Comment on resynchronization of connection status proposal
Postel suggests better names for connection recovery commands.
Postel, J., "Comment on resynchronization of connection status proposal", RFC 489, DOI 10.17487/RFC0489, March 1973, <https://www.rfc-editor.org/info/rfc489>.
@misc{rfc489,
series = {Request for Comments},
number = 489,
howpublished = {RFC 489},
publisher = {RFC Editor},
doi = {10.17487/RFC0489},
url = {https://www.rfc-editor.org/info/rfc489},
author = {J. Postel},
title = {{Comment on resynchronization of connection status proposal}},
pagetotal = 1,
year = 1973,
month = mar,
} RFC text
Network Working Group Jon Postel
Request for Comments: #489 UCLA-NMC
NIC #15298 March 26, 1973
Comment on Resynchronization of Connection Status Proposal
This is a comment on the proposal by Burchfiel and Tomlinson in RFC 467
for a procedure in the host-to host protocol for resynchronization of
connection status. I endorse their proposal with the following trivial
change. The commands proposed might be more appropriately be called
"reset connection allocation sender" and "reset connection allocation
receiver" since the only aspect of the connection which is reset is the
allocation. I therefore use the names RAS and RAR respectively.
The table below shows in overly concise notation my interpretation of
the resynchronizing procedure proposed by Burchfiel and Tomlinson, this
presentation is not intended to supersede their document but to clarify
the procedure. The sequence shown here can be initiated by either the
sender or receiver either for internally generated reasons or upon the
receipt of a RAS or RAR, if this latter is the case then sender step 5
or receiver step 4 is satisfied.
SENDER RECEIVER
1. Set state to "wait-for-RAR" 1. Set state to "wait-for RAS"
2. Wait till no RFNM outstanding 2. Send RAR
3. Send RAS 3. Process messages until
4. Process allocates until 4. RAS received then
5. RAR received then 5. Zero allocation quantities
6. Zero allocation quantities 6. Set state to "open"
7. Set state to "open" 7. Send a new allocate
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AI ELI5
On this page
§1Connection Recovery
This RFC is Jon Postel's brief comment on a proposal by Burchfiel and Tomlinson in RFC 467. The Host-Host protocol needs a way to recover when both communicating hosts lose synchronization about how much data each side is allowed to send. The allocation is a critical part of the flow control mechanism, and when it gets out of sync, the connection becomes stuck.
Computers talking over the network need a way to fix the situation when they forget who said what and get confused.
§2The RAS and RAR Commands
Postel proposes renaming the recovery commands to RAS (reset allocation sender) and RAR (reset allocation receiver). These names are more precise than the original proposal, because they emphasize that only the allocation quantities are being reset, not the whole connection. The sender and receiver follow a sequence: the sender sets a wait state, waits for outstanding acknowledgments, sends RAS, and processes responses until receiving RAR. The receiver sends RAR, processes incoming messages, receives RAS, zeros its allocation, and returns to open state.
Two new commands, RAS and RAR, let the sender and receiver fix how much data each one can send, step by step, until they agree again.
§3Synchronization Procedure
The procedure can be initiated by either the sender or receiver, and either for reasons of its own or after receiving a RAS or RAR command from the other side. The RFC provides a concise side-by-side table showing what each side does at each step. This recovery mechanism is critical to ensuring reliable connection management in the early Host-Host protocol.
Either side of the conversation can start the fix, and there is a clear sequence of steps that brings them back into sync.