Title: CPDLC - Range is Wrong for VHF Frequency Variable

PDR Reference: 				97060012
Originator Reference: 			PDRVHF
SARPs Document Reference: 		CPDLC SARPs, Section 2.3.4.2.1
Status: 					WITHDRAWN
PDR Revision Date: 			18/08/97 (ACCEPTED->PROPOSED)
						06/10/97 (PROPOSED -> WITHDRAWN)
PDR Submission Date:			27/06/97
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 indicated range for the VHF frequency choice does not meet the requirements. Non operational values (138.025 to 192.000) may be encoded with the current ASN.1 definition of the frequency.
If the defect is not resolved, a specific rule for converting the operational value to the exchanged value (and vice-versa) shall be applied for that particular parameter. The ASN.1 is inconsistent with itself. 

Assigned SME: 				Sub-Volume II SME

Proposed SARPs amendment: 

1/ add a note in the ASN.1 as follows:
	Frequencyvhf ::= INTEGER (14000..17000) 
	-- unit = Megahertz, Range (117.00000..138.00000), resolution = 0.025
        -- The conversion between the encoded/decoded value and the operational 
        -- value is to be done as follows:
        -- for encoding: value to encode = operational value / 0.025 + 9320
        -- for decoding: operational value = (decoded value - 9320)* 0.025

2/ change the ASN.1 with the rules used for all CPDLC parameters (Section 2.3.4.2.1) from
	Frequencyvhf ::= INTEGER (14000..17000) 
	-- unit = Megahertz, Range (117.00000..138.00000), resolution = 0.025

To:
	Frequencyvhf ::= INTEGER (4680..5520) 
	-- unit = Megahertz, Range (117.00000..138.00000), resolution = 0.025


3/ in order to keep the bits-on-the-wire, change the ASN.1 lower bound of the field but maintain the range (3000 values). 
Section 2.3.4.2.1 is changed from
	Frequencyvhf ::= INTEGER (14000..17000) 
	-- unit = Megahertz, Range (117.00000..192.00000), resolution = 0.025
      -- note that only values in the range 117.000 to 138.000 are used
To:
	Frequencyvhf ::= INTEGER (4680..7680) 
	-- unit = Megahertz, Range (117.00000..192.00000), resolution = 0.025


SME Recommendation to CCB: 		WITHDRAWN

Solution 2 is recommended. Both solutions 1 and 3 will be rejected by ICAO which mandates the parameter range and resolution to conform to existing values (i.e. VHF values assigned by ITU-T to ICAO). Solution 3 maintains the bits-on-the-wire but does not guarantee full interoperability with implementations based on previous versions of the SARPs.

However, it turns out that the Frequencychf variable as defined in the SARPs is useless since the Frequencyvhfchannel support identification of frequencies for both 25 and 8.33 MHz spacing. Therefore, a new PDR is issued for that purpose and the present PDR becomes obsolete and is withdrawn by its author.

CCB Decision:				CCB-2(Langen): ACCEPTED