Revenue Recognition On January 1, 2018 we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in Topic 605, Revenue Recognition. Accounting Policy under Topic 606 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. 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. Shipping fees are recorded as revenue and the related cost is included in cost of sales. Sales, value-added, and other taxes collected concurrently 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 if greater than one year. We have elected to apply the practical expedient related to the incremental costs of obtaining contracts and recognize those costs as an 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. A portion of our products is sold to a non-exclusive distribution network of major technology distributors in the United States. These large organizations then distribute or provide fulfillment services to an extensive network of VARs and Sis. VARs and Sis may be affiliated with us as a channel partner, or they may purchase from the distributor in an unaffiliated fashion. Additionally, with certain limitations our distributors may return unused and unopened product for stock-balancing purposes when such returns are accompanied by offsetting orders for products of equal or greater value. We participate in cooperative advertising and market development programs with certain customers. We use these programs to reimburse customers for certain forms of advertising, and in general, to allow our customers credits up to a specified percentage of their net purchases. Our costs associated with these programs are estimated and included in marketing expenses in our consolidated statements of income. We also participate in rebate programs to provide sales incentives for certain products. Our costs associated with these programs are estimated and accrued at the time of sale, and are recorded as a reduction of sales in our consolidated statements of income. Accounting Policy under Topic 605 Revenue was generally recognized when persuasive evidence of an arrangement exists, delivery has occurred, the product price was fixed or determinable, collection of the resulting receivable was reasonably assured, and product returns were reasonably estimable. For product sales, revenue was generally recognized upon shipment of the product to our customer in accordance with the title transfer terms of the sales agreement, generally Ex Works, per International Commercial Terms. In the case of consigned inventory, revenue was recognized when the end customer assumes ownership of the product. Contracts that contained multiple deliverables were evaluated to determine the units of accounting, and the consideration from the arrangement was allocated to each unit of accounting based on the relative selling price and corresponding terms of the contract. When this was not available, we were generally not able to determine third-party evidence of selling price because of the extent of customization among competing products or services from other companies. In these instances, we used best estimates to allocate consideration to each respective unit of accounting. These estimates included analysis of respective bills of material and review and analysis of similar product and service offerings. We recorded revenue associated with installation services when respective contractual obligations are complete. In instances where customer acceptance was required, revenue was deferred until respective acceptance criteria were met. Contracts that included both installation services and product sales were evaluated for revenue recognition in accordance with contract terms. As a result, installation services may have been considered a separate deliverable or may have been considered a combined single unit of accounting with the delivered product. Generally, either the purchaser, ADTRAN, or a third party would perform the installation of our products. Shipping fees were recorded as revenue and the related costs were included in cost of sales. Sales taxes invoiced to customers were included in revenues, and represented less than one percent of total revenues. The corresponding sales taxes paid were included in cost of goods sold. Value-added taxes collected from customers in international jurisdictions were recorded in accrued expenses as a liability. Revenue was recorded net of discounts. Sales returns were recorded as a reduction of revenue and accrued based on historical sales return experience, which we believed provided a reasonable estimate of future returns.