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<chapter>
  <header>
    <copyright>
      <year>1997</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
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      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
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    <title>SNMP Introduction</title>
    <prepared></prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date></date>
    <rev></rev>
    <file>snmp_intro.xml</file>
  </header>
  <p>The SNMP development toolkit contains the following parts:
    </p>
  <list type="bulleted">
    <item>An Extensible multi-lingual SNMP agent, which understands SNMPv1
     (RFC1157), SNMPv2c (RFC1901, 1905, 1906 and 1907), SNMPv3
     (RFC2271, 2272, 2273, 2274 and 2275), or any combination of
     these protocols.
    </item>
    <item>A multi-lingual SNMP manager.
    </item>
    <item>A MIB compiler, which understands SMIv1 (RFC1155, 1212, and
     1215) and SMIv2 (RFC1902, 1903, and 1904).
    </item>
  </list>
  <p>The SNMP development tool provides an environment for
    rapid agent/manager prototyping and construction. With the 
    following information provided, this tool is used to set up a 
    running multi-lingual SNMP agent/manager:
    </p>
  <list type="bulleted">
    <item>a description of a Management Information Base (MIB) in
     Abstract Syntax Notation One (ASN.1)
    </item>
    <item>instrumentation functions for the managed objects in the MIB,
     written in Erlang.
    </item>
  </list>
  <p>The advantage of using an extensible (agent/manager) toolkit is to 
    remove details such as type-checking, access rights, Protocol Data Unit
    (PDU), encoding, decoding, and trap distribution from the
    programmer, who only has to write the instrumentation functions,
    which implement the MIBs. The <c>get-next</c> function only
    has to be implemented for tables, and not for every variable in
    the global naming tree. This information can be deduced from the
    ASN.1 file.
    </p>

  <section>
    <title>Scope and Purpose</title>
    <p>This manual describes the SNMP development tool,
      as a component of the Erlang/Open Telecom Platform development
      environment. It is assumed that the reader is familiar with the
      Erlang Development Environment, which is described in a separate
      User's Guide.</p>
  </section>

  <section>
    <title>Prerequisites</title>
    <p>The following prerequisites
      is required for understanding the material in the SNMP
      User's Guide:
      </p>
    <list type="bulleted">
      <item>the basics of the Simple Network Management Protocol
       version 1 (SNMPv1)
      </item>
      <item>the basics of the community-based Simple Network
       Management Protocol version 2 (SNMPv2c)
      </item>
      <item>the basics of the Simple Network Management Protocol
       version 3 (SNMPv3)
      </item>
      <item>the knowledge of defining MIBs using SMIv1 and SMIv2
      </item>
      <item>familiarity with the Erlang system and Erlang programming
      </item>
    </list>
    <p>The tool requires Erlang release 4.7 or later.
      </p>
  </section>

  <section>
    <title>Definitions</title>
    <p>The following definitions are used in the SNMP User's Guide.
      </p>
    <taglist>
      <tag>MIB</tag>
      <item>The conceptual repository for management information is
       called the Management Information Base (MIB). It  does not
       hold any data, merely a definition of what
       data can be accessed.  A definition of an MIB is a
       description of a collection of managed objects.
      </item>
      <tag>SMI</tag>
      <item>The MIB is specified in an adapted subset of the Abstract
       Syntax Notation One (ASN.1) language.  This adapted subset is
       called the Structure of Management Information (SMI).
      </item>
      <tag>ASN.1</tag>
      <item>ASN.1 is used in two different ways in SNMP.  The SMI is
       based on ASN.1, and the messages in the protocol are defined by
       using ASN.1.
      </item>
      <tag>Managed object</tag>
      <item>
        <p>A resource to be managed is represented by a managed
          object, which resides in the MIB. In an SNMP MIB, the managed
          objects are either:</p>
        <list type="bulleted">
          <item><em>scalar variables</em>, which have only one instance
           per context. They have single values, not multiple values like
           vectors or structures.
          </item>
          <item><em>tables</em>, which can grow dynamically.
          </item>
          <item>a <em>table element</em>, which is a special type of
           scalar variable.</item>
        </list>
      </item>
      <tag>Operations</tag>
      <item>SNMP relies on the three basic operations: get (object),
       set (object, value) and get-next (object).
      </item>
      <tag>Instrumentation function</tag>
      <item>An instrumentation function is associated with each
       managed object. This is the function, which actually implements
       the operations and will be called by the agent when it receives
       a request from the management station.</item>
      <tag>Manager</tag>
      <item>A manager generates commands and receives notifications 
       from agents. There usually are only a few managers in a system.</item>
      <tag>Agent</tag>
      <item>An agent responds to commands from the manager, and sends
       notification to the manager. There are potentially many agents 
       in a system.</item>
    </taglist>
  </section>

