COPS is described in the following IETF document: RFC 2748.
It specifies a simple client/server model for supporting policy control over Quality of Service (QoS) signaling protocols (e.g. RSVP).
Policies are stored on servers, also known as Policy Decision Points (PDP), and are enforced on clients, also known as Policy Enforcement Points (PEP).
There are two 'flavors', or models of COPS: The Outsourcing Model and the Provisioning Model.
The Outsourcing Model is the simplest flavor of COPS. In this model, all policies are stored at the PDP. Whenever the PEP needs to make a decision, it sends all relevant information to the PDP. The PDP analyzes the information, takes the decision, and relays it to the PEP. The PEP then simply enforces the decision.
In the Provisioning Model, the PEP reports its decision-making capabilities to the PDP. The PDP then downloads relevant policies on to the PEP. The PEP can then make its own decisions based on these policies. The Provisioning Model uses the Policy Information Base as a repository of the policies.