Using AADL to Model a Protodol StackUsing AADL to Model a Protodol StackDidier Delanote, Stefan Van Baelen, Wouter Joosen and Yolande BerbersDidier Delanote, Stefan Van Baelen, Wouter Joosen and Yolande Berbers

Katholieke Universiteit LeuvenKatholieke Universiteit Leuven

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ContentsContents

• Modeling process• Structural aspect• Behavioral aspect• Non-functional aspect• Conclusion• Discussion

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Modeling processModeling 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

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layer 1

layer 2

layer n - 1

layer n

layer 1

layer 2

layer n - 1

Modeling processModeling process

protocol ninterface n interface nlayer

n

protocol n - 1

interface n - 1

interface n - 1

protocol 2interface 2 interface 2

protocol 1interface 1 interface 1

entity 1 entity 2

• OSI: Open Systems Interconnection reference model

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Modeling processModeling process

UDP, ICMP

interface 4 interface 4Transport layer

IP, ARPinterface 3 interface 3

MACinterface 2 interface 2

IEEE 802.3interface 1 interface 1

entity 1 entity 2

Network layer

Data link layer

Ethernet layer

Transport layer

Network layer

Data link layer

Ethernet layer

• UDP/IP concrete protocol stack

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Modeling processModeling 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

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ContentsContents

• Modeling process• Structural aspect• Behavioral aspect• Non-functional aspect• Conclusion• Discussion

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Structural aspectStructural 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

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Structural aspectStructural aspect

Ada AADL

package package

hardware + application system

application process

task thread

procedure subprogram

function subprogram

subprogram parameter subprogram parameter

function call subprogram call

type data component

… …

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Structural aspectStructural aspect

interface 4Transport 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_Layerpublic -- 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;

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Structural aspectStructural 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• …

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Structural aspectStructural 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

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Structural aspectStructural 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;

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ContentsContents

• Modeling process• Structural aspect• Behavioral aspect• Non-functional aspect• Conclusion• Discussion

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BehavioralBehavioral aspectaspect

• 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

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ContentsContents

• Modeling process• Structural aspect• Behavioral aspect• Non-functional aspect• Conclusion• Discussion

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Non-functional aspectNon-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• …

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ContentsContents

• Modeling process• Structural aspect• Behavioral aspect• Non-functional aspect• Conclusion• Discussion

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ConclusionsConclusions

• 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?

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ConclusionsConclusions

• 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

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ConclusionsConclusions

• Benefits• graphical representation• analysis mechanism

• Drawbacks• same abstraction level as code• similar effort

can we make it easier to build an AADL model?

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ContentsContents

• Modeling process• Structural aspect• Behavioral aspect• Non-functional aspect• Conclusion• Discussion