1. Jaringan Telekomunikasi, Sukiswo ST, MT Sukiswo sukiswok@yahoo.com
ASN.1 & BER
Sukiswo
Manajemen Jaringan, Sukiswo ST, MT

2. Manajemen Jaringan, Sukiswo ST, MT
Table of Contents
Abstract Syntax Notation One (ASN.1)
Overview
Properties & Restrictions
Type and Value Definitions
ASN.1 Simple Types
ASN.1 Structured Types
ASN.1 Macro Definitions
Basic Encoding Rules (BER)
Tags, Lengths & Values
Encoding Examples
Manajemen Jaringan, Sukiswo ST, MT

3. Manajemen Jaringan, Sukiswo ST, MT
Overview of ASN.1
a machine independent data description language
CCITT (X.208) and ISO (ISO 8824) standard
define abstract syntax of application data
define the structure of application and presentation protocol data units (PDUs)
define SNMP and OSI Management Information Base (MIB)
Manajemen Jaringan, Sukiswo ST, MT

4. Manajemen Jaringan, Sukiswo ST, MT
ASN.1 Terminology
Abstract Syntax
describes the generic structure of data
allows data types and values to be defined
Data Type
a named set of values -- may be simple or structured
Encoding
sequence of octets used to represent a data value
Encoding Rules
specifies the mapping from one syntax to another
Transfer Syntax
describes how data are actually represented in terms of bit patterns while in transit
Manajemen Jaringan, Sukiswo ST, MT

5. Abstract & Transfer Syntaxes
Jaringan Telekomunikasi, Sukiswo ST, MT
Abstract & Transfer Syntaxes
Application
component
data transfer
(e.g, TCP, OSI
session)
Local storage
(e.g, MIB)
User
local
mapping
user presentation
Abstract
Syntax
(e.g., ASN.1)
encoding
rules
Transfer
(e.g., BER)
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6. Manajemen Jaringan, Sukiswo ST, MT
ASN.1 Module Definition
The basic building block of an ASN.1 specification is the module
See Figure B.2 (BNF grammar for ASN.1)
Modules have the following basic form
<modulereference> DEFINITIONS ::=
BEGIN
EXPORTS
IMPORTS
AssignmentList
END
Definitions in this module that may be imported by other modules.
Definitions that are to be imported from other modules.
Type assignments, value assignments, and macro definitions that are defined in this module.
Manajemen Jaringan, Sukiswo ST, MT

7. Manajemen Jaringan, Sukiswo ST, MT
Lexical Conventions
Comments begin with two hyphens (“--”) and terminated either by another set (“--”) or the end of line character
Identifiers begin with a letter, and may contain letters, digits, and hyphens, but may not end with a hyphen or contain two consecutive hyphens
Manajemen Jaringan, Sukiswo ST, MT

8. Manajemen Jaringan, Sukiswo ST, MT
Lexical Conventions
The type identifier must start with an uppercase letter
The value identifier must start with a lowercase letter
Reserved keywords are all uppercase
Multiple spaces and blank lines can be considered as a single space
Manajemen Jaringan, Sukiswo ST, MT

9. Categories of ASN.1 Data Types
Simple (Primitive)
atomic types, with no components
Structured
types with components
Tagged
types derived from other types
Other
CHOICE and ANY types
Manajemen Jaringan, Sukiswo ST, MT

10. Categories of ASN.1 Data Types
Every ASN.1 data type, with the exception of CHOICE and ANY types, has an associated TAG, which consists of a class name and nonnegative integer tag number
Manajemen Jaringan, Sukiswo ST, MT

11. Manajemen Jaringan, Sukiswo ST, MT
Classes of TAG
UNIVERSAL
Built-in types, application independent types
See Table B.2
APPLICATION
Application specific types
CONTEXT-SPECIFIC
limited to a context within an application
PRIVATE
defined by users and not covered by any standard
Manajemen Jaringan, Sukiswo ST, MT

12. Manajemen Jaringan, Sukiswo ST, MT
ASN.1 Simple Types
INTEGER
the positive and negative whole numbers, including zero
OCTET STRING
a sequence of zero or more octets (8-bit bytes)
OBJECT IDENTIFIER (OID)
the set of values associated with information objects allocated by the standard
NULL
the single value NULL
Other ASN.1 simple types include boolean, bit string, real, enumerated, PrintableString, etc.
Manajemen Jaringan, Sukiswo ST, MT

