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UNIVERSITE D’OTTAWA
UNIVERSITY OF OTTAWA
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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
[email protected]
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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)
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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.
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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
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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.
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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.
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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 highbandwidth 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
TSERG GSM Network.
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PTP-CLNS
Connectionless Network
Service
PTP
Point to Point
GPRS Services
PTM
Point to Multipoint
PTP-CONS
Connection Oriented
Network Service
PTM-M
Multicast
PTM-G
Group Call
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GPRS PTP Services
• Retrieval services (www, Databases..).
• Messaging services which offer user-to-user
communication between individual users (store-andforward).
• 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, ..).
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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).
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GPRS Network Architecture
HLR
MSC/VLR
Gs
A
BTS
BSC Gb SGSN
Um
Cell
Gr
EIR
Gn
Gp
GGSN
GGSN
Gi
PDN
Other GPRS Network
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High Level Functions Required for GPRS
Network Access Control
Packet Routing and Transfer
•Registration
•Authentication and Authorization
•Admission Control
•Message Screening
•Packet Terminal Adaptation Charging Data Collection
Logical Link Management
•Relay
•Routing
•Address Translation and Mapping
•Encapsulation
•Tunneling
•Compression
•Ciphering
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
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Transmission Plane
IP/X.25
SNDCP
LLC
RLC/MAC
GSM RF
MS
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SNDCP GTP
LLC TCP/UDP
BSS
BSSGP
Frame Relay
IP / L2
L1bis
L1
SGSN
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IP/X.25
GTP
UDP / TCP
IP / L2
L1
GGSN
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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.
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An Example Scenario
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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.
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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.
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