Loop Access  products are used by carrier and enterprise customers for access to copper-based communications networks. The Loop Access category includes the following product areas and related services: In addition, we identify subcategories of product revenues, which we divide into core products and legacy products. Our core products consist of Broadband Access and Optical products (included in Carrier Systems) and Internetworking  products (included in Business Networking). Our legacy products include HDSL products (included in Loop Access) and  other products not included in the aforementioned core products. Many of our customers are migrating their networks to  deliver higher bandwidth services by utilizing newer technologies. We believe that products and services offered in our core  product areas position us well for this migration. Despite occasional increases, we anticipate that revenues of many of our  legacy products, including HDSL, will decline over time; however, revenues from these products may continue for years  because of the time required for our customers to transition to newer technologies. Sales were $641.7 million in 2013 compared to $620.6 million in 2012 and $717.2 million in 2011. Total sales of products in our three core areas, Broadband Access, Optical and Internetworking, increased 8.9% in 2013 compared to 2012 and decreased 1.7% in 2012 compared to 2011. Our gross profit margin decreased in 2013 to 48.1% from 51.0% in 2012 and 57.8% in 2011. Net income was $45.8 million in 2013 compared to $47.3 million in 2012 and $138.6 million in 2011. Earnings per share, assuming dilution, were $0.77 in 2013 compared to $0.74 in 2012 and $2.12 in 2011. Earnings per share in 2013, 2012 and 2011 include the effect of the repurchase of 5.6 million, 1.8 million and 1.1 million shares of our stock in  those years, respectively. Our operating results have fluctuated on a quarterly basis in the past, and may vary significantly in future periods due to a number of factors, including customer order activity and backlog. Backlog levels vary because of seasonal trends, the timing of customer projects and other factors that affect customer order lead times. Many of our customers require prompt delivery of products. This requires us to maintain sufficient inventory levels to satisfy anticipated customer demand. If near-term demand for our products declines, or if potential sales in any quarter do not occur as anticipated, our financial  results could be adversely affected. Operating expenses are relatively fixed in the short term; therefore, a shortfall in quarterly  revenues could significantly impact our financial results in a given quarter. Our operating results may also fluctuate as a result of a number of other factors, including a decline in general economic and market conditions, increased competition, customer order patterns, changes in product and services mix, timing differences between price decreases and product cost reductions, product warranty returns, expediting costs and announcements of new products by us or our competitors. Additionally, maintaining sufficient inventory levels to assure  prompt delivery of our products increases the amount of inventory that may become obsolete and increases the risk that  the obsolescence of this inventory may have an adverse effect on our business and operating results. Also, not maintaining  sufficient inventory levels to assure prompt delivery of our products may cause us to incur expediting costs to meet customer  delivery requirements, which may negatively impact our operating results in a given quarter. Accordingly, our historical financial performance is not necessarily a meaningful indicator of future results, and, in  general, management expects that our financial results may vary from period to period. See Note 15 of Notes to Consolidated  Financial Statements for additional information. For a discussion of risks associated with our operating results, see Item 1A of our Form 10-K for the year ended December 31, 2013. An accounting policy is deemed to be critical if it requires an accounting estimate to be made based on assumptions about  matters that are highly uncertain at the time the estimate is made, if different estimates reasonably could have been used, or if changes in the accounting estimate that are reasonably likely to occur could materially impact the results of financial operations. We believe the following critical accounting policies affect our more significant judgments and estimates used in the preparation of our consolidated financial statements. These policies have been consistently applied across our two  reportable segments: (1) Carrier Networks Division and (2) Enterprise Networks Division. Critical Accounting Policies and Estimates ADTRAN 2013 Annual Report 18 • High bit-rate Digital Subscriber Line (HDSL) products Digital Data Service (DDS) • Integrated Services Digital Network (ISDN) products T1/E1/T3 Channel Service Units/Data Service Units (CSUs/DSUs) • TRACER fixed-wireless products