FLC DSNDS BELOW ASSIGNED ALT AND EXPERIENCES TCASII RA.

Narrative

ON A FLT FROM BOS-PHL AT FL310 WE WERE GIVEN A CLRNC TO CROSS 70 NE OF BRIGS INTXN AT FL200. I PROGRAMMED THE FMC ACCORDINGLY. TOP OF DSCNT POINT WAS STILL ABOUT 25 NM AHEAD. A FEW MOMENTS LATER ATC CALLED AND WE UNDERSTOOD THE CTLR TO SAY; BEGIN DSCNT NOW THROUGH FL250 FOR TFC. I PRESSED THE CAPTURE BUTTON ON THE DSCNT PAGE OF THE FMC AND STARTED DOWN TO INTERCEPT THE 'PATH' TO FL200. PASSING FL240 WE GOT A TCASII TA AND THEN RA FOR TFC AT OUR ALT AND LESS THAN 10 MI AHEAD. SIMULTANEOUSLY ATC CALLS AND TELLS US TO 'CLB NOW!!' BACK TO FL250. TCASII WAS TELLING US TO DSND TO AVOID BUT WE HAD THE TFC VISUALLY AHEAD AND OFF TO OUR R SO WE STOPPED THE DSCNT AND CLBED BACK TO FL250. OUR SUBSEQUENT DISCUSSION WITH THE CTLR REVEALED HE SAID DSND NOW TO FL250 FOR TFC (NOT THROUGH FL250 AS BOTH THE CAPT AND I HEARD). BOTTOM LINE IS THERE WAS A MISCOM BTWN US AND ATC. I THINK IF THE CTLR HAD SAID 'RECLRED' TO FL250 OR 'CHANGE CLRNC TO FL250' OR BETTER YET; 'CANCEL CLRNC TO FL200; RECLRED TO DSND AND MAINTAIN FL250' THIS SIT WOULD NOT HAVE OCCURRED.