SNAX/APN Application Programming Manual

Introduction to SNAX/APN High-Level APIs

SNAX/APN Application Programming Manual—420111-001

1-4

SNA Layers Supported by the Protocols

SNA functions are organized into layers. The functions that are automatically handled

by the high-level APIs are shaded in Figure 1-2. When you use the CRT protocol, your

application process must perform the presentation services functions (except when used

with the Tandem Pathway/TS product, in which case Pathway/TS performs them).

When you use the ITI protocol, however, the presentation services functions are

automatically handled by SNAX/APN.

Communication Using the Protocols

The high-level APIs to SNAX/APN allow an application process to communicate with

devices as though the devices were ordinary files residing on a Tandem NonStop system.

The application process receives and transmits data only, without SNA headers and

trailers.

Obtaining Device Type, Device Subtype, and Record Size

The SNAX/APN high-level protocols allow the application process to get the device

type and subtype, using the FILE_GETINFOBYNAME_ procedure call. (See the

Guardian Procedure Calls Reference Manual for more information about the

FILE_GETINFOBYNAME_ procedure.)

FILE_GETINFOBYNAME_ returns a one-word integer variable. Bits 4 through 9 of

the variable indicate the device type; bits 10 through 15 indicate the device subtype.

Table 1-1

lists the values of these bits, along with the device types and subtypes these

values represent. The subtypes indicate the screen sizes supported, which are the same

Figure 1-2. SNA Layers Handled by the High-Level APIs

102CDT .CDD

SNA Layers Handled

by the CRT Protocol

Transaction Services

Presentation Services

Data Flow Control

Transmission Control

Path Control

Data Link Control

Physical Control