Software-Defined Network (SDN) is a networking criterion designed to sort out traditional IP network shortcomings by breaking the vertical meshing of the control and data planes. Quality of Service (QoS) in networking is a way of managing network resources effectually. The primary goal of QoS is to provide priority concerning QoS parameters, such as
 •  Bandwidth
 •  Delay
 •  Jitter
 •  Loss

QoS can benefit from SDN, such as:

 •  Multimedia flows routing mechanisms
 •  network monitoring mechanisms
 •  resource reservation mechanisms
 •  inter-domain routing mechanisms
 •  queue management
 •  scheduling mechanisms.

QoS can be estimated quantitatively with two categories :

 •  user connections performance
 •  collection of quantitative target parameters.

QoS provisioning mostly relies on Service Level Agreements (SLAs) between end users and service providers. QoS is mainly implemented in two approaches:

 •  Hard QoS
 •  Soft QoS

Hard QoS: The Hard QoS method assures the QoS requirements of connections with resource limitations.
Soft QoS: Soft QoS method is not as rigid as hard QoS methods regarding QoS requirements of flows sent from source to destination throughout the entire session.

QoS is mainly used in SDN to monitor the network bandwidth, transmission and latency. To enrich QoS in SDN, the shortest path algorithm has been used in multipath SDN networks that ultimately attain optimization. Despite this, SDN appears to be an effective way to guarantee the QoS for network flows and can somewhat bring QoS satisfaction. QoS necessity is the essential overall network performance, considered the main performance criteria.

Traditional industrial networks can barely satisfy the QoS requirements for some mission control industrial applications (fault detection, advanced control, remote monitoring) due to the:

 •  Traffic congestion
 •  Reliability issues
 •  Dynamic end-to-end latency
 •  Network heterogeneity

In hybrid industrial internet, the advantages of flexibility and scalability brought up by the SDN can simplify network management and enhance network performance by improving industrial services QoS. Different performances based on certain parameters present in QoS are,

 •  Reliability
 •  Scalability
 •  Consistency
 •  Load Balancing.