In 2000, the service field, Type of Service( ToS), a data field in the IP header in which the services of the datagrams are defined, was reconfigured and divided into two subfields with six and two bits. After the reconfiguration, the former Type of Service field was renamed Differential Service Code Point (DSCP). It is described in RFC 2474.
A major difference between the ToS data field and DSCP is the prioritization. While the ToS field has only three bits for priority control, the DSCP field has 6 bits for priority classification and can theoretically differentiate up to 64 priorities, called codepoints. The 64 codepoints are divided into three groups. Group 1 (Pool 1) has 32 codepoints and is used for instructions and management, a second group (Pool 2) with 16 codepoints is for experimental and local use, and the third group (Pool 3) also has 16 codepoints that can be used when Group 1 is exhausted.
The first three bits correspond to the IP precedence of the ToS data field. Together with the following three bits, they are referred to as the DCSP bits. Prioritization allows data packets to be passed through with high priority even in the event of congestion. This has the advantage that Internet traffic can be handled selectively and Internet service providers(ISPs) can offer their users special features and rates: Cost-effective rates for simple service qualities for private users, real-time communication for Internet telephony or interference-free operation for corporate networks.
So far, four classes have been specified, each with three different packet loss guarantees in the per- hop behavior( PHB) with assured forwarding, Assured Forwarding: Low Drop Preference, Medium Drop Preference, and High Drop Preference.