ets, which focus on speed- ing communications along the supply chain; distributor extranets, which focus on the demand side and provide great access to information; and peer extranets, which create increased intraindustry competition. The key applications for extranets include distribution of marketing and prod- uct information, online ordering, billing and account history, training policies and VPN Client Remote Worker Local ISP Public Network Internal LAN Server Headquarters Figure 9.17 A remote access VPN Partner A Partner B Server 1 Firewall/Router/ VPN Gateway Server 2 Extranet User on Firewall/Router/ Server 2 VPN Gateway User on Server 2 User on Server 2 Figure 9.18 An extranet VPN standards, inventory management, collaborative research and development, and e-mail, chat, news, and content. Benefits and Evolution of VPNs The main benefit of VPNs as compared to leased-line or Frame Relay networks is cost savings. VPNs also optimize environments that use IP; they have less overhead than Frame Relay, and tunneling protocols may eliminate the need for proprietary encapsulation of protocols. Provisioned VPNs also have the additional benefits of Frame Relay and ATM in the administration of virtual circuits and QoS. VPNs also provide the capability to support dialup access, and greater redundancy is achieved in the network by virtue of meshed nets. In addition, VPNs do not necessarily demand an end-to-end digital fiber infrastructure. VPNs are undergoing an evolution, and various parameters still need to be addressed. Among those are the QoS guarantees. Effective traffic prioritization is at the heart of QoS, and currently available mechanisms include Differentiated Ser- vices (DiffServ), Class-Based Queuing (CBQ), Common Open Policy Service (COPS), and MPLS. (These mechanisms are covered in Chapter 10.) Other areas of evolu- tion in VPNs are tiering of VPN services (i.e., bandwidth tiering and different pol- icy management), the capability to support autoprovisioning, and the emphasis on security. Chapter 9 IP Se