er as a trap observer, registered observers use an EventObserver method. After an application has de-registered, no notification will be sent to it when FMS receives a trap. FMS uses a feature called "common trap receiver". This allows more than one application to listen for traps at the same port(s) simultaneously. Without common trap receiver, when a management system is configured to listen for traps at a par- ticular port, no other application would be able to listen for traps at that port. Any network management software application can register for multiple ports. To do this, the developer of the application would first write a class implementing a "SocketListener" API.9 Next, this class is registered with the trap receiver mech- anism for the desired ports, using either the method for registering with a single port or the method for multiple ports. Then, when a trap is received, a method is invoked on a "SocketListener" interface. The PDU encapsulates the trap information and passes on that information as an argument. 4.6 Conclusion The major benefit of SNMP is that it is vendor-independent, and so helps in achiev- ing all of the benefits expected from an industry standard. The development of tools 8 We assume some basic knowledge of object-oriented programming. It is enough for the reader to know what a "class" is and what a "method" is. 9 A "socket" is an abstract pipe between which pieces of software communicate. To "listen" at a socket is to wait for incoming data from that socket. OSS for Telecom Networks for SNMP has enhanced the usefulness of the protocol. Now, no network hardware would fail to include SNMP support in their products. SNMP is enjoying a virtuous cycle and so we can expect broadening and increasingly advanced support for the more recent versions of SNMP, both on the management side and on the managed device side. We thank AdventNet for allowing us to use its material and for other assistance with this chapter. Network Management Using Telnet/CLI and TL1 5.1 Introduction to CLI Command