Network Protocol Design and Evaluation 04 - Protocol Specification, - PowerPoint PPT Presentation

Network Protocol Design and Evaluation 04 - Protocol Specification, Part III Stefan Rührup University of Freiburg Computer Networks and Telematics Summer 2009

Overview ‣ In previous parts of this chapter: • Modeling behaviour with state machines, state charts ‣ Part III: • Specifying data/message formats Network Protocol Design and Evaluation Computer Networks and Telematics 2 Stefan Rührup, Summer 2009 University of Freiburg

Data Format Specification ‣ Structuring data is part of the design process ... however, it is usually not of primary importance. ‣ Design decisions should not be driven by data format or encoding issues ‣ A defined data/message format and the corresponding encoding is important for the interoperability ‣ Some notation needed during the specification process (...and also for documentation) Network Protocol Design and Evaluation Computer Networks and Telematics 3 Stefan Rührup, Summer 2009 University of Freiburg

Tabular and Box Notation ‣ Tabular Notation • Listing of message fields with types, lengths and descriptions ‣ Box Notation • Table of message fields, where the size of the boxes indicate the field length • used by the IETF in RFCs Network Protocol Design and Evaluation Computer Networks and Telematics 4 Stefan Rührup, Summer 2009 University of Freiburg

Tabular Notation, Example C)&&*+)'-/5)D';EFGHCI#;GE @%+,%9%<*,<)D'J2<*8'=E2-)'!> K%1)<-%2,D'L2-$ 8&F$G%()*$&+"@"%"&) !"F"G"&#" I*G"#)*$& >JK" L"&E)M 1DH?#@(HD"6 M12-2<28'7%&<1%(%,*-21 N:O L2-$ C ! P*88'1)9)1),<) N:A L2-$ C'=E2-)'O> O?Q C)&&*+)'-/5) N:N L2-$ C ! @),7%,+'<2(58)-) N:" L2-$ G'=E2-)'A> ! K%&58*/ N:" G'=E2-)'N> =E2-)'"> ,' → '0 R)/5*7'9*<%8%-/ N:" G'=E2-)'S> O?AN 0' → ', @%+,*8 N:" G'=E2-)'B> O?A ,' → '0 P*88)7'5*1-/',0(.)1 N:" .2-$ G'=E2-)'T> O?Q Contents of an ISDN Information Message ISDN Basic Call Control Specification [ITU Q.931] Network Protocol Design and Evaluation Computer Networks and Telematics 5 Stefan Rührup, Summer 2009 University of Freiburg

Tabular and Box Notation, Example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eneral Message Organization and Message Types ISDN Basic Call Control Specification [ITU Q.931] Network Protocol Design and Evaluation Computer Networks and Telematics 6 Stefan Rührup, Summer 2009 University of Freiburg

Box Notation, Example ‣ Data format specification of the internet protocols ‣ TCP and IP packets have a header and a data part ‣ Header information: • destination address (IP) and port (TCP) • source address and port • TTL (IP), sequence number (TCP), and checksums (both) • flags and options • etc. Network Protocol Design and Evaluation Computer Networks and Telematics 7 Stefan Rührup, Summer 2009 University of Freiburg

Box Notation, Example (1) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL |Type of Service| Total Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identification |Flags| Fragment Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time to Live | Protocol | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ASCII Box Notation for the IPv4 Header Format [RFC 791] Network Protocol Design and Evaluation Computer Networks and Telematics 8 Stefan Rührup, Summer 2009 University of Freiburg

Box Notation, Example (2) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Acknowledgment Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data | |U|A|P|R|S|F| | | Offset| Reserved |R|C|S|S|Y|I| Window | | | |G|K|H|T|N|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Urgent Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ASCII Box Notation for the TCP Header Format [RFC 793] Network Protocol Design and Evaluation Computer Networks and Telematics 9 Stefan Rührup, Summer 2009 University of Freiburg

Box Notation and TLVs ‣ Box Notation • Intuitive way of describing a data format • Field types/encoding have to be specified separately • Limitations: no variable length fields ‣ Type-Length-Value (TLV) • Representation of variable size or optional message fields • Can be parsed without understanding the meaning of the field Network Protocol Design and Evaluation Computer Networks and Telematics 10 Stefan Rührup, Summer 2009 University of Freiburg

TLV Example 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Header Option1 Type Option1 Length Option1 Value 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Option1 Value Option2 Type Option2 Length +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option2 Value Padding | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Acknowledgment Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Data | Data | |U|A|P|R|S|F| | | Offset| Reserved |R|C|S|S|Y|I| Window | | | |G|K|H|T|N|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Urgent Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Field in the TCP Header [RFC 793] Network Protocol Design and Evaluation Computer Networks and Telematics 11 Stefan Rührup, Summer 2009 University of Freiburg

Getting more formal: ABNF ‣ Augmented Backus-Naur Form ‣ Defined in RFC 5234 (older def. in RFC 822) ‣ Definition language for some IETF protocols ‣ BNF describes context-free grammars (Chomsky 2) by derivation rules of the form < symbol> ::= expression ‣ Left side symbols: non-terminals , right side symbols: terminals and non-terminals ‣ Right side expression: sequence of symbols (or choice of sequences) Network Protocol Design and Evaluation Computer Networks and Telematics 12 Stefan Rührup, Summer 2009 University of Freiburg