Re: [WARNING: ATTACHMENT(S) MAY CONTAIN MALWARE]Re: HTTP(3) priorities

"Oliver, Wesley, Vodacom South Africa (External)" <Wesley.Oliver@vcontractor.co.za> Thu, 25 July 2019 12:43 UTC

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From: "Oliver, Wesley, Vodacom South Africa (External)" <Wesley.Oliver@vcontractor.co.za>
To: Kazuho Oku <kazuhooku@gmail.com>
CC: Ian Swett <ianswett=40google.com@dmarc.ietf.org>, IETF QUIC WG <quic@ietf.org>, HTTP Working Group <ietf-http-wg@w3.org>
Thread-Topic: [WARNING: ATTACHMENT(S) MAY CONTAIN MALWARE]Re: HTTP(3) priorities
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Date: Thu, 25 Jul 2019 12:39:56 +0000
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Subject: Re: [WARNING: ATTACHMENT(S) MAY CONTAIN MALWARE]Re: HTTP(3) priorities
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Hi,

One other thing to consider with the priority header byte that exists I the frame, is that
The orchestrator of the priority header values, needs to be able to identify when it can re-use
A priority header value, to deal with the fact all buffers in route, are required to have been flushed and empty,
So that there are no duplicate or old state datagrams in route, which can be put ahead of the new information data frame
Reusing that priority value. May there should be a flush frame, but there is no guarantee, goes sought the same route , so that wouldn’t work.

A TTL won’t work, because we want to support large buffers.

So routers, would have to detect sequence frame numbers, being re-cycle for stream-priority pair,
Then drop all stale packets. This means that each frame sequence number must be increasing even for drop frames, packets.
Sequence number can only be recycled if, AK has been received for specific sequence number.
This means that the larger-buffer will be limited respectively by sequence number size 2bytes times data frame payload size,
Before blocking will be experience and there sender will stall, having to wait for the buffers to be flushed, so it can get an AK from a frame in flight.

2^16 * (dataframe payload size) = max buffer size.


Ideally the sequence number if going to be used, needs to be large to support massive buffers with out AK blocking on the window as in tcp.
Assuming that window size here is unlimited, which what would be ideal for massive files and streams, were rather can re-read with Direct memory access the data for restransmission of lost packets.

If don’t have sequence number, which is highly unlikely, the larger priority byte would bee need to avoid collisions for inflight traffic.

My feeling is that sequence number + priority number should be used and should be larger enough, to support unlimited window size for AK,
So routers will truly know a frame correct re-transmission ordering.

Maybe allow MSB of the sequence number or potentially priority frame to extend the size in bytes 1,2,4,8,12,14,16,18,20.
Ideall look at the total buffer data size, that the sequence number would allow to be transmitted and considered inflight,
Before blocking would occur.


Kind Regards,

Wesley Oliver

> On 25 Jul 2019, at 08:48, Oliver, Wesley, Vodacom South Africa (External) <Wesley.Oliver@vcontractor.co.za> wrote:
> 
> Hi,
> 
> The only thing I could suggest is that you make those priority flags increments of 20,
> So that if there are changes or minor priority preference per website, then
> That in between numbers can be used. If there is any new future priority conventions
> Then just add them in the middle of the 20 group splitting the existing group.
> Maybe make the field 2 bytes, which allows for future expansion, were there are many files, streams
> Which require a new priority order.
> 
> Otherwise one needs to build a priority map, over the deps, converting a high resolution to low resolution.
> 
> Kind Regards,
> 
> Wesley Oliver
> 
>> On 24 Jul 2019, at 19:14, Kazuho Oku <kazuhooku@gmail.com> wrote:
>> 
>> Hi!
>> 
>> Attached are the slides that Lucas and I presented during the side meeting.
>> 
>> Thank you all for the feedback.
>> 
>> 2019年7月9日(火) 21:00 Ian Swett <ianswett=40google.com@dmarc.ietf.org>rg>:
>>> 
>>> There has been quite a bit of discussion of HTTP priorities lately on both the QUIC and HTTP mailing lists, with more to follow.  The plan for IETF in Montreal is as follows:
>>> 
>>> Monday: Overview of priorities for 15 minutes in HTTP, with 15 minutes discussion.
>>> Wednesday: A side meeting will be held from 8:30-9:45am in Van Horne.
>>> Thursday: I'll summarise the side meeting in Wednesday's HTTP session.
>>> 
>>> Thanks, Ian
>> 
>> 
>> 
>> --
>> Kazuho Oku
>> <The Priority Header Field.pdf>
> 
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