1. Second part needs improvement (encoding, Compilers)

2. What is ASN.1
Internationally standardised, vendor, platform & language independent notation for specifying data structures at a high level of abstraction
It is supported by encoding rules that determine the precise bit patterns to represent values of these data-structures that will be transferred over computer network.
It is supported by tools which map ASN.1 notation into data structure definition in a computer language of choice.
Q: Why we need vendor, platform & language independent notation
A: Telecommunication involves connection of many different IS produced by different vendors, running on different Oss and different microprocessors running SW developed using different languages. We still need to exchange date between all those Information Systems (IS s).
Q: What are “data structures at high level of abstraction A:

3. ASN.1 - Outline ASN.1 Specification ASN.1 Basic Encoding Rules
ASN.1 Compilers
ASN.1 & SDL

4. Abstract Syntax Notation 1 (ASN.1)
ASN.1 was defined by ISO, as generic means of allowing differing computer systems, with different internal data representations to interchange data.
ASN.1 is now extensively used by the ITU & ISO to define protocol headers and formats.
In OSI, ASN.1 is used to define presentation layer applications.

5. ASN.1 Standards X.680 (12/97) ASN.1: Specification of basic notation
X.681 (12/97) ASN.1: Information object specification
X.682 (12/97) ASN.1: Constraint specification
X.683 (12/97) ASN.1: Parameterization of ASN.1 specifications
X.690 (12/97) ASN.1 encoding rules - Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)
X.691 (12/97) ASN.1 encoding rules - Specification of Packed Encoding Rules (PER)

6. ASN.1 Introduction Basic Data Types
INTEGER,
BOOLEAN,
UFT8String and other
Production Mechanisms for constructing more complex data types
SEQUENCE, SEQUENCE OF
SET, SET OF
CHOICE and other
Elements for Structuring the ASN.1 specification
Modules, Module Headers
Exports/Imports Statements

7. ASN.1 Character Set
An ASN.1 item shall consist of a sequence of the characters:
A to Z
a to z
0 to 9
: = , { } < ( ) [ ] - ' " | & ^ * ; !
ASN.1 is case sensitive !
Font type (bold, italic, size …) is not significant

8. Naming Rules
Names of fields, elements & items can be arbitrarily long. Quite long names are common
Names of Types must start with uppercase
Names of Identifiers must start with lowercase
Production
Mechanism
Type Name
Person-type ::= SEQUENCE
{name VisibleString
age INTEGER,
employed BOOLEAN}
Identifier
Built-in, Simple Type

9. Built-In Types BOOLEAN Type INTEGER Type ENUMERATED Type
Has two values: TRUE and FALSE
INTEGER Type
Integer numbers … -2,-1, 0, 1, 2 …
ENUMERATED Type
- Enumeration is way to assign name (identifier) to integers
Example:
LeadTime-type ::= ENUMERATED
{ tomorrow (0),
three-day (1),
week (2)}
Latest ASN.1
doesn’t require
numbers

10. More Built-In Types REAL Type BIT STRING Type NULL Type
values: {mantissa , base 10, exponent -5} , 0 , PLUS-INIFINITY, MINUS-INFINITY
BIT STRING Type
value example: ‘ ’B or ‘B31’H (in Hex)
NULL Type
NULL Type has just one value: NULL
It is most often used in CHOICE constructs
E.G. Toys ::= CHOICE { cars Cars, dolls Dolls, none NULL}

11. ANY Type A type of type ANY can be set to any type
e.g. MyThing ::= ANY
This states that the definition of the type is beyond the scope of ASN.1
Sometimes is referring to items that are to be defined in future.

12. Object Identifier Type
Object identifiers are defining a globally unique naming space
Object identifier name space is defined by hierarchically allocated tree-structure
Each arc of the tree is labeled by a numeric value.
Global authorities are responsible for allocation of top level arcs
More local authorities are responsible for the lower-level arcs

13. Example Object Identifier
{iso standard 8571 pci (1)} or { }
Would each identify an object, “pci”, defined in ISO 8571.
With the following additional definition: ftam OBJECT IDENTIFIER ::= {iso standard 8571}
Above defined pci object may be then also uniquely identified as {ftam pci(1)}

14. Built-In Character String Types
PrintableString
old “telex” character set (not very useful today)
VisibleString
all printiable ASCII characters plus “space”
UTF8String
any character (form Egyptian hieroglyphs to ASCII)
Other like:
NumericString, TeletexString, VideotexString, IA5String, GraphicString, GeneralString, UniversalString, BMPString
Value Notation
simple: “This is example of value notation”
or more complex: {null,{0,0,4,29} cyrillicCapitalLetterIe, “ABC”}
Q:Why we would use different String types
A: Because different type are encoded in different length Visible sting 1 octet, while UTF8Sting 3-7 octets

