AAL0 - AAL5: ATM Adaptation Layer Type 0-5 reserved for variable bit rate video transfer
From Network Dictionary Wiki
AAL1 supports a connection-oriented service in which the bit rate is constant.AAL2 supports a connection-oriented service in which the bit rate is variable but requires a bounded delay for delivery. For connection-oriented file transfer and, in general, data network applications where a connection is set up before data is transferred. This type of service has variable bit rate and does not require bounded delay for delivery. Two AAL protocols were defined to support this service class and have been merged into a single type, called AAL3/AAL4. Connectionless data service: Examples of this service include datagram traffic and, in general, data network applications where no connection is set up before data is transferred. Either AAL3/4 or AAL5 can be used to support this class of service.
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