pped with a Connection Handler class to establish a TL1 session with a TL1 device. The IP address of the TL1 device to be discovered must be specified. The TL1 device needs a login command to communicate. This command gen- erally corresponds to a particular user and password. FMS uses this command to open a session with the TL1 device as part of connection establishment and uses this session for all subsequent communication with the device. Other commands can also be specified as part of connection establishment. A maximum of two commands for specific initialization of the TL1 device can be specified. The initialization command ("init") is for clearing the memory of the device, device error counts, dealing with pre-existing data in the device and so on. The login and init commands are sent to the device whenever a TL1 session is opened by the fault management system. 12.7 Filtering and Processing Notifications A trap may need processing before it is converted into an event. Trap filters can be used to modify the properties of the trap before converting it into an event. The fol- lowing are characteristics of the functioning of trap filters: Process and modify the SNMP PDU and return the SNMP PDU passed to it. After successful modification of the properties, if the PDU properties match any filter criteria, then an attempt will be made to match the PDU returned with the remaining trap parsers and filters and event parsers and filters. Construct an event object from the trap PDU that was passed to it and return the event object. The event object will be passed through the event parsers and filters, but not through trap parsers. Return extended event objects. Drop the trap by returning "null". This restricts the trap from further processing by FMS. A custom trap filter can be made to carry out any of these functions. Figure 12.3 illustrates where trap filters are configured, with the evident functions of: adding a trap filter modifying a trap filter's details deleting a trap filter enabling/disabling a trap filter vi