Synchronization levels

Systems Network Architecture (SNA) defines three levels of synchronization for conversation using the APPC protocol.

At sync level 0, there is no CICS support for synchronization of remote resources on connected systems. But it is still possible, under the control of the application to achieve some degree of synchronization by interchanging data, using the SEND and RECEIVE commands.

At sync level 1, you can use special commands for communication between the two conversation partners. One transaction can confirm the continued presence and readiness of the other. Both transactions are responsible for preserving the data integrity of recoverable resources by issuing syncpoint requests at the appropriate times.

At sync level 2, all syncpoint requests are automatically propagated across multiple systems. CICS implies a syncpoint when it starts a transaction; that is, it initiates logging of changes to recoverable resources, but no control flows take place. CICS takes a syncpoint when one of the transactions terminates normally. One abending transaction causes all to rollback. The transactions themselves can initiate syncpoint or rollback requests. However, a syncpoint or rollback request is propagated to another transaction only when the originating transaction is in conversation with the other transaction, and sync level 2 has been selected.

Bear in mind that syncpoint and rollback are not limited to any one conversation within a transaction. They are propagated on every conversation currently active at sync level 2.