ASN.1 lecture v.0.2. Abstract Syntax Notation One. Máté J. Csorba

Transcription

1 ASN.1 lecture v.0.2 Abstract Syntax Notation One Máté J. Csorba 1

2 Contents Past, present and future of ASN.1 Why ASN.1? Tools and integration Training material Basic conventions, built-in types Tagging, extensions Subtyping, constraints, etc... Introduction to BER (PER skipped) Short examples 2

3 Credits Some of the material includes intellectual property from: Dr. Andreas Steffen, Zürcher Hochschule Winterthur Prof. John Larmouth, Salford University, UK Dr. György Réthy, János Zoltán Szabó, Test Competence Center, Ericsson Hungary 3

4 The stone-age Diagrams of bits and bytes - e.g. IPv4 (The earliest approach, simple and clear, but focusing totally on the bits-on-the-line.) Tool support not possible Extensibility support crude - based on reserved fields. 4

5 The stone-age Simple command lines in ASCII, e.g. Telnet Simple character mnemonics and error codes (e.g. 200 OK ) Simple comma-separated parameters Good for simple dialogues Extensibility by adding commands in V2, with unknown commands ignored by V1 systems 5

6 The bronze-age TLV and Tabular Notation Each PDU and each parameter has an ID (or Tag), a Length, and a Value Nested TLVs in TLVs? Tables list each parameter: Tabular Notation 6

7 And finally: ASN.1 ASN.1 was borne around 1982 First ASN.1 Standard (CCITT X.409) in 1984 International Standard : ITU-T X.680 to X.683 ISO/IEC to 4 There was a need for A means of syntax (data structure) specification Procedure (sequence) specification Test suite specification Validation And tools to support rapid implementation! 7

8 ASN.1: What is it? Describes the data exchanged between two communicating applications Supported by efficient encodings of the data Supports a diversity of operating systems and programming languages 8

9 ASN.1: What is it? Formal notation, supported by tools, means: no ambiguity validation is easier, at lower cost reduced time-to-market Translates easily, with tool support, into any programming language (C, C++, Java, Cobol, Pascal, and many others) Integration also with SDL 9

10 Abstract vs. Transfer Syntax *Taken from: Dr. Andreas Steffen, Zürcher Hochschule Winterthur 10

11 So. ASN.1 offers today. Wide use in a large range of industries: Keeping the lights burning Portable phones we need them Birthday presents on time Traffic lights Aircraft fly safely Multimedia standards Many other industrial sectors 11

12 So thanks to ASN.1 Without ASN.1: The lights go out! Portable phones don t work! Parcels get lost! X Traffic lights fail! X Aircraft fall from the sky! Your impending marriage suffers as Net Meeting fails! X X X X 12

13 The near future Recognition of: Separation of "abstract syntax" (content) from encoding Encoding rules Work continues on the full integration of ASN.1 with XML Use of ASN.1 in web services 13

14 Tool Vendors Adrenta Technologies ATOS Origin France Telecom R&D Nikolaus Computertechnik Objective Systems OSS Nokalva Talura Aps unigone * (according to ASN.1 consortium, ITU-T) 14

15 Ericsson s TITAN TTCN-3 test executor => Data definition language for protocol testing - Conformance - Interoperability - Load/stress - Regression In my time 15

16 And now for something completely different Next => Training material, prepare some coffee in the break! Recommended bookmark: 16

17 Abstract Syntax introduction *Taken from: Dr. György Réthy, TCC Ericsson 17

18 Structure of ASN.1 18

19 Recommended reading John Larmouth, ASN.1 Complete, Elsevier-Morgan Kaufmann, 1999 Downloadable PDF version: Olivier Dubuisson, ASN.1 - Communication between heterogeneous systems, Elsevier-Morgan Kaufmann, 2000 Downloadable PDF version: 19

