Towards a High Quality Standards Development Process for

Towards a High Quality Standards Development Process for Mobile Telephony Luigi Logrippo Telecommunications SE Research Group School of Information. Technology and Engineering University of Ottawa, Canada luigi@site. uottawa. ca www. site. uottawa. ca/~luigi WIRELESS FORUM IX

Claudine Simson, Nortel. Networks VP recently identified “Correct and Unambiguous Standards and Specifications” as one of the challenges to be addressed by the Company WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 1

Importance of a correctly specified standard • Implementation is simplified (and possibly even automated) • Reduced reliance on testing, last minute ‘fixes’ • Interworking between different implementations has a better chance • Standard updates can be traced to affected code WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 2

The three stages of the standardization process in telecom • Stage 1: Specification of requirements, main functionalities, user view • Stage 2: Identification of components and messages. Protocol scenarios expressed in the form of Message Sequence Charts (MSCs) • Stage 3: Detailed description of the protocol WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 3

Issues • How to guarantee a disciplined, high-quality, development process among the three stages • How to specify properly each stage • How to guarantee consistency and traceability among the stages • How to obtain automatically implementations from Stage 3 • How to derive test cases from all stages • How to do design-time performance assessments (work by Prof. M. Woodside, Carleton University). WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 4

Relevant techniques at different design stages UCM MSC LOTOS SDL TTCN WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 5

Use Case Maps for Stage 1 A semi-formal notation for presenting sequences of abstract responsibilities in distributed systems. Matches well the abstract descriptions of Stage 1. Assignment of responsibilities to components to be added in stage 2. [Resource Manager] Failure Allocate Resources Timer Initiate. Call Status Reported WIRELESS FORUM IX [Timeout] [Switching Center] Get. Answer Get. No. Answer Towards a High Quality Standards Development Process for Mobile Telephony - 6

Use Case Maps basic notation WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 7

LOTOS • Language of Temporal Ordering Specification • Formal Description Technique • Process Algebra Properties • Interprocess Synchronization (rendezvous) • Appropriate for systems prototyping and validation • Several possible specification/representation styles • Higher level languages that map into LOTOS have been defined • Clear representation of system structures • Validation tools WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 8

From UCM to LOTOS Stubs Processes Or-Fork/Join [ ] operator Responsibilities Actions Components/maps Processes And-Fork/Join |[ ]| operator Rendezvous Synchronization Time. Outs Special Action WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 9

LOTOS Allows to Execute Stage 1 • Scenarios can be derived and validated • Message Sequence Charts can be derived • Functional Test Suites can be derived WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 10

Bound UCM between Stages 1 and 2 User System Resource Manager Failure Allocate Resources Timer Initiate. Call Status Reported WIRELESS FORUM IX [Timeout] Switching Center Get. Answer Get. No. Answer Towards a High Quality Standards Development Process for Mobile Telephony - 11

Stage 2: Message Sequence Chart Notation (MSCs) an ITU-T standard Originating System MSC Serving System HLR SCP VLR MSC MS call origination a LOCREQ [DGTSDIAL, TRANSCAP] b SERVREQ [SRVID, DGTSDIAL] SVRT servreq [ACTCODE, ALRTCODE] ROUTREQ [MIN, ALRTCODE] LRT RRT d e ROUTREQ [MIN, ALRTCODE] RRT routreq [TLDN] locreq [TERMLIST] c TLDNAT f g h i call setup j call setup [ALRTCODE] k (Example taken from WIN) WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 12

Stage 3: SDL • ITU-T’s Specification and Description Language • Appropriate for detailed specification of architectures and protocols • MSCs can be input to SDL and validated • Code can be obtained from SDL • Test suites can be obtained from SDL WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 13

Our method Requirements Architectural Model UCM Stage 1 scenarios Stage 2 Stage 3 Test Cases (TTCN) WIRELESS FORUM IX LOTOS scenarios MSCs SDL scenarios SDL Implementation Towards a High Quality Standards Development Process for Mobile Telephony - 14

