Definition of Client and Server
Refer to Figure 36-2 on page 1111. The illustration shows two applications associated with each of the two CAs.
Figure 36-2. Communications Management Overview
A client application is one that submits a request to its local CM to establish a connection with a service provided by an application associated with a remote CA. In its request, the client application supplies the CM with the 64-bit Service ID that identifies the desired service. The local and remote CMs take the following actions:
At an earlier moment in time (most likely, during initialization of the CA), all server applications local to a CA may have registered the ServiceIDs of their respective services with the CA's CM.
The local CM creates a local QP to handle its end of the communications channel between the client and the remote service.
The local CM sends a connection request (i.e., a REQ MAD) to the remote CA's CM. The REQ MAD contains the ServiceID and instructs the remote CM to set up a QP to handle the server application's end of the communications channel.
Upon receipt of the REQ MAD, the remote CM verifies that a local server application provides the desired service.
The remote CM creates a QP of the type requested in the REQ MAD to handle the server application end of the communications channel.
The remote CM provides the remote server application with the QP Handle of its associated local QP.
The remote CM issues a REP MAD back to the local CM. The REP MAD contains the information about the newly created remote QP.
The local CM uses this information to finish programming the context of its local QP.
The local CM passes the local QP handle back to the client application.
The client application can now use the local QP to send messages to and receive messages from the remote server application.
An application may act as both a server (providing services to prospective clients) and as a client (soliciting service from one or more server applications).
The illustration also shows the possibility that, upon receipt of a CM MAD from a remote CM (see item 1 in the figure), a CM may send back a response MAD (see item 2 in the figure) with the MAD's Status field (see Table 27-2 on page 776) indicating that all future CM MADs should be redirected to another location (a different QP and, perhaps, a different port).