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  <xs:element id="sncr_PeriodTwoMember" abstract="true" name="PeriodTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sncr_DebtInstrumentBasisSpreadOnVariableRateFloor" abstract="false" name="DebtInstrumentBasisSpreadOnVariableRateFloor" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="sncr_DebtInstrumentExitFeeRequiredIfConditionsMet" abstract="false" name="DebtInstrumentExitFeeRequiredIfConditionsMet" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_BRPIMember" abstract="true" name="BRPIMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sncr_RepurchaseOfDebtAndEquityConsiderationTransferredLiabilitiesIncurredFromDebt" abstract="false" name="RepurchaseOfDebtAndEquityConsiderationTransferredLiabilitiesIncurredFromDebt" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_RepurchaseOfDebtAndEquityConsiderationTransferredLiabilitiesIncurredFromCurrentNonInterestBearingDeferredConsideration" abstract="false" name="RepurchaseOfDebtAndEquityConsiderationTransferredLiabilitiesIncurredFromCurrentNonInterestBearingDeferredConsideration" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_RepurchaseOfDebtAndEquityConsiderationTransferred" abstract="false" name="RepurchaseOfDebtAndEquityConsiderationTransferred" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_PreferredStockRepurchasePercentage" abstract="false" name="PreferredStockRepurchasePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="sncr_DebtInstrumentNumberOfNotesRepurchased" abstract="false" name="DebtInstrumentNumberOfNotesRepurchased" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="sncr_DebtInstrumentRepurchasePercentage" abstract="false" name="DebtInstrumentRepurchasePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="sncr_PreferredStockRepurchasedCarryingValue" abstract="false" name="PreferredStockRepurchasedCarryingValue" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_PaymentsForRepurchaseOfSeniorDebt" abstract="false" name="PaymentsForRepurchaseOfSeniorDebt" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_DebtInstrumentParValue" abstract="false" name="DebtInstrumentParValue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase" abstract="false" name="DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_DebtInstrumentUnderwritersOptionToPurchase" abstract="false" name="DebtInstrumentUnderwritersOptionToPurchase" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_DebtInstrumentRedemptionPrice" abstract="false" name="DebtInstrumentRedemptionPrice" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount" abstract="false" name="DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="sncr_DebtInstrumentSalesAgentCompensationPercentage" abstract="false" name="DebtInstrumentSalesAgentCompensationPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember" abstract="true" name="AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="sncr_SeriesBPerpetualNonConvertiblePreferredStockMember" abstract="true" name="SeriesBPerpetualNonConvertiblePreferredStockMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="sncr_CapitalStockSharesAuthorized" abstract="false" name="CapitalStockSharesAuthorized" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="sncr_CapitalStockParOrStatedValuePerShare" abstract="false" name="CapitalStockParOrStatedValuePerShare" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="sncr_NumberOfVotesEachShare" abstract="false" name="NumberOfVotesEachShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="sncr_PreferredStockOwnershipPercentage" abstract="false" name="PreferredStockOwnershipPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="sncr_TemporaryEquityPaymentOfPreferredDividendShares" abstract="false" name="TemporaryEquityPaymentOfPreferredDividendShares" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="sncr_TemporaryEquityPaymentOfPreferredDividendValue" abstract="false" name="TemporaryEquityPaymentOfPreferredDividendValue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_TemporaryEquityPreferredStockRedemptionShares" abstract="false" name="TemporaryEquityPreferredStockRedemptionShares" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="sncr_TemporaryEquityPreferredStockRedemptionValue" abstract="false" name="TemporaryEquityPreferredStockRedemptionValue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_TemporaryEquityUnamortizedIssuanceCosts" abstract="false" name="TemporaryEquityUnamortizedIssuanceCosts" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_TemporaryEquityCarryingAmount" abstract="false" name="TemporaryEquityCarryingAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_TemporaryEquityGrossAmount" abstract="false" name="TemporaryEquityGrossAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="sncr_EquityIncentivePlan2015Member" abstract="true" name="EquityIncentivePlan2015Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="sncr_NewHireEquityIncentivePlan2017Member" abstract="true" name="NewHireEquityIncentivePlan2017Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="sncr_NumberOfStockBasedCompensationPlans" abstract="false" name="NumberOfStockBasedCompensationPlans" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="sncr_EmployeeAndDirectorsStockOptionsMember" abstract="false" name="EmployeeAndDirectorsStockOptionsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="sncr_OptionsAndUnvestedRestrictedSharesMember" abstract="true" name="OptionsAndUnvestedRestrictedSharesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="sncr_LossContingencyPaymentTerms" abstract="false" name="LossContingencyPaymentTerms" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="sncr_OtherSundryNonoperatingIncomeExpenseNet" abstract="false" name="OtherSundryNonoperatingIncomeExpenseNet" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