20 Contents 1. Basic conventions 2. Built-in ASN.1 types (basics of tagging and extensibility) NULL, BOOLEAN, INTEGER, BIT STRING, OCTET STRING, ENUMERATED, SEQUENCE (OF), SET (OF), CHOICE, Character string types, time types, REAL, ANY & other hole types: EMBEDDED PDV, EXTERNAL, Unrestricted character string 3. Tagging - additions Types of tags, IMPLICIT, EXPLICIT, AUTOMATIC tagging, tagging rules 4. Subtyping & constraints Single value, value range, size constraint, type constraint, permitted alphabet, contained subtype, inner subtyping 5. Extensibility - further rules ASN.1 model of extensions, extension marker, exception identifier, extensibility rules, version brackets 20

21 Naming conventions -1 21

22 Naming conventions -2 22

23 Module definition 23

24 Contents 1. Basic conventions 2. Built-in ASN.1 types (basics of tagging and extensibility) NULL, BOOLEAN, INTEGER, BIT STRING, OCTET STRING, ENUMERATED, SEQUENCE (OF), SET (OF), CHOICE, Character string types, time types, REAL, ANY & other hole types: EMBEDDED PDV, EXTERNAL, Unrestricted character string 3. Tagging - additions Types of tags, IMPLICIT, EXPLICIT, AUTOMATIC tagging, tagging rules 4. Subtyping & constraints Single value, value range, size constraint, type constraint, permitted alphabet, contained subtype, inner subtyping 5. Extensibility - further rules ASN.1 model of extensions, extension marker, exception identifier, extensibility rules, version brackets 24

25 NULL, BOOLEAN 25

26 Integer 26

27 Bitstring 27

28 Octetstring 28

29 Enumerated 29

30 Enumerated, extension 30

31 Rules to extension 31

32 Sequence 32

33 Tagging example -1 33

34 When tags shall be distinct 34

35 Sequence additions 35

36 Extension of a Sequence 36

37 Rules for extension 37

38 Rules for extension 38

39 Rules for extension 39

40 Set 40

41 Set 41

42 Choice 42

43 Tagging example 2 43

44 When tags shall be distinct 44

45 Choice 45

46 Version brackets 46

47 Selection type 47

48 Sequence of and Set of 48

49 Object identifiers 49

50 Real 50

51 Restricted charstring types 51

52 Time types 52

53 Embedded PDV 53

54 External 54

55 Contents 1. Basic conventions 2. Built-in ASN.1 types (basics of tagging and extensibility) NULL, BOOLEAN, INTEGER, BIT STRING, OCTET STRING, ENUMERATED, SEQUENCE (OF), SET (OF), CHOICE, Character string types, time types, REAL, ANY & other hole types: EMBEDDED PDV, EXTERNAL, Unrestricted character string 3. Tagging - additions Types of tags, IMPLICIT, EXPLICIT, AUTOMATIC tagging, tagging rules 4. Subtyping & constraints Single value, value range, size constraint, type constraint, permitted alphabet, contained subtype, inner subtyping 5. Extensibility - further rules ASN.1 model of extensions, extension marker, exception identifier, extensibility rules, version brackets 55

56 Tagging example 3 56

57 Tagging 57

58 Tagging 58

59 Universal class tags 59

60 Module definition again 60

61 Contents 1. Basic conventions 2. Built-in ASN.1 types (basics of tagging and extensibility) NULL, BOOLEAN, INTEGER, BIT STRING, OCTET STRING, ENUMERATED, SEQUENCE (OF), SET (OF), CHOICE, Character string types, time types, REAL, ANY & other hole types: EMBEDDED PDV, EXTERNAL, Unrestricted character string 3. Tagging - additions Types of tags, IMPLICIT, EXPLICIT, AUTOMATIC tagging, tagging rules 4. Subtyping & constraints Single value, value range, size constraint, type constraint, permitted alphabet, contained subtype, inner subtyping 5. Extensibility - further rules ASN.1 model of extensions, extension marker, exception identifier, extensibility rules, version brackets 61

