dential users, enterprises), LINPs are able to provide to them the same services as provided by networks without applied virtualization. This approach is in fact the basic concept for network softwarization, which is in fact a convenient short description of network virtualization. So, a network slice is a LINP (or vice versa), which can be considered as a unit of programmable resources, where the resources can be network, storage, or computation. ITU's architecture for network virtualization is shown in Figure 3.13, the LINP archi- tecture. Each LINP is built from multiple virtual resources, which are mapped on the Services Services Services Services LINP 2 manager LINP 1 LINP 3 manager manager LINR 2 LINP 1. LINP 3 Virtual networks Virtual Virtual Virtual Virtual resource manager (VRM) Virtual Virtual node Virtual Virtual resources Resource Resource Resource Resource manager manager manager manager Physical link resources Transport (e.g. VLAN, IP tunnel) Storage Computing resources resources resources Physical resources LINP - Logically isolated network partitions VLAN - Virtual local area network Figure 3.13 Architecture for network virtualization. 3 QoS in NGN and Future Networks physical resources (e.g. switches, routers, servers). However, each physical resource may have multiple virtual instances, in other words it can be shared among multiple LINPs. The sharing of physical resources between virtual networks is provided by using virtual resource managers (VRMs). On one hand, one of the main targets of network virtu- alization is to provide higher utilization of physical resources (through their sharing between LINPs) and hence better cost-efficiency. On the other hand, virtualization helps toward better adaptation of the networks to the requirements from existing services and end-users, as well as easy introduction of new services with given QoS and security requirements without a need to build a parallel network infrastructure or to change the existing network infrastructure. Overall, there are four parts