ATM Adaptation Layer 5 (AAL5) is used to send variable-length packets up to 65,535 octets in size across an Asynchronous Transfer Mode (ATM) network.Unlike most network frames, which place control information in the header, AAL5 places control information in an 8-octet trailer at the end of the packet. The AAL5 trailer contains a 16-bit length field, a 32-bit cyclic redundancy check (CRC) and two 8-bit fields labeled UU and CPI that are currently unused.
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