Subject: Why one spin bit and not more in the QUIC header

From: Roni Even <[email-masked]>
Date: Wed, 15 Nov 2017 14:40:19 +0000

Hi,
There is a reason why we are asking for one bit.
The QUIC transport header has starts with one type byte.
The long header start with 1 and the rest 7 bits are the type. The long header is used only in the handshake where the message is in the clear so we can get the RTT from the handshake.
The short header starts with a zero bit followed by C and K bits and 5 type bits, so bits are scarce resource.  The spin bit proposal in the github issue #609 propose using one but and making the type only 4 bits. The defined types are in the quic transport table 2, three types are used to specify the packet number size (values 1-3). So it looks like there are more bits available but that may prevent other usages for the first type byte.
Roni