What is DSCP (packet priority marking)?
In one sentence: A small label inside each internet parcel that can ask for special treatment, such as a quick lane for calls; anyone can set it, so most networks ignore or wipe it.
A little more
DSCP (short for Differentiated Services Code Point) is a six-bit field in every internet parcel's header. An app or a router can set it to ask for different treatment, for example a quick lane for a voice call and a back-seat lane for backups.
The catch is that the sender picks the label, so anyone could mark a huge download as urgent. That is why most internet providers ignore or wipe labels coming from outside, and why smart home queues such as fq_codel judge traffic by how it behaves instead. Where labels are honoured, careful routers (CAKE's diffserv mode, for example) only let a priority lane go first up to a small share of the line.
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