c format and display the logs in a GUI (graphical user interface). Each log is generated in the network element to notify the occurrence of a specific event. Fault logs from different network elements are collected at the network management system in the network management layer. Logs correspond- ing to different events on different network elements are correlated at the NMS. An event handler implemented at the NMS can take corrective actions to rectify a trouble scenario. Since this is a network management layer functionality let us explain it in more detail with an example. When the connection between a call processing switch/call agent (CA) and a media gateway (MGW) goes down due to installation failure of a software module Fundamentals of EMS, NMS and OSS/BSS on the MGW, a set of event logs are generated. The CA will create a log showing loss of connection with MGW and the MGW, which is a different network ele- ment, will generate its own log specifying loss of connection with the CA. There will also be logs in the MGW specifying failure of a software module on MGW and many other logs corresponding to the status of the links that connect the CA and MGW. While at EMS level only collection of data from a specific element like CA or MGW occurs, at the NMS level log data from both these elements are available. So the event logs from different network elements can be correlated and in this scenario the logs from the CA and MGW are correlated and the actual problem can be identified, which is not possible at the EMS level by just a connec- tion down log at CA. Knowledge of the actual problem at the NMS level, leads to the capability of creating applications that can take corrective actions when a predefined problem occurs. The fault logs generated at the network element is also used in layers above the network layer. The time duration for which a link is down can be used as input information for a service assurance application in the service layer, and this can be used to provide a discount in the billing module on