ATM Adaptation Layers (AAL)
ATM can be used to provide very different types of services
To facilitate these services, the work of developing five different ATM Adaptation Layers (AAL 1 through AAL 5) on top of ATM was started
Later AAL 3 and 4 were combined
The current ATM Adaptation Layers are:
- AAL 1 - Constant Bit Rate (CBR) service (circuit emulation)
- AAL 2 - Variable Bit Rate (VBR) service (voice and video)
- AAL 3/4 - non-real-time VBR service
- AAL 5 - for implementing Frame Relay service on ATM
AAL is divided into two sublayers:
- Convergence sublayer
- Segmentation and Reassembly (SAR) sublayer