Prioritizations are mechanisms with which priority is regulated. Prioritization mechanisms are intended to prevent data loss in time-critical applications and in the event of overload, because services are restricted as a result.
The prioritization mechanism determines the sequence of data packets and provides them with corresponding priority features. Since data loss always occurs when networks are overloaded, the prioritization mechanism ensures that it is shifted to non-real-time applications. These mechanisms are commonly referred to as Class of Service( CoS).
The prioritization of data is regulated in various networks and protocols, such as by means of priority bits or priority field. IEEE and the Internet Engineering Task Force( IETF) have developed standards for the prioritization of data. The prioritization standardized by IEEE in 802.1Q takes place at the link layer and is based on an extension of the Ethernet frame. Eight priorities, from 0 to 7, are defined by the three priority bits and transmitted in the priority field of the header. How the switches implement the prioritization depends on the implementation of the queuing.
The extensions of the Internet Engineering Task Force (IETF), on the other hand, start in the network layer and affect the service field( ToS) and the DiffServ procedure. In the ToS procedure, the three IP precedencebits in the service field of the IP header are assigned according to priority, whereby eight priority levels are also possible. Differentiated Services (DiffServ), on the other hand, extends the number of possible priority levels to a total of 64.