13. LIABILITY FOR WARRANTY RETURNS

Our products generally include warranties of 90 days to ten years for product defects. We accrue for warranty returns at the time revenue is recognized based on our estimate of the cost to repair or replace the defective products. We engage in extensive product quality programs and processes, including actively monitoring and evaluating the quality of our component suppliers. Our products continue to become more complex in both size and functionality as many of our product offerings migrate from line card applications to total systems. The increasing complexity of our products will cause warranty incidences, when they arise, to be more costly. Our estimates regarding future warranty obligations may change due to product failure rates, material usage, and other rework costs incurred in correcting a product failure. In addition, from time to time, specific warranty accruals may be recorded if unforeseen problems arise. Should our actual experience relative to these factors be worse than our estimates, we will be required to record additional warranty expense. Alternatively, if we provide for more reserves than we require, we will reverse a portion of such provisions in future periods. The liability for warranty obligations totaled $8.8 million and $8.7 million at September 30, 2016 and December 31, 2015, respectively. During the three months ended September 30, 2016, we incurred an increase in warranty expense related to a product recall caused by a defect in a part provided by a third party supplier. These liabilities are included in accrued expenses in the accompanying Consolidated Balance Sheets.

A summary of warranty expense and write-off activity for the three and nine months ended September 30, 2016 and 2015 is as follows:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
(In thousands)	2016			2015			2016			2015
Balance at beginning of period	$	8,935		$	8,933		$	8,739		$	8,415
Plus: Amounts charged to cost and expenses		4,012			777			6,341			1,905
Less: Deductions		(4,195	)		(994	)		(6,328	)		(1,604	)
Balance at end of period	$	8,752		$	8,716		$	8,752		$	8,716