This ensures that every site has full control of its future locally, whether a full collaborator or not. All of these levels are achievable on the lowest cost workstations. If the medium allows it, many clients and servers can simultaneously sustain these rates. Once a client has expressed an interest in certain data to a server, the server notifies the client only when the data changes. This not only minimizes traffic, but signals both the health of the server and the freshness of the data.
All data carry time-stamps.
Any client can obtain data with guaranteed matching time-stamps from multiple servers. Data also carry validation information based on both the quality of connection, and validity down to the hardware layer as explained later. Thus, a critical client implementing a global feedback loop can assure it is operating only with fully validated data. The third software layer is the server layer. It insulates all clients from the database layer below.