[ih] TCP RTT Estimator

[Dave Crocker]

On 4/12/2025 7:00 PM, Greg Skinner via Internet-history wrote:
> There are two problems that have the same symptoms - losing segments due to poor communications media, and delayed segments due to congestion.  These two problems call for distinctly different solutions.  In a lossy network, one would retransmit more frequently; in a congested network, one would retransmit less frequently.

I never worked on the development of TCP or its constituent components.  
Just an innocent bystander, curious to watch things developing.  I think 
Jon Postel was still at UCLA and therefore stuck with me as an 
office-mate, which also meant he was usually my source of technical 
explanations for me.

I was shocked to see how simplistic (and weak) the TCP checksum was.  
(Since I was just learning about such components, I of course assumed 
that the strongest possible data integrity mechanisms were always 
essential.)

Similarly, given the considerable network distances data traveled, I was 
skeptical that the TCP retransmission mechanism would suffice if there 
were serious problems.

Jon suggested that a) more robust data integrity was a lot more 
expensive, and b) TCP's mechanisms were meant for occasional and major 
problems.

He said that any transit section with chronic issues needed to have its 
own, underlying and more-robust mechanisms, to bring its reliability and 
throughput up to an acceptable level.

d/

-- 
Dave Crocker

Brandenburg InternetWorking
bbiw.net
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