This topic is very exciting and I appreciate your enthusiasm on QoS. Unfortunately there isn't any really good single documentation to understand the high-level nature of this. I will describe and answer this difficult topic to the best of my abiliti...
In order to run a full Border Gateway Protocol (BGP) table stably, more than 696MB might be needed. The recommended minimum in order to run SSO is 8GB total DRAM.
Check site: https://www.cisco.com/c/en/us/support/docs/routers/asr-1000-series-aggregat...
I believe your answer should be in the following links. Read both of them, don't skim, and let me know!
https://networklessons.com/quality-of-service/ip-precedence-dscp-values/https://en.wikipedia.org/wiki/Differentiated_services