Aggregated MPDU allows aggregation of multiple MPDUs (MAC protocol data units) in one PSDU (PHY service data unit). See the A-MPDU formats below. An A-MPDU consists of a number of MPDU delimiters each followed by an MPDU. The MPDU delimiter is 4 bytes. Except when it is the last MPDU, padding octets are appended to make each section a multiple of 4 bytes in length.