B727 AND C172 HAD NMAC IN C90 CLASS E.

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A COUPLE MINS BEFORE THE OCCURRENCE; WE LEVELED AT 6000 FT MSL. ATC ADVISED US OF TFC AT 12:30-1 O'CLOCK POS; AT 6500 FT MSL. WE WERE THEN INFORMED OF PARACHUTE JUMPERS AT 11 O'CLOCK POS. ATC GAVE US A R TURN DIRECT MIDWAY TO AVOID THE PARACHUTE JUMPERS; WHICH WE COMPLIED WITH. UNBEKNOWNST TO US THE 12:30-1 O'CLOCK POS; HAD CHANGED COURSE AND DSNDED TOWARDS US. WE RECEIVED A TA/RA CLB/XING CLB; THEN CLB NOW; WHICH WE COMPLIED WITH. AT OUR CLOSEST POINT; WHEN I OBTAINED VISUAL CONTACT WITH THE CESSNA 172 TFC WAS ABOUT 100-200 FT HORIZLY AND MOMENTARILY THE SAME ALT. WE CLBED IMMEDIATELY PER OUR TCASII TA/RA ALERT TO 7000 FT MSL TO AVOID THE CESSNA. WE IMMEDIATELY NOTIFIED ATC OF OUR CLB TO AVOID TFC AND OUR DSCNT BACK TO 6000 FT MSL. WHEN THE CESSNA 172 NOTICED US; THEY TURNED HARD R AND DSNDED. THERE WAS A LOT GOING ON DURING THIS PHASE OF FLT AND ATC WAS VERY BUSY. THE TCASII WORKED GREAT AND AVOIDED A MUCH WORSE SIT. A POSSIBLE FIX TO THE SIT WOULD BE NOT ALLOWING PARACHUTE JUMPING ON THE MOTIF 2 ARR NEAR JOLIET. THE MAIN ARR TO CHICAGO MIDWAY ARPT FROM THE NW; W; SW; AND S. ANOTHER FIX WOULD REQUIRE POSITIVE RADIO CONTACT WITH ATC FOR ALL ACFT NEAR THE MOTIF 2 ARR ALTS NEAR JOLIET. THIS WOULD ALLOW ATC TO MORE EFFICIENTLY SEPARATE VFR AND IFR AND PARACHUTE JUMPER TFC.