 16.6.1.1 Common Application Layer standards within OSI TO ANOTHER SYSTEM SYSTEM Association Control Service Element (ACSE) SERVICES FROM LAYER BELOW This Application Service Element has functions to enable the identification and approval of communicating end users; negotia- tion of the protocol functional units which will be used by the applications concerned; the establishment and release of application Figure 16.10 Communications using services within the associations between processes. ACSE can be used directly by an seven layer OSI model application, or it may be used by other Layer 7 Application Service Elements. system data from the originator has headers (and sometimes a Remote Operation Service Element (ROSE) trailer) added to it as it moves down the stack. At the receiving end these are stripped off as the message moves up the stack, and this This Application Service Element has functions for supporting information is used by those layers, until eventually the end user remote operations in a distributed open system environment. It has receives the raw data from the sender. the ability to request that a remote operation be performed on The Application Layer includes both the Application Entities another open system, a response or an error being returned. (AEs), which provide the semantics (the communications between the end user applications) as well as the Application Service Ele- Commitment, Concurrency and Recovery (CCR) ments (ASEs) such as CMISE, ACSE and ROSE, which provide the communication services according to a defined protocol. This provides a facility for ensuring the correct performance of a The Presentation Layer transforms the local syntax used in the multi-step operation, where a step is dependent on the previous one Application Layer, which may be unique, into a transfer syntax, being successfully implemented. It is used when there is need to which is common between communicating applications. The local guarantee distributed data consistency amongst two or more inter- syntax for a given 