This upstream problem is back again. It is line #3, again. The upstream sync rate was 442k, not very good compared with the others.
(Janet had got two of the modems (not links) mixed up, in the sense that each has a label on it and has a configuration with a unique, non-clashing admin interface IP address, and the units on links #2 (mux switch port 2, VLAN 102, line #2) and #3 (mux switch port #3, VLAN 103, line #3) were swapped, so that the FireBrick was trying to talk to a modem at 192.168.2.1 and that modem was listening to 192.168.3.1, thinking ‘I am modem #3’, and the reverse for the modem on link #3. So I asked her to switch them over.)
This involved powering them down, as I always think that is safer from the point of view of DLM. When powered back up, modem on link #3 had now dropped its upstream sync speed from 442k to 347k. So remembering the previous fix, left modem off for 45 mins, back on, no good, now the upstream sync was down to 338kbps.
Last time, I left a modem on this line turned off for several hours. I will try that again at some point. But I still wonder what on earth is going on. Why does this line lose 24% of its upstream sync rate ? And if turning it off for ages works, how long is an age, and why does some particular, greater length of time work?
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Another matter - another modem: Much earlier this morning, I did a target SNRM reset on line #2. Unfortunately this dropped the upstream sync rate from 568kbps to 496kbps on this modem too. (But its downstream sync did go up by 67k, so not all bad.) So a total loss of 176k of upstream, which is over 10%, so not a good day for upstream, whilst downstream rates improved. Why is it that I can just lose a fair sized chunk of upstream on these modems ?
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AA staff noticed that the upstream side loop loss has increased by 0.3dB on that line. There has been a massive amount of rain, but it is not raining right this minute. Makes me wonder if the line is lying in a lot of water - wonder if that could make a difference at lower frequencies?