Packet Loss on FTTC

Hi all,

My FTTC connection finally went in - after a botched order system with BTW/BTO held things up for 2 months. Even then they mucked up by cancelling the existing ADSL connection, leaving us without anything. Serious escalation from Plusnet got the FTTC install 2 days later...

However, all is not quite right at the moment - in particular my TBB BQM, which shows about 5% packet loss all day long.

Does anyone else have a graph like this? Or do FTTC graphs usually show more usual behaviour with no loss at all?

I was synced with an IP profile of 38717 yesterday (I can't check right now), but my speedtest.net results have been in the region of 33-34.5Mbps, which seems a little low. Don't people get nearer 36-37Mbps with that kind of IP profile?

Peculiar...

..as a starter for 10, try getting a totally different ethernet cable and going from the openreach modem directly to a computer (turn the firewall on first mind you). See if the problems persist - that would assist in identifying whether anything in your home is at fault, or if it's further up the line.

I'd imagine your slightly slower speed measurements are going hand-in-hand with the packet loss.

That continuous packet loss definitely isn't normal- there's a link to my live BQM in my sig for comparison. It probably accounts for your lowered speed, I get in the high 36's for a profile of 38282Mbps (with interleave on).

You've got those periodic spike in pings at about 2-hour intervals too... unlikely to be anything to worry about, but some users get these periodic spikes for no good reason we've been able to discover

Another oddity is that black period at ~1pm, I can't see how that can happen. Either a ping is successful and recorded or it isn't and it shows up as a lost packet in red. The only time I've ever seen black was a bug in tbb's pingbox when I was running an IPv6 BQM over a 6to4 tunnel, and then the whole thing was black! Don't understand it...


eta- as Blueacid suggests, try to rule out local causes first.

Edited by billford (Sun 05-Jun-11 10:52:54)

I suspect you are right over the relation between speed loss & packet loss.

I tried setting up an outbound ping - to the first location in a traceroute (which would be the Plusnet end to a BT central, or whatever they are called now) - and got 4% packet loss over 15 minutes. That suggests the problem lies between the two, so I'll be testing various components in the link.

I reached the conclusion that the black hole could only be the Firebrick, rather than my end, so I've been ignoring that part. And I hadn't even noticed the regular spikes in the max-latency figures. I'll watch for those, but not be too worried just yet

Thanks for the link to your BQM - Some packet loss seems inevitable - especially if there's a spot where the ISP lets P2P traffic loose (such as Midnight).

I'll work on the local causes first - I just wanted to be sure I wasn't trying to fix something that *everyone* sufered from! So it is good to know that there is something worth chasing here...

I'm also suffering from relatively slow download speeds from everything that is NOT a speedtester. That's on the list to do later too - but is the TBB "downloads" page capable of sustaining FTTC speeds for those files (at the smaller end of the scale, anyway)?

In reply to a post by WWWombat:

I reached the conclusion that the black hole could only be the Firebrick, rather than my end, so I've been ignoring that part.

I checked on my BQM for that day and there was no black hole, so it may not be the Firebrick. Not worth worrying about unless it gets to be a regular occurrence, in which case a post in TTTS would be indicated!

is the TBB "downloads" page capable of sustaining FTTC speeds for those files (at the smaller end of the scale, anyway)?

It's certainly capable of it, even the big files, I've downloaded them (and others, eg >1GB movies from iTunes) at a steady ~4.5MB/sec, but you need a modicum of luck. FTTC seems much more sensitive to congestion, I've seen my speeds drop by 40-50% at times of day when ADSL2+ would only have dropped by ~10%.

And of course, it doesn't take many people hitting a popular server with high-speed connections to cause problems there, regardless of any congestion along the route.

But it's still a lot faster so I'm not really complaining

LOL...

I was wondering why the DLM hadn't cut in to change speed and/or add interleaving.

After posting my previous replies, I thought I'd check on the latest graph, and found that DLM has done exactly that!

Sunday's BQM - with a step change at 9:30 AM, which I think comes exactly 48 hours after the first installation.

BT's speedtester is working today, and gave a 32/1.5 result with a 38717 profile still. Speedtest.net is still in the region of 34/1.7

Edit: Adding this test image too:


So it looks like an addition of interleaving, but no reduction in speed. However, we don't seem to have changed much in the net download speeds...

