Title: CPDLC - Reduction on Potential Message Size

PDR Reference: 				97100011
Originator Reference: 			size
SARPs Document Reference: 		CPDLC SARPs, Section 2.3.4.2.1
						and Section 2.3.7.2.3
Status: 					ADOPTED
PDR Revision Date: 			20/10/97 (SUBMITTED -> ACCEPTED -> PROPOSED)
						29/10/97 (RESOLVED)
PDR Submission Date:			06/10/97
Submitting State/Organization: 	ATNP WG3/SG2
Submitting Author Name: 		Hamelink, J
Submitting Author E-mail Address: 	jhamelin@adsystech.com
Submitting Author Supplemental 
Contact Information:
SARPs Date: 				IV1.1, March 97
SARPs Language: 				English

Summary of Defect:
 
The CPDLC SARPs allow up to 5 message elements in any CPDLC message. Moreover the definition of the route clearance variable allows a given message element to be very large (128 waypoints can each be specified with 128 lat/long).  This 128 squared size times 5 (message elements) can result in a very large message.  

Although operationally this size is not considered realistic, as the SARPs are currently specified, it requires system implementors (both air and ground) to 
develop systems with sufficient processing and memory to handle the maximum message size.  A consideration was given to putting a restriction in 2.3.7 to limit a CPDLC message to containing only two message elements with a route clearance element.  

Based on input from the ADSP which stated that the track detail and airwayidentifier were not necessary, and that a maximum of two route clearance elements would be required in a CPDLC message the CPDLC SARPs should be modified as follows.

Assigned SME: 				Sub-Volume II SME

Proposed SARPs amendments:
 
1. Modify ASN.1 from: (Section 2.3.4.2.1)

RouteClearance ::= SEQUENCE
	{
	airportDeparture			[0]	Airport				OPTIONAL,
	airportDestination		[1]	Airport				OPTIONAL,
	runwayDeparture			[2]	Runway				OPTIONAL,
	procedureDeparture		[3]	ProcedureName			OPTIONAL,
	runwayArrival			[4]	Runway				OPTIONAL,
	procedureApproach			[5]	ProcedureName			OPTIONAL,
	procedureArrival			[6]	ProcedureName			OPTIONAL,
	airwayIntercept			[7]	AirwayIdentifier 		OPTIONAL,
	routeInformations			[8]	SEQUENCE SIZE (1..128)
							OF RouteInformation		OPTIONAL,
	routeInformationAdditional	[9]	RouteInformationAdditional	OPTIONAL
	} 

RouteInformation ::= CHOICE
	{
	publishedIdentifier 		[0]	PublishedIdentifier,
	latitudeLongitude 		[1]	LatitudeLongitude,
	placeBearingPlaceBearing 	[2]	PlaceBearingPlaceBearing,
	placeBearingDistance 		[3]	PlaceBearingDistance,
	airwayIdentifier 			[4]	AirwayIdentifier,
	trackDetail 			[5]	TrackDetail
	}

TrackDetail ::= SEQUENCE
	{
	trackName				TrackName,
	latitudeLongitudes		SEQUENCE SIZE (1..128) OF LatitudeLongitude
	} 

TrackName ::= IA5String (SIZE (3..6))  

To:
	
RouteClearance ::= SEQUENCE
	{
	airportDeparture			[0]	Airport				OPTIONAL,
	airportDestination		[1]	Airport				OPTIONAL,
	runwayDeparture			[2]	Runway				OPTIONAL,
	procedureDeparture		[3]	ProcedureName			OPTIONAL,
	runwayArrival			[4]	Runway				OPTIONAL,
	procedureApproach			[5]	ProcedureName			OPTIONAL,
	procedureArrival			[6]	ProcedureName			OPTIONAL,
	routeInformations			[7]	SEQUENCE SIZE (1..128)
							OF RouteInformation		OPTIONAL,
	routeInformationAdditional	[8]	RouteInformationAdditional	OPTIONAL
	} 

RouteInformation ::= CHOICE
	{
	publishedIdentifier 		[0]	PublishedIdentifier,
	latitudeLongitude 		[1]	LatitudeLongitude,
	placeBearingPlaceBearing 	[2]	PlaceBearingPlaceBearing,
	placeBearingDistance 		[3]	PlaceBearingDistance,
	airwayIdentifier 			[4]	AirwayIdentifier
	} 

(delete the definition of TrackDetail and TrackName)

2.  Modify 2.3.7 to include a restriction to two RouteClearance message elements in a given message.

 New section in 2.3.7:

2.3.7.2.3.4 A CPDLC message shall contain no more than two message elements with the [routeClearance] variable. 

SME Recommendation to CCB: 		-

CCB Decision:				atnp_ccb_chair: ACCEPTED (20/10/97)
						CCB-3: RESOLVED