As we all know the recent mass blocking of social media sites is done by TSPU boxes. But little is known about the technical details of these DPI boxes (for example, what are they - netfilter? Are they on-path or in-path?).
I’ve been trying to gather information online, but so far what I got is very limited. Two posts   about Roskomnadzor’s order for ISPs and two articles   on interviews where TSPU got (briefly) mentioned.
Is there any other source of information on the technical aspect of TSPUs? Any pointer is greatly appreciated. Thank you in advance.