Title: CPDLC - Frequency Definition and Extensibility MArkers

PDR Reference:              		M1030003
Originator Reference:            	-
SARPs Document Reference:         	CPDLC, Section 2.4.4.3 
Status:                       	FORWARDED
Impact:					
PDR Revision Date:              	08/03/01 (SUBMITTED -> FORWARDED)
PDR Submission Date:           	05/03/01 (SUBMITTED)
Submitting State/Organization:    	ATNP/WGA
Submitting Author Name:          	Picard, F 
Submitting Author E-mail Address:  	picard_frederic@stna.dgac.fr
Submitting Author Supplemental 
Contact Information:               	tel. +33.5.62.14.55.33
						fax. +33.5.62.14.54.01
SARPs Date:                      	Doc 9705 Draft Ed 3 (ICAO web site - 11/00) 
SARPs Language:                  	English

Summary of Defect:

A paper prepared by Rob Morganstern presented at WG-SGA2/02 (Honolulu, March 2001) proposed changes which would (a) allow three HF frequencies to be passed to the pilot at a time, and (b) increase the resolution of the Frequencyvhf from 0.005 MHz to 0.001 MHz, the latter to allow the use in specifying VDL M3 channels.  

If implemented, this change would lead to backward compatibility problems, unless use of extensibility markers was invoked. The SME2 Team is of the opinion that extensibility markers are fine for simple addition of material, but not a lot of use for changes and deletions.  The significant use of extension markers would reduce the ability to ever 'sunset' a particular version, which would just grow bigger, and contain a lot of bypassed and redundant information.  It was proposed that there should be a new version for version 2 - this would allow version 1 to be sunsetted as required, and subsequently removed from systems.

CCB-13/2 felt that the issue should be reviewed in more detail before any decision to roll the CPDLC version number be taken. The PDR is therefore forwarded to WGA for further consideration.

Assigned SME:                    	Sub-Volume II SME

Proposed SARPs amendment: 

Impact on interoperability: 		

PDR Validation Status:			

SME Recommendation to CCB: 		-

CCB Decision:                    	SGA2/02 (Honolulu): SUBMITTED (05/03/01)
						CCB-13/1 (Honolulu): FORWARDED (08/03/01)