Sample LUA Communication Sequence

The following is an example of an LUA communication sequence. It shows the LUA verbs used to start a session, exchange data, and end the session, and the SNA messages sent and received. The arrows indicate the direction in which SNA messages flow.

The following abbreviations are used:

SSCP norm: LU-SSCP session, normal flow
LU norm: LU-LU session, normal flow
LU exp: LU-LU session, expedited flow
+rsp: Positive response to the indicated message
BC: Begin chain
MC: Middle of chain
EC: End chain
CD: Change direction indicator set
RQD: Definite response required

Verb issued by LUA application	SNA message	Flow direction Application Host
RUI_INIT	(ACTLU)	<-----
	(ACTLU +rsp)	----->
RUI_WRITE (SSCP norm)	INITSELF	----->
RUI_READ (SSCP norm)	INITSELF +rsp	<-----
RUI_READ (LU exp)	BIND	<-----
RUI_WRITE (LU exp)	BIND +rsp	----->
RUI_READ (LU exp)	SDT	<-----
RUI_WRITE (LU exp)	SDT +rsp	----->
RUI_WRITE (LU norm)	data, BC	----->
RUI_WRITE (LU norm)	data, MC	----->
RUI_WRITE (LU norm)	data, EC, CD, RQD	----->
RUI_READ (LU norm)	data +rsp	<-----
RUI_READ (LU norm)	data, BC	<-----
RUI_READ (LU norm)	data, MC	<-----
RUI_READ (LU norm)	data, EC, RQD	<-----
RUI_WRITE (LU norm)	data +rsp	----->
RUI_READ (LU exp)	UNBIND	<-----
RUI_WRITE (LU exp)	UNBIND +rsp	----->
RUI_TERM	(NOTIFY)	----->
	(NOTIFY +rsp)	<-----

In this example, the application performs the following steps:

Issues the RUI_INIT verb to establish the LU-SSCP session. (The RUI_INIT verb does not complete until Personal Communications programs have received an ACTLU message from the host and sent a positive response; however, these messages are handled by each program and 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-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-LU session.
Issues the RUI_TERM verb to terminate the LU-SSCP session. (Personal Communications programs send a NOTIFY message to the host and waits for a positive response; however, these messages are handled by each program and are not exposed to the LUA application.)