In The Economist December 21st 2019:
But vloggers such as Mr Wen are attracting huge audiences among overseas Chinese with commentary that does not follow the party line. They also appear to be penetrating the great firewall of China, as the country’s system of online censorship is often known.
So, the structure of the last sentence appears to be "as
<something> is often known". I don't quite get the meaning of it, especially what the role "as" plays here.
My understanding is like:
it means "because the country’s system of online censorship is very famous or famous for being strict."
OR it means "the great firewall is often known to people as the role of online censorship."