Network Working Group                                       Dave Walden
RFC # 449                                                   BBN-NET
NIC # 14133                                                 Jan. 6, 1973
Updates RFC 442


              The Current Flow-control Scheme for IMPSYS.
	

    While Vint's notes on IMPSYS flow-control from the March 16, 1972,
meeting (RFC 442) seem reasonably accurate and while he does cite our
Quarterly Technical Report #13, he might have done better to cite BBN's
two formal publications relevant to the IMPSYS flow-control scheme:

    1.  McQuillan et al, Improvements in the Design and Performance of
        the ARPA Network, Proceedings AFIPS 1972 FJCC, pp. 741-754.

    2.  BBN Report 1822, Specifications for the Interconnection of a
        Host and an IMP, December 1972 Revision, section 3, pp. 17-35.

Reference 2 is particularly important reading for NCP programmers -
things have recently changed somewhat.

    The inter-IMP acknowledgement mechanism, described in the last
section of Vint's RFC 442, is also described in reference 1 and an
almost identical mechanism is described in Appendix F of reference 2.
The acknowledgement is of only intellectual interest to most Hosts as it
is transparent to network users.  However, the description in reference
2 is of vital interest to so-called Very Distant Hosts.










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