HP rp4440 ACSE/Presentation and ROSE Interface Programmer's Guide - Page 54
Managing Data - end of support
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Programming Guide 3. Managing Data 3. Managing Data ACSE/Presentation (A/P) defines two types of data: control data and user data. Control data (cdata) is associated with the primitives and its content is specific to each primitive. User data (ubuf) is managed by the application and is defined by the context and transfer syntax selected. Control Data Control data is associated with the supported ACSE/Presentation primitives and is managed by the A/P library. Control data is stored in the cdata structure and consists of additional protocol information that must be conveyed to the receiving process using the ap_snd() and ap_rcv() calls. An example of a primitive that contains the cdata structure is A_ASSOC_REQ which passes the proposed initial token assignment to the responder. For each A/P primitive, the specific information required for the primitive is saved in its own cdata structure. User Data User data is managed by the application. User data must be encoded and decoded by the application. The two applications or processes in an association must agree to the presentation context used as previously discussed. Refer to the ACSE/Presentation interface manpages for information on encoding each primitive. Multiple Sends and Receives of Data If you decide to send a single primitive using multiple ap_snd() calls, or the user data is too large to send in one buffer, you can set the AP_MORE bit in the flags parameter to help assure complete receipt of the data by the other process. Each additional ap_snd() call must use the same sptype. The last ap_snd() call must reset the AP_MORE bit to indicate the end of the data. For example: 54 Chapter 4