Re: [core] core-block-04: Applicability and general remarks draft-bosh-core-new-block-04.txt

[[e-mail]]

Hi Christian, all, 

We finally managed to prepare a candidate -01 of the draft that hopefully addresses your review. The main changes are:

* Update the Applicability Scope 
* Remove the TBA3 (Missing Payloads), but use 4.08 instead
* The options are marked as unsafe. The caching behaviour is updated
* Move the CC text to a (new) dedicated section
* Avoid the normative language for the usage of Tokens. A new (short) section is added for the token discussion.
* Rename the options to Quick-Block1/2

We made other edits to enhance the readability of the document. 

The candidate version is available at: https://core-wg.github.io/new-block/draft-ietf-core-new-block.txt 

A diff to track the changes can be seen here: https://tools.ietf.org/rfcdiff?url1=https://tools.ietf.org/id/draft-ietf-core-new-block.txt&url2=https://core-wg.github.io/new-block/draft-ietf-core-new-block.txt 

Please check the candidate version. 

Thank you. 

Cheers,
Jon & Med

> -----Message d'origine-----
> De : [e-mail] [mailto:[e-mail]]
> Envoyé : mercredi 5 août 2020 22:01
> À : [e-mail]; BOUCADAIR Mohamed TGI/OLN
> <[e-mail]>; [e-mail]
> Objet : RE: core-block-04: Applicability and general remarks draft-
> bosh-core-new-block-04.txt
> 
> Hi Christian,
> 
> Thanks for this review.  Med and I will update the draft as
> appropriate.
> 
> Otherwise, comments inline
> 
> Regards
> 
> Jon
> 
> > -----Original Message-----
> > From: [e-mail] [mailto:[e-mail]]
> > Sent: 05 August 2020 15:25
> > To: [e-mail]; Jon Shallow (supjps-
> > [e-mail]); [e-mail]
> > Subject: core-block-04: Applicability and general remarks
> > draft-bosh-core- new-block-04.txt
> >
> > Hello Med, hello Jon,
> >
> > here's a few concrete points I'd like to suggest for new-block:
> >
> > * Applicability: I'd have expected to read something like this in
> the
> >   introduction:
> >
> >   > The block-wise transfer of [RFC7959] covers the general case,
> but
> >   > falls short in situations where packet loss is highly
> asymmetrical.
> >   >
> >   > The new options introduced here provide roughly similar
> features to
> >   > the Block1/Block2 options. They provide additional properties
> that
> >   > are tailored towards the intended use case, and leave out
> mechanisms
> >   > like non-atomic access and proxy support that would complicate
> their
> >   > description.
> >   >
> >   > They are not intended for general CoAP usage, and any use
> outside
> >   > the DOTS use case should be carefully weighed against the loss
> of
> >   > interoperability with generic CoAP applications. It is hoped
> that
> >   > experience gained with these options can go into future
> extensions
> >   > of the block-wise mechanism that are both generally applicable
> and
> >   > serve this particular use case.
> 
> Jon> Thanks for the suggestions
> >
> > * Separation of layers, sub-topic "congestion control": It should
> be
> >   possible to phrase all congestion control parts of this in a
> dedicated
> >   section (which may also make sense as an appendix).
> 
> Jon> Good idea
> 
> >
> >   I'd avoid all other mentions of things like PROBING_RATE: For
> example,
> >   Section 3.4 right in the middle of a paragraph on re-requesting
> >   missing blocks states that
> >
> >   > The rate of requests for missing blocks is subject to
> PROBING_RATE.
> >
> >   Yes it is, but so is every single CoAP request until the client
> hears
> >   back from the server. Repeating these things in places where are
> not a
> >   new requirement may make it easier for some implementers that
> try to
> >   build the whole stack in a single go, but even for them is prone
> to
> >   the authors missing a spot -- and for everyone else this will
> each
> >   time trigger the question of "is this new here or isn't this
> already
> >   handled by a component two layers down the stack?".
> 
> Jon> OK
> >
> >   I haven't tracked every single retransmission and rate limiting
> >   statement throughout the document, but I expect that this
> section
> >   could boil down to something like
> >
> >   > For the DOTS use case, the following default CoAP parameters
> are
> >   > updated to better reflect the typical deployments:
> >   >
> >   > * PROBING_RATE: 10 kilobyte/second
> >   >
> >   > The averaging process mentioned in RFC7252 Section 4.7 after
> which
> >   > PROBING_RATE applies is not fully defined there. For the above
> >   > applications, a new parameter PROBING_RATE_WINDOW is
> introduced.
> >   > Messages up to a total size of PROBING_RATE_WINDOW may be sent
> >   > before PROBING_RATE is considered, and the probing rate may
> >   > generally be exceeded by that amount of data in short term.
> >   >
> >   > * PROBING_RATE_WINDOW: 15 kilobyte
> >
> >   (The latter replaces MAX_PAYLOADS, and I'm not sure whether it
> is
> >   better to express this in terms of package count or bytes on the
> wire,
> >   just giving an example here. All numbers in the above were
> pulled out
> >   of uninformed air.)
> 
> Jon> My leaning is towards packet count - circuit speeds cover a
> Jon> significant
> range. I need to think this through.
> Jon> The default RFC7252 PROBING_RATE is too low in my humble
> estimation
> Jon> - a
> large packet can cause long inter-packet gaps (300 bytes is a 5
> minute
> delay)
> >
> > * Separation of layers, sub-topic "Tokens": Same thing, next
> layer.
> >
> >   Whenever you're tempted to talk of a token, consider some of
> these
> >   replacement phrases as a first step:
> >
> >   * "MUST be sent with a new token" -> "is a new request".
