Title: FIS - Simultaneous air and ground cancellation

PDR Reference:					98040001
Originator Reference: 				collision
SARPs Document Reference: 			FIS SARPs, Section 2.4.5.1 and 2.4.5.3
Status: 						RESOLVED
Impact :						C (Clarification)
PDR Revision Date: 				25/06/98 (PROPOSED -> RESOLVED)
							20/05/98 (ACCEPTED->PROPOSED)
							20/04/98 (SUBMITTED->ACCEPTED)
PDR Submission Date:  				01/04/98
Submitting State/Organization: 		STNA
Submitting Author Name: 			Picard, F
Submitting Author E-mail Address: 		PICARD_Frederic@stna.dgac.fr
Submitting Author Supplemental 
Contact Information:			
SARPs Date:  					IV2.2
SARPs Language:	 				English

Summary of Defect:
 
A figure describing a collision case is missing: 
1/ the FIS-air-user invokes the FIS-cancel-contracts request for a given type of contracts (atis, for instance),
2/ at the same time the FIS-ground-user invokes the FIS-cancel-update-contract request on a particular pending update contract of this type (atis, for instance).

The protocol description does not take into account this situation. 

With the current description, when the collision situation occurs, the FIS-air-ASE CL module sends a [FISCancelContracts] APDU to the FIS-ground-ASE CL module and stop the operation of all UC and DC modules. At the same time, the FIS-ground-ASE UC module sends a [FISCancelUpdateContract] APDU to the corresponding FIS-air-ASE UC module. As this FIS-air-ASE UC module has been stopped, the FIS-air-ASE LI module is unable to forward the APDU to the UC module. An abort is therefore generated by the air LI module. 

Impact on interoperability:
None. An abort is generated and all FIS contracts are cancelled.

Impact on safety:
This situation results in the abort of the air/ground dialogue and the automatic cancellation of all pending contracts. This situation generates a false alarm to the pilot which has to figure out what is the source of the abort and then to re-install the FIS contracts which should not have normally been cancelled. This will disturb the pilot and increase the crew workload.

Assigned SME: 				Sub-Volume II SME

Proposed SARPs amendment: 

The FIS-cancel-contracts service shall take precedence over the FIS-cancel-update-contract service. It is therefore proposed, when the FIS-cancel-contracts service has been invoked, to stop in the FIS-air-ASE the processing any subsequent FIS-cancel-update-contract service (i.e. by discarding the received APDU requesting the cancellation). 











1/ Add a new figure 2.4.5-18 as follows:

     FIS-ground-user                             FIS Service Provider                     FIS-air-user

FIS-cancel-update-contract req      |                                            |     FIS-cancel-contracts req
---------------------------------------> |                                            | <------------------------------------
 

FIS-cancel-contracts ind                |
<--------------------------------------  |

                                                                                                    |  ------------------------------------->
                                                                                                    |    FIS-cancel-contracts cnf

2/ Add a test on reception of a [FISCancelUpdateContract] APDU to check whether a FIS-cancel-contracts has already been initiated. If this is the case, the APDU is discarded.

In 2.4.5.3.12.10.1, replace the bullets b) and c) by  the following:

b) if the APDU is not a [FISCancelUpdateContract] APDU, pass the APDU to that module,

c) if the APDU is a [FISCancelUpdateContract] APDU, then:
	
     1) if the FIS-air-user has not initiated a global cancellation (FIS-cancel-contracts) for the type of FIS contracts identified in the APDU-element FISCancelUpdateData, pass the APDU to that module, or

       2) otherwise, discard the APDU, and

d) remain in the same state.

SME Recommendation to CCB: 		

CCB Decision:			atnp_ccb_chair: SUBMITTED (01/04/98)
					atnp_ccb_chair: ACCEPTED (20/04/98)
					CCB-6 (Utrech): RESOLVED (25/06/98)