What is Connectivity?

In general terms, connectivity is the ability to connect systems or application programs. Ideally, these connections are established without requiring many changes to the applications or the systems on which they run. Application programs may need to communicate with each other to complete transactions or to effectively balance resources at an installation.

However, application programs are often written in different programming languages and processors may use different operating systems or they may be in different locations. To enable communications, application programs must follow common rules and a physical connection must be established between the processors on which the programs run.

For communications among guest systems within a z/VM image, you can define a virtual network that deploys Internet Protocol (Layer 3) or Ethernet (Layer 2) as the transport. Either of these transports supports Transmission Control Protocol/Internet Protocol (TCP/IP) communications. The Ethernet transport also provides the ability to support non-IP based applications on the virtual network (such as SNA, IPX, etc.).

IBM's Systems Network Architecture (SNA) defines a set of communications functions and protocols for sending data between systems. The set of protocols that application programs most commonly use is called LU Type 6.2 or Advanced Program-to-Program Communications (APPC). The z/VM implementation of the APPC communications functions is called Advanced Program-to-Program Communications/VM (APPC/VM).

IBM's Systems Application Architecture® (SAA) also defines a set of programming languages and common programming interfaces that are common across different operating systems. Application programs that are written in SAA languages and use only SAA common programming interfaces are portable between different computer systems. The interfaces to SAA functions for functions that use APPC are called Common Programming Interfaces (CPI) Communications. CPI Communications is a common high-level language and REXX programming interface for APPC.

z/VM provides the following components and facilities that enable logical connections between systems and application programs that use TCP/IP, APPC/VM, or CPI-Communications protocols:
  • APPC/VM VTAM® Support (AVS)
  • Control Program (CP)
  • Conversational Monitor System (CMS)
  • Inter-System Facility for Communications (ISFC)
  • TCP/IP for z/VM
  • Transparent Service Access Facility (TSAF)

These components and facilities support the APPC/VM and CPI-Communications protocols between application programs. Application programs that use these protocols can use the logical connections provided by z/VM to communicate and exchange data.

CMS and CP support communications between applications that reside on the same z/VM system. CMS supports CPI-Communications protocols for application programs and CP supports APPC/VM communications between application programs. When application programs reside in a collection of systems, TSAF and ISFC provide the services necessary to route communications between the application programs. AVS provides services that let application programs communicate with other programs on z/VM or non-z/VM systems in an SNA network. TCP/IP supports communications between networks through universal communication services (see TCP/IP Communications below for more information).