The Open Communication Facility is a set of programs that make use of VTAM Advanced Program-to-Program Communication (APPC/VTAM) and Beta Subsystem Function Facility (SFF) services to enable the efficient transfer of information between application subsystems residing on the same computing systems on different LPARs, or on different computing systems. These application subsystems may either be running on z/OS as a Beta product subsystem, or on an end-user workstation as a Beta product server application or end-user presentation interface.
OCF uses the Beta Subsystem Function Facility services for task dispatching, storage control, program control and serialization of OCF functions. Among the benefits of SFF services are the efficient startup, termination and dispatching of work to and from the OCF and application service transactions executed in the course of information transfer.
OCF uses the VTAM implementation of Advanced Program-to-Program Communication services to provide communication between application service programs. APPC/VTAM is the VTAM implementation of a subset of the Systems Network Architecture LU6.2 communications protocol, which is also used by a variety of other hardware and software manufacturers.
Among the benefits of APPC services are the protection of application programs from changes to the communications hardware environment, independence from the type of processor hardware being communicated with, automatic service transaction startup and termination, transmission buffering and program synchronization services.
With OCF and APPC, the application service programs can concentrate on executing and distributing the actual application functions across multiple CPU platforms without having to consider how, to where or on what type of connection the information transfer takes place. This type of environment is called a distributed transaction processing environment, or, more commonly, a client-server environment.
OCF complements APPC by providing additional services that enable more efficient use of APPC resources when transferring information between Beta product functions. In this respect, OCF is the window to communications services for Beta product functions.
Each OCF node in the OCF network exchanges information with other OCF nodes about the Beta product type and subsystem identification of Beta product address spaces running on the local z/OS. This information is contained in the BETA.PARMLIB member BnnLSTxx, which is processed during subsystem startup by each OCF node started task. In this way, remote OCF nodes automatically know where to route work requests if the target subsystem does not reside on the local z/OS system.
Consequently, the subsystem identification (SSID) names of the subsystems communicating through an OCF network must be unique. Furthermore, each OCF node can be a member of only one OCF network.
In the following instructions we describe specific environments and Beta functions in which the OCF is implemented. For definition purposes, we will refer to the set of OCF functions that are logically connected to each other via a VTAM network as the "OCF Network".