Subject: [core] #341: Observe sequence number specification not robust against imprecise clocks

From: "core issue tracker" <[email-masked]>
Date: Tue, 24 Sep 2013 10:14:25 -0000

#341: Observe sequence number specification not robust against imprecise clocks

 The specification of sequence number arithmetic in observe-10 appears
 to assume that the clocks of clients and servers are perfectly in sync.
 However, constrained nodes often have rather imprecise clocks.
 (In particular, they may want to fall back to RC clocks during
 low-power idle times.  These are often accurate only to ± 5 %, if
 that.)
 Inaccuracies of the client and server side may cancel out or add in
 effect.

 It is not hard to add robustness to the existing scheme, by reducing
 the maximum notification rate.
 Section 4.4 notes that the current scheme can support a notification
 rate of up to 64 KiHz.
 Reducing this to 32 KiHz is still well beyond the highest known design
 objective of around 1 kHz (most CoAP applications will be several
 orders of magnitude below that), but allows total clock inaccuracies
 of up to -50/+100 %.

 New language should point out that client and server clocks may differ
 in their realization of the SI second, and that staying at a sequence
 number increase rate of less than 32 KiHz (enabling the same
 notification rate if there is a strict relationship between sequence
 number increases and notificatione) should still be safe in most
 real-world cases.

-- 
-------------------------+-------------------------------------------------
 Reporter:               |      Owner:  draft-ietf-core-
  [email-masked]           |  [email-masked]
     Type:  other        |     Status:  new
  technical              |  Milestone:  post-WGLC-1
 Priority:  major        |    Version:  observe-10
Component:  observe      |   Keywords:
 Severity:  Active WG    |
  Document               |
-------------------------+-------------------------------------------------

Ticket URL: <http://tools.ietf.org/wg/core/trac/ticket/341>
core <http://tools.ietf.org/core/>

---

From: "core issue tracker" <[email-masked]>
Date: Fri, 27 Sep 2013 02:35:34 -0000

Changes (by [email-masked]):

 * status:  new => closed
 * resolution:   => fixed

Comment:

 Fixed in [1503]:

 Close #341

-- 
-------------------------+-------------------------------------------------
 Reporter:               |       Owner:  draft-ietf-core-
  [email-masked]           |  [email-masked]
     Type:  other        |      Status:  closed
  technical              |   Milestone:  post-WGLC-1
 Priority:  major        |     Version:  observe-10
Component:  observe      |  Resolution:  fixed
 Severity:  Active WG    |
  Document               |
 Keywords:               |
-------------------------+-------------------------------------------------

Ticket URL: </ticket/341#comment:1>
core <http://tools.ietf.org/core/>