1. TTCN-3 and ASN.1 interworking Analysis of backward compatibility in ASN.1 Géza Horváth geza.horvath@nsn.com TTCN-3 User Conference 2011 7 – 9 June 2011 - Bled, Slovenia

2. 2© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Introduction Géza Horváth Release 4 Product Support Engineer Nokia Siemens Networks Joint Venture of Nokia and Siemens Started operations on April 1, 2007 65,000+ employees 75 of top 100 operators worldwide 150 countries 3 billion mobile subscribers and ¼ of world’s voice households served

3. 3© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Agenda Concept of ASN.1 – TTCN-3 Compatibility of ASN.1 Planning a comparator tool Result, future

4. 4© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth ASN.1 introduction Avoid the transfer of concrete syntax Vendor- and language- independent Recursive notation for complex data types Encoding rules ？

5. 5© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Using ASN.1 with TTCN-3 TTCN-3 provides a clean interface for using ASN.1 specifications: ETSI ES 201 873-7 Alternative data type and value syntax Implicit mapping: import Internal representation of imported objects Without any lost information

6. 6© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Agenda Concept of ASN.1 – TTCN-3 Compatibility of ASN.1 Planning a comparator tool Result, future

7. 7© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth The need of ASN.1 compatibility Extension marker ”...” – Specification v2 must include v1 Two compatible specifications are not necessarily syntactically identical Syntactic differences should be detected Semantics are very bound to syntax Two distinct specifications of the same protocol can be compared to evaluate the impact on the interface INTEGER(1..10) INTEGER(1..10,...)

8. 8© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Syntactic compatibility between ASN.1 specifications OPTIONAL keyword Extensible subtyping constraints Permutation of SET components What if v1 does not send the INTEGER to v2? We should know all the changes on the interface In case of SEQUENCE? What if v2 sends the value 11 to v1? Without the extensions marker?

9. 9© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Agenda Concept of ASN.1 – TTCN-3 Compatibility of ASN.1 Planning a comparator tool Result, future

10. 10© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Structure of the comparator Parser: syntactic error messages as well Transitive closure: checking references, imports Normalization: avoiding circular definitions

11. 11© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Comparator algorithm A diff-like (textual) algorithm? Detailed comparison algorithm on graphs! The goal is the find a matching between two trees Nodes of the two trees are numbered A global default mark is assigned to the root It is divided between each branch of the root, and so on recursively According to how each node matches with the corresponding one – The mark is inherited completely or – Decreased portionally to the result of the comparison Root PDU 1 PDU 2 statement 1 statement 2 Root PDU 1 PDU 2 statement 1 statement 2

12. 12© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Comparator algorithm Synthesised mark at highest level can be considered as the global level of syntactic mapping Compare each PDU of v1 to all PDU of v2 to determine the best matching

13. 13© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Agenda Concept of ASN.1 – TTCN-3 Compatibility of ASN.1 Planning a comparator tool Result, future

14. 14© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Result Simple semantic deductions based on syntactic differences – *Only notice, not incompatibility – **In some cases it can be incompatibility – ***Incompatibility Important to build up an effective visualization – A specification can be very huge

15. 15© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Extension for future Complete formalization of all the comparison rules – Fortunately the algorithm is easily extensible All the error messages are mainly syntactic Addition of the semantics in order to refine messages Integration with specification environment

16. 16© Nokia Siemens Networks TTCN-3 and ASN.1 interworking / Géza Horváth Thank you for your attention! Géza Horváth geza.horvath@nsn.com