The ATM adaptation layer AAL is primarily responsible for the cell forwarding process between the ATM layer and the high layer. After receiving the forwarding information from the upper layer, AAL divides the data into a cell; after receiving forwarding information from the ATM layer, the AAL must recapstate the load to form an upper layer to identify format. The above operation is called segmentation and recombinant SAR, which is the main task of AAL. In addition, different AAL supports different traffic or service types. Various services and corresponding AAL classes are as follows:
Class a Class A: Constant Location Rate CBR Service: AAL1 supports connection service for constant positioning rates. Examples of this service include 64 speech, fixed rates of non-compressed video and private lines of dedicated data networks.
Class B: Variable Rate VBR Service: AAL2 supports the connection service, the bit rate varies, the transfer process needs to provide a cell transfer delay. Examples of this service include compressed bag voice or voice. The transmitting delay process is necessary when reconstructing the initial non-compressed voice or speech.
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