15. Built-In Date/Time Types
UTCTime
two digits for year (+49, -50 from the current year)
value example: yymmddhhmmZ : Z (Z is for GMT)
GeneralizedTime
same as UTCTime but with four digits for year

16. Production
Each production consists of the following parts, on one or several lines, in order:
a name for the new collection of production sequences;
the characters ::=
one or more alternative collections of production sequences (defined later)
Example:
ClassMember ::= CHOICE {
student Student,
lecturer Lecturer }

17. SEQUENCE Production Mechanism
A SEQUENCE is a sequence of elements of differing type where the order is important.
Example Type notation: SEQUENCE {name IA5String, age INTEGER}
Value Notation: {name “John”, age 26}
A SEQUENCE OF is a sequence of elements of the same type where order is important.
Example Type notation: SEQUENCE OF INTEGER
Value Notation: {12,13,14}

18. SET Production Mechanism
A SET is a sequence of elements of differing type where the order is not important.
Example Type notation: SET { name IA5String, age INTEGER }
Value Notation: {age 26, name “John”,age 23, age 6}
A SET OF is a sequence of elements of the same type where the order is not important.
Example Type Notation: SET OF INTEGER
Example Value Notation: {12,13,14}
SETs are more expensive for encoding so SEQUENCES are preferable

19. Default & Optional Keyword DEFAULT Keyword OPTIONAL Example:
Identifies a default value for an element of a SEQUENCE or SET to be assumed if value for that element is not included
Keyword OPTIONAL
Identifies an element for which a value can be omitted
Example:
Person::= SEQUENCE {
name UTF8String,
number-of-parents INTEGER DEFAULT 2,
spouse-name UTF8String OPTIONAL }

20. CHOICE Production Mechanism
A CHOICE is an element that can be constructed as one of a finite set of types.
Example of type notation:
CHOICE {name IA5String, nickname IA5String , TFN INTEGER}
value notation :
{name:“Brad”} or {nickname:“Braddles” } or {TFN:123456}

21. Tagged types
A tagged type is a new type which is decoded and encoded identically to the type it derives from, but has a different tag
Tags are used to differentiate between items of the same base type
Example:
Flight ::= SEQUENCE { origin IA5String, stop [0] IA5String OPTIONAL, stop [1] IA5String OPTIONAL, destination IA5String }

22. Subtyping Simple Subtyping
INTEGER (1..56) subset of integers in the range of 1 to 56 inclusive
It is used to improve encoding efficiency (subtypes require less bytes for encoding then full length types)
Complex Subtyping involves using construct like:
SIZE, FROM
INTERSECTION, UNION, EXCEPT, ALL
Example of Complex Subtyping
INTEGER (ALL EXCEPT (1..20))
(“yes” UNION “no” UNION “maybe”)
PrintableString (SIZE (10)) limit to exactly 10 characters
PrintableString (SIZE (1..10))

23. Soft Typing
The value of ANY types can be constrained using the DEFINED BY syntax. Eg X.500 or CMIP;
Attribute ::= SEQUENCE {
type OBJECT IDENTIFIER,
value ANY DEFINED BY type }
This is sometimes called Soft Typing.

24. Soft typing
When receiving a message containing these messages, a presentation entity should in theory look in an "attribute catalogue", using the specific value of the "type" as a key.
The attribute catalogue will specify, among other things, contain the ASN.1 specification of the attribute values.

25. Soft Typing Example
TextBook ::= SEQUENCE { author IA5String, CitationType INTEGER, reference ANY DEFINED BY CitationType },
Type TextBook requires a list of CitationTypes defined elsewhere that specifies the ASN.1 type for each permitted value of INTEGER
Possible Values are: { author ”Milan Kundera", CitationType 0, reference IA5String "ISBN " }
or { author "Milan Kundera", CitationType 1, reference INTEGER 1995 }
or { author "Milan Kundera", CitationType 2, reference PrintableString ”Slowness" }

26. ASN.1 Macros
Macros are a mechanism for the user to define a new notation with which they can then construct and reference ASN.1 types or specify values of types.
Shorthand notation.

