RFC 516 (rfc516) - Page 2 of 2
Lost message detection
Alternative Format: Original Text Document
RFC 516 LOST MESSAGE DETECTION May 1973 hosts is set to zero. Each time a message is sent the current send message number is entered into a field in the message header, and the current send message number is incremented (modulo N, say N=256) Each time a message is received the message number from the message is compared to the current receive message number and: if the received message is the expected one then the message is acceptable and current receive message number is incremented (modulo N); if the received message is not the expected one then a message has been lost. What to do when a missing message is detected, not clear, but at least can be logged and reported to the network control center. A missing message may not be fatal to an interactive conversation, but it is critical in a file transfer, thus I suggest that missing messages which are not recovered be cause to close the conversation. The third scheme: Host to host acknowledgements could be required. Such an acknowledgement scheme could be implemented similarly to the IMP to IMP scheme. This is a serious change to the current protocols so I will not elaborate on it here, feeling that deeper study will be necessary to fully specify a reasonable host to host acknowledgement strategy. Of these three suggestions the first is the most immediately practical and implementable; in fact several hosts all ready do this. These schemes also are non-conflicting, they could be implemented and used simultaneously. [ This RFC was put into machine readable form for entry ] [ into the online RFC archives by Alex McKenzie with ] [ support from GTE, formerly BBN Corp. 9/99 ] Postel
