Networking on z/OS
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SNA Advanced Peer-to-Peer Networking (APPN)

Networking on z/OS

APPN is dynamic in nature and reduces the amount of predefinition required in an SNA subarea network.

APPN is the IBM strategic SNA protocol in the mainframe. It is required for sysplex, Enterprise Extender implementation, and many other technologies.

APPN/HPR was introduced in the mid-1990s and supports nondisruptive route switching for failure recovery and connectionless intermediate routing of packets.

APPN/HPR still maintains the class of service (CoS) and data flow control using a more advance pacing mechanism, adaptive session pacing.

In contrast to subarea networking, where special hardware and software (VTAM in the mainframe and the network control program in the 3745) are required for intermediate session routing, every node that can act as network node can perform routing of SNA packets.

  • Introduction to APPN
    In the mid-1980s, SNA subarea networking was the dominant networking protocol used for data processing. Its robustness, management tools, and predictable response time attracted many organizations to SNA, and they used SNA in their mission-critical applications. The major drawback of SNA subarea network was the requirement to provide static definitions for most SNA resources.
  • APPN node types
    The building block for an APPN node is the T2.1 (low-entry networking, LEN) node. Be aware that T2.1 by itself does not provide any APPN functionality; additional software is required to make a T2.1 node an APPN node.
  • Control point (CP-CP) sessions
    To perform directory services and topology and route selection services, adjacent APPN nodes throughout the APPN network use the pair of CP-CP sessions to exchange network and control information.
  • APPN databases
    APPN provides automatic network topology and directory support within APPN networks that simplifies network definition and permits dynamic selection of network routes. Some of the functions of APPN are topology and route selection services, and distributed directory searches.
  • APPN network topology
    Each network node starts with a topology database containing only itself. When it joins the network, a network node receives a copy of the current network topology database through a topology exchange with another network node in the network. As long as it remains connected to the network, its local copy of the network topology database is updated whenever changes occur to intermediate routing resources within the network to maintain consistency with the topology databases of all other connected network nodes.
  • High performance routing (HPR)
    High performance routing (HPR) is an addition to APPN that improves reliability, increases network performance, and was designed to exploit higher link speed technologies.
  • Connection networks
    A connection network is a representation of a shared access transport facility (SATF), enabling dynamic direct connectivity between any pair of link stations attaching to the facility. An example of a shared access transport facility is a local area network (LAN) where two nodes can communicate directly with each other without the need to use a router.
  • Dependent LU requester/server (DLUR/DLUS)
  • Defining a VTAM APPN network
    Definitions are put together in the ATCSTRxx in VTAMLST and by defining various VTAM major nodes.
Parent topic: SNA and SNA/IP implementation on the mainframe

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