What is the internal differentiated services code point (DSCP)?
A. Each frame has an internal class of service (CoS) assigned, either the received CoS or the default port CoS. This includes untagged frames that do not carry any real CoS. This internal CoS and the received DSCP are written in a special packet header (called a Data Bus header) and are sent over the Data Bus to the switching engine. This happens at the ingress line card. At this point, it is not known yet whether this internal CoS is carried to the egress application-specific integrated circuit (ASIC) and inserted in the outgoing frame. Once the header reaches the switching engine, the switching engine Encoded Address Recognition Logic (EARL) assigns each frame an internal DSCP. This internal DSCP is an internal priority assigned to the frame by the Policy Feature Card (PFC) as it transits the switch. This is not the DSCP in the IPv4 header. It is derived from an existing CoS or type of service (ToS) setting, and is used to reset the CoS or ToS as the frame exits the switch. This inte
