rvices QoS and security are the two most important considerations in administering VPNs, SO uptimes, delays, and SLAs need to be structured. For example, QoS guar- antees could promise 100% premises-to-premises network availability, with a max- imum latency of 80 milliseconds. Some vendors offer separate SLAs for dedicated and remote access. For dedicated access, the SLA may offer an availability guaran- tee of 99.9% and a maximum latency guarantee of 125 milliseconds. On remote access SLAs, a busy-free dial availability guarantee of 97% may be stipulated, and the latency guarantee would depend on the initial modem connection speed. Today, three basic types of carrier-managed IP VPN services are offered: CPE-based IPsec VPNs-These VPNs are generally used to support site-to- site enterprise VPNs and have, in many ways, become the gold standard for VPN security, especially when traffic is running over the public Internet. Network-based IPsec VPNs-These VPNs may run over the Internet or the service provider's private IP facilities. Customers use leased-line connec- tions from the premises router to the service provider's POP. Network-based MPLS VPNs-These VPNs are receiving the most attention today. Service providers' VPN solutions can be deployed using partial mesh, full mesh, and hub-and-spoke designs. They can provide point-to-point and multipoint connectivity. They support a multitude of services and are avail- able from multiple providers around the world. VPN Standards The initial VPN service standardization efforts focused on service provider Layer 3 solutions, where multiple competing implementations had already been developed. The main driving forces of the standards initiatives included multivendor interop- erability and applicability scenarios of each of those Layer 3 solutions. Later, the interest in Layer 2 provider edge-based solutions was driven by the growing attrac- tiveness of the metro-Ethernet market and the capability to offer relatively simple migration paths from traditional Layer 2 ATM and Fr