20MB Jitter and packet loss against UBR

[xintas]

Hello folks,
I have been lurking here since taking VM services three years ago, but now have a questions I hope someone can help me with :)

The performance of my 20MB service seems to have become gradually worse over the last few months. First thing I went off to check was my levels:

Downstream Receive Power Level : 3.6 dBmV
Downstream SNR : 39.0 dB
Upstream transmit Power Level : 42.5 dBmV

According to http://www.cableforum.co.uk/board/12/26006-cable-modem-signal-levels.html, these levels seem to be about right.

FWIW, cable modem is one of the blue ambit 250 NTL modems, and registers on a DOCSIS 1.1 network.

So I decided to test for over-subscribed UBR with a traceroute:

traceroute to www-fmt.bbc.net.uk (212.58.244.143), 64 hops max, 40 byte packets
1 10.121.56.1 (10.121.56.1) 46.210 ms 13.340 ms 21.460 ms
2 nrwh-cam-1a-ge94.network.virginmedia.net (81.100.32.9) 10.007 ms 27.436 ms 26.280 ms
3 pete-core-1a-ge-012-0.network.virginmedia.net (62.252.35.6) 27.029 ms 17.492 ms 26.851 ms
4 nth-bb-a-so-200-0.network.virginmedia.net (212.43.162.245) 81.960 ms 76.415 ms 35.690 ms
5 nth-bb-b-ae0-0.network.virginmedia.net (62.253.185.118) 25.768 ms 18.017 ms 23.566 ms
6 tele-ic-1-as0-0.network.virginmedia.net (62.253.184.2) 19.472 ms 59.478 ms 40.723 ms
7 pos6-1.rt0.thdo.bbc.co.uk (212.58.239.237) 123.182 ms 80.216 ms 248.401 ms
8 * 212.58.238.153 (212.58.238.153) 40.686 ms 18.412 ms
9 212.58.239.62 (212.58.239.62) 19.523 ms 54.608 ms 45.075 ms
10 212.58.251.43 (212.58.251.43) 39.888 ms 46.811 ms 40.005 ms
11 fmt-vip04.telhc.bbc.co.uk (212.58.244.143) 31.345 ms 25.733 ms 47.070 ms

lag seems to be between myself and the UBR. Pings to the external-side of the UBR (internal IP wouldnt reply - I'm guessing it has an ACL):

--- 81.100.32.9 ping statistics ---
100 packets transmitted, 98 packets received, 2.0% packet loss
round-trip min/avg/max/stddev = 6.650/27.581/82.198/14.815 ms

76ms jitter to my UBR seems high, and with 2% loss is concerning.

And just to check it is not internal:

Ping statistics for 192.168.100.1:
Packets: Sent = 100, Received = 100, Lost = 0 (0% loss),
Minimum = 1ms, Maximum = 2ms, Average = 1ms

Now, most of my experience is with ethernet networks, but I normally have a good sense of when something isn't right, and the above smacks of having something wrong to me.

Surely if my problem was an over-subscribed UBR, it wouldn't manifest itself as jitter and loss against the URB? Or have I got it completely wrong and my levels are out?

Your comments, ladies and gents, would be greatly appreciated.

Xin

[Ignitionnet]

Surely if my problem was an over-subscribed UBR, it wouldn't manifest itself as jitter and loss against the URB?

That is exactly how it would manifest itself if the oversubscription were upstream.

[xintas]

Oh joy.

I will set up some cron jobs to re-test this in the small hours of the morning to see if the problems evaporate off-peak, and if it does I guess I will have to get onto VM about it.

Thanks Ignitionnet!

[Spectato]

Try a free download or two from Virgin's game server:

http://playgames.virginmedia.com/

(A tip from someone else on this forum - forgot whom - but thanks!)

I was shocked at how fast my 20Mb connection can run, even at around midnight, after struggling to hit 7Mb on all non-Virgin domains, throughout regular waking hours.

[Ignitionnet]

Oh joy.

I will set up some cron jobs to re-test this in the small hours of the morning to see if the problems evaporate off-peak, and if it does I guess I will have to get onto VM about it.

Thanks Ignitionnet!

Yep yep no worries.

Don't worry about download tests, takes a fair amount of jitter and packet loss to put a serious dent in the download speeds. Just check it during off-peak and if it's all gone then 2+2=....

EDIT: Ah btw if you want to ping your uBR you should be able to get to it with...

Name: nrwh-cmts-03.network.virginmedia.net
Address: 62.253.186.186

More robust test than pinging the CAMs as you are now, they are somewhat aged 7600 routers :)