62 Subtyping 62

63 Subtyping 63

64 Subtyping 64

65 Subtyping 65

66 Subtyping 66

67 Subtyping 67

68 Contents 1. Basic conventions 2. Built-in ASN.1 types (basics of tagging and extensibility) NULL, BOOLEAN, INTEGER, BIT STRING, OCTET STRING, ENUMERATED, SEQUENCE (OF), SET (OF), CHOICE, Character string types, time types, REAL, ANY & other hole types: EMBEDDED PDV, EXTERNAL, Unrestricted character string 3. Tagging - additions Types of tags, IMPLICIT, EXPLICIT, AUTOMATIC tagging, tagging rules 4. Subtyping & constraints Single value, value range, size constraint, type constraint, permitted alphabet, contained subtype, inner subtyping 5. Extensibility - further rules ASN.1 model of extensions, extension marker, exception identifier, extensibility rules, version brackets 68

69 Exeption handling 69

70 Extension examples 70

71 Parameterization 71

72 Parameterization 72

73 Parameterization 73

74 Jump to the topic of coding BER Tagging Tag of ASN.1 types Encoding of different types 74

75 Basics of coding 75

76 Coding of tag values higher then 30 76

77 Coding of the length field 77

78 Coding of the length field 78

79 When the length is null 79

80 Encoding of tags 80

81 Null, Boolean and Enumerated 81

82 Integer 82

83 Choice 83

84 Octetstring 84

85 Bitstring 85

86 Sequence (of), Set (of) 86

87 Obj. ID. 87

88 Real, base 10 88

89 Real, base 2 89

90 Ellipsis 90

91 Time for some practice 91

92 Example 1 Given the definition Company ::= SET { name [0] IA5String, zipcode [1] IA5String, CitationType INTEGER, other ANY DEFINED BY CitationType } where the INTEGER value of CitationType can be 0 = INTEGER, 1 = REAL, or 2 BOOLEAN, which of the following values are valid? Assume tagging has been done accurately. 1. CyberReal, , 1, TRUE , Villaland, 0, , 450, HomeNet 4. SitCom, 1,

93 Example 2 A base-ball card value in XML syntax: <BBCard> <name>jorge Posada</name> <team>new York Yankees</team> <age>29</age> <position>c</position> <handedness>right-handed</handedness> <batting-average>0.277</batting-average> </BBCard> Definition in ASN.1 (type and value)? 93

94 Solution 2 ASN.1 notation: BBCard ::= SEQUENCE { name IA5String, team IA5String, age INTEGER, position IA5String, handedness ENUMERATED { left-handed, right-handed, ambidextrous }, batting-average REAL } 94

95 ASN.1 value: Solution 2 cont d player1 BBCard ::= { name Jorge Posada, team New York Yankees, age 29, position C, handedness right-handed, batting-average } 95

96 Example 3 The C data-structure for the base-ball card: typedef struct BBCard { char name [61] ; char team [61] ; short age ; char position [61] ; enum { left_handed = 0, right_handed = 1, ambidextrous = 2, } handedness ; float batting_average ; } BBCard ; Define in ASN.1 using subtyping/constraints! 96

97 Solution 3 BBCard ::= SEQUENCE { name IA5String (SIZE (1..60)), team IA5String (SIZE (1..60)), age INTEGER (1..100), position IA5String (SIZE (1..60)), handedness ENUMERATED { left-handed, right-handed, ambidextrous }, batting-average REAL } 97

98 Example 4 FooProtocol defined using ASN.1: FooProtocol DEFINITIONS ::= BEGIN FooQuestion ::= SEQUENCE { trackingnumber INTEGER, question VisibleString } FooAnswer ::= SEQUENCE { questionnumber INTEGER, answer BOOLEAN } END Example message (PDU): myquestion FooQuestion ::= { trackingnumber 5, question "Anybody there?" } Cookbook: Tags of a SEQUENCE : 30 an INTEGER: 02 a VisibleString: 1a "Anybody there?" in ASCII: 41 6e f f Encode using simple TLV triplets and XER! 98

99 Solution 4 TLV, 21 octets: a 0e 41 6e f f XER, 108 octets but more readable: <FooQuestion> <trackingnumber>5</trackingnumber> <question>anybody there?</question> </FooQuestion> 99