Consider a dataset comprised of n blocks, numbered 0, 1, 2, . . . , i, . . . , n - 1.
Let us now send that dataset from some source s to some sink S over a 'network' that contains multiple paths from s to S. Transmitted in the canonical sequence 0, 1, 2, . . . , n - 1, they may arrive in a different sequence, in principle in any permutation of these n block numbers. The presence of a block sequence number (relative block number) in each block [or block extension] then permits the transmission sequence at s to be recovered from the arrival sequence at S (if there are sufficient buffers available at S). Note also that that what are buffered by access methods are blocks not [logical] records and that with SAM-E the historically clearcut distinction between BSAM and QSAM, if not abolished, was certainly muddied. John Gilmore, Ashland, MA 01721 - USA
