Figure 60: DSCP queues and translation functions
As explained in previous sections, it could be desired to do a relationship between
DSCP and CoS values, to mix IP and 802.1Q priority mechanisms and increase its
performance over the network. At Reason Switches this function is called DSCP
classification, and it is possible to do a direct mapping of DSCP values to each CoS
possible values. By default, all DSCP priorities are classified as CoS 0 (best-effort
service).
If there is no direct VLAN-mapped priority or IP DSCP mechanism specified at a given
LAN, the switch can search for traffic or addresses involved to map them as a
specific QoS queue (CoS value and DSCP value), making a real traffic-prioritized
function. If, for any reason, IED or hosts at a given network do not allow to configure
specific messages to the VLAN, this mechanism can be used to ensure types of
message prioritization over other ones.
Reason Switches can perform protocol-to-CoS mapping over several filters, where
there is the freedom to select which ports will be filter designed. To schedule traffic in
specific queues, Reason Switches use the following methods:
Destination MAC address;
Source MAC address;
VLAN parameters:
o Untagged frames to CoS queue;
o Specific tagged frames to CoS queue;
o A range of tagged frames to CoS queue;
CoS and DEI values;
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