[e2e] Stupid Question: Why are missing ACKs not considered as indicator for congestion?

Joe Touch touch at ISI.EDU
Thu Feb 1 11:26:20 PST 2007

David Borman wrote:
> On Feb 1, 2007, at 12:45 PM, Joe Touch wrote:
>> They need to represent 'real time'; the offset is irrelevant (except for
>> PAWS, as you note), but it needs to be incremented in a realistic way:
>>       The timestamp value to be sent in TSval is to be obtained from a
>>       (virtual) clock that we call the "timestamp clock".  Its values
>>       must be at least approximately proportional to real time, in order
>>       to measure actual RTT.
>> I don't see how they could represent different scales and be compliant
>> with current spec, although, as you hint, the scale could be kept on a
>> per connection basis, but that would be off-spec.
> The key point of this part of the RFC is "in order to measure actual
> RTT".  
> If an implementor chooses to implement a mapping scheme that obfuscates
> the values that it puts into the Timestamps option, that does not
> violate the the spirit of the RFC as long as the obfuscated values kind
> of look like timestamps, i.e. they do not go backwards over time and go
> up by at least 1 for every wrap of the sequence space so that PAWS isn't
> broken.

AOK - I guess the devil is in "proportional". The actual ratio can be
kept private, but the trick of "use a table of nonces" doesn't work for
the reasons you note.


Joe Touch
Sr. Network Engineer, USAF TSAT Space Segment

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