Until recently, reliable communication has meant the use of leased lines to maintain a wide-area network (WAN). Leased lines, ranging from Integrated Services Digital Network (ISDN, which runs at 144 Kbps) to Optical Carrier-3 (OC3, which runs at 155 Mbps) fiber, provide a company with a way to expand their private network beyond their immediate geographic area. A WAN has obvious advantages over a public network like the Internet when it comes to reliability, performance, and security; but maintaining a WAN, particularly when using leased lines, can become quite expensive (it often rises in cost as the distance between the offices increases). Additionally, leased lines are not a viable solution for organizations where part of the work force is highly mobile (as is the case with the marketing staff) and might frequently need to connect to the corporate network remotely and access sensitive data.