On 25/03/2019 10:41, Patrick McManus wrote:
I've seen this confusion before, so I can clear it up!
Ray is (I believe) referring to the flexible re-ordering of DNS
request-reply pairs of a TCP channel.. similar to HTTP/2 (though with
less flexibility in granularity iirc). That addresses hol-blocking
problems due to the time the server spends building replies.
Ian is (I believe) referring to head of line blocking problems related
to TCP's in-order delivery semantic and packet loss. TCP packet loss
will delay the delivery of received packets if there are outstanding
unreceived lower-numbered packets. If the data in these packets are
unrelated (e.g. different DNS request/reply pairs) - that causes head of
line blocking to the application. That's true of http/2 and RFC7766
(anything tcp based really). QUIC streams provide a mechanism for
identifying which sequences actually need to have that dependency. DoH
with H3 would use separate streams for separate requests (as different
HTTP exchanges are inherently on different streams).
Its a shame that the term hol blocking is used for both scenarios - it
has caused a lot of confusion.
hth
Yes, that dh :)
I was indeed talking about DNS message re-ordering, and wasn't aware of
this particular distinction at the TCP layer itself when compared to QUIC.
thanks,
Ray
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