27. Example Macro
Suppose it is desired to have a notation for type definition of the form
PAIR TYPEX = TYPEY =
with a corresponding value notation allowing
(X = ----, Y = ----)
Where the and the ---- refer to any ASN.1 type and corresponding value respectively.
* Example from X.208

28. Production Rules
A macro definition consists of a set of "production rules", described in "Bakus-Naur" like form.
Several alternatives separated by "|"
Each alternative described by a list of "tokens", which can be:
place holders for ASN.1 types or values,
keywords enclosed within quotes, like "TYPEX", "=" or "=" in our example,
place holders for identifiers, or strings

29. Macro Definitions
A macro definition must always contain at least two production rules, called "TYPE NOTATION" and "VALUE NOTATION".
The "TYPE NOTATION", preceded by the MACRO name, can be used wherever a "type definition" is expected within the ASN.1 language,
the syntax defined in the "VALUE NOTATION" can be used to define a value for a type defined by a macro

30. Macro Type Notation PAIR MACRO ::= BEGIN TYPE NOTATION ::= “TYPEX” “=”
type (Local-type-1)
-- Expects any ASN.1 type and assigns it
-- to the variable Local-type-1;
“TYPEY”
type (Local-type-2)
-- Expects a second ASN.1 type and assigns
--it to the variable Local-type-2;

31. Macro Value Notation VALUE NOTATION ::= “(” “X” “=”
value (Local-value-1 Local-type-1)
-- Expects a value for the type in Local-type-1, and assigns it
-- to the variable Local-value-1;
“,” “Y” “=”
value (Local-value-2 Local-type-2)
-- Expects a value for the type in Local-type-2 and assigns it
-- to the variable Local-value-2;
<VALUE SEQUENCE {Local-type-1, Local-type-2}
::= {Local-value-1, Local-value-2}>
-- This “embedded definition” returns
-- the final value as the value
-- of a sequence of the two types.
“)”
END

32. Example Macro T1 ::= PAIR TYPEX = INTEGER TYPEY = BOOLEAN T2 ::= PAIR
TYPEX = VisibleString TYPEY = T1
Then a value of type T1 might be:
(X = 3, Y = TRUE)
and a value of type T2 might be:
(X = “Name”, Y = (X = 4, Y = FALSE))

33. Use of Macros in Protocol Definition
Its usually more important to know how to use a particular Macro than how to define new Macros.
The following protocols use ASN.1 Macros.
X.500
Directory Databases
ROSE
Remote operations
TCAP
IN protocol
X.509
Security Protocol
X.400
Messaging
Q.932
USSD
Supplementary Service Data for GSM
ISDN Supplementary Services
CMIP
Network Management
*This is list is by no way complete.

34. Structuring an ASN.1 Specification
ASN.1 definitions are defined in modules.
Modules contain a complete set of type definitions that are self contained.
Modules can import definitions from other modules, and export definitions to other modules.

35. EXPORTS/IMPORTS Statements
IMPORTS - specifies list of types defined in other modules
EXPORTS - specifies list of types defined in this module that are available for use in other modules
if EXPORTS statements is omitted all types are available
EXPORTS ; (empty list of types) means that nothing is available
IMPORTS/EXPORTS Statements are optional and if exist they should be located at the head of the module after BEGIN statement and before any type definition
Semicolon is used to terminate EXPORT/IMPORT statements

36. Example ASN.1 Module ExampleASN.1 DEFINITIONS ::= -- This is a comment
-- Start of module
BEGIN
EXPORTS Student;
-- This can be re-used in other definitions
Student ::= SEQUENCE {
-- A sequence order is important
age INTEGER,
name IA5String }
ClassRoom ::= SET OF Student
-- order is not important in a SET
END

37. Basic Encoding Rules
An abstract syntax is converted into a transfer syntax using an encoding rule.
ASN.1 has a set of basic encoding rules defined in ISO 8825/ X.209.
X.209 is very inefficient, so Packed Encoding Rules are defined which are more compact

38. Basic Encoding Rules Each data item is encoded to contain:
an identifier (tag or type)
a length indicating the size of the data field
a data, which contains the actual contents of the object.
an optional end-of-content flag if data length is unknown
Aligned on octet boundaries

39. Encoding Length - Definite Form
If length < 128, use a single byte, with the high bit set to zero.
if high bit is set to one, the low seven bits set to the length of length field.
The length is then encoded in that many bytes.
IDENTIFIER LENGTH CONTENTS
OCTETS OCTETS OCTETS
The number of octets in the contents octets.

40. Encoding length - Indefinite Form.
If length field has a value of 0 - i.e. [1000|0000].
The object is ended by sending two zero bytes.
IDENTIFIER LENGTH CONTENTS END OF
OCTETS OCTETS OCTETS CONTENTS
Indicates that the there
are no more contents octets.
Indicates that the end of contents, is used instead of length.

