Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2018

Customers accounting for more than 10% of our total revenue and revenue from our top five customers for the years ended December 31, 2018, 2017 and 2016 were as follows:



	Years Ended December 31,
	2018		2017		2016
Percent of revenue from customers accounting for 10% or more of total revenue:
Huawei Technologies Co., Ltd	46	%	40	%	50	%
Ciena Corporation	24	%	16	%	15	%
Percent of revenue from top five customers	87	%	78	%	82	%

Estimated Useful Lives of Property, Plant and Equipment

Depreciation and amortization are computed using the straight-line method over the following estimated useful lives:



Buildings	20-30 years
Machinery and equipment	2-7 years
Furniture, fixtures and office equipment	3-5 years
Software	5-7 years
Leasehold improvements	life of the asset or lease term, if shorter