Edited by deleted (Sun 05-Jun-11 12:57:27)

The ways of DLM are mysterious indeed... it's not in my list of favourite software

In reply to a post by billford:

The ways of DLM are mysterious indeed... it's not in my list of favourite software

Indeed. I'd like to see an online web-portal that allows users to manually set their target SNR and interleaving options - auto settings for the majority but with the option to tweak them if you like and if you get into trouble a reset to put them all back to normal - but that makes too much sense I suppose.

In reply to a post by WWWombat:

I was synced with an IP profile of 38717 yesterday (I can't check right now), but my speedtest.net results have been in the region of 33-34.5Mbps, which seems a little low. Don't people get nearer 36-37Mbps with that kind of IP profile?

It varies for me, sometimes 33-35ish, sometimes 36-37ish, mind you I just got this, which is clearly overstating it a bit!

I've got a 38717 profile and get 37.5Mbps throughput, apart from on TBB.

Actual file downloads from rapidshare for example run at max speed 37.5Mbps, however TBB test file downloads run at 3-4Mbps.

Speedtest sites run at full speed:
http://speedtest.net/result/1327894941.png
http://www.mybroadbandspeed.co.uk/results/99493542.png

Apart from TBB:
http://www.thinkbroadband.com/speedtest/button/13072...

I'm with BT and currently using the hub so can't setup a BQM untill I replace it, but pingtest.net and manual pings don't show any packet loss. Maybe your packetloss will sort itself out.

You're more right than you know!

DLM cut in again, around 7:30pm - and you can probably see the little burst of packet loss in the graph from my earlier post. This time it left the interleaving on, but dropped the speed - the IP Profile went from 38717 to 34799, or around a 4Mbps drop.

The actual download result wasn't much lower though - 31.4Mbps, where I had results of around 33Mbps yesterday. Same for MBS.

Speedtest.net is giving me around 33Mbps, where it was 34Mbps yesterday.

Then DLM cut in *again* - just after midnight. It has taken interleaving away again (so reducing latency), but restoring the packet loss. The IP profile has stayed at 34799.

Yesterday's BQM link
Today's BQM link

I think my most positive face says "its nice that BT is giving me the opportunity to experience & tests different line conditions"

Thanks Croftie (you're not Dave Croft are you?). Those are useful things to know.

It is interesting watching the packet loss disappear and reappear as DLM changes things

Thanks Kevin. Is the Plusnet profile set to 37Mb or 20Mb?

I only ask, because my experience seems to be that the 37Mb profile holds speeds back around 2Mb, and that the 20Mb one is the best one.

The DLM decided to knock about 3Mbps off my profile at around 7:30 this morning for no obvious reason

That would be good, but I'd be reasonably happy just to get the line stats back!

(Mainly the SNRM, so I could tell whether forcing a quick re-sync would be profitable )

if we take aside whether or not higher latency is an issue etc.

Arent all these interleaving cut ins causing line drops? what happens when running software that needs a always on connection but DLM is changing settings twice a day?

In reply to a post by WWWombat:

Thanks Kevin. Is the Plusnet profile set to 37Mb or 20Mb?

I only ask, because my experience seems to be that the 37Mb profile holds speeds back around 2Mb, and that the 20Mb one is the best one.

It's set to 37Mb - surely if it were set to 20Mb I'd be limited to that? Incidentally, I think Plusnet's 37Mb is proper computer Mb, i.e. 37*1024*1024, which equates to 38797312 bps.

Some of them seem to be causing line drops - or at least I'm getting a spike in the red packet loss on the BQM. But not all.

Right now, the router thinks the connection has been up for 18 hours - putting the last connection time at 7pm yesterday. That certainly means the 7pm change of speed was seen, and that the Midnight change of interleaving was not seen.

As for the software running at higher layers... Any ongoing sessions would notice at the moment of the change, but anything critical would be in TCP, and would get retried. Anything that establishes a new connection would just do that, and see nothing. They probably do depend on having the same IP address afterwards, but I'm already on a static IP.

They are both strange profiles...

Back at the time of the trial, the triallists were set on a profile that was named 20Mb, but wasn't actually restricted at that rate.

It was a long way into the trial before the 37Mb profile was created, and some people were put onto that. It isn't clear whether it is an unrestricted profile, or is restricted.

Certainly someone has seen better performance, by 2Mbps, when on the 20Mb profile compared with the 37Mb profile.

My (very limited) experience suggests that the actual download reduction, from a BT-IP-Profile of 38717 to 34799 (roughly 4Mbps drop), is nearer 1-2Mbps (from 34.5Mbps to 33.5Mbps).

No I'm not but I do enjoy his commantairy on a GP weekend