The AAL5 on the receiving side knows how many cells comprise a packet because the sending AAL5 uses the low-order bit of the "PAYLOAD TYPE" field of the ATM cell header to mark the final cell in a packet. This final cell header can be thought of as an "end-to-end bit". Thus, the receiving AAL5 collects incoming cells until it finds one with an end-of-packet bit set. ATM standards use the term "convergence" to describe mechanisms that recognize the end of a packet. Although AAL5 uses a single bit in the cell header for convergence, other ATM adaptation layer protocols are free to use other convergence mechanisms.