13. Manajemen Jaringan, Sukiswo ST, MT
ASN.1 Structured Types
SET
a collection of one or more types
SET OF
a collection of zero or more occurrences of a given type
SEQUENCE
an ordered collection of one or more types
SEQUENCE OF
an ordered collection of zero or more occurrences of a given type
CHOICE
a list of alternatives
Manajemen Jaringan, Sukiswo ST, MT

14. Manajemen Jaringan, Sukiswo ST, MT
ASN.1 Example
Informal Description of Personnel Record
Name: James W Hong
Title: Associate Professor
Employee Number:
Date of Hire: May 26, 1995
Name of Spouse: In-Young B Hong
Number of Children: 2
Child Information
Name: Suk D Hong
Date of Birth: 29 March 1988
Name: Myungdo M Hong
Date of Birth: 10 August 1994
Manajemen Jaringan, Sukiswo ST, MT

15. ASN.1 Description of the Record Structure
PersonalRecord ::= [APPLICATION 0] IMPLICIT SET {
Name,
title [0] VisibleString,
number EmployeeNo,
dateOfHire [1] Date,
nameOfSpouse [2] Name,
children [3] IMPLICIT SEQUENCE OF ChildInfo
DEFAULT {} }
ChildInfo ::= SET {
dateOfBirth [0] Date}
Name ::= [APPLICATION 1] IMPLICIT SEQUENCE {
givenName VisibleString,
initial VisibleString,
familyName VisibleString}
EmployeeNo ::= [APPLICATION 2] IMPLICIT INTEGER
Date ::= [APPLICATION 3] IMPLICIT VisibleString
Manajemen Jaringan, Sukiswo ST, MT

16. Jaringan Telekomunikasi, Sukiswo ST, MT
ASN.1 Description of a Record Value
{ {givenName “James”, initial “W”, familyName “Hong”},
title “Associate Professor”
number
dateOfHire “ ”
nameOfSpouse {givenName “In-Young”, initial “B”,
familyName “Hong”},
children
{ { {givenName “Suk”, initial “D”,
dateOfBirth “ ”},
{ {givenName “Myungdo”, initial “M”,
dateOfBirth “ ”} }
Manajemen Jaringan, Sukiswo ST, MT 4

17. Jaringan Telekomunikasi, Sukiswo ST, MT
ASN.1 Macro Definitions
ASN.1 macro notation can be used to extend the syntax of ASN.1 to define new types and values
a macro definition is expressed in the macro notation and used to define a set of macro instances
a macro instance is generated from a macro definition by substituting values for variables
the macro is used to extend the ASN.1 syntax but does not extend the encoding
Manajemen Jaringan, Sukiswo ST, MT 4

18. Macro Definition Format
Jaringan Telekomunikasi, Sukiswo ST, MT
Macro Definition Format
<macroname> MACRO ::=
BEGIN
TYPE NOTATION ::= <new-type-syntax>
VALUE NOTATION ::= <new-value-syntax>
<supporting-productions>
END
Manajemen Jaringan, Sukiswo ST, MT 4

19. Macro Definition Example
Jaringan Telekomunikasi, Sukiswo ST, MT
Macro Definition Example
OBJECT-TYPE MACRO ::=
BEGIN
TYPE NOTATION ::= “SYNTAX” type (TYPE ObjectSyntax)
“ACCESS” Access
“STATUS” Status
VALUE NOTATION ::= value (VALUE ObjectName)
Access ::= “read-only” | “read-write” | “write-only” |
“not-accessible”
Status ::= “mandatory” | “optional” | “obsolete”
END
Manajemen Jaringan, Sukiswo ST, MT 4

20. Overview of BER Fields of a BER encoded ASN.1 value
BER – Basic Encoding Rules
an encoding specification
CCITT (X.209) and ISO (ISO 8825) standard
describes a method for encoding values of each ASN.1 type as a string of octets
based on the use of a type-length-value (TLV) structure
Type
Length
Value
Fields of a BER encoded ASN.1 value
Manajemen Jaringan, Sukiswo ST, MT

