SNAX/XF and SNAX/APN Configuration and Management Manual

PTrace Reference for SNAX/XF and SNAX/APN
SNAX/XF and SNAX/APN Configuration and Management Manual—425836-006
15-5
SNAX Architectural Overview
be submitted to HP. In PTrace, you can either view all trace records (with the SELECT
ALL command) or use the SELMASK command to select specific types of records.
SNAX Architectural Overview
SNAX traces record messages sent between processes and controllers on NonStop
systems, and also messages sent and events occurring within various parts of the
SNAX software. For this reason, in interpreting traces it helps to understand the basic
structure of the SNAX software and how it communicates with other entities within the
NonStop system. There are minor differences between the SNAX/XF and SNAX/APN
implementations in several SNA levels, noted below.
The SNAX software consists of two processes: the line handler and the service
manager. For historical reasons, the abbreviation TS (Transmission Subsystem) is
often used in trace-record displays to refer to the line handler.
Within the line handler, the activity of each SNA layer (level) is traced separately.
Modules within the line handler correspond to SNA level-2, level-3, level-4, level-5, and
level-6 processing. At levels 4, 5, and 6, additional modules perform specific functions.

Level 1 and 2 (physical control and data link control) functions are implemented
differently depending on the type of line. Level-1 functions are handled by the
controller. Level-2 functions for line type 58,5 are handled by SNAX level 2. Level-
2 functions for X.25 lines are performed by SNAX level 2 and the X25AM I/O
process.

Level 3 (path control) functions are handled by SNAX level 3.

Level 4 (transmission control) functions are handled by SNAX level 4, which
communicates with the service manager. SNAX/APN configuration services (CS)
and the SNAX/APN address space manager (ASM) also support level-4 functions.
The principal function of the address space manager is to manage session identity.

Level 5 (data flow control) functions are handled by SNAX level 5, SNA 3270 data
flow control and SNAX/APN session services. Data flow control for SNALU/XS
applications is the responsibility of the application.

Level 6 (presentation services) functions are handled by the protocol modules for
the CRT, ITI, and PRT protocols. (The CRT protocol is handled by either the CRT
or the CRT30 protocol module, depending on the value of the DEVTYPE attribute
for the LU. Likewise, the ITI protocol is handled by either the ITI or the ITI30
protocol module, depending on the value of DEVTYPE.) Presentation services for
SNALU applications are the responsibility of the application.

The SNAX I/O subsystem provides an interface for communication with
applications.
The service manager performs the following functions:

Command and control (DSM control and inquiry) services through the SPI interface

Configuration services for lines, PUs, and LUs