Re: Structuring the BKK spin bit discussion

Mikkel Fahnøe Jørgensen <mikkelfj@gmail.com> Sun, 04 November 2018 09:24 UTC

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Date: Sun, 4 Nov 2018 01:24:40 -0800
Message-ID: <CAN1APdd=3CmNzw-584NPOjnXRa_NmpDWjAMs6y0n8S_CyULwSw@mail.gmail.com>
Subject: Re: Structuring the BKK spin bit discussion
To: roni.even@huawei.com, Kazuho Oku <kazuhooku@gmail.com>
Cc: Dmitri Tikhonov <dtikhonov@litespeedtech.com>, IETF QUIC WG <quic@ietf.org>, Lars Eggert <lars@eggert.org>, Brian Trammell <ietf@trammell.ch>, Christian Huitema <huitema@huitema.net>, marcus.ihlar@ericsson.com
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On 4 November 2018 at 02.52.44, Kazuho Oku (kazuhooku@gmail.com) wrote:

> Roni Even: In this case since there are large packets to one direction
and short to the other an observer can map the download file to its ack
message and calculate the RTT without the spin bit

My understanding is that you cannot.

Because the payload of the packets are encrypted, you cannot tell
which ACK packets sent by the client correspond to which packets sent
by the server. All you can observe is that something is flowing
steadily from the server to the client.


If there are timing gaps or traffic rate changes in the transmission, it is
not hard to associate packets with high probability. Gaps can occur due to
source task switching or when congestion control adapts the flow rate, or
when other connections appear or disappear. They can also appear due to
buffering in middle boxes.