RE: The first octet

["Roni Even (A)" <[e-mail]>]

+1

If  in the future there will be consensus that an extra byte is needed it is not related to the first octet as an invariant.  It does not conflict with the invariant draft since it will be version dependent, it only means that it will have to be after the invariants parts of the short header.

Roni

From: QUIC [mailto:[e-mail]] On Behalf Of Ian Swett
Sent: Wednesday, August 08, 2018 4:30 PM
To: [e-mail]
Cc: IETF QUIC WG; Martin Thomson; Kazuho Oku
Subject: Re: The first octet

I'm having a hard time understanding why you'd need 7 bits to measure packet loss(1 seems sufficient in most cases), can you send a link to the spin + VEC and 7 bit proposals you mentioned?

I'll also note I think the chances the WG will agree to 7 bits is extremely close to 0, but I'm curious why you'd even want them.

On Wed, Aug 8, 2018 at 9:22 AM <[e-mail]<mailto:[e-mail]>> wrote:
On 08/08/18 12:05, Martin Thomson wrote:
>
> I know you discussed taking more bits and even bytes, but the case
> hasn't been made in this working group to my knowledge.  I certainly
> don't think that's justified; it improved fidelity of measurements,
> but the spin bit appears to be pretty good at that without the extra
> overheads.

Fidelity is indeed the criterion to decide 1 (spin bit) vs 3 (spin bit + VEC)
for RTT measurements, right.

However, measurements also include packet loss, which is typically more
widespread than delay in big pipes (which don't have enough RAM to keep a packet
for too long at line rate). And spin+VEC do not address packet loss at all,
hence our 7-bit spin counter proposal shown in London.

I admit that 7 is hefty if you're starting from Christian's songle spin bit ;
however:

  - I assume nobody will emit any doubt about the criticality of
non-delay-related (big pipe) loss location. Unless everybody here has perfect
networks and ideal reporting, that is.

  - Stick the spin bit on top of these 7, make that an extra easurement byte and
you've got your three spare bits again in the first byte.


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