Network system having plural networks for performing quality guarantee among the networks having different policies

A network system having a plurality of interconnected networks each having a policy server, the policy server setting a quality-guaranteed path in the network according to a policy held in the policy server, the policy server comprising:

• a policy holding unit to hold a policy defining a quality that can be guaranteed in its own network, or local network, for an inter-network communication;
• a policy publicizing unit to make public the policy held in the policy holding unit to the policy servers of other networks;
• a guaranteed quality calculation unit to calculate, from a policy publicized by a policy server of a network on a path between the local network and other network, a quality that can be guaranteed for the path between the local network and the other network;
• and
• a quality-guaranteed path setting unit to provide a quality-guaranteed path, the quality-guaranteed path having a guaranteed quality within the quality calculated by the guaranteed quality calculation unit for the path between the local network and the other network.