When planning your communication functions between different CICS® systems you must consider:
These questions are examined in the following sections.
CICS intersystem communication supports five basic functions:
For more information about these functions, see CICS intercommunication functions.
If two systems are to communicate successfully they must use a common set of rules that both understand. A communications protocol is such a set of rules that defines, for example, a set of standard requests and responses, and the order in which they can be sent.
For CICS products, three communication protocols are important:
CICS can make use of the AnyNet® product, which allows SNA flows to be transmitted over a TCP/IP network.
All CICS products support the LU 6.2 protocol.
TCP/IP is supported natively by CICS Transaction Server for Windows, CICS on Open Systems, and versions of CICS Transaction Server for z/OS® from Version 2.2 onwards.
All CICS on System/390® products except CICS TS for VSE/ESA and CICS/VSE 2.3 can make use of the AnyNet product, which allows SNA flows to be transmitted over a TCP/IP network.
You can use IBM® NetBIOS, or another NetBIOS emulator. For example, Novell’s NetBIOS emulator provides NetBIOS flows over its Internetwork Packet eXchange (IPX) protocol.
During CICS interproduct communication, partner transactions may make logically-related updates to their data stores -- data sets, databases, temporary storage, transient data, and so on. Data integrity would be lost if both transactions did not commit (or back out) the updates they made to their resources.
The process used to ensure data integrity is called synchronization. Synchronization has to prevent one transaction completing normally and committing its updates while its partner transaction abends and backs out its updates. Synchronization must also handle situations when network problems prevent the transactions from communicating and informing each other of their actions.
SNA APPC architecture defines three levels of synchronization, which it calls NONE, CONFIRM, and SYNCPOINT. CICS refers to these as synchronization levels 0, 1, and 2, respectively.
Synchronization level 2 provides two-phase commit. In a two-phase commit process, one CICS system initiates the syncpointing and acts as coordinator for the operation. The coordinating system:
The synchronization level that two connected CICS systems can use is established when they first establish the connection. A connection established at synchronization level 2 can support a synchronization level 0, 1, or 2 conversation, and a connection established at synchronization level 1 can support a synchronization level 0 or 1 conversation.
The synchronization level you can use depends upon the capabilities of the particular CICS systems, and the capability of the network that they are using for the connection. The synchronization levels for all pairings of CICS systems is summarized in CICS product communication support.
CICS products use two interchange codes for character data representation, EBCDIC and ASCII. Data in CICS on System/390 products and CICS/400 is held in EBCDIC format. Data in CICS Transaction Server for Windows and CICS on Open Systems is typically held in ASCII format.
Support of an intersystem communication function between two products requires support for any necessary data conversion. For further information, see Data conversion.