R: spin bit in QUIC: troubleshooting

[Fioccola Giuseppe <[e-mail]>]

good way to measure the reordering with 1 or 2 bits.
In addition, to answer the previous question, draft-ietf-ippm-alt-mark suggests how to use 1 or 2 bits for packet loss and  RTT calculation.

Giuseppe

-----Messaggio originale-----
Da: QUIC [mailto:[e-mail]] Per conto di Gorry Fairhurst
Inviato: mercoledì 15 novembre 2017 07:40
A: Piotr Galecki
Cc: Ian Swett; QUIC WG; MORTON, ALFRED C (AL); [e-mail]
Oggetto: Re: spin bit in QUIC: troubleshooting

I think (even pathological) reordering would be largely undetected with 1-bit. Since in thsi case, the bit simply flips 1->0 and 0->1,

With 2 bits the first flip is 0->1 and then the next RTT , the flip is 
1->2, then re-ordering of the spin may become detectable. It's not
perfect, but you may see some pathologies for low additional cost.

ACK visibility is needed for some of the things below.

Gorry

On 15/11/2017, 13:59, Piotr Galecki wrote:
> How would a network probe be able to measure the level of packet reordering in QUIC stream with only a spin bit?
>
> I'm asking because one of the common techniques to diagnose network issues
> is to insert a probe in different points in the network and measure:
> * RTT
> * TCP segment loss
> * TCP segment retransmissions
> * TCP segment out-of-order
> as a few basic data points.
> With measurements in point A and point B one can determine for example if a network device is misordering packets.
>
> -Piotr
>
> -----Original Message-----
> From: QUIC [mailto:[e-mail]] On Behalf Of Gorry Fairhurst
> Sent: Wednesday, November 15, 2017 12:48 AM
> To: MORTON, ALFRED C (AL)<[e-mail]>
> Cc: Ian Swett<[e-mail]>; QUIC WG<[e-mail]>; [e-mail]
> Subject: Re: spin bit in QUIC: troubleshooting
>
> As I said at the mic: I think the spin-bit analysis was helpful, thanks.
>
> I can see how spin-bit is really useful to get basic diagnostics of RTT if it can be relied to be present in every packet. (It is important to measure latency within the network).
>
> There are places where 1-bit gives restricted value, and using more would help: My additional comment at the Mic related to how much extra would be the gain from an additional one or two bits?
>
> In particular, I'd like to see a method that can let me detect some loss patterns and measure reordering, at least I think it is important to know and measure when there is small-scale reordering<3.
>
> A suggestion:is to use a 2-bit counter for the spin (
> 00->01->10->11->00), that would help detect these path anomlies.
>
> Gorry
>
> On 15/11/2017, 09:51, MORTON, ALFRED C (AL) wrote:
>> I’d like to offer support for Spin Bit (and one or two
>>
>> bits for management if they can be justified quickly) in v1.
>>
>> On this topic of more bits,
>>
>> asking further clarification from Emile, below [ACM].
>>
>> Al
>>
>> *From:*QUIC [mailto:[e-mail]] *On Behalf Of *Ian Swett
>> *Sent:* Tuesday, November 14, 2017 4:21 PM
>> *To:* [e-mail]
>> *Cc:* QUIC WG
>> *Subject:* Re: spin bit in QUIC: troubleshooting
>>
>> Thanks for clarifying Emile.
>>
>> On Tue, Nov 14, 2017 at 1:06 PM,<[e-mail]
>> <mailto:[e-mail]>>  wrote:
>>
>> Hi Ian,
>>
>> It was suggested in the latest discussion on the RTT design team
>> mailing list to have one bit for packet lost, one for latency (spin
>> bit or eq.) and one for congestion.
>>
>> */[ACM] /* There may be some overlap with ECN and « one bit for
>> congestion ».
>>
>> Did you also consider this dependency, Emile ? (I’m echoing a hallway
>> discussion)
>>
>> It seems a simplistic approach on one hand but an invariant on the
>> long term.
>>
>> Regards
>>
>> Emile
>>
>> *De :*Ian Swett [mailto:[e-mail]
>> <mailto:[e-mail]>] *Envoyé :* mardi 14 novembre 2017 22:51
>> *À :* STEPHAN Emile IMT/OLN *Cc :* QUIC WG *Objet :* Re: spin bit in
>> QUIC: troubleshooting
>>
>> What would the other bit or two be used for?  If there is no
>> standardized use of those bits in v1, then I believe we should wait to
>> reserve them when their usage is defined, given we'd need a version
>> bump to specify how they were being used.  At the moment, the
>> management use case is not competing with anyone else for bits in the
>> short header.
>>
>> On Tue, Nov 14, 2017 at 5:14 AM,<[e-mail]
>> <mailto:[e-mail]>>  wrote:
>>
>> Hi
>>
>> Last week Orange experienced a fallback of QUIC to TCP on one of its
>> networks. The issues were not visible in QUIC traffic. The
>> troubleshooting was made using TCP packets information. This is not
>> sustainable on the long term when numerous applications using
>> different versions of QUIC will stop to fallback to TCP.
>>
>> Based on the exchange we had in the RTT design team and in today
>> meeting , it sounds reasonable to reserve at least 2 bits (ideally 3
>> bits as discussed in the design team) for manageability in the QUIC
>> invariants and to start experimenting the spin bit in QUIC V1.
>>
>> Regards
>>
>> Emile
>>
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