AN MD80 CREW EXPERIENCED A LOSS OF COMS WITH ZAU CRUISING AT FL220.

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WE RECEIVED A CLRNC WITH A HDG FOR DIRECT TO UIN AT FL220. WE WERE TOLD THAT FL220 WOULD BE THE FINAL DUE TO 'FLOW' INTO STL. WE WERE USING FREQ XXX ON ZAU. A COUPLE OF MINS LATER WE WERE ABOUT 95 MI N OF UIN AND HEARD SEVERAL ACFT TRY TO CHK IN WITH ZAU WITH NO RESPONSE FROM CTR. THEN THE FREQ BECAME CONGESTED WITH ACFT MAKING SECOND AND THIRD CALLS TO CTR. WE COULD NOT HEAR ANY RESPONSE. FO SWITCHED TO THE NEXT FREQ ON OUR RTE WHICH WAS ZKC. THEY INSTRUCTED US TO GO BACK TO XXX. HE STATED THAT THEY (MEANING ZAU) LOST COM; BUT WERE IN THE PROCESS OF GETTING IT BACK AND THAT ZAU NEEDED US BACK UP ON XXX. SO WE SWITCHED BACK TO XXX AND TRIED TO CHK IN. WE WERE UNABLE TO HEAR ZAU. AFTER A FEW MINS; WE GOT A CALL FROM ANOTHER ACFT ON THE FREQ AND HE STATED THAT ZAU HAD ASKED HIM TO RELAY A CLRNC TO US TO DSND TO FL200. WE ACKNOWLEDGED THE CLRNC AND RPTED OUT OF FL220 FOR FL200. AT ABOUT 75 DME FROM UIN; WE SAW A TCASII TARGET JUST ENTER THE SCREEN AT FL220. AS WE DSNDED TO FL200 WE WERE ABOUT 70 DME FROM UIN; WHEN THE ACFT ON THE TCASII PASSED ABOUT 5 MI OFF TO OUR L. WE NEVER SAW THE OTHER ACFT. A MIN OR SO LATER; WE COULD HEAR ZAU AGAIN AND HE HANDED US OFF TO ZKC.