This Technical Report (TR) introduces the concepts for use in assessing the availability of access to IP-based telecommunications network. The calculation is based on the access availability of IP routers in the network. The TR presents alternate methods for weighting the availability calculation in terms of customers, ports, and bandwidth. This Technical Report is intended as the first in a series of Technical Reports, on the reliability metrics for IP-based networks. The next report will include Backbone networks thereby permitting a complete network availability assessment.