What are the types of APPN Nodes?

Advanced Peer-to-Peer Networking (APPN) is a key component of IBM's Systems Network Architecture (SNA). It enables protocols where computers communicate directly with each other without being controlled by a central server or mainframe.

APPN was developed as the second generation of SNA to address several key requirements: providing dynamic routing protocols, enabling direct session establishment between end users, reducing overhead for resource planning, and maintaining quality of service within SNA networks.

Network Node (NN)

A Network Node functions as a router in an APPN network. It manages network resources and handles session establishment and resource location services for connected nodes. Network nodes maintain topology databases and provide routing services for end nodes and LEN nodes.

End Node (EN)

An End Node serves as an application host that accesses the network through an adjacent Network Node server. While it contains APPN functionality, it lacks capabilities for network topology maintenance and rerouting. End nodes establish CP-CP sessions with adjacent network nodes to register resources and request directory services.

Low Entry Node (LEN)

A Low Entry Node represents the original peer-to-peer nodes in IBM systems like AS/400s and S/36s. LEN nodes are pre-APPN nodes that can participate in APPN networks by using services from adjacent network nodes. However, session partners and resources must be predefined, and they cannot perform dynamic routing.

Composite Network Node (CNN)

A Composite Network Node describes APPN functionality that exists in both VTAM (Virtual Telecommunications Access Method) and Network Control Program (NCP). Since NCP cannot function as a standalone network node, it works together with VTAM to represent a single network node.

Branch Network Node (BrNN)

A Branch Network Node appears as an end node to upstream network nodes while providing network node services to downstream end nodes and LEN nodes. This functionality, also called Branch Extender (BX), eliminates APPN topology broadcasts between network nodes, making the APPN network more scalable.

Comparison of APPN Node Types

Key Features of APPN

• Distributed network management − No central control point required

• Dynamic configuration − Automatic exchange of network topology information

• Simplified connectivity − Easy connection, reconfiguration, and route selection

• Automated resource discovery − Dynamic definition and location of network resources

Conclusion

APPN node types provide different levels of network functionality, from basic LEN nodes requiring predefined configurations to full-featured Network Nodes offering complete routing and management services. Understanding these node types is essential for designing efficient APPN network architectures.