is a proble, just that the router is reporting the odd lost packet which is retransmitted that quick that you would never notice.

In reply to a post by griff_90:

NOTE - Between 00.10AM and 11.05AM NO DEVICE was connected to the internet at all.

(You mean you weren't using anything connected to the router. The modem and router were connected to the internet).

Main reason for replying though is that errors are pretty well independent of your usage. Packets are constantly travelling between the cabinet and modem, with all their control gubbbage, even if there is no data, and any single bit in a packet can be reversed whether or not it is relevant to data.

My line started at 40/2 without interleaving, and ran like that for 2 days. However, it ran with about 4% packet loss - as seen on the BQM, and measured (at the end of the period) by my SamKnows box.

In this time, the profile was 38717, but I could only get speedtest results (from speedtest.net) of around 34.5Mbps. I guess the packet loss was stopping the tester working flat-out.

After exactly 48 hours, DLM added interleaving, so the latency change was immediately noticeable on the BQM - and this killed off the packet loss immediately.

I did speedtests that confirmed the Profile was still 38717, but it didn't seem to give any faster throughput.

Later on in the day, DLM intervened again, and gave me a lower sync - where the Profile was now around 34800. Speedtests then dropped to around 33.5Mbps.

This went on for a day, but I was then regraded onto a 10Mbps upstream. That obviously reset DLM entirely - because I went through the exact same set of events a second time.

BQM on day 1
BQM on day 3
BQM on day 4, regrade just after midnight
BQM on day 6

Interesting that you've seen a gradual increase in latency, while I've seen a sudden step change.

I have checked my line and it's been in sync for 24 hours now

I have no CRC errors what so ever.

Have about 800ish FEC errors and 100ish HEC errors.

I think it may be a case of interference from an external source.

Not sure if the old AM radio trick would help here.