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Network Working Group                                        Dave WaldenRequest for Comments: 65                       A/S Norsk Data-Elektonikk                                                         August 29, 1970Comments on Host-Host Protocol Document No. 1 (S. Crocker - 8/3/70)   Page 3.   Eliminate marking.  Instead, make all regular messages into   two message: The first containing just the leader and indicating that   the data follows in the second (next) message.  Do this both from the   source Host to its IMP and from the destination IMP to its Host.   Thus, no more hunting for the beginning of the data is necessary.   Once this adjustment is made, an additional simplification is   available.  If the maximum message length is a common multiple of the   word sizes of all the computers in the network (perhaps 2880*2 bits),   successive messages of long files can be dropped in place without   shifting.   Page 4.   Control messages should be sent to and from the _control   socket_  -- not over the control link.  The concept of the control   link causes a great big, unnecessary special case.   Page 5.   Assigning sockets permanently to certain network resources   should be encouraged and a directory of the socket/resource   associations should be available somewhere in the network, perhaps in   physical book form at each site.   Page 6.  Links have no Host-Host purpose other than identifying a   connection so that socket numbers don't have to be included in all   messages and to simplify table look-ups in the NCPs.  However, since   there are possibly 512 links* with the same number, links don't aid   table look-ups very much.  Also finding the next available link to a   particular destination is very ugly .  Therefore, I suggest limiting   the number of links to a total of n (where n = 32, 64, or 256 or some   other good number) for all destinations.  In other words, a   particular link is only in use to one destination at a time(actually   from one destination at a time since the receiver picks the link to   be used for a connection).  This change makes picking the next   available link very simple and,I feel,is a worthwhile change if only   for this reason.  The question of simplifying table look-ups is a   little more complex.  It is easy to use the link directly as an index   into tables in the receive portion of the NCP since the receiver   picks the link.  But a hash table or linear search or something is   still necessary in the send portion of the NCP.  This too can be   fixed with the following changes.  Add to STR a _pseudo link_  chosen   by the sender. This link is sent in all non-control messages in the 8   --------------------------------------   *A destination number is 9 bits.Walden                                                          [Page 1]

RFC 65               Comments on Host-Host Protocol          August 1970   bits to the right of the link in the leader.  The IMP must preserve   these bits and return them with RFNMs and the receiver must use the   pseudo link instead of the link in RET and INR.  The extra memory   necessary to store the pseudo link in the NCP receive tables (which   are indexed by link) and the link in the NCP send tables (which are   indexed by pseudo link) is certainly less than the overhead necessary   to maintain associative tables.   Page 8.   The allocate mechanism seems very inconvenient for the   receive portion of the NCP to use.  The receiver wants the allocation   to be used up in units of the receiver's buffer size not in units of   sender messages which may be variable length.  Otherwise the receiver   has a memory compaction problem.   Page 9.   The new irregular message to make the "cease" mechanism   work are unnecessary, I think.  The sender can keep track (probably   with a one bit counter) of ALLs and GVBs and ignore GVB 0s for which   resume ALLs have already arrived.   This the receiver need not know   whether the cease has been sent or not.   Page 15.  If I implemented an NCP, all ERRs would be treated like   NOP.  As an error control mechanism ERR is complicated and   insufficient.  Who wants to debug a complicated mechanism which only   catches bugs due to the primary mechanism being undebugged.  The one   error control mechanism I would provide is a receive process to send   process acknowledgment on every message.  If this is not received for   too long, the send process can send the message again if it has been   saving it.  This acknowledgment catches errors causing message loss   at the process/NCP, NCP/NCP, Host/IMP, IMP/IMP, etc.  levels.   Currently the Host/IMP interface is particularly lacking in useful   error controls.  I wouldn't worry about kinds of errors check-sums   are designed to pick up.  If dropped and picked up bits ever become a   problem either add hardware to more interfaces or let the receive   process not send the process to process acknowledgment if a software   checksum does not check.   The page 3 and page 6 comments involve a change to the IMP program.   I feel a tiny bit guilty suggesting changes I don't have to implement   any more.  However, I trust Crowther and Cosell will, as always,   resist bad changes while making sensible ones.  The page 9 comment is   aimed at avoiding a change in the IMP program.         [ This RFC was put into machine readable form for entry ]           [ into the online RFC archives by Luke Hollins 8/99]Walden                                                          [Page 2]