Re: [core] TSV-ART review of draft-ietf-core-coap-tcp-tls-07

Hi all, 

Transfering CoAP defined in -08 draft for reliable transmission facilities is as important as CoAP over CON/NON message. 
In -08 draft, it is just clear how to make a new message for tranfering over TCP, 
or other reliable facilities in the scenario (I) CoAP/UDP ---> (C2C) Proxy ----> CoAP over TCP. 
But in -08 draft it is unclear how to work for the scenario (II) CoAP/TCP ---> (C2C) Proxy ----> CoAP over UDP. 

The problem is when the C2C Proxy have got a message form the CoAP/TCP side, 
how the Proxy make a decision to delivery CON or NON message carrying CoAP over UDP? 
Even for the scenario (I), the problem is the same when delivering the CoAP response.

In these scenarios a key problem is that should the CoAP semantics be End-to-End or Hop-by-Hop when a C2C proxy is existed. 

Regards, 

Gengyu WEI
Network Technology Center
School of Computer 
Beijing University of Posts and Telecommunications

From: Yoshifumi Nishida 
Sent: Sunday, April 30, 2017 12:24 PM
To: Brian Raymor 
Cc: tsv-art@ietf.org ; Yoshifumi Nishida ; draft-ietf-core-coap-tcp-tls@ietf.org ; core@ietf.org ; ietf@ietf.org 
Subject: Re: [core] TSV-ART review of draft-ietf-core-coap-tcp-tls-07

Hello, 
As far as I've read -08 draft, I think this point has not been addressed yet. I hope some folks could elaborate a bit more if they think this is not an important point for the draft.
--
Yoshi

On Fri, Apr 21, 2017 at 2:57 PM, Brian Raymor <Brian.Raymor@microsoft.com> wrote:

  I think that I understand your perceptions better. Prior to adoption of coap-tcp-tls and before I was active in the WG, I recall discussions related to the confusion over application vs transport reliability in CoAP especially as related to CON and NON. What was intended?

  Tim Carey outlined some concerns in:

  https://tools.ietf.org/html/draft-carey-core-std-msg-vs-trans-adapt-00#section-2

  This topic was presented in detail at IETF 93 - https://www.ietf.org/proceedings/93/slides/slides-93-core-0.pdf - starting on slide 23.

  And in a related thread on the mailing list back in 2015 - https://www.ietf.org/mail-archive/web/core/current/msg06280.html - Carsten responded:

  > In any case, CON and NON are about message layer semantics, not about application semantics

  > -- you gave them a meaning they don't have. 

  By IETF 94, the authors were reporting – “Most of the Confusion around              CON/NON was resolved”. 

  Where relevant, I’ve added clarifications - such as the Appendix related to differences in Observe for reliable transports.

  Both Carsten and Hannes could probably offer more context if needed.

  From: Yoshifumi Nishida [mailto:nishida@sfc.wide.ad.jp] 
  Sent: Friday, April 21, 2017 2:08 PM
  To: Brian Raymor <Brian.Raymor@microsoft.com>
  Cc: Yoshifumi Nishida <nishida@sfc.wide.ad.jp>; tsv-art@ietf.org; draft-ietf-core-coap-tcp-tls@ietf.org; core@ietf.org; ietf@ietf.org
  Subject: Re: TSV-ART review of draft-ietf-core-coap-tcp-tls-07

  Hi Brian,

  Just in case,

  Reliable transports only provide reliability at transport level. It doesn't provide reliability in application protocol level. 

  RFC7252 has reliability mechanisms in it since it uses UDP. This means it has abilities to check both transport and app level reliability.

  This draft only provides transport level reliability and apps will need to detect app protocol failure by themselves. 

  This means 7252 and this draft are not totally equivalent from the viewpoint of applications. 

  I am not saying this is wrong or bad, but I believe app developer should aware this point.

  --

  Yoshi

  On Fri, Apr 21, 2017 at 11:15 AM, Brian Raymor <Brian.Raymor@microsoft.com> wrote:

    Hi Yoshi,

    > OK. I also think we should state that the protocol should notify the failure events to applications. 

    > Since errors can happen not only in TCP, but also TLS and websocket level, mentioning only TCP close or reset might not 

    > be enough.

    After reviewing with the authors, an additional clarification was appended to 3.4 Connection Health - https://github.com/core-wg/coap-tcp-tls/pull/140/files

    The opinion of the authors (and Gengyu WEI’s recent response - https://www.ietf.org/mail-archive/web/core/current/msg08622.html) is that RFC6455 covers the WebSocket case and does not need to be repeated here.

    > When we use 7252, I think applications basically don't need to implement timeouts or retry mechanisms as the protocol

    > provides such things. 

    RFC7252 provides timeouts and retries because it's implementing a TCP-like reliability mechanism over UDP - https://tools.ietf.org/html/rfc7252#section-2.1

    > However, when we use this one, it seems applications will need to have such mechanisms. Isn't it a bit confusing? I am thinking that

    > there need to be some guidance here.

    > BTW, PONG is one example.

    For coap-tcp-tls, there are multiple early implementations. This has never been reported as a source of confusion. 

    >> My sense is that we should treat this as an update to RFC7959 based on the original language:

    > I don't have a strong opinion here. Updating 7959 is fine for me if it's clearer to CoAP people.

    I've merged the change - https://github.com/core-wg/coap-tcp-tls/pull/138/files

    Thanks again for helping us to improve the quality of the draft,

    …Brian

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