Hi，
It's possible to add language similar to the abort case, along the lines
of "When the underlying TCP connection is closed or reset,
the CoAP connection is closed and in flight messages may be lost".
It is not necessary when CoAP over WEBSocket is concerned, I think.
By the API or the interface, CoAP only interacts with WEB socket, does not
need to touch issues of TCP.
CoAP would react to the events of WebSokcet.
But, issues on TCP should be concerned if it is CoAP over TCP.
Regards,
Gengyu WEI
Network Technology Center
School of Computer
Beijing University of Posts and Telecommunications
-----原始邮件-----
From: Brian Raymor
Sent: Friday, April 21, 2017 3:31 AM
To: Yoshifumi Nishida ; tsv-art@xxxxxxxx
Cc: draft-ietf-core-coap-tcp-tls@xxxxxxxx ; core@xxxxxxxx ; ietf@xxxxxxxx
Subject: Re: [core] TSV-ART review of draft-ietf-core-coap-tcp-tls-07
Thanks for your feedback.
1: It is not clear how the protocol reacts the errors from transport
layers (e.g. connection failure).
The protocol will just inform apps of the events and the app will
decide what to do or the protocol itself will do something?
The WebSockets case is addressed by RFC6455:
When the underlying TCP connection is closed, it is said that _The
WebSocket Connection is Closed_ and that the WebSocket connection is
in the CLOSED state. If the TCP connection was closed after the
WebSocket closing handshake was completed, the WebSocket connection
is said to have been closed _cleanly_.
-and-
If at any point the underlying transport layer connection is
unexpectedly lost, the client MUST _Fail the WebSocket Connection_.
It's possible to add language similar to the abort case, along the lines of
"When the underlying TCP connection is closed or reset, the CoAP connection
is closed and in flight messages may be lost".
2: There will be situations where the app layer is freezing while the
transport layer is still working. Since transport layers cannot detect
this type of failures, there should be some mechanisms for it somewhere in
the protocol or in the app layer. The doc needs to address
this point. For example, what will happen when a PONG message is not
returned for a certain amount of time?
PONG is modeled on similar mechanisms in RFC6455 and RFC7540. Neither
provides any guidance for this case. It's expected that an application
framework would define and enforce the appropriate policy for timeouts or
retries.
3: Since this draft defines new SZX value, I think the doc needs to update
RFC7959. This point should be clarified more in the doc.
Carsten responded to this issue and the final exchange is here -
https://www.ietf.org/mail-archive/web/core/current/msg08562.html
My sense is that we should treat this as an update to RFC7959 based on the
original language:
The value 7 for SZX (which would
indicate a block size of 2048) is reserved, i.e., MUST NOT be sent
and MUST lead to a 4.00 Bad Request response code upon reception
in a request.
and the use of "extension" in coap-tcp-tls:
The ’Block-wise Extension for Reliable Transport (BERT)’ extends the
Block protocol
to enable the use of larger messages over a reliable transport.
The existing IANA entries for Block1 and Block2 will also need to reference
coap-tcp-tls in addition to RFC7959.
Tracking in https://github.com/core-wg/coap-tcp-tls/issues/129
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