  <section>
    <title>About This Manual</title>
    <p>In addition to this introductory chapter, the SNMP User's Guide
      contains the following chapters:
      </p>
    <list type="bulleted">
      <item>Chapter 2: "Functional Description" describes the features
       and operation of the SNMP development toolkit. It includes
       topics on Sub-agents and MIB loading, Internal MIBs, and Traps.
      </item>
      <item>Chapter 3: "The MIB Compiler" describes the features and the
       operation of the MIB compiler.
      </item>
      <item>Chapter 4: "Running the application" describes how to start and
       configure the application. Topics on how to debug the application 
       are also included.
      </item>
      <item>Chapter 5: "Definition of Agent Configuration Files" is a
       reference chapter, which contains more detailed information about
       the agent configuration files.
      </item>
      <item>Chapter 6: "Definition of Manager Configuration Files" is a
       reference chapter, which contains more detailed information about
       the manager configuration files.
      </item>
      <item>Chapter 7: "Agent Implementation Example" describes how an MIB
       can be implemented with the SNMP Development Toolkit. 
       Implementation examples are included.
      </item>
      <item>Chapter 8: "Instrumentation Functions" describes how
       instrumentation functions should be defined in Erlang for the
       different operations.
      </item>
      <item>Chapter 9: "Definition of Instrumentation Functions" is a
       reference chapter which contains more detailed information
       about the instrumentation functions.
      </item>
      <item>Chapter 10: "Definition of Agent Net if" is a reference chapter,
       which describes the Agent Net if function in detail.
      </item>
      <item>Chapter 11: "Definition of Manager Net if" is a reference chapter,
       which describes the Manager Net if function in detail.
      </item>
      <item>Chapter 12: "Advanced Agent Topics" describes sub-agents, agent
       semantics, audit trail logging, and the consideration of
       distributed tables.
      </item>
      <item>Appendix A describes the conversion of SNMPv2 to SNMPv1
       error messages.
      </item>
      <item>Appendix B contains the RFC1903 text on <c>RowStatus</c>.
      </item>
    </list>
  </section>

  <section>
    <title>Where to Find More Information</title>
    <p>Refer to the following documentation for more information about
      SNMP and about the Erlang/OTP development system:
      </p>
    <list type="bulleted">
      <item>Marshall T. Rose (1991), "The Simple Book - An
       Introduction to Internet Management", Prentice-Hall
      </item>
      <item>Evan McGinnis and David Perkins (1997), "Understanding SNMP
       MIBs", Prentice-Hall
      </item>
      <item>RFC1155, 1157, 1212 and 1215 (SNMPv1)
      </item>
      <item>RFC1901-1907 (SNMPv2c)
      </item>
      <item>RFC1908, 2089 (coexistence between SNMPv1 and SNMPv2)
      </item>
      <item>RFC2271, RFC2273 (SNMP std MIBs)
      </item>
      <item>the Mnesia User's Guide
      </item>
      <item>the Erlang 4.4 Extensions User's Guide
      </item>
      <item>the Reference Manual
      </item>
      <item>the Erlang Embedded Systems User's Guide
      </item>
      <item>the System Architecture Support Libraries (SASL) User's
       Guide
      </item>
      <item>the Installation Guide
      </item>
      <item>the Asn1 User's Guide
      </item>
      <item>Concurrent Programming in Erlang, 2nd Edition (1996),
       Prentice-Hall, ISBN 0-13-508301-X.
      </item>
    </list>
  </section>
</chapter>

