MAJOR CUSTOMERS

The following customers contributed 10% or more of the Company's revenue in the three months ended March 31, 2020 and 2019:



	Three months ended
	March 31, 2020	March 31, 2019
Verizon Communications Inc.	13%	15%
AT&T Inc.	10%	10%

At March 31, 2020, there were no customers that accounted for 10% or more of the Company's accounts receivable balance. At December 31, 2019, one customer accounted for 10% or more of the Company's accounts receivable balance, representing approximately 22% of total accounts receivable. The Company performs ongoing credit evaluations of its customers and generally does not require collateral on accounts receivable, although in some instances the Company may require letters of credit to support customer outstanding accounts receivable balances. The Company maintains an allowance for doubtful accounts and such losses have been within management's expectations.