All Wal-Mart suppliers must participate in Retail Link, a computerized system in which they "plan, execute, and analyze thair businesses. Along with execute, electronic data interchange, suppliers receive purchase order information and supply invoices electronically, thereby lowering expenses and increasing productivity. Suppliers must meet Wal-Mart's strict lead-time and shipping requirements by using the technology and complying with operating procedures. The Wal-Mart logistics team uses an Internet-based Transportation Link system that complements a Backhaul Betty telephone voice-response system to help them move goods. In one year, Wal-Mart estimated nearly 1 million loads of general merchandise moved to Distribution Centers throughout the country. Store-bound shipments travel by the company's 7,000 trucks, one of the largest fleets in the world. The company relentlessly strives to develop its supply-chain process. For example ensure greater supply chain visibility, satellite-based tracking technology is being installed in the Company's entire fleet of over-the-road trailers. The data generated increases productivity, reduces costs and enhances security