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<chapter>
  <header>
    <copyright>
      <year>1997</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
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          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
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    <title>Introduction</title>
    <prepared></prepared>
    <docno></docno>
    <date>2015-03-31</date>
    <rev>A</rev>
    <file>asn1_introduction.xml</file>
  </header>

  <p>The <c>ASN.1</c> application provides the following:</p>

  <list type="bulleted">
    <item>An ASN.1 compiler for Erlang, which generates encode and
    decode functions to be used by Erlang programs sending and
    receiving ASN.1 specified data.</item>
    <item>Runtime functions used by the generated code.</item>
    <item>Support for the following encoding rules:
    <list><item>Basic Encoding Rules (BER)</item>
    <item>Distinguished Encoding Rules (DER), a specialized form of
    BER that is used in security-conscious applications</item>
    <item>Packed Encoding Rules (PER), both the aligned and
    unaligned variant</item>
    </list>
    </item>
  </list>

  <section>
    <title>Scope</title>
      <p>This application covers all features of ASN.1 up to the 1997
      edition of the specification. In the 2002 edition,
      new features were introduced. The following features
      of the 2002 edition are fully or partly supported:</p>
      <list type="bulleted">
	<item>
	  <p>Decimal notation (for example, <c>"1.5e3</c>) for REAL values.
	  The NR1, NR2, and NR3 formats as explained in ISO 6093 are
	  supported.</p>
	</item>
	<item>
	  <p>The <c>RELATIVE-OID</c> type for relative object identifiers is
	  fully supported.</p>
	</item>
	<item>
	  <p>The subtype constraint (<c>CONTAINING</c>/<c>ENCODED BY</c>) to
	  constrain the content of an octet string or a bit string is
	  parsed when compiling, but no further action is taken. This
	  constraint is not a PER-visible constraint.</p>
	</item>
	<item>
	  <p>The subtype constraint by regular expressions (<c>PATTERN</c>)
	  for character string types is parsed when compiling, but no
	  further action is taken. This constraint is not a
	  PER-visible constraint.</p>
	</item>
	<item>
	  <p>Multiple-line comments as in C, <c>/* ... */</c>, are
	  supported.</p>
	</item>
      </list>
  </section>

  <section>
    <title>Prerequisites</title>
      <p>It is assumed that the reader is familiar with the Erlang
      programming language, concepts of OTP, and is familiar with the
      ASN.1 notation. The ASN.1 notation is documented in the standard
      definition X.680, which is the primary text. It can also be
      helpful, but not necessary, to read the standard definitions
      X.681, X.682, X.683, X.690, and X.691.</p>
      <p>A good book explaining those reference texts is
      Dubuisson: ASN.1 - Communication Between Heterogeneous Systems,
      is free to download at
      <url href="http://www.oss.com/asn1/dubuisson.html">http://www.oss.com/asn1/dubuisson.html</url>.</p>
  </section>

</chapter>

