In a multi-tenant data center, nodes and links of tenants' virtual networks (VNs) share a single component of the physical substrate network (SN). The failure of a single SN component can thereby cause the simultaneous failures of multiple nodes and links in a single VN; this complex of failures must significantly disrupt the services offered on the VN. In the present paper, we clarify how the fault tolerance of each VN is affected by a single SN failure, especially from the perspective of VN allocation in the SN. We propose a VN allocation model for multi-tenant data centers and formulate a problem that deals with the bandwidth loss in a single VN due a single SN failure. We conduct numerical simulations (with the setting that has 1.7×108bit/s bandwidth demand on each VN, (denoted by Ci)). When each node in each VN is scattered and mapped to an individual physical server, each VN can have the minimum bandwidth loss (5.3×102bit/s (3.0×10-6×Ci)) but the maximum required bandwidth between physical servers (1.0×109bit/s (5.7×Ci)). The balance between the bandwidth loss and the required physical resources can be optimized by assigning every four nodes of each VN to an individual physical server, meaning that we minimize the bandwidth loss without over-provisioning of core switches.

As the performance of each node becomes higher, it is expected that the ad hoc network is used for the community network in which a few thousands of mobile nodes exist. In such a network, the number of hops between a source node and a destination node also becomes longer. However, as the route becomes longer, it is difficult to provide the robust and reliable route for mobile ad hoc networks since the multiple route breaks occur at the same time due to the topology change. Therefore, this paper proposes a Route-Split Routing resilient to simultaneous failure (RSR). RSR sets up multiple Subroute Management Nodes (SMN's) on the route and each SMN manages the subroute between the SMN and the neighboring SMN. When the multiple route breaks occur at the same time, each subroute is repaired by the SMN. Consequently, RSR can reduce the number of control packets used for the route repair and mitigate the network congestion even in case that the number of nodes in the network becomes very larger.