3. REVENUE

Revenue is measured based on the consideration we expect to receive in exchange for transferring goods or providing services to a customer and as performance obligations under the terms of the contract are satisfied. Generally, this occurs with the transfer of control of a product or service to the customer. For transactions where there are multiple performance obligations, we account for individual products and services separately if they are distinct (if a product or service is separately identifiable from other items and if a customer can benefit from it on its own or with other resources that are readily available to the customer). The consideration, including any discounts, is allocated between separate products and services based on their stand-alone selling prices using the most likely amount. The stand-alone selling prices are determined based on the prices at which we sell the separate products and services. For items that are not sold separately, we estimate stand-alone selling prices primarily using reasonable internal analysis. Shipping fees are recorded as revenue and the related cost is included in cost of sales. Sales, value added, and other taxes collected concurrent with revenue-producing activities are excluded from revenue. Costs of obtaining a contract are capitalized and amortized over the period that the related revenue is recognized. We have elected to apply the practical expedient related to the incremental costs of obtaining contracts and recognize those costs as expense when incurred if the amortization period of the assets is one year or less. These costs are included in selling, general and administrative expenses. Capitalized costs with an amortization period greater than one year were immaterial.

The following is a description of the principal activities from which we generate our revenue by reportable segment.

Network Solutions Segment

Network Solutions includes hardware products and next-generation virtualized solutions used in service provider or business networks, as well as prior generation products.

Hardware

The majority of the revenue from this segment is from hardware sales and is recognized when control is transferred to our customers, which is generally when we ship the products. Shipping terms are generally FOB shipping point. Revenue is recorded net of discounts and rebates using the most likely amount. Customers are typically invoiced when control is transferred and revenue is recognized. Our products generally include assurance-based warranties of 90 days to five years for product defects, which are accrued at the time revenue is recognized.

In certain transactions, we are also the lessor in sales-type lease arrangements for network equipment, which have terms of 18 months to five years. These arrangements typically include network equipment, network implementation services and maintenance services. Product revenue for these leases is generally recorded when we transfer control of the product to our customers. Revenue for network implementation and maintenance services is recognized as described below. Customers are typically invoiced and pay in equal installments over the lease term.

Services & Support Segment

To complement our Network Solutions segment, we offer a complete portfolio of maintenance, network implementation, solutions integration and managed services, which include hosted, cloud services and subscription services.

Maintenance

Our maintenance service periods range from one month to five years. Customers are typically invoiced and pay for maintenance services at the beginning of the maintenance period, which is recorded in current or non-current unearned revenue depending on the length of the service period. Maintenance services are provided on an as-needed basis and our customers benefit evenly throughout the contract term. Accordingly, we recognize revenue for maintenance services on a straight-line basis over the maintenance period in services revenue.

Network Implementation

We recognize revenue for network implementation, which primarily consists of engineering, execution and enablement services, when performance obligations are complete at a point in time. If we have recognized revenue, but not billed the customer, the right to consideration is recognized as a contract asset, which is included in other receivables in the Consolidated Balance Sheet. The contract asset is transferred to accounts receivable when the right to consideration to payment becomes unconditional.

As of March 31, 2018, we did not have any remaining performance obligations related to customer contracts that had an original expected duration of one year or more, other than maintenance services, which are satisfied over time.

The following table provides information about receivables, contract assets, and unearned revenue from contracts with customers:

(In thousands)	March 31, 2018		December 31, 2017
Accounts receivable	$	80,883	$	144,150
Contract assets		1,442		—
Unearned revenue		13,948		13,070
Non-current unearned revenue		4,154		4,556

During the three months ended March 31, 2018, we recognized $3.5 million of revenue that was included in unearned revenue at the beginning of the period.

The following table disaggregates our revenue by major source:

(In thousands)	Network Solutions		Services & Support		Total
Access & Aggregation	$	69,385	$	12,295	$	81,680
Customer Devices		28,777		1,324		30,101
Traditional & Other Products		7,091		1,934		9,025
Total	$	105,253	$	15,553	$	120,806