CTLR MISSPOKE SIMILAR SOUNDING CALL SIGNS AND FLT CREW TOOK CLIMB MEANT FOR ANOTHER FLT; RESULTING IN LESS THAN STANDARD SEPARATION.

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I WAS WORKING R31 AT XA15 PM; 4/THURS/88. MLG Y WAS A RNO DEP GOING TO SFO. HE WAS CLRED ILA-ENI-PYE-SFO AT FL260. AFTER MLG Y PASSED ILA; I CLRED HIM DIRECT PYE FOR SEQUENCING INTO SFO. I HAD 2 XXXX AIRLINE FLTS ON FREQ; MLG XYX; SFO DIRECT RBL AND MLG ABX SJC DIRECT RBL. ON INITIAL CALL I CLBED MLG ABX TO FL280; HE REQUESTED FL310; BUT I WAS UNABLE TO DO THAT BECAUSE OF SAME DIRECTION TFC AT FL310; A ZZZZ AIRLINES FLT. ON INITIAL CALL I CLBED MLG XYX TO FL250. HE REQUESTED HIGHER; BUT I WAS UNABLE TO CLB HIM HIGHER DUE TO TFC AT FL260; WHICH WAS MLG Y. I TOLD MLG XYX TO EXPECT HIGHER IN 3 MINS; THEN I CORRECTED THAT AND SAID IN 5 MINS. MLG XYX WAS THEN 10-15 MI AWAY FROM MLG Y. I MEANT TO CALL MLG ABX TO TELL HIM TO CLB TO FL290; BUT I MISTAKENLY CALLED MLG AGX; WHO WAS NOT ON FREQ; TO CLB TO FL290. MLG XYX TOOK THE CLRNC FOR MLG AGX AND RESPONDED; 'MLG XYX MAINTAIN FL290.' I DID NOT CATCH THE FACT THAT MLG XYX ANSWERED BY MISTAKE. I HAD THE J-RING CIRCLE ON MLG Y; SO WHEN I HAD 5 MI SEP WITH MLG XYX; I COULD CLB MLG XYX. MLG Y'S DATA BLOCK SHOWED LEVEL AT FL260. MLG XYX DATA BLOCK SHOWED A TEMPORARY ALT OF FL250 AND THE MODE C SHOWED LEVEL AT FL250. NOW BOTH TARGETS WERE WITHIN THE J-RING CIRCLE AND I SAW MLG XYX AT FL254; 400' HIGH. I ASKED MLG XYX HIS ALT; BELIEVING THE 400' WAS A BAD MODE C HIT BY THE RADAR. MLG XYX ANSWERED 'CLBING TO FL290.' I TOLD HIM HE WAS NOT ASSIGNED ABOVE FL250. HE ANSWERED THAT HE WOULD DSND BACK TO FL250. AFTER MLG XYX SAID HE WOULD GO BACK DOWN TO FL250; THE 2 ACFT HAD PASSED BY 5 MI AND SEP WAS INCREASING. NO FURTHER ACTION WAS TAKEN. THE SECTOR WAS BECOMING VERY BUSY WITH THE DEPS GOING NBOUND LEAVING OAK; SFO AND SJC. THE MLG Y WAS TFC FOR THE SFO AND OAK DEPS. THE SJC DEPS ARE FAR ENOUGH S TO EASILY TOP MLG Y AT FL260. I WAS GIVEN 3 ACFT WELL S OF MLG Y (30-40 MI) ON PARALLEL OR NEAR PARALLEL HDGS GOING NBND. THESE DO NOT INCLUDE MLG XYX; WHO WAS WITHIN 20 MI OF MLG Y OR MLG ABX; WHO WAS 50-60 MI AWAY FROM MLG Y. THE 3 ACFT FROM THE S WERE CLBING TO FL240 OR 250 FROM A LOWER ALT SECTOR. I WAS NOT TALKING TO THESE ACFT WHEN I MADE DECISIONS CONCERNING THE SEQUENCING AND SEP OF MY SECTOR. MLG Y REQUESTED LOWER ALT DUE TO A BAD RIDE AT FL260. I LOOKED AT THE SITUATION WITH THE 3 ACFT TO THE S OF MLG Y AND I BELIEVED MLG Y COULD PROBABLY GET TO FL240 AND THE 3 ACFT COULD CLB ABOVE FL250 IN PLENTY OF TIME TO ENSURE SEP. MLG Y WAS STILL PROCEEDING DIRECT ENI AT THIS TIME; HAVING PASSED ILA. THE SEQUENCE FOR SFO WAS SUCH THAT MLG Y WAS FOLLOWING A BBBB FLT AND LEADING A ZZZZ FLT. I DECIDED TO SEND MLG Y DIRECT PYE TO HELP THE SEQUENCING FOR SFO. IF I HAD NOT SENT MLG Y DIRECT PYE; THIS WOULD HAVE FORCED THE ZZZZ FLT TO STAY ON A VECTOR FOR SPACING LONGER THAN NEEDED. TURNING MLG Y DIRECT PYE TURNED HIM INTO MLG XYX; WHICH MADE IT IMPOSSIBLE TO DSND HIM BELOW FL260. IT ALSO MADE IT IMPOSSIBLE TO CLB MLG XYX. THE 3 ACFT FROM THE S OF MLG Y ALSO COULD THEN GO NO HIGHER THAN FL250 UNTIL PASSING MLG XYX. I DON'T KNOW WHERE THIS GOES. AFTER MLG XYX READ BACK THE INCORRECT CLRNC; I TURNED HIM TO A HDG OF 360 DEGS. THIS HAD NOTHING TO DO WITH TRYING TO MAINTAIN SEP WITH MLG Y; AS I THOUGHT MLG XYX WAS STILL ASSIGNED FL250. I GAVE MLG XYX THIS VECTOR FOR SPACING; SO THAT MLG XYX WOULD BE CLR OF MLG Y SOONER. THE ERROR OCCURRED BECAUSE I THOUGHT I HEARD MLG ABX RESPOND TO MLG AGX'S CLRNC AND BECAUSE MLG XYX THOUGHT HE HEARD MLG XYX'S CALL SIGN WHEN IN FACT HE HEARD MLG AGX'S. REMEMBER; I SAID MLG AGX INCORRECTLY. WHY I SAID MLG AGX INSTEAD OF MLG ABX; I DON'T KNOW. IN CONCLUSION; MLG XYX HEARD WHAT HE WANTED TO HEAR; I HEARD WHAT I WANTED TO HEAR AND BOTH OF US HEARD SOMETHING ENTIRELY DIFFERENT. ONE AREA TO LOOK INTO IS WHAT NUMBERS SOUND ALIKE--DOES MLG XYX SOUND LIKE MLG AGX? DOES MLG ABX SOUND LIKE MLG XYX? THE MOST IMPORTANT POINT HERE IS THEY BOTH END IN X'S. IS THE LAST NUMBER THE ONE THAT PEOPLE KEY INTO? WOULD MLG XYX SOUND LIKE MLG XYW? IF MLG XYX IS LISTENING FOR THE X; SUCH AS MLG AGX ENDS IN;WOULD MLG XYW JUST PASS BY HIM AND GET NO RESPONSE.