> >   * "Tokens MUST be included" -> (nothing -- transports use tokens
> by
> >     construction)
> >   * "MUST be sent with the same token as the response" -> "is sent
> as a
> >     response to" / "is sent as an additional response to that
> request".
> >     (Here it may make sense to refer to the tokens in an
> additional "
> >     (which means it uses the same token, the same way an
> observation
> >     response uses the requests's token for multiple responses)").
> 
> Jon> Agreed - Token references needs to be tidied up.  Will work on
> this.
> "additional" may help us here to clarify which token 'value' should
> be used where.
> >
> > * Naming: It's technically a minor thing, but people have already
> >   complained to me about how hard the Block[12] names are to
> > comprehend,
> >   and introducing these options as Block[34] would not help here.
> >
> >   I'd like to suggest QuickBlock-Block[12].
> 
> Jon> Certainly Block[34] are likely to transfer data more quickly
> than
> Block[12].  However xxxx [12] implies a replacement for Block[12]
> which I am not so sure about.
> 
> >
> >   (I know that this part of designing a new option is annoying. In
> the
> >   interest of winding up with something that can be learned
> easily, it
> >   is unfortunately essential).
> >
> >   In connection with that, it may make sense to briefly think
> about a
> >   draft name before it is submitted as a WG draft. new-block
> sounds like
> >   a 7959bis, which in my understanding this does not aim to be.
> 
> Jon> Good idea.
> >
> > * 4.TBA3 Missing Payloads: I don't quite see why this needs a
> distinct
> >   code. 4.08 Request Entity Incomplete sounds perfectly suitable
> to me.
> 
> Jon> As we have to define the diagnostic payload as containing the
> Jon> missing
> blocks, we did not want to change the semantics of how 4.08 is used
> - hence TBA3.
> 
> Jon> That said, a 4.08 response could contain 1 or more Block3
> options
> Jon> but
> that would take up more space.
> >
> >   If you think that sending an existing 4.xx code in the middle of
> a
> >   block-wise transfer would cancel the transfer, there's still two
> ways
> >   out of this:
> 
> Jon> I was concerned about the 4.08 diagnostic payload changing
> format,
> Jon> but
> yes, an 'unexpected' error code could terminate the transfer.
> >
> >   * You're just defining what a block-wise transfer is; just allow
> it.
> >
> >     (In a RFC7959 block-wise transfer that runs over a proxy, the
> proxy
> >     may be currently incapable of doing any forwarding and return
> 5.03
> >     Service Unavailable Max-Age:5. The client would then just
> pause 5
> >     seconds and send the latest block again.)
> >
> >   * For all but the last block, it may also be an option to send
> it as a
> >     payload to a 2.31 code -- I don't think that would be outright
> >     forbidden (and at any rate, all involved clients speak the
> protocol
> >     anyway).
> 
> Jon> I have an issue with changing the 2.31 reporting on the last
> Jon> successful
> block received - this currently fails if block num of 0 is missing
> as we cannot indicate block num = -1 has been received.
> Jon> If the last block is received, but a previous one was not, a
> 2.31
> Jon> could
> be used to re-request the missing block, but a 2.01/2.04 would need
> to be held back for the final block acknowledgement.
> >
> > * The draft describes this all as "just working through a proxy" -
> -
> >   original block-wise does not, and I'd like to hear how this is
> hoping
> >   to get away without the options being proxy-unsafe.
> 
> Jon> I was not aware of CoAP to CoAP proxy issues with BLOCK[12]
> when
> Jon> this
> was written, but your comment implies that there is.  Certainly CoAP
> to other protocol proxies could run into issues.
> 
> Jon> I was thinking of block by block proxying working and hence
> could
> Jon> be
> proxy unsafe.
> >
> >   Is there any point at all in using block-by-block proxying for
> these
> >   use cases? Unless a proxy is sitting right inside the link under
> >   attack, and unless the bodies get huge, it may be way easier for
> this
> >   to be purely hop-by-hop. Proxies would reassemble the full
> bodies and,
> >   for the next hop, just decide what works best there (be it
> regular
> >   block-wise, Block34 or BERT).
> 
> Jon> Yes, there could be full body re-assembly and the full body
> held in
> cache if needed.  This would add in a bit of latency.  However this
> would restrict a Block[34] possibility of supporting streaming of
> data should that be required.
> >
> >   (If there's a point in allowing block-by-block forwarding, we
> can talk
> >   it through and work through the initial ideas that will come up
> like
> >   "We use large enough Request-Tag values so they are unique",
> "how
> >   large does that need to be", "why do we end up having a Request-
> Tag in
> >   every request now" and "why do we not want that", but my gut
> feeling
> >   is we won't need to go there.)
> 
> Jon> For Block3 which would use Request-Tag, I would expect that for
> a
> specific body of data for a specific resource the Request-Tag to
> remain the same - and if the body changes a new Request-Tag is used.
> Jon> As this is the same Request-Tag for whether the whole body is
> Jon> cached,
> or individual blocks of the body the Request-Tag usage will not
> change.
> 2^32 should be large enough - 2^64 even better - but re-usage has to
> be generally considered.
> 
> ~Jon
> >
> > Kind regards
> > Christian
> >
> > --
> > To use raw power is to make yourself infinitely vulnerable to
> greater
> > powers.
> >   -- Bene Gesserit axiom


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