Advanced Peer-to-Peer Networking (APPN), part of IBM's Systems Network Architecture ( SNA ), is a group of protocols for setting up or configuring program-to-program communication within an IBM SNA network. Using APPN, a group of computers can be automatically configured by one of the computers acting as a network controller so that peer programs in various computers will be able to communicate with other using specified network routing.
APPN features include:
- Better distributed network control; because the organization is peer-to-peer rather than solely hierarchical, terminal failures can be isolated
- Dynamic peer-to-peer exchange of information about network topology , which enables easier connections, reconfigurations, and routing
- Dynamic definition of available network resources
- Automation of resource registration and directory lookup
- Flexibility, which allows APPN to be used in any type of network topology
How Dynamic Configuration Works
APPN works with Advanced Program-to-Program Communication (APPC) software that defines how programs will communicate with each other through two interfaces: one that responds to requests from application programs that want to communicate and one that exchanges information with communications hardware. When one program wants to communicate with another, it sends out a request (called an allocate call ) that includes the destination's logical unit (LU) name - the APPC program on each computer that uniquely identifies it). APPC sets up a session between the originating and destination LUs.
APPN network nodes are differentiated as low entry networking (LEN) nodes, end nodes (ENs), and network nodes (NNs). When the network computers are powered on and the software activated, links are established throughout the specified topology. The linked nodes exchange information automatically. If we consider a simplified APPN network, with one end node connected to a network node, the following would describe the sequence of events:
- Each node indicates APPN capability and defines its node type.
- The network node asks the end node if it requires a network node server, which handles requests for LU locations.
- If it responds that it does, the two nodes establish APPC sessions to exchange program-to-program information.
- The end node registers any other LUs defined at its node by sending the networked node formatted information gathered from the APPC session.
- After this sequence is completed, the network node knows the location of the EN and what LUs are located there. This information, multiplied across the network, enables LU location and routing.