A Sample LUA Communication Sequence

This section illustrates how RUI and SLI verbs are used for an LUA communication sequence. The two figures illustrate the LUA verbs used to start a session, to exchange data, and to end the session, as well as the SNA messages sent and received. The arrows indicate the direction in which SNA messages flow.

Communication Sequence Using RUI Verbs

In the example shown here, the application performs the following tasks:

• Issues an RUI_INIT verb to establish the SSCP session. (RUI_INIT does not complete until the LUA application has received an ACTLU message from the host and sent a positive response; however, these messages are handled by SNA Server and are not exposed to the LUA application.)
• Sends an INITSELF message to the SSCP to request a BIND and reads the response.
• Reads a BIND message from the host and writes the response. This establishes the LU session.
• Reads an SDT message from the host, which indicates that initialization is complete and data transfer can begin.
• Sends a chain of data consisting of three RUs (the last indicates that a definite response is required) and reads the response.
• Reads a chain of data consisting of three RUs and writes the response.
• Reads an UNBIND message from the host and writes the response. This terminates the LU session.
• Issues RUI_TERM to terminate the SSCP session. (SNA Server sends a NOTIFY message to the host and waits for a positive response; however, these messages are handled by SNA Server and are not exposed to the LUA application.)

Communication Sequence Using SLI Verbs

In the example shown here, the application performs the following tasks:

• Issues an SLI_OPEN verb to establish the SSCP session.
• Sends an INITSELF message to the SSCP to request a BIND and reads the response.
• Reads a BIND message from the host and writes the response. This establishes the LU session.
• Reads an SDT message from the host, which indicates that initialization is complete and data transfer can begin.

  Note INITSELF, BIND, and SDT messages are handled by SNA Server if the application is using SLI. The SLI_OPEN does not return until SNA Server has sent an SDT and response.

• Issues SLI_SEND and SLI_RECEIVE to transfer data, SNA commands, or SNA responses between the host and the application.
• Issues SLI_CLOSE to terminate the SSCP session. (SNA Server sends a NOTIFY message to the host and waits for a positive response; however, these messages are handled by SNA Server and are not exposed to the LUA application.)