This supplement to Committee T1 Technical Report No. 24 (TR No. 24) on Network Survivability Performance addresses the need for a common understanding and for techniques assessing network survivability. This Technical Report resolves some of the issues and questions left for further study, and clarifies several TR No. 24 definitions. TR No. 24 emphasizes the classification of network failures (i.e., identifying whether or not a service outage has occurred) and addresses the quantification of failure events, and techniques to measure the severity of the failure. This report also provides improved measures of failures with respect to service outage severity. It classifies the architectures and services of industry segments other than wireline (i.e., wireless, cable TV, and satellite) and provides methods in the corresponding appendices to calculate outage index values for voiceband telephony service outages.