I wasnt requested to reply but will, am sorry if you dont appreciate my reply.
Firstly I do not suggest turning off bitswapping, bitswapping on noisy lines is very effective, without it, if a snr for a tone goes down, the bits wont be adjusted, you could have negative snr for that tone, and either high errors or loss of sync. a line as long as yours to have no variance I think would be unusual.
In terms of what you call the running out of bits, at first I thought you meant does bitswapping eventually stop functioning (I had these problems in the adsl max days when bitswapping was new and was buggy on various firmwares, but never recently), I actually however think you mean where it turns off specific bits/tones? Bitswapping I believe will disable a tone if the bit loading gets too low, in my experience if it ever hits 0, then the tone gets turned off for the remainder of the sync uptime, in my opinion this is a good thing. But the consequence is a lower SNRM for the duration of the sync. (or lower sync if using SRA). ADSL2 has an advantage here over ADSL1 as ADSL1 has a min bitloading of 2, so would go from 2>0 whilst ADSL2 can support a bitloading of 1, so a tone can survive with 1 bit.
I would expect all Zyxel modems to have behaviours that match up with the Broadcom chip and firmware version.
I didnt know what you meant by monitored tones, but found your older post from a search.
https://forum.kitz.co.uk/index.php?topic=19326.0I have never used a modem that doesnt do that, as far as I know thats expected behaviour within the DSL spec. However I cant verify on any of the modern zyxel modems as my VDSL line doesnt have any disabled tones, the only one's that get low are in the power cut back range due to openreach applying extremely aggressive power cutback. They dont get disabled, but doesnt mean thats due to lack of monitoring it could just be they never get weak enough. of course also i am running VDSL instead of ADSL so the behaviour may have changed anyway. But i can tell you from my ADSL days when I had a very poor line, every modem I used would disable tones when they hit 0 bitloading.
I noticed ejs replied indicating he thinks the behaviour changed on newer modems vs old ones.
According to ejs you can use this command to check if the feature is enabled.
xdslcmd info –cfg
but on my zyxel its actually
xdslctl info –cfg
There is no mention of tone monitoring in the output however, there is an ability to turn it on and off.
xdslctl configure/configure1 [--mod <a|d|l|t|2|p|e|m|M3|M5|v>] [--lpair <(i)nner|(o)uter>]
[--trellis <on|off>] [--snr <snrQ4>] [--bitswap <on|off>] [--sesdrop <on|off>]
[--sra <on|off>] [--CoMinMgn <on|off>] [--minINP <sym>] [--maxDelay <ms>] [--i24k <on|off>] [--phyReXmt <0xBitMap-UsDs>]
[--Ginp <0xBitMap-UsDs>] [--TpsTc <0xBitMap-AvPvAaPa>] [[b]--monitorTone <on|off[/b]>]
I be very surprised if this is not available on your zyxel.