Title: CPDLC - Out-of-synchronisation abort reason
PDR Reference:                          M2090001
Originator Reference:                   -
SARPs Document Reference:               CPDLC SARPs, 
Status:                                 RESOLVED
Impact:					     C
PDR Revision Date: 			     04/10/02 (PROPOSED -> RESOLVED)
     02/10/02 (text reworded)
30/09/02 (SUBMITTED -> ACCEPTED)
PDR Submission Date:                    16/09/02
Submitting State/Organization:          ATNP WGA SGA2
Submitting Author Name:                 F. Picard
Submitting Author E-mail Address:       picardf@tlse.sofreavia.fr 
Submitting Author Supplemental
Contact Information:
SARPs Date:                             ICAO 9705 Edition 3
SARPs Language:                         English
     
Summary of Defect:

Current implementations check that received CPDLC messages are not out-of-synchronisation. This is the case when for instance the timestamp of the received message is ahead of the current time at the receiving side.

In that case, CPDLC communications must be immediately stopped and pilot/controllers shall revert to voice.

The abort reason which would be used with CPDLC version 1 and 2 is "undefined". 

It is proposed that a more explicit reason be added "out-of-synchronisation", and be used by version 2 CPDLC-users when available.

Assigned SME:                      	     SV2 SME

Proposed SARPs Amendment:


1/ Replace the ASN.1 definition from :

CPDLCUserAbortReason ::= ENUMERATED
	{
	undefined					(0),
	no-message-identification-numbers-available	(1),
	duplicate-message-identification-numbers	(2),
	no-longer-next-data-authority			(3),
	current-data-authority-abort			(4),
	commanded-termination			(5),
	invalid-response				(6),
	...
	}

to:

CPDLCUserAbortReason ::= ENUMERATED
	{
	undefined					(0),
	no-message-identification-numbers-available	(1),
	duplicate-message-identification-numbers	(2),
	no-longer-next-data-authority			(3),
	current-data-authority-abort			(4),
	commanded-termination			(5),
	invalid-response			           (6),
	...,
             time-out-of-synchronisation        (7)
	}


2/ In Chapter 7 add a new user requirement as section 2.3.7.3.11.9.2

2.3.7.3.11.9.1 When talking to a version 1 CPDLC system, a version 2 CPDLC-user shall be prohibited from invoking the CPDLC-user-abort request with reason "out-of-synchronisation".

3/ In chapter 7, add the following user requirement and note:

2.3.7.3.11.10.1 If the CPDLC-user receives a message containing a timestamp that is out of synchronisation with its own clock, the CPDLC-user shall invoke the the CPDLC-user-abort request with a CPDLC message containing the CPDLCUserAbortReason with the value [time-out-of-synchronisation] as the Reason parameter.

Note. - The amount of time out of synchronisation that will trigger this event is a local implementation issue.

Impact on Interoperability:  

The change is proposed for version 2 only. Implementors of version 2 CPDLC can choose to implement or not this change.

No impact on interoperability :

. (version 2 / version 1) : a version 2 is not allowed to send the new abort reason to a version 1 (via CM information). If it does, the receiving version 1 system will not be able to decode the ABORT PDU and the user will be indicated a PROVIDER ABORT (decoding error) instead of a USER ABORT (undefined). 

. (version 2 with the change / version 2 without the change) : a version 2 not supporting the new abort reason could either abort (decoding error on ERROR) or ignore the reason (after extensibility) and provide the user with the abort reason "undefined". 

PDR Validation Status:			
       
SME Recommendation to CCB:		      
     
CCB Decision:				      CCB-16 (Toulouse): RESOLVED