Prototyping and Validation of the General Packet Radio Service: A Data Service of GSM

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 bghribi@csi.uottawa.ca

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)

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.

4. Problems With Standards • 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

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.

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.

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 1998 -1999. => rates up to 115 kbit/s. => Packet Switched data capability. => Requires additional functional elements to the existing GSM Network.

8. PTP-CLNS Connectionless Network Service PTP Point to Point PTP-CONS Connection Oriented Network Service GPRS Services PTM-M Multicast PTM Point to Multipoint PTM-G Group Call

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, ..).

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).

11. GPRS Network Architecture HLR MSC/VLR Gr Gs A EIR BTS Gn SGSN GGSN BSC Gb Um Gp Gi Cell PDN GGSN Other GPRS Network

12. High Level Functions Required for GPRS Network Access Control Packet Routing and Transfer • Relay • Routing • Address Translation and Mapping • Encapsulation • Tunneling • Compression • Ciphering • Registration • Authentication and Authorization • Admission Control • Message Screening • Packet Terminal Adaptation Charging Data Collection Logical Link Management Mobility Management • GPRS Attach and Detach • Routing and Location Update • PDP Context Activate/Deactivate • Security • Logical Link Establishment • Logical Link Maintenance • Logical Link Release Radio Resource Management

13. IP/X.25 IP/X.25 SNDCP SNDCP GTP GTP LLC LLC TCP/UDP UDP / TCP BSS RLC/MAC BSSGP Frame Relay IP / L2 IP / L2 GSM RF L1bis L1 L1 GGSN MS SGSN Transmission Plane

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.

15. An Example Scenario

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.

17. Future Work • Similar work towards: - UMTS/IMT-2000. - 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.