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Network Working Group                                        A. ShoshaniRequest for Comments: 161                                            SDCNIC #6772                                                    19 May 1971A SOLUTION TO THE RACE CONDITION IN THE ICP   In NWG/RFC #143 a race condition in the ICP was described and a   solution was suggested.  The problem arises because the Host-Host   protocol does not specify what the NCP should do when it gets more   than one request of STR (or RTS) to the same socket.  As a result   this decision depends on the particular implementation: some may   queue these requests (SDC for example), some will refuse a request if   the socket is already connected (UCLA for example), etc.   The solution is not to change the Host-Host protocol, but find a   third level ICP which does not depend on this issue.  Such a solution   is the following: the INITs from server to user and user to server   ((S5), (S6), (U5), (U6) on page 3 in RFC #143) should use another   socket -- say U+2 and U+3.  The sequences in RFC #143 would be:      Server                             User      ------                             ----      (S1) LISTEN(L,32)                  (U1) INIT(U,L,32)      (S2) [wait for match]              (U2)      (S3) SEND(L,S)                     (U3) RECEIVE(U,S)      (S4) CLOSE(L)                      (U4) CLOSE(U)      (S5) INIT(S,U+3,Bu)                (U5) INIT(U+3,S,Bu)      (S6) INIT(S+1,U+2,Bs)              (U6) INIT(U+2,S+1,Bs)This solution will solve the problems pointed out in RFC #143 withoutany assumptions made about the NCP implementation.  The solution in RFC#143 assumes that the NCP can notify a process when a command (e.g.,close) comes in, which is implementation dependent.       [ This RFC was put into machine readable form for entry ]          [ into the online RFC archives by Alan Ford 08/99]Shoshani                                                        [Page 1]