OPDEV SET UP A POTENTIAL CONFLICT BTWN OPPOSITE DIRECTION TFC DURING AN ERRED DSCNT CLRNC ISSUED BY ARTCC RADAR CTLR IN A TRANSPOSITION OF SIMILAR SOUNDING CALL SIGNS WITH 2 ACFT 50 NM E OF VHP; IN.

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WE HAD JUST CHKED IN WITH ZID. WE RPTED 'LEVEL FL290.' THE CTLR RESPONDED 'ROGER; FLT X; DSND AND MAINTAIN FL260.' I RESPONDED 'FLT X VACATING FL290 FOR FL260.' THE CAPT INITIATED A DSCNT WITH THE AUTOPLT. AT FL285; CTR ASKED US WHAT OUR ALT WAS. I RESPONDED THAT WE WERE DSNDING TO FL260. THE CTLR TOLD US FLT Z WAS 'X MI AND 1000 FT BELOW.' I ASKED WHAT ALT HE WANTED US AT. HE RESPONDED WITH THE QUESTION OF WHO ISSUED THE DSCNT. THE AUTOPLT WAS DISENGAGED; AND A CLB WAS STARTED. ABOUT THIS TIME; THE TCASII ISSUED A TA. I AGAIN ASKED WHAT ALT HE NEEDED US AT. HE RESPONDED FL290; AND TO RPT REACHING. AFTER WHICH; NO FURTHER QUESTIONS WERE ASKED AND THE FLT CONTINUED NORMALLY. MOMENTS LATER; FLT Y (WE WERE FLT X) WAS TOLD TO DSND AND MAINTAIN FL260. FACTORS CONTRIBUTING: CTR CONGESTION (HE WAS BUSY). SIMILAR CALL SIGN. CTLR CONFUSION DELAYING RESOLUTION COMMAND(S). CTLR SHOULD HAVE; UPON NOTICING THE POTENTIAL CONFLICT; ISSUED A COMMAND TO RESOLVE THE SIT IN LIEU OF QUESTIONING OUR ACTIONS. I BELIEVE THE CTLR ISSUED US THE DSCNT BY CONFUSING US WITH ANOTHER COMPANY ON FREQ. THE CAPT CONCURRED THAT WE WERE ISSUED THE DSCNT. IF I HAD MADE THE MISTAKE; MY RESPONSE WAS NOT UNDERSTOOD BY THE CTLR AS A POTENTIAL/ACTUAL MISTAKE. SINCE WE HAD 1000 FT SEPARATION WITHIN 5 MI; I BELIEVE NO ACTION WILL BE TAKEN AGAINST CTLR/CREW. SUPPLEMENTAL INFO FROM ACN 539827: N733 WBOUND AND CTLED BY ZID 89 AT FL280. E145 EBOUND AND CTLED BY ZID 88 AT FL290. ZID 88 ISSUED A CLRNC TO THE E145 TO DSND TO FL240. THIS CLRNC MEANT FOR A COMPANY ACFT WITH A SIMILAR CALL SIGN. THE CTLR TRANSPOSED NUMBERS. THE E145 BEGAN TO DSND. THE B733 WAS AT FL280; OPPOSITE DIRECTION AND CONVERGING. WITH ACFT 10 MI APART; B7334 RPTED AN RA AND DSNDED. I NOTICED THE 3145 DSNDING JUST AS CONFLICT ALERT WENT OFF AND THE RA WAS RPTED. I AFFIRMED THE TFC TO THE B733. ZID 88 CLRED THE E145 BACK TO FL290. I GAVE THE B733 APPROVAL TO MANEUVER AS NEEDED. VERT SEPARATION WAS NOT LOST. B733 DSNDED TO FL270. E145 DSNDED TO FL283 AND THEN CLBED BACK TO FL290.