Policy-based networks can be customized by users by injecting programs called policies into the network nodes. So if general-purpose functions can be specified in a policy-based network, the network can be regarded as an active network in the wider sense. In a policy-based network, two or more policies must often cooperate to provide a high-level function or policy. To support such building-block policies, two architectures for modeling a set of policies have bene developed: pipe-connection architecture and label-connection architecture. It is shown that rule-based building blocks are better for policy-based network control and that the label-connection architecture is currently better. However, the pipe-connection architecture is better in regards to parallelism, which is very important in network environments.
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