  A NoC is composed by IP cores (Intellectual Propriety) and switches connected
among themselves by communication channels. End-to-End Delay (EED)
communication is accomplished by the exchange of data among IP cores. Often,
the structure of particular messages is not adequate for the communication
purposes. This leads to the concept of packet switching. In the context of
NoCs, packets are composed by header, payload, and trailer. Packets are divided
into small pieces called Flits. It appears of importance, to meet the required
performance in NoC hardware resources. It should be specified in an earlier
step of the system design. The main attention should be given to the choice of
some network parameters such as the physical buffer size in the node. The EED
and packet loss are some of the critical QoS metrics. Some real-time and
multimedia applications bound up these parameters and require specific hardware
resources and particular management approaches in the NoC switch. A traffic
contract (SLA, Service Level Agreement) specifies the ability of a network or
protocol to give guaranteed performance, throughput or latency bounds based on
mutually agreed measures, usually by prioritizing traffic. A defined Quality of
Service (QoS) may be required for some types of network real time traffic or
multimedia applications. The main goal of this paper is, using the Network on
Chip modeling architecture, to define a QoS metric. We focus on the network
delay bound and packet losses. This approach is based on the Network Calculus
theory, a mathematical model to represent the data flows behavior between IPs
interconnected over NoC. We propose an approach of QoS-metric based on
QoS-parameter prioritization factors for multi applications-service using
calculus model.
