The ATM Adaptation Layer (AAL) is defined to enhance the services provided by the ATM layer to support the functions required by the next higher layer. One particular type of AAL service is the Signalling AAL (SAAL) which comprises AAL functions necessary to support a signalling entity. The structure of the SAAL is defined in Recommendation Q.2100.
The SAAL consists of a Segmentation And Reassembly (SAR) function, and a Convergence Sublayer which is divided into two sublayers: a Common Part Convergence Sublayer (CPCS) and a Service Specific Convergence Sublayer (SSCS). The common part protocol is defined in clause 6/I.363, and is used as the underlying protocol for the service specific part for signalling. The SSCS is functionally divided into two parts. The Service Specific Connection Oriented Protocol (SSCOP), which provides an assured data transfer service and the Service Specific Coordination Function (SSCF). The SSCOP is defined in Recommendation Q.2110 and is suitable for use by various SSCFs. This Recommendation specifies the layer management functions for the SAAL at the Network Node Interface (NNI).
The layer management functions at the NNI perform error monitoring and a coordination function between the systems management function and the SAAL.
This Recommendation describes the NNI layer management functions associated with the management primitives between the SAAL sublayers and the layer management entity.