1. Using AADL to Model a Protodol Stack Didier Delanote, Stefan Van Baelen, Wouter Joosen and Yolande Berbers Katholieke Universiteit Leuven

2. 2 Contents Modeling process Structural aspect Behavioral aspect Non-functional aspect Conclusion Discussion

3. 3 Modeling process Network architecture set of layers and protocols Layer collection of services offered to higher layers, using services from lower layers Service set of operations implemented using protocols Protocol format and semantics of messages specific to one layer

4. 4 layer 1 layer 2 layer n - 1 layer n layer 1 layer 2 layer n - 1 Modeling process protocol ninterface n layer n protocol n - 1interface n - 1 protocol 2 interface 2 protocol 1 interface 1 entity 1entity 2 OSI: Open Systems Interconnection reference model

5. 5 Modeling process UDP, ICMPinterface 4 Transport layer IP, ARPinterface 3 MAC interface 2 IEEE 802.3 interface 1 entity 1entity 2 Network layer Data link layer Ethernet layer Transport layer Network layer Data link layer Ethernet layer UDP/IP concrete protocol stack

6. 6 Modeling process Use AADL to model UDP/IP protocol stack What requirements should this model conform to? High-level Implementation independent Structured Precise Significant level of detail Unambiguous Complete Functional properties Non-functional properties

7. 7 Contents Modeling process Structural aspect Behavioral aspect Non-functional aspect Conclusion Discussion

8. 8 Structural aspect Let’s go back for a moment… Hardware and software description hardware, software and composite components predefined component categories execution platform components application software components composite components Processor Memory Device bus System Process Subprogram Threadgroup Thread Data

9. 9 Structural aspect AdaAADL package hardware + applicationsystem applicationprocess taskthread proceduresubprogram functionsubprogram subprogram parameter function callsubprogram call typedata component ……

10. 10 Structural aspect interface 4 Transport layer interface 3 interface 2 interface 1 entity 1 Network layer Data link layer Ethernet layer Model layer, socket, queue,… as packages of subprograms package Transport_Layer public -- data types data PDU_Length properties Language_Support::Data_Format=> Positive; end PDU_Length; data Receive_Fifo properties Language_Support::Data_Format=> Record; end Receive_Fifo; -- … -- subprograms subprogram Init end Init; subprogram Bind features socket: in parameter Network_Entity; end Bind; -- … end Transport_Layer;

11. 11 Structural aspect No generic software component in AADL Model protocol types as data components So how to model… a protocol layer a software cache a software fifo a socket …

12. 12 Structural aspect Packages represent logical grouping of component declarations AADL packages and Ada packages are similar Can we use packages to introduce structure in the model? ARP IP UDP/ICMP Ethernet layer UDP/ICMP-frame IP-frame Ethernet-frame

13. 13 Structural aspect Problem: packages are no more than grouped declarations no representation in model no semantic requirements that enforce package structure nested packages not allowed package Application public --public part of package -- Processes ------------ process UDPIPdriver end UDPIPdriver; … end Application;

14. 14 Contents Modeling process Structural aspect Behavioral aspect Non-functional aspect Conclusion Discussion

15. 15 Behavioral aspect Example subprogram Create_Socket features Domain : in parameter Domain; Con_Type : in parameter Connection; Protocol : in parameter Protocol; Socket_Handle : out parameter Valid_Handle; end Create_Socket; Allow to model method interfaces Calls in thread implementation Behavior of subprogram modeled with behavior annex

16. 16 Contents Modeling process Structural aspect Behavioral aspect Non-functional aspect Conclusion Discussion

17. 17 Non-functional aspect Add properties to analyze system for non-functional properties Some properties are easy to model pragma Priority (100); becomes Language_Support::Priority => 100; for Application_Task'Storage_Size use 2000; becomes SEI::RAMBudget => 2000.0 B; Others need to be calculated or measured Period => 5 ms; Compute_Execution_Time => 1 ms.. 2ms; Analyses depending on available properties Schedulability analysis Resource allocation analysis …

18. 18 Contents Modeling process Structural aspect Behavioral aspect Non-functional aspect Conclusion Discussion

19. 19 Conclusions Goals High-level Implementation-independent Structured Precise Significant level of detail Unambiguous Complete Functional properties Non-functional properties  is it possible to achieve these goals?

20. 20 Conclusions Goals High-level Implementation independent  rather implementation dependent Structured  packages, components and subprograms Precise Significant level of detail  using language compliance annex, behavior annex,… Unambiguous  close to implementation Complete Functional properties  structure, behavior and interfaces Non-functional properties  model or measure

21. 21 Conclusions Benefits graphical representation analysis mechanism Drawbacks same abstraction level as code similar effort  can we make it easier to build an AADL model?

22. 22 Contents Modeling process Structural aspect Behavioral aspect Non-functional aspect Conclusion Discussion