HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic SNA Concepts
Figure 1–3 Communication between Transaction Programs and Logical Units
Node A
Conversation
Session
Link
LU
LU
Response
Request
Response
Request
TP
TP
Node B
SNA defines two types of conversations: basic and mapped. These two types of conversations use different methods
to indicate the length of transmitted or received data packages to be passed between SNAplus2 and the TP.
• In a basic conversation, data must be formatted by the TP as logical records before being presented to the SEND
function.
A logical record consists of a two- or four-byte header starting with a two-byte length field, often represented
as “LL,” followed by up to 32,765 bytes of data. Logical records can be grouped together and sent as a block,
transmitting more than one logical record with a single call to the SEND function.
• In a mapped conversation, information is passed to the SEND function as a pointer to a single, unformatted
block of data; the length of the block is passed as another parameter. The block cannot be received as one or
more logical records; the receiving TP must do whatever record-level formatting is required.
1.2.9 Modes
Each LU-LU session has an associated mode that defines a set of session characteristics. These session characteristics
include pacing parameters, session limits (such as the maximum number of sessions between two LUs), message
sizes, and routing parameters.
Each mode is identified by a unique mode name. The mode name must be the same on all SNA nodes that use that
mode.
1.2.10 Route Selection
To establish an LU-LU session, a route must be calculated between the nodes where the two LUs reside. A route
is an ordered sequence of links and nodes that represents a path between the two nodes.
SNA networks support the following methods of route selection:
• For subarea networks, you must predefine all routes between subarea nodes.
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