Welcome to the forum!
As Burakkucat says, your ISP will be able to set your downstream target SNR margin back down to 6 dB or whatever suits your needs. If you find that they don’t understand what you’re talking about, then you obviously need to ask to speak to someone more technical, and, failing that, to change to a much more clued-up ISP. Reducing the SNRM will make the line faster but less reliable - it’s always a speed-reliability tradeoff. But your line might now be perfectly fine at 6 dB SNRM, which is the usual downstream target SNRM value, if the line had a problem in the past and it has now gone away. Some network operators have an automatic system that adjusts target SNRM depending on how many errors they have seen over a certain period of time, raising the target SNRM if there are a lot of errors and then hopefully (!) reducing it back down when things improve, but that can sometimes take ages.
By ‘reliable’ I mean that there will be fewer corrupt packets (messages) received by either modem. Corrupt messages are thrown away. Sometimes these “dropped packets” are resent by the computer that sent them, sometimes they are not, depending on the type of “transport layer” protocol used over the internet. This at best slows things down a lot or at worst lost packets cause some kind of failure of a conversation between computers. Some top quality modems can break messages up into parts and resend these parts over the DSL link to the other modem if these part-messages get corrupted. Modems based on a Broadcom internal chipset are the ones to go for. This modem-to-modem ("layer 2") retransmission software gives superb reliabilty and high speed. The ADSL2 version of this modem-internal software from Broadcom is called "PhyR". In FTTC modems, the same thing is called G.INP.
‘Reliable’ can also mean that the modems sometimes cannot cope with the level of noise and packet corruption and have to drop the connection and reconnect (called a resynch or retrain), which takes about 70 secs and so is a big nuisance. This will more frequently occur with a lower target SNRM whenever there is temporary high level of external interference (noise) or some line fault and this overwhelms the error correction abilities of the modem, which are greater with higher SNRM.
Both types of unreliability can be prevented, as well as by having a higher SNRM, by increasing the "interleaving depth" setting. This is not something you can control exactly, but your ISP will be able to turn interleaving on (best reliabilty), or off (bad) or use a medium interleaving depth setting. Setting interleaving to "on" will make things more reliable, especially in the case where there is a noise spike/burst. Noise bursts that are of really long duration are a big problem, one for which there are no clear answers as far as I’m aware.
I see that indeed your SNRM gargling both up and down are very high. You have interleaving turned on, on a high interleave depth setting, which is good.
@Fellow kitizens, what on earth is interleave depth 320 supposed to be? Looks like a bug in the modem’s stats display routines? Also the delay values look insanely high. What’s going on?
