HP-UX SNAplus2 R7 LUA Programmer's Guide

Designing and Writing LUA Applications
SNA Information for RUI Primary
• Compression (if required).
2.5.2 Pacing
Pacing is handled by the LUA interface; an LUA application does not need to control pacing, and should never set
the Pacing Indicator flag.
If pacing is being used on data sent from the LUA application to the host (this is determined by the BIND), an
RUI_WRITE verb may take some time to complete. This is because SNAplus2 has to wait for a pacing response
from the host before it can send more data.
If an LUA application is used to transfer large quantities of data in one direction, either to the host or from the
host (for example, a file transfer application), then the host configuration should specify that pacing is used in that
direction; this is to ensure that the node receiving the data is not flooded with data and does not run out of data
storage.
2.5.3 Segmentation
Segmentation of RUs is handled by the LUA interface. LUA always passes complete RUs to the application, and
the application should pass complete RUs to LUA.
2.5.4 Restrictions
SNAplus2 does not support the following for Primary RUI applications:
• Downstream PUs over DLUR
• Dynamically Defined Dependent LUs (DDDLU)
• Sending STSN (to reset sequence numbers, the application should UNBIND and re-BIND the session).
2.5.5 Courtesy Acknowledgments
SNAplus2 keeps a record of requests received from the host in order to correlate any response sent by the application
with the appropriate request. When the application sends a response, SNAplus2 correlates this with the data from
the original request, and can then free the storage associated with it.
If the host specifies exception response only (a negative response can be sent but a positive response should not
be sent), SNAplus2 must still keep a record of the request in case the application subsequently sends a negative
response. If the application does not send a response, the storage associated with this request cannot be freed.
Because of this, SNAplus2 allows the LUA application to issue a positive response to an exception-response-only
request from the host (this is known as a courtesy acknowledgment). The response is not sent to the host, but is
used by SNAplus2 to clear the storage associated with the request.
2.5.6 Purging Data to End of Chain
When the host sends a chain of request units to an LUA application, the application may wait until the last RU in
the chain is received before sending a response, or it may send a negative response to an RU that is not the last in
the chain. If a negative response is sent mid-chain, SNAplus2 purges all subsequent RUs from this chain, and does
not send them to the application.
When SNAplus2 receives the last RU in the chain, it indicates this to the application by setting the primary return
code of an RUI_READ or RUI_BID verb to
LUA_NEGATIVE_RSP with a
0 (zero) secondary return code.
The host may terminate the chain by sending a message such as CANCEL while in mid-chain. In this case, the
CANCEL message is returned to the application on an RUI_READ verb, and the
LUA_NEGATIVE_RSP return code
(see Section 2.4.3, Negative Responses and SNA Sense Codes) is not used.
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