VENTION: This tag is used to refine the seman- tics of existing types. For defining the set of states the switch can have, we could use the TEXTUAL CONVENTION tag as shown in the example. In this example the type INTEGER has been refined. Example: State : := TEXTUAL CONVENTION STATUS current DESCRIPTION "Run Time States" SYNTAX INTEGER { Offline (0), Busy (1), Active (2) } 15.5 Conclusion Another important item to be discussed before we conclude is GDMO. The GDMO, a part of the SMI document, is a structured description language that pro- vides a way of specifying the class for objects, object behaviors, attributes, and class hierarchy. GDMO uses a set of templates for information modeling. Some of the templates include definitions for managed object, packages, attributes, and notifica- tions. Packages are used to group characteristics of a managed object and they can be included using a CHARACTERIZED BY or CONDITIONAL PACKAGES tag. Inheritance property is achieved using a DERIVED FROM tag and the object class is registered with an identifier using a REGISTERED AS tag. Refer X.722 document for more details about GDMO and tags like ALLOMORPHIC, PARAMETERS, and SO on that are not discussed here. A sample managed object class template is shown below: <class> MANAGED OBJECT CLASS [DERIVED FROM <class> [,<class>]*;] [ALLOMORPHIC SET <class> [,<class>]*; [CHARACTERIZED BY <package> [, <package>]*;] [CONDITIONAL PACKAGES <package> PRESENT IF <condition> [, <package> PRESENT IF <condition>]*; [PARAMETERS <parameter> [, <parameter>]*;] REGISTERED AS <object-identifier>; This chapter gives the reader an overview on ASN.1, BER, and SMI. These con- cepts form an important part of coding the network management information framework. Fundamentals of EMS, NMS and OSS/BSS Additional Reading 1. ISO/IEC/JTC 1/SC 6. ISO/IEC 8825-1:2002, Information technology: ASN.1 encod- ing rules. Washington, DC: ANSI, 2007. 2. John Larmouth and Morgan Kaufmann. ASN.1 Complete. San Francisco, CA: Morgan Kaufmann Publishers, 1999. 3. Olivier Dubui