Subject: Re: [core] #393 (coap-tcp-tls): Observing resource over reliable transports

From: "core issue tracker" <[email-masked]>
Date: Thu, 28 Apr 2016 08:03:53 -0000

#393: Observing resource over reliable transports

Comment (by [email-masked]):

 In a conference call with Klaus, Simon, Bill and myself we discussed the
 issue and the raised questions.

 > QUESTION #1: Do servers need to include a sequence number in
 notifications, given that TCP/TLS provides reliable, in-order delivery?

 The text from the CoAP over Websockets could be re-used. Here is what it
 could say:

 ------

    Since the TCP provides ordered delivery of messages,
    the mechanism for reordering detection when observing resources
    [RFC7641] is not needed.  The value of the Observe Option in
    notifications therefore MAY be empty on transmission and MUST be
    ignored on reception.

 ------

 The Observe Option still has to be sent since it contains other
 information as well.

 > QUESTION #2: Does a client have to re-register its interest in a
 resource if it hasn't received a notification for a while but the
 connection is still up?

 We believe it is enough to send keep-alive message for the CoAP over TCP
 draft
 (as opposed to send a re-registration message when used over UDP).

 > QUESTION #3: How do servers throttle the stream of notifications when
 the resource changes its state more frequently than the server can send
 notifications?

 TCP offers a flow control mechanism as a means for the receiver to govern
 the amount of data sent by the sender. This is functionality that can be
 re-used.

-- 
-------------------------+-------------------------------------------------
 Reporter:               |       Owner:  draft-ietf-core-coap-tcp-
  [email-masked]         |  [email-masked]
     Type:  other        |      Status:  new
  technical              |   Milestone:
 Priority:  minor        |     Version:
Component:  coap-tcp-    |  Resolution:
  tls                    |
 Severity:  Active WG    |
  Document               |
 Keywords:               |
-------------------------+-------------------------------------------------

Ticket URL: <https://trac.tools.ietf.org/wg/core/trac/ticket/393#comment:1>
core <https://tools.ietf.org/core/>