Network Service Sharing

Even though each slice is independent from the other slices, we cannot forget that one of the objectives of SDN/NFV is to improve the network resource efficiency. Due to this and together to the previous feature, Network Slice Manager must have the "ability" to manage NSs that can be shared among multiple Network Slices.

For example, let us imagine there are two different NSTds (NST_1 and NST_2) and both of them using the exact same NS as fig [@Figure:shared_slice] shows. Inside of any NSTd, each description of the selected NSs (subnets) composing the Network Slice has a field (called "is-shared") that determines wheter that NS can be shared or not. A NS can only be shared between Network Slices if thi field is defined as "True" in both used NSTds, otherwise the two resultin NSIrs will have no NS shared. Following the previous example with two different NSTds (NSTd_1 & NSTd_2) composed by three NSs each one: NS_A, NS_shared, NS_B for NSTd_1 and NS_C, NS_shared, NS_D for NSTd_2. They both have in common the usage of one NS (NS_shared) and in each NSTd this NS is defined to be shared ("is-shared" = True):

When NSTd_1 is instantiated (resulting in NSIr_1), the instantiation process follows the service composition procedure described in the previous section and all networks and NS are deployed into VIM. Similarly, when NSTd_2 is instantiated (resulting in NSIr_2), the Network Slice manager follows the exact same instantiation procedure but with one difference. Once it finds out that NS_shared can be shared, it will check among the NSIr database if there is any NSIr (in the example NSIr_1) with the same shared NS (NS_shared) already instantiated. If so, the Network Slice manager will request to instantiate only the "not shared" NSs and get the information of the already instantiated shared NS to fill in section regarding the shared NS within the NSIr_2.

Regarding the termination procedure, only the last remaining active NSIr will request to terminate the shared NS, while the other will simply not ask anything and mark this NS inside ther NSIr data objects as "TERMINATED".