Evaluation of method • Not limited to standards. – can be applied generally to software design – and probably also to hardware design, with adaptations • Intensive and rigorous at the design level • Simplifies significantly implementation, testing and probably maintenance WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 15

Patterns: towards an architectural approach to telecom software engineering (with R. Andrade) • Focus on common solutions to recurring problems regarding mobile wireless communication systems – requirements and analysis stages • Capture common behavior and architectural elements – documentation for legacy systems – source of initial design decisions for new systems (Wireless IP, IMT 2000) • Patterns can be validated (e. g. by using LOTOS methods) WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 16

Finding Patterns: authentication Use Case Maps System Descriptions WATM S e S a b c d e E 1 d E 2 Pattern Form Name Problem Context Forces Solution Resulting Context IMT-2000 S S a b c E 1 E 2 e d E 1 E 2 E 3 e S a b c GSM Common Behavior ANSI-41 a b c d E 3 e Stub e d E 1 E 2 WIRELESS FORUM IX S a b c E 1 E 3 Plug-in d E 2 Grap. Spec. of the Pattern Solution Towards a High Quality Standards Development Process for Mobile Telephony - 17

A Summary of the Authentication Pattern • Problem: Preventing unauthorized or fraudulent access to cellular networks by mobile stations illegally programmed with counterfeit identification and electronic serial number. • Solution: Perform an authentication operation in both the mobile station and the network sides based on an encryption algorithm and a secret key number. WIRELESS FORUM IX SAuth s. AI a. AA c. AR [a 1] n. S [a 2] E 2 Auth n. AD E 1 Auth Legend : Auth S : Start Authentication [a 1]: [Auth. Success] [a 2]: [Auth. Denied] s. AI : send Authentication Information a. AA: apply Auth. Algorithm c. AR : check Authentication Result n. S : notify Success n. AD : notify Access Denied Auth E 2 : end Successful Auth E 1 : end Unsuccessful Auth. Towards a High Quality Standards Development Process for Mobile Telephony - 18

Pattern Language • A collection of patterns that build on each other to generate a system Starting pattern potential sequences in which the patterns occur exchanges of data between two patterns WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 19

Reusability Common Solutions for Protocol Design Problems describes System Description with Different Techniques LOTOS Use Case Maps Patterns for Mobility and Radio Resource Management (Wm. ATMSwitch [ms_to_wsh, wsh_to_link, vlr_to_wsh] (zone_2) |[vlr_to_wsh]| VLR [vlr_to_wsh] (vlr_2, Initial. VLRSet 2)) Message Sequence Charts reuses Home Current Database Wm. ATMSwitch Initiate. Reg. REQ (user_A, info_A, zone_1) Initiate. Reg. CONF (user_A, zone_1) Auth. Usr. Result (user_A, zone_1, hlr_1, r) Auth. Usr ( user zone_1, hlr_1, info_A) _A, Auth. Net. Result (user_A, zone_1, hlr_1, r) Auth. Success (user_A, zone_1) Mobile. Station WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 20

Approach for Pattern Reuse 2 nd Development Cycle 1 st Development Cycle Requirements Capture (Stage 1) Requirements Model Unbound Use Case Maps Analysis (Stage 2) Analysis Model Bound Use Case Maps Design Model (Stage 2) LOTOS WIRELESS FORUM IX Patterns for Mobility and Radio Resource Management Scenario Model Message Sequence Charts Towards a High Quality Standards Development Process for Mobile Telephony - 21

Evaluation • Our patterns represent established expertise in the design domain • This method captures such expertise in a rigorous, implementation-independent way • Future designers of similar systems won’t have to ‘reinvent the wheel’ WIRELESS FORUM IX Towards a High Quality Standards Development Process for Mobile Telephony - 22