NMAC BTWN 2 CESSNA 172 TYPE ACFT IN THE TFC PATTERN OF A CTLED ARPT WITH PARALLEL RWYS. THE RPTR WAS UPWIND ON THE L RWY AND THE OTHER WAS TURNING IN FRONT OF HIM FROM AN UPWIND FOR THE R RWY. THE RPTR TOOK EVASIVE ACTION. THE TWR WAS USING DIFFERENT CTLRS ON DIFFERENT FREQS FOR THE PARALLEL RWYS.

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ON UPWIND FOR RWY 21L; TFC WAS JUST A LITTLE WAYS AHEAD OF ME ON UPWIND FOR RWY 21R. TFC WAS TOLD THAT I WAS BEHIND THEM ON THEIR L; AND THAT THEY WERE TO FOLLOW ME! THEY CALLED ME IN SIGHT. THE TFC PATTEN WAS VERY BUSY AT THIS TIME; AND TFC WAS SUPPOSED TO FLY ON AN EXTENDED UPWIND TO A SPECIFIC PLACE. I WAS FLYING TO THIS PLACE. FLYING THROUGH 5700 FT MSL; THE TFC ON MY R STARTED TO TURN L; DIRECTLY IN FRONT OF ME! WE WERE AT THE SAME ALT! I THROTTLED BACK; PUSHED THE NOSE OVER; QUICKLY LOOKED R FOR A CLRING TURN; THEN JUST AS THE PLANE WAS COMING DIRECTLY IN FRONT OF ME; I TURNED R ABOUT 20-30 DEGS. I SAID MY INTENTIONS OVER TWR FREQ AND EXPLAINED WHAT I WAS DOING; SO ALL COULD HEAR ME. IT WAS CLOSE; ABOUT 150-200 FT HORIZ. I COULD SEE THE SILHOUETTE OF THE PERSON SITTING IN THE L SEAT. I BELIEVE THAT THE OTHER ACFT WAS A C172. TWR; AFTERWARDS; WOULD NOT TELL ME ANY DETAILS ABOUT THE OTHER ACFT. BECAUSE THE PATTERN WAS SO BUSY; I NEVER FIGURED OUT WHO OR WHAT N-NUMBER THE OTHER ACFT WAS. A MISCOM BTWN UPWIND AND DOWNWIND MAY HAVE OCCURRED. A WAY TO FIX THIS MIGHT BE TO ENUNCIATE UP; CROSS; OR DOWN. PUT SOME INFLECTION ON THEM ALSO. THE OTHER ACFT MAY HAVE THOUGHT THEY HEARD DOWNWIND AND NOT UPWIND. SUPPLEMENTAL INFO FROM ACN 420436:TWR TOLD US TO RPT TFC BTWN US AND THE TWR ON L DOWNWIND LEG. WE RPTED TFC INSIGHT BTWN US AND TWR ON DOWNWIND LEG. TWR CLRED US TO FOLLOW THAT TFC; DID NOT MENTION TFC ON UPWIND RWY 21L. WE DID NOT SEE TFC ON UPWIND RWY 21L. POSSIBLE PROBS: PHRASEOLOGY; SATURATED PATTERN; AND HANDING OVER TFC BTWN CTLRS! THIS IS THE SECOND TIME WITHIN 1 MONTH THAT TWR HAS TURNED ME IN FRONT OF ANOTHER ACFT WHILE ON UPWIND FOR THE PARALLEL RWYS WHILE SWITCHING TWR CTLRS.