21. Jaringan Telekomunikasi, Sukiswo ST, MT
BER Type Field
Class
BIT 8 7 6 5 4 3 2 1
Constructed
Most significant
Least significant
Tag number
CLASS
Bit 8
Bit 7
Description
Universal
Built-in types
Application 1
SNMP defined types
Context-Specific 1
Used in context
Private 1 1
Not used in the SNMP protocol
Manajemen Jaringan, Sukiswo ST, MT 4

22. Tag Values for SNMP Types
Jaringan Telekomunikasi, Sukiswo ST, MT
Tag Values for SNMP Types
Type
SNMPv1
protocol
SNMPv2
ASN.1 Tag
Tag
Number
Value
INTEGER/Integer32
OCTET STRING
NULL
OBJECT IDENTIFIER
SEQUENCE
IpAddress
Counter/Counter32
Gauge/Gauge32
TimeTicks
Opaque
Counter64
UNIVERSAL 2
UNIVERSAL 4
UNIVERSAL 5
UNIVERSAL 6
UNIVERSAL 16
APPLICATION 0
APPLICATION 1
APPLICATION 2
APPLICATION 3
APPLICATION 4
APPLICATION 6
0x02
0x04
0x05
0x06
0x10
0x00
0x01
0x03
0x30
0x40
0x41
0x42
0x43
0x44
0x46
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23. Manajemen Jaringan, Sukiswo ST, MT
Encoding Methods
The TLV structure is recursive – for any ASN.1 value that consists of one or more components, the “value” portion of its TLV encoding itself consists of one or more TLV structures
Three methods for encoding an ASN.1 value:
Primitive, definite-length encoding
Constructed, definite-length encoding
Constructed, indefinite-length encoding
The method chosen depends on the ASN.1 type of the value to be encoded and whether or not the length of the value is known based on the type (see Table B.4)
Manajemen Jaringan, Sukiswo ST, MT

24. Jaringan Telekomunikasi, Sukiswo ST, MT
BER Length Field
two forms of length field exist:
short form: specified in a single octet
long form: specified in multiple octets
Value
= 102 1
Short(0)/Long(1) form indicator
Value 1 1 1 1 1 1
Short/Long form indicator =
Length of length
Length value
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25. BER Examples - Integers
Jaringan Telekomunikasi, Sukiswo ST, MT
BER Examples - Integers 1
Tag Universal 2
Length 1
Value 0
What value was encoded? 1
Tag Universal 2
Length 2
Value (1 of 2)
Value (2 of 2)
What value was encoded?
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26. BER Example - Octet String
Jaringan Telekomunikasi, Sukiswo ST, MT
BER Example - Octet String 1
Tag Universal 4
Length 4
1st octet
2nd octet
3rd octet
4th octet
Overall Length = 6
Value of Octet String encoded is ‘EB069937’
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27. Jaringan Telekomunikasi, Sukiswo ST, MT
BER Example - SEQUENCE
Message ::= SEQUENCE {
version INTEGER { version-1(0) },
community OCTET STRING }
Given the above definition,
what is the BER encoding of
sampleMessage ::= { 0, ‘EB069937’h } ?
Manajemen Jaringan, Sukiswo ST, MT 4

28. Jaringan Telekomunikasi, Sukiswo ST, MT
... and its BER encoding is 1
Value (6 of 9) OCTET STRING
Value (7 of 9) OCTET STRING
Value (8 of 9) OCTET STRING
Value (1 of 9) integer
Value (2 of 9) integer
Value (3 of 9) integer
Tag universal 16
Length 9
Value (4 of 9) OCTET STRING
Value (5 of 9) OCTET STRING
Value (9 of 9) OCTET STRING
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29. Manajemen Jaringan, Sukiswo ST, MT
Summary
We have covered a subset of ASN.1 and BER which are used in SNMP and OSI Management Frameworks
ASN.1 is widely used in defining application data and protocol data units
BER is widely used in defining transfer syntaxes
READ:
Stallings, SNMP, SNMPv2, SNMPv3 and RMON 1 and 2, 3rd Edition, Addison-Wesley, Appendix B
Manajemen Jaringan, Sukiswo ST, MT