41. Basic Encoding Rules Constructor Types
Types contained within types, are sent in the content portion of the message.
Value B is a part of structure A.
Identifier and length of B is carried in content
part of A.
IDENTIFIER-A LENGTH-A IDENTIFIER-B LENGTH-B CONTENTS

42. ASN.1 Example Types PersonnelRecord ::= SET { Name,
title [0] VisibleString,
children [1] IMPLICIT SEQUENCE OF
ChildInformation DEFAULT {} }
ChildInformation ::= SET {
Name, dateOfBirth [0] Date}
Name:: = SEQUENCE {
givenName VisibleString,
familyName VisibleString}

43. ASN.1 Example Value { {givenName "John",familyName "Smith"},
A set of records with one value (John Smiths might be as follows);
{ {givenName "John",familyName "Smith"},
title "Director",
children
{{{givenName "Ralph",familyName "Smith"},
dateOfBirth " "},
{{givenName "Susan",familyName "Jones"},
dateOfBirth " "}} }

44. ASN.1 Example Encoding Personnel Record Length Contents
Set Length Contents
Name Length Contents
Visible- Length Contents
String
1A 04 "John"
Visible- Length Contents
1A 05 "Smith"
Title Length Contents
A0 0A Visible- Length Contents
1A 08 "Director'
(removed for brevity) ...

45. ASN.1 Example Encoding (cont)
[1] Length Contents
A Set Length Contents
31 IF Name Length Contents
Visible- Length Contents
String
1A 05 "Ralph"
Visible- Length Contents
1A 01 "T"
1A 05 "Smith"
(removed for brevity) ...

46. Packed Encoding Rules Specialised encoding based on the data type.
Only generates tags when they are needed to prevent ambiguity.
Only generates lengths when the size of an object can vary.
lengths represented in compact form.

47. Packed Encoding Rules Encoding not always aligned on byte boundaries
unless 'aligned' variant of the rules is used
Optional elements in a sequence are indicated by a list of single bit flags placed at the start of a sequence .

48. To implement a protocol defined in ASN.1
Hand code
or feed the ASN.1 specification in an "ASN.1 compiler", that will automatically generate the conversion routines.

49. ASN.1 Compilers Compiled Manual Develop an application Days Months
Update a protocol Hours Weeks
Achieve conformance Correct Test and
Input fail
Reliability of code Good Dubious
Debugging tools Yes ???
Speed of decoding Good Excellent...
...or poor
Respect of layering Natural Depends
on discipline

50. Using ASN.1 for Protocol Specification & Implementation.
ASN.1 compilers can be used to create C structures or C++ classes from ASN.1 specifications.
Public domain ASN.1 compilers available unfortunately, very few implement MACROs or SoftTyping required for most applications that use ASN.1

51. Comparison Between SDL and ASN.1
Definition of types X X
Notation for values X X
Definition of operators X
Expressions X
Encoding of values X

52. SDL and ASN.1 (ITU-Z.105)
Z.105 describes ways in which ASN.1 code can be directly included in SDL specifications.
Subset of both SDL and ASN.1 is used.
Describes how to use SDL combined with ASN.1 as follows:
the System structure and behavior are defined using SDL concepts
the parameters of signals are defined by ASN.1 types or SDL sorts
data can be defined with ASN.1 type definitions or with SDL sort definitions
encoding of ASN.1 data values can be defined by reference to the relevant encoding rules. Encoding is not in the scope of this Recommendation.

53. Other ways of using SDL and ASN.1
More common way is to describe structure and behavior using pure SDL
Separately describe data using ASN.1, using the same names in both ASN.1 and SDL
Encoding of ASN.1 data values using ASN.1 BER rules.

54. Use of ASN.1
From the approximately 1000 ETSI & ITU standards produced over the last 5 years roughly 10% make use of ASN.1
Extensively used in areas like ISDN supplementary services, IN protocols and GSM.
Tendency to use ASN.1 in specification of conformance tests even when the protocol specification is not defined in ASN.1

55. ASN.1 - Summary
Provides notation for specification of complex data types base on simple types and production rules
Specifies also how data values shall be specified
Defines Encoding rules which define how data will be represented between two systems (on the “line”)
ASN.1 Tools are available which provide support for ASN.1 data manipulation and encoding/decoding for various OSs and programming languages
ASN.1 can be used in conjunction with SDL

56. Summary: ASN.1Types, Values and BER
Abstract: message as it appears in an ETSI standard
(X.680)
MSG::= SEQUENCE
{ item1 INTEGER,
item2 STRING }
Value
MSG m1 { item1 123,
item2 "XYZ" }
Encoding Rules
Concrete: message as it is transferred over a real network
(X.690)
Bitstream … t