2.1.2.2 White Box Diagram

This section describes the primary relationship between the Windows Update Services: Client-Server Protocol (WUSP) and the Windows Update Services: Server-Server Protocol (WSUSSS). The primary relationship between the Windows Update Services: Client-Server Protocol (WUSP) and the Windows Update Services: Server-Server Protocol (WSUSSS) is based on shared data among the member protocols.

State sharing of the information passed using WSUSSS and WUSP takes place on an update server. An update server can participate in protocol exchanges with a USS or a DSS using WSUSSS as well as protocol exchanges with update clients using WUSP. WSUS maintains data for each protocol, and there is substantial overlap among the data maintained for each protocol. Data that is modified by a WSUSSS protocol exchange can be consumed by a WUSP protocol exchange, and vice versa.

The following diagram illustrates WSUS topology.

Example of a WSUS topology

Figure 3: Example of a WSUS topology

An update client synchronizes updates from an update server, which can be a DSS that itself synchronizes updates from a USS. Two examples are illustrated in the preceding figure.

In the first example, a new update is introduced to the USS. The DSS initiates an update synchronization from the USS using WSUSSS, which returns the new update. The DSS adds the new update to its WSUSSS ADM. Later, the update client initiates an update synchronization from the downstream server (DSS) using WUSP. Since an update is shared data, it also appears in the DSS's WUSP data and is returned to the update client.

The second example describes data introduced from the client computer. The update client can report client computer information to the DSS by using WUSP. The DSS inserts this data into its WUSP data model. Because this data is shared with its WSUSSS data counterpart, this data (or a derivative of it) is sent to the USS by using a WSUSSS protocol exchange.

A data dependency between the protocols is introduced through the sharing of data. In the first example, the update client cannot synchronize the new update via WUSP until the DSS has synchronized it from the USS via WSUSSS. In the second example, the USS cannot learn of the client computer information until the update client has reported its client computer information to the DSS.