dscp...

otherwise known as diffserv

this was originally the type of service (ToS) field in an ipv4/ipv6 header, redefined by  http://www.rfc-editor.org/rfc/rfc2474.txt for differentiated services... real time data streaming technologies have emerged like voice over ip that make use of this field...

diffserv or differentiated services code point should not be confused with mpls (more on that later)... it is used to carry information about ip packet service requirements and operates only at layer 3

traffic is treated by intermediate systems based on priorities of the type of service