ZOA CTLR DESCRIBED A RECURRING PROB WITH CPDLC-ADS FAILURES.

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ON JUL/TUE/06; I CAME IN FOR MY SHIFT AT ZOA. I WAS DIRECTED TO RELIEVE THE OCEANIC OC3 CTLR. DURING THE BRIEFING THE CTLR BEING RELIEVED ADVISED ME THAT ACR X (ON CPDLC/ADS) HAD NOT YET READ BACK HIS CLRNC FROM FL310 TO FL330. THIS ACFT WAS APPROX 10 MINS AWAY FROM THE ZLA BOUNDARY AND RAPIDLY APCHING ZLA AIRSPACE. I WAS BRIEFED THAT ZLA WAS IN DARC AND WAS BUSY WHEN THE ZOA CTLR HAD TRIED TO PASS THE ALT TO THEM -- ZLA HAD ADVISED ZOA THAT THEY WOULD CALL US BACK. AS SOON AS I SAT DOWN AND SIGNED ON TO THE POS; I RECEIVED AN UPLINK UNDELIVERABLE MESSAGE ON ACR X. ACR X HAD STILL NOT RECEIVED THE CLRNC. I IMMEDIATELY CANCELED THE CPDLC CLRNC AND ISSUED THE SAME CLRNC VIA HF RADIO. BY THIS TIME ACR X WAS APPROX 2-4 MINS FROM THE COMMON BOUNDARY. I IMMEDIATELY CALLED ZLA AND ADVISED THE CTLR OF THE SITUATION WITH ACR X AND ADVISED HIM TO SHOW THE FLT IN A BLOCK OF FL310-FL350 AS I COULD NOT VERIFY WHAT ALT HE WAS ACTUALLY AT. UPON RECEIVING THE CLRNC VIA HF RADIO; I RECEIVED THIS REPLY FROM ACR X; 'IS CPDLC WORKING TONIGHT SENT REQUEST THROUGH CPDLC RECEIVED CLRNC THROUGH SFO COMMERCIAL RADIO HF.' THIS IS A RECURRING PROB WHICH I FIRMLY BELIEVE WILL CONTRIBUTE TO/CAUSE AN ACCIDENT OR INCIDENT IN THE OCEAN ONE DAY! I AM EXTREMELY CONCERNED WITH THE CPDLC/ADS FAILURES IN THE OCEAN; AS I HAVE RPTED SEVERAL CPDLC/ADS PROBS AND I HAVE NOT RECEIVED A RESPONSE ON ANY OF THE PREVIOUS UCR'S FROM MGMNT.