Communication Using Adapter Runtime 
A central component of the adapter runtime is the Adapter Framework, with services for messaging, queuing, and security handling. The adapter framework supports the JCA standard (JCA: Java Connection Architecture) and communicates with Resource Adapters, which are either a component of use case case Process Integration or are provided by SAP partners.
All adapters shipped by SAP are resource adapters, apart from the IDoc adapter. The following adapter components are based on the adapter framework:
Advanced Adapter Engine for adapter communication within a system network.
Partner Connectivity Kit (PCK): Enables business partners who do not have Process Integration installed to receive and send messages
For more information, see: Integrating Smaller Business Partners with the PCK
The following graphic provides an overview:
The Adapter Engine and the Business Process Engine are tightly linked to the Integration Engine. Whether the Adapter Engine is employed or not depends on the requirements of the collaborative process.
You normally use the central Advanced Adapter Engine. It covers the conversion of the majority of collaborative processes within a system landscape and allows local message processing with a special configuration without including the Integration Server.
You can use the non-central Advanced Adapter Engine when you require it to work closer to the application systems. This may be necessary if a system is separated from the Integration Server by a firewall.
You configure both the central and non-central Advanced Adapter Engines centrally in the Integration Directory, and both have a central monitor. You configure the Partner Connectivity Kit (PCK), on the other hand, locally because usage type Process Integration is not installed.
The Adapter Engine (Java SE ) is only used in a few special cases. In this case, configuration and monitoring are both local.