3: ZigBee Software Architecture > Application Framework and SAPs

Application Framework and SAPs

This page describes the Application Framework and associated SAPs (not shown in the architecture diagram on the previous page).

Application Framework

The Application Framework (AF) contains the application objects and facilitates interaction between the applications and the APS layer. An application object interacts with the APS layer through an interface known as a Service Access Point (SAP).

Service Access Points

A Service Access Point (SAP) implements a set of operations to pass information and commands between layers. There are usually four types of operation implemented by a SAP:

Request: Typically, a layer using the services of another layer generates a Request to the lower layer.

Confirm: In general, the lower layer responds with a Confirm, which indicates whether it has accepted or rejected the request. A rejection could occur if the Request is invalid or the layer does not implement the operation concerned (the operation could be defined as optional).

Response: Normally, Requests result in some sort of Response from the lower layer. This may be a simple status message indicating that the Request has been performed, or may contain further information that the Request has asked for. Responses can be immediate or delayed:

• Synchronous Response: Responses may be generated immediately after the Request has been issued - for example, if the information or command is available on the local node.
• Asynchronous Response: A Request may require messages to be sent over the network to a remote node, in which case there will be a delay between issuing the Request and the arrival of the Response.

The SAP mechanism allows both types of Response to be handled and delivered to the higher layer.

Indication: An Indication is generated when the lower layer has unsolicited information or commands to be delivered to the higher layer, possibly as a result of a Request from a remote node for local information.

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