FLC OF AN AIRBUS A310-200 OVERSHOT XING RESTR DUE TO MISUNDERSTANDING OF CLRNC.

Narrative

ON ARR TO MEM; VECTORED PRIOR TO BWG; THEN DIRECT BWG; TOLD TO KEEP SPD UP. ON INITIAL DSCNT; GIVEN 'DIRECT LTOWN; FL240.' TURNED OVER TO ANOTHER CTLR WHO SAID 'CLRED TO 10000 FT; CROSS SPKER AT OR ABOVE 15000 FT.' WE WERE CONFUSED. WE HAD BEEN CLRED DIRECT TO LTOWN. WE QUERIED THE CTLR AND HE SAID HE WAS NOT AWARE OF OUR DIRECT TO LTOWN CLRNC. HE THEN SAID TO CONTINUE DIRECT TO LTOWN BUT TO CROSS 15 NM NE OF LTOWN AT 15000 FT. WE ENTERED 15000 FT INTO THE FMS AT A POINT 15 NM NE OF LTOWN; BUT ERRED BY PUTTING IN 'AT OR BELOW;' NOT 'AT' OR 'AT OR ABOVE.' FLEW THE DSCNT AND CROSSED 15 NM NE OF LTOWN AT APPROX 13000 FT; THEN WE WONDERED ABOUT THE RESTR CLRNC: WAS IT 'AT OR ABOVE;' 'ABOVE;' 'AT;' OR 'AT OR BELOW;' OR 'BELOW.' VERY CONFUSING. ATC GAVE US THE DIRECT AND TOLD US TO GO FAST TO KEEP US AHEAD OF THE INBOUND CARGO FLTS INTO MEM. WE SHOULD HAVE (AND WILL IN THE FUTURE) ASK THE CTLR TO REPEAT HIS RESTR/XING ALT DIRECTIONS AND THEN CORRECT THE FMS. WE GOT INTO A RUSH TO LOAD THE FMS; BUT WE FAILED TO CLARIFY THE EXACT WORDING OF THE DSCNT CLRNC.