AAL: ATM Adaption Layer

Applications need data segmentation for cell transmission and reassembly. Some need real-time transmission (voice/video), others don't (data). Therefore, various adaption layers ensure proper operation: different applications need different adaption layers.

AAL 1

teal-time / fixed bandwidth / connection-oriented

AAL 1 served telephony (voice transmission).

AAL 2

real-time / variable bandwidth / connection oriented

AAL 2 serves video transmissions.

AAL 3/4

no real-time / variable bandwidth / connection-oriented, connectionless

AAL 3/4 serves connectionless or connection-oriented data transfer; meanwhile, it is replaced by AAL 5.

Connection-oriented data transfer uses Frame Relay, connectionless data transfer uses SMDS/CBDS.

AAL 5

no real-time / variable bandwidth / connection-oriented, connectionless

AAL 5 served data transmissions and replaces the former AAL 3/4.

Connection-oriented data transfer uses Frame Relay, connectionless data transfer uses SMDS/CBDS.

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