SCOPE PURPOSE Availability is a key measure in Service Level Agreements (SLA) between service providers and their customers@ as well as their vendors and suppliers. Metrics for estimating IP packet layer availability [Y.1540] and service level availability [ATIS-0100020.2008] have received considerable attention in various standards bodies. At the same time@ service providers need to constantly evaluate network element reliability; hence@ availability metric estimation for network elements plays a critical role in SLA interactions with equipment vendors and suppliers. IP-based networks and related evolving technologies -- such as Multi-Protocol Label Switching (MPLS) -- are expected to form the basis for Next Generation Networks (NGN) and Services. The specifics of SLA interactions between service providers and IP equipment vendors are driven by the following: ? Degree of reliability and availability of individual network elements (e.g.@ Line Cards@ Routers@ etc.). ? Degree of redundancy built into the network design (e.g.@ redundant line cards). Thus@ the development of an appropriate availability metric@ and subsequent techniques for metric estimation@ can be very beneficial to service providers. An Technical Report@ T1.TR.78-2003@ proposed a metric for assessing the access availability of routers in IP-based networks by characterizing fractional availability of access routers in terms of lost ports that can be further weighted by some factor (e.g.@ port bandwidth). This Technical Report proposes a methodology for estimating the availability of IP-based access routers in terms of customer facing router line card availability. This is based on what a customer experiences during network failure occurrences. If such failures result in downtime for the customer facing Line Card@ then the Line Card is considered to be unavailable regardless of the actual failure. The purpose is to stimulate interactions between service providers@ equipment vendors@ and suppliers in the development of appropriate reliability/availability SLA's. It should be noted that this methodology can also be applied to other types of packet network technologies. For example@ it can be utilized to assess the access availability of line cards in Frame Relay switches.