er interfaces function 1 function 2 function 3 function 1 Interface Interface Infrastructure interface function 2 Infrastructure function 3 interface Traditional system Partially virtualized system Figure 1.6 Traditional and virtualized network functions [40]. 5G Network Architecture VNF management and orchestration function MANO/VNF interfaces Management and orchestration function Legacy management Virtualized interface interface Management Virtualized VNF 2 VNF 3 interfaces interface Network Network Network Network Container interfaces function 1 function 2 function 3 function 1 Interface Interface Infrastructure interface function 2 Infrastructure function 3 interface MANO/VNF interfaces Infrastructure management and orchestration function Traditional system Partially virtualized system Figure 1.7 MANO of traditional and virtualized network functions [40]. existence and if the host function is interrupted, or disappears, then the VNF will be inter- rupted or disappear. Similarly, the container interface reflects this existence dependency between a VNF and its host function. The relationship between the VNF and its host func- tion can be described as follows: the VNF is a configuration of the host function and the VNF is an abstract view of the host function when the host function is configured by the VNF. Therefore a host function, when configured with a VNF, has the external appearance as a functional block in traditional sense, implementing the VNF specification. It is the host function that is the functional block, but it externally appears to be the VNF. Equivalently, the VNF is an abstract view of the host function. In an operator's network, NFs can be remotely configured and managed. For this purpose, the NFs have an interface, often referred to as a north-bound interface, to the MANO function. The MANO function is often complex and includes a large number of distributed components. However, it can be characterized using the same system model comprising functional blocks and their interfaces (see Fig. 1.