Draytek Vigor2620 LTE Series User Manual page 322

Vigor routers as edge routers of DS domain shall check the marked DSCP value in the IP header
of bypassing traffic, to allocate certain amount of resource execute appropriate policing,
classification or scheduling. The core routers in the backbone will do the same checking
before executing treatments in order to ensure service-level consistency throughout the
whole QoS-enabled network.
However, each node may take different attitude toward packets with high priority marking
since it may bind with the business deal of SLA among different DS domain owners. It's not
easy to achieve deterministic and consistent high-priority QoS traffic throughout the whole
network with merely Vigor router's effort.
310 Vigor2620 Series User's Guide