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MAJOR CUSTOMERS
12 Months Ended
Dec. 31, 2018
Risks and Uncertainties [Abstract]  
MAJOR CUSTOMERS
MAJOR CUSTOMERS

The following customers contributed 10% or more of the Company's revenue in at least one of the years ended December 31, 2018, 2017 and 2016:
 
Year ended December 31,
 
2018
 
2017
 
2016
Verizon Communications Inc.
17%
 
17%
 
*
AT&T Inc.
*
 
*
 
12%


At December 31, 2018, two customers accounted for 10% or more of the Company's accounts receivable balance, representing approximately 32% in the aggregate of total accounts receivable. At December 31, 2017, two customers accounted for 10% or more of the Company's accounts receivable balance, representing approximately 31% in the aggregate of total accounts receivable. The Company performs ongoing credit evaluations of its customers and generally does not require collateral on accounts receivable. The Company maintains an allowance for doubtful accounts and such losses have been within management's expectations.