So we got back online, but performance was really bad. On Monday I received an email asking to confirm that I was back online, which I did, but complained about the performance. Then today I received another email from tech support to let me know that they’d increased my line speed to 7MB. I verified this with a speed test which reported 6356 kb/s down and 684 kb/s.
However, I’ve noticed considerable line instability. The modem confirms this,
|Bandwidth Down/Up(kbps)||7476 / 435|
|SNR Margin Down/Up(dB)||6.0 / 6.0|
|Attenuation Down/Up(dB)||50.0 / 28.1|
That Signal to Noise ratio margin sounds ok, but low for LLU, and the downstream attenuation is really high – I guess meaning that we’re physically a long way from the exchange, so subject to loss of power through dampening of certain frequencies?
There are more concerning stats from the modem,
|Tx Frames Count||3933560||Rx Frames Count||3869705|
|Tx Errors Count||10156||Rx Errors Count||7509746|
|Tx Drops Count||10156||Rx Drops Count||7509746|
I don’t know what’s going on with the reception of packets, but the problem seems off the scale! These are WLAN stats, so does that suggest there’s (additionally) a problem with the built-in WiFi rather than the DSL itself? I recently swapped channels because the glorious KisMac revealed a clash with our neighbour, and after fixing it ping times halved.
FEC seems very high, though I don’t know what this is a measure of (FEC errors presumably), nor what are reasonable values. I imagine it’s a measure of how much data the modem is having to recalculate as a result of errors during transmission as a result of the poor signal quality on the line, and hence also perhaps an indication of why performance is bad – if the modem’s unable to rebuild this corrupt data then many packets may need to be re-sent.
|CRC Down/Up||27 / 65408|
|FEC Down/Up||31281 / 65193|
|HEC Down/Up||432 / 0|
There does look like a consistent problem with upstream data though, but also perhaps HEC down? Incidentally FEC down was continually increasing by a couple of thousand each time I refreshed the modem stats every 5-10 seconds.
I think we’re experiencing periodic loss of DSL, but can’t be sure at what frequency. Looks like it might be every few minutes?
I’ve just received a reply from tech support. They agreed that attenuation was high, recommended connecting to the test socket, and suggested G.DMT instead of ADSL2 as being more stable. Unfortunately it disconnected almost immediately. The second time it stayed up for a couple of minutes only.
G.lite stayed up for about 5 minutes, and offered a bandwidth of 4MB down.
Multimode offered a bandwidth of 4MB down (each of these three modes all presented themselves as G.dmt in the other screen), and stayed up for 1 minute.
T1.413 did not connect.
ADSL offered 5MB down and stayed up for 1 minute.
Every time I’ve emailed I ask them to send an engineer to test the line. I’ll let you know how that goes!
14th Nov: They still haven’t replied, but I notice that my modem’s now been connected for over 5 hours, which is unprecedented! However, the line’s settings are different:
Operation Mode G.dmt Bandwidth Down/Up(kbps) 2720 / 64 SNR Margin Down/Up(dB) 15.5 / 9.0 Attenuation Down/Up(dB) 52.0 / 28.5 Power Down/Up(dBm) 18.5 / 10.5 CRC Down/Up 68 / 7 FEC Down/Up 51221 / 0 HEC Down/Up 101 / 3 System Up Time 18:36:24 DSL Up Time 5:45:02
Speedtest confirms 1832 kbps down and 51 kbps up, which is pretty shoddy if you ask me.