TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 1 Prototyping and Validation of the General Packet Radio Service: A Data Service of GSM Telecommunications Software Engineering Research Group Brahim Ghribi, Laurent Andriantsiferana Luigi Logrippo

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 2 Research Goals Develop validated protocol suites and use cases for mobile systems Develop prototypes of these systems. This is done by using formal methods (LOTOS)

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 3 Why Develop a Formal Prototype? The protocols and services can be validated early during the standardization process. Ambiguities and errors can be detected and fixed before the implementation phase. Feedback and suggestions can be provided to the standardization committee. The prototype can provide a way to observe and simulate the behaviour of the system before the actual implementation.

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 4 Abstraction and separation of concerns not used Information is spread through out the draft documents Changes may have unknown global effects Incomplete details and ambiguities Slow process ==> A Need to address these issues by defining a methodology for Standard development Problems With Standards

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 5 LOTOS LOTOS (Language of Temporal Ordering Specifications) A formal Specification Language for Distributed Systems => An ISO standard Application Areas: Protocols, Telephony, Distributed Systems. Used for: Formal Specification, Design, Design Validation, Test Case Generation.

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 6 GSM GSM (Global System for Mobile Communications) is an open standard. Mainly voice (Telephony). Circuit switched connection (9.6 kbit/s). Sim (Subscriber Id Module) Roaming. SMS (Short Message Service). Updated to work at 1800MHz for the European PCN and at 1900 MHz for the PCS systems in the US.

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 7 GSM and Data HSCSD (High Speed Circuit Switched Data) is a new part of the GSM standard and will boost user capacity to 64 kbit/s. => Requires only new radio link protocol. GPRS (General Packet Radio Service) useful for high- bandwidth data. It will be ready for implementation by => rates up to 115 kbit/s. => Packet Switched data capability. => Requires additional functional elements to the existing GSM Network.

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 8 PTP Point to Point PTM Point to Multipoint PTP-CLNS Connectionless Network Service PTP-CONS Connection Oriented Network Service PTM-M Multicast PTM-G Group Call GPRS Services

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 9 GPRS PTP Services Retrieval services (www, Databases..). Messaging services which offer user-to-user communication between individual users (store-and- forward). Conversational services which provide bi-directional communication in real-time (no store-and-forward). Tele-action services which are characterized by short data transactions (credit card validations, electronic monitoring and surveillance,..).

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 10 GPRS PTM services Distribution services which provide uni-directional flow of information from a given point in the network to other multiple locations (news, weather and traffic reports,..). Dispatching services which provide bi-directional flow of information (Taxi, fleet services,..). Conferencing services which provide multi-directional communication by means of real-time information transfer between multiple users (PTM-Group call).

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 11 GPRS Network Architecture Cell BTS BSC SGSN Other GPRS Network GGSN PDN GGSN MSC/VLR HLR EIR Gi Gn Gp Gb Um A Gs Gr

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 12 Registration Authentication and Authorization Admission Control Message Screening Packet Terminal Adaptation Charging Data Collection Relay Routing Address Translation and Mapping Encapsulation Tunneling Compression Ciphering Logical Link Establishment Logical Link Maintenance Logical Link Release GPRS Attach and Detach Routing and Location Update PDP Context Activate/Deactivate Security Network Access ControlPacket Routing and Transfer Logical Link ManagementMobility Management Radio Resource Management High Level Functions Required for GPRS

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 13 GSM RF RLC/MAC LLC SNDCP IP/X.25 L1 IP / L2 UDP / TCP GTP IP/X.25 L1bis BSSGP Frame Relay LLC SNDCP L1 IP / L2 TCP/UDP GTP BSS MSSGSN GGSN Transmission Plane

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 14 Validation Activities By using various tools such as ELUDO (LOTOS toolkit developed at the University of Ottawa) and LOLA (developed at the University of Madrid) we can: Execute the LOTOS specification in a Step-by-Step mode. Generate a number of representative use cases, thus providing a set of behaviour scenarios. Generate finite state machines that can be used for verification such as model checking. Generate MSCs (Message Sequence Charts) to visually inspect the different scenarios.

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 15 An Example Scenario

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 16 Related Work Specification of GPRS PTM-Group call service using LOTOS (Pascal Forhan, Daniel Amyot). Emphasis on the service from the subscriber’s point of view. The specification simulates the service by providing the various functionalities specified in the standard such as: Initiating a group call, joining or leaving the call, etc.

TSERGPCS Workshop-98 UNIVERSITE D’OTTAWA UNIVERSITY OF OTTAWA SITE p 17 Future Work Similar work towards: - UMTS/IMT WIN (Wireless Intelligent Network) Services Investigate the application of SDL versus LOTOS in prototyping Wireless Networks This project is funded by: ARRC (Advanced Radio Data Research center) of MOTOROLA Canada. NSERC under an IOR grant.