Our chief operating decision maker regularly reviews our financial performance based on two reportable segments across our segments– (1) Network Solutions and (2) Services & Support. Network Solutions includes hardware and software products and next-generation virtualized solutions used in service provider or business networks, as well as prior-generation products. Services & Support includes a portfolio of maintenance, network implementation and solutions integration services, which include hosted cloud services and subscription services.

We evaluate the performance of our segments based on gross profit. Selling, general and administrative expenses, research and development expenses, interest and dividend income, interest expense, net investment gain (loss), other income (expense) and income tax (expense) benefit are reported on a company-wide, functional basis only. There are no inter-segment revenues.

The following table presents information about the reported sales and gross profit of our reportable segments for each of the years ended December 31, 2019, 2018 and 2017. Asset information by reportable segment is not reported, since we do not produce such information internally.

(In thousands)	2019				2018				2017
	Sales		Gross Profit		Sales		Gross Profit		Sales		Gross Profit
Network Solutions	$	455,226	$	191,549	$	458,232	$	179,303	$	540,396	$	260,833
Services & Support		74,835		27,618		71,045		24,262		126,504		42,802
Total	$	530,061	$	219,167	$	529,277	$	203,565	$	666,900	$	303,635

In addition to the above reporting segments, we also report revenue for the following three categories – (1) Access & Aggregation, (2) Subscriber Solutions & Experience and (3) Traditional & Other Products.

The following tables disaggregates our revenue by major source for the years ended December 31, 2019, 2018 and 2017:

	2019
(In thousands)	Network Solutions		Services & Support		Total
Access & Aggregation	$	289,980	$	58,894	$	348,874
Subscriber Solutions & Experience⁽¹⁾		144,651		8,269		152,920
Traditional & Other Products		20,595		7,672		28,267
Total	$	455,226	$	74,835	$	530,061

	2018
(In thousands)	Network Solutions		Services & Support		Total
Access & Aggregation	$	301,801	$	57,069	$	358,870
Subscriber Solutions & Experience⁽¹⁾		129,067		5,393		134,460
Traditional & Other Products		27,364		8,583		35,947
Total	$	458,232	$	71,045	$	529,277

	2017
(In thousands)	Network Solutions		Services & Support		Total
Access & Aggregation	$	361,955	$	111,989	$	473,944
Subscriber Solutions & Experience⁽¹⁾		132,294		6,162		138,456
Traditional & Other Products		46,147		8,353		54,500
Total	$	540,396	$	126,504	$	666,900

The following table presents sales information by geographic area for the years ended December 31, 2019, 2018 and 2017:

(In thousands)	2019		2018		2017
United States	$	300,853	$	288,843	$	508,178
Mexico		90,795		12,186		2,246
Germany		78,062		167,251		119,502
Other international		60,351		60,997		36,974
Total	$	530,061	$	529,277	$	666,900

Customers comprising more than 10% of revenue can change from year to year. Single customers comprising more than 10% of our revenue in 2019 included three customers at 19%, 17% and 13%. Single customers comprising more than 10% of our revenue in 2018 included two customers at 27% and 17%. Single customers comprising more than 10% of our revenue in 2017 included two customers at 40% and 16%. Other than those with more than 10% of revenues disclosed above, and excluding distributors, our next five largest customers can change, and has historically changed, from year-to-year. These combined customers represented 15%, 18% and 15% of total revenue in 2019, 2018 and 2017, respectively.

As of December 31, 2019, property, plant and equipment, net totaled $73.7 million, which included $69.9 million held in the U.S. and $3.9 million held outside the U.S. As of December 31, 2018, property, plant and equipment, net totaled $80.6 million, which included $77.3 million held in the U.S. and $3.3 million held outside the U.S. Property, plant and equipment, net is reported on a company-wide, functional basis only.