RFC 410 (rfc410) - Page 1 of 2


Removal of the 30-Second Delay When Hosts Come Up



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Network Working Group                      John M. McQuillan
Request for Comments #410                  Bolt Beranek and Newman
NIC #12402                                 10 November 1972
Categories:  B-1


           Removal of the 30-Second Delay When Hosts Come Up
           -------------------------------------------------


     The IMP currently delays accepting input from a Host for 30
seconds after the Host has come up.  This delay serves to allow
the fact that the Host is up to propagate through the network.
The fundamental problem is that a Host must not be permitted
to communicate with a second Host until the second Host
(actually its IMP) has been made aware that the first Host is
up.  Otherwise, one Host may come up and send a "hello"
message to another Host, whose reply is discarded by the IMP
because it is for a dead destination.

     All this reasoning is based on a dead destination de-
tection mechanism at the source IMP.  The 30-second delay is
based on the worst-case propagation delay for routing information
in the network, so that every potential source IMP can update
its host up/down table.  There are several drawbacks to this
scheme:

         1.  Hosts should not have to wait the worst-case time
             of 30 seconds to send to Hosts at their IMP or
             nearby in the network.

         2.  The operation of half-duplex interfaces is made
             even more complicated because of the startup delay.

         3.  The timeout period of 30 seconds is really a
             function of network topology and we would like to
             be able to change it when necessary as the network
             expands.

     We propose to eliminate the 30-second delay altogether.
The IMP subnetwork will detect messages for a dead Host at the
destination IMP instead of at the source IMP.  There is no delay


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