HP -UX SNAplus2 Manual do Utilizador descarregar pdf (Página 41)

Chapter 1 41

SNA Terms and Concepts

Basic SNA Concepts

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.

NOTE Only LU type 6.2 supports mapped conversations.

Modes

Each LU-LU session has an associated mode that deﬁnes a set of session

characteristics. These session characteristics include throughput

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.

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.

• For peer networks that do not support APPN, type 2.1 nodes can

support sessions only with adjacent nodes; their sessions cannot be

routed through intermediate nodes.

• For APPN networks, SNA can compute routes dynamically at the

time of session initiation, using a class of service speciﬁed for the

mode used by the session (see “Class of Service”).

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HP -UX SNAplus2 Manual do Utilizador Página 41