Network Working Group Jonathan B. Postel
RFC # 516 UCLA-NMC
NIC # 16683 May 18, 1973
LOST MESSAGE DETECTION
I have three suggestions for detecting the loss of messages by the
communications subsystem. The first of these is perhaps the more
powerful and simpler to implement since it uses no new concepts and has
the power to retransmit the message detected as lost.
The first scheme:
If upon sending a message the host saved a copy of that message and
waited until either:
a RFNM was returned, in which case everything is ok and the next
message is processed.
a INCOMPLETE TRANSMISSION is returned, in which case the copy of
the message is retransmitted (this could be a loop so put a
finite upper bound on the number of times to retransmit the same
a DESTINATION DEAD is returned, in which case mark the
destination down and require the exchange of reset commands
before further communication is allowed.
something else is received indicating an error in the network or
local IMP, in which case at least log the error, and probably
close the conversation.
Following the above procedures either on a per host basis or a per
link basis should prevent a lost message problem from
The second scheme:
If on a per host basis, message numbers are included in the host to
host header of messages,, and messages are delivered in order (this
is currently the case in the network, except for priority messages
so this proposal requires that each host either send everything as
priority or nothing as priority) then each receiving host can detect
a missing message by comparing the message number of the received
message with the previously received message.
On exchanging resets the sequence numbers between that pair of