As mentioned in another post, I started to respond to this a few days ago and had to stop. I was going to attempt to look up some links to post but never got that far... so rather than completely abandon the post, I'll just paste where I'd got up to before xmas, so here it is warts and all----
I think it works something like this kitz.
Yes I know that bit and standard DMT stuff which I'm au-fait with.. but I was referring to the more complex workings of PHY management, which is something seldom ever discussed, but is essential for DLM (& DSM) to work. PHY is part of the modem firmware and thus something I don't know too much about, but I think ejs dabbles in this area when hacking firmware, which is why I said he may know more about what ASUS have done.
The ATU-R expects to receive certain configuration parameters from the DSLAM prior to initialisation be able to achieve a successful sync.
It's not anything to do with specific (BCM) chipsets, but is a defined ITU-T standard in its own right.
G.997.1 (Physical layer management for digital subscriber line transceivers/ PHY management) is quite an interesting document if you have time to sit down and digest it all.
I attempted to several years ago purely because G.997.1 was central to the BT-v-ASSIA courtcase and BT/Openreach RAMBO boxes' use of something called ploam. Ploam is what is referred to as the Q interface in G.997.1
I'm not 100% certain, but I think (or at least thought)* it was impossible to over-ride some of these settings, which is why I always wondered how ASUS modems were managing to do what they do on the Openreach system.
However I believe it's possible that the modem could adjust GAIN and bitloading during show-time (ie after the modem has sync'd). It has to be able to do this because thats in part what bitswap process is about. So my pause for thought moment yesterday, was that these modems could be messing with BER/GAIN/bitload perhaps during Showtime. We know that part of the bitswap process, the modem can increase GAIN for specific tones. Now suppose for example you forceably increased GAIN over the full range of tones, which would increase the dB power, which in turn increases SNRM.
*Back to the 2 different types of DLM management I was talking about yesterday which I still cant recall the names of.
Type 1 uses a target SNRm as a parameter, so it could be possible to get the modem to adjust the SNRM. 20CN/21CN uses this type of system.
Type 2 uses capping/banding rather than target SNRm as its primary parameter. NGA uses this type of system and thus a straight forward over-ride of Target SNRM
should be impossible on a DSM based system.
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As a side note, the courts threw out any breach of patent claims on the type 1 system. ASSIA won for type 2, but from what I read it was more to do with the ILQ aspect. ILQ being the DLM status colour which I long ago explained and we knew about before the ASSIA couft case.
Reading between the lines ASSIA's successful claim was based on the fact the NGA system monitored some data via RAMBO to get information for ILQ to decide when to change DLM parameters.
- ASSIA systems also use Type 2 DLM and DSM
- Courts dismissed claims of patient breach on ILQ method used on BT's Type 1 DLM, because it was general practice
- Since the court case Openreach DLM for removal of banding/capping is borked, yet ILQ continues to work for INP.