HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic APPN Concepts
• 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 Section 1.2.11,
Class of Service).
The High-Performance Routing (HPR) feature of APPN provides the following functions:
• Rapid Transport Protocol (RTP) minimizes cycles and storage requirements for routing network layer packets
through intermediate nodes on a session route.
• Automatic network routing (ANR) enables APPN networks to automatically reroute sessions if a portion of the
originally computed route fails.
1.2.11 Class of Service
Class of service (COS) is a definition of the transport network (data link control and path control) characteristics—
such as route security, transmission priority, and bandwidth—that the local node can use to establish a particular
session. The COS definition assigns relative values to factors such as acceptable levels of security, cost per byte,
cost per connect-time, propagation delay, and effective capacity.
In a subarea network, a COS is derived from the mode associated with a session, as defined in the host system.
APPN network nodes use the COS to compute session routes between independent LUs. For more information
about session routing in APPN networks, see Section 1.3.4, Session Routing.
1.3 Basic APPN Concepts
Advanced Peer-to-Peer Networking (APPN) is a network architecture that supports distributed network control.
It makes networks easy to configure and use, provides centralized network management, and supports flexible
connectivity.
An APPN network is composed of type 2.1 nodes. Each node in the network is connected by a link to at least
one other node in the APPN network. CP-CP sessions are established over each of these links to adjacent nodes
(nodes in the same network that can establish direct links without going through a third node). All of the nodes in
an APPN network share a common network name.
APPN nodes can include processors of various sizes, such as the Application System/400 (AS/400), PCs running
CS/NT, systems using Virtual Terminal Access Method (VTAM), and HP-UX servers running SNAplus2.
APPN provides the following functions:
• Support for APPN network nodes and end nodes as well as non-APPN peer nodes (see Section 1.3.1, APPN
Node Types)
• APPN control point functions (see Section 1.3.2, APPN Control Point)
• Directory services to support finding specific logical units (see Section 1.3.3, Locating Resources)
• Topology and routing services to support session establishment using intermediate session routing (ISR),
automatic network routing (ANR), or connection networks (CNs) (see Section 1.3.4, Session Routing and Figure
1–10, Definitions Needed for Direct Links from Node EN1 to Every Node in an APPN Network)
Note
An APPN node can also be connected to a subarea network, serving as both an APPN node
in a peer network and a peripheral node in a subarea network.
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