Title:                              ADS - Redundant Reason code

PDR Reference                       97080002
Originator reference:               PDR-1
SARPs Document Reference:           ADS SARPs, Section 2.2.1.4.2.1
Status:                             ADOPTED
PDR Revision Date:                  22/09/97 (SUBMITTED -> ACCEPTED)
				    		 22/09/97 (ACCEPTED -> PROPOSED)
						 20/10/97 (PROPOSED -> RESOLVED)
PDR Submission Date:                18/08/97
Submitting State/Organisation:      ATNP/WG3/SG2
Submitting Author Name:             T I Maude
Submitting Author E-mail Address:   maude@level-7.co.uk
Submitting Author Supplemental
Contact Information:                Fax +44 1344 868 442
SARPs Date:                         IV1.1, March 97
SARPs Language:                     English

Summary of defect:

The Negative acknowledgement definition includes a reason code. The definition of "Reason" in ASN.1 is a CHOICE, one value of which is "cannot-meet-reporting-rate [1] NULL". This is no longer needed since the SARPs now has a non-compliance notification for this purpose. 2.2.1.7.4.3 is the requirement that requires its use. There is no requirement, therefore, for the Negative acknowledgement Reason "cannot-meet-reporting-rate". (This was left over from an earlier version).

If is it left as it is, there is a certain amount of confusion over what to do if a periodic contract is requested and the aircraft cannot meet the reporting rate. There is therefore a danger that different implementors will interpret the SARPs in different way.

Assigned SME:                       Sub volume II SME

Proposed SARPs amendment:

To avoid changing the ASN.1 to the extent that it affects the bit pattern produced, the following change is recommended in the ASN.1 definition of Reason:

Replace 
"cannot-meet-reporting-rate   [1] NULL,"
by 
"undefined                    [1] NULL,
-- the undefined value should not be used"

Further explanation should be provided in the ADS guidance material.

SME Recommendation to CCB:           -

CCB Decision:                        atnp_ccb_chair: SUBMITTED (18/08/97)
				    	       atnp_ccb_chair: ACCEPTED (22/09/97)
						 atnp_ccb_chair: RESOLVED (20/10/97)