[ih] TCP RTT Estimator

[John Day]

Correct me if I am wrong, but I thought the TCP checksum covered the entire TCP packet plus the pseudo-header.

The IP checksum only covered the IP header plus the pseudo-header.

Am I wrong?

John 

> On Apr 18, 2025, at 14:00, Jack Haverty via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> Memory errors caused at least some ARPANET crashes, but I suspect few people outside of BBN knew such details.  But memory errors could affect any part of the data.  The checksums in TCP only covered some parts of the headers.   If they were designed to protect against memory problems, shouldn't they have covered the entire datagrams?
> 
> Subsequently, changes to the TCP/IP architecture made checksums even less potent, when devices along the path through the Internet started recalculating checksums.  Mechanisms such as NAT, for example.
> 
> So I still can't recall why checksums were included in TCP...
> 
> Jack
> 
> On 4/18/25 10:30, Craig Partridge wrote:
>> 
>> 
>> On Fri, Apr 18, 2025 at 11:25 AM Andrew G. Malis via Internet-history <internet-history at elists.isoc.org> wrote:
>> 
>>    Jack,
>> 
>>    > Thinking back, I can't recall the reason for including checksums
>>    in TCP
>>    at all.
>> 
>>    It was primarily to catch memory errors, which were a real thing
>>    back in
>>    the core memory days. Errors during transmission were generally
>>    caught by
>>    the lower layers.
>> 
>> 
>> Memory errors are back.... I'm on a team that has caught them in disk caches :-(
>> Craig
>> 
>> 
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