Subject: Re: [6lowpan] #31: 011 11111 is in conflict with ESC; IANA actions

From: "6lowpan issue tracker" <[email-masked]>
Date: Tue, 28 Jul 2009 16:17:07 -0000

#31: 011 11111 is in conflict with ESC; IANA actions
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 Reporter:  [email-masked]        |        Owner:  [email-masked]
     Type:  defect              |       Status:  new              
 Priority:  major               |    Milestone:                   
Component:  hc                  |      Version:                   
 Severity:  Active WG Document  |   Resolution:                   
 Keywords:                      |  
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Comment(by [email-masked]):

 I believe that the ESC dispatch value was created (and assigned this
 specific value) as a reserve for future expansion.
 This expansion has not yet occurred, so it is appropriate to reassign the
 value.

 The combination TF=11, NH=1, HLIM=11 is reasonably likely.  Making an
 exception for this combination (even by assigning another value) creates
 code complexity.  Moving the 32-value range to a different place requires
 a subtraction where now a bitmask suffices.

 The obvious replacement ESC value to choose is 01 000000.

 HC should include IANA language to reassign this value.

 Downside: An implementation that went ahead and actually implemented ESC
 with 4944 semantics will be confused by the next byte.  However, any
 actual implementation of HC would take care not to make this mistake.

-- 
Ticket URL: <http://trac.tools.ietf.org/wg/6lowpan/trac/ticket/31#comment:2>
6lowpan <http://tools.ietf.org/6lowpan/>