extending ccm for real-time. assessment on a umts … · assessment on a umts protocol case study....
TRANSCRIPT
Aug
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OMG SBC Workshop 2004
Extending CCM for real-time. Assessment on a UMTS protocol case study.
Vincent Seignole1, Virginie Watine1,
Sylvain Robert2, Ansgar Radermacher2,
Sébastien Gérard2, François Terrier2
2 CEA-LIST CEA Saclay 91191 Gif sur Yvette France
1 THALES/ALICE pilot programme THALES 91300 Massy France
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Context
RT and embedded systems sw-engineering via composition
motivations
Communication equipments less and less dedicated to specific functions
become multi-functions, multi-usage, need migration to modular design
partially open
may not be able to know completely at design time all functions they will execute
relevance of the component-based approach
provides systematic approach to deal with complexity and reuse
natural modularity of resulting system
ultimate goals (among others) :
have a library of components running on standard and common platform
allow to focus more independently on integration of components and on component programming
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Context (cont')
Component-based approach
on its way since some years in mainstream systems
needs adaptations to apply to real-time and embedded :
provision of real-time environment
richer, configurable inter-components interaction support
Topics for present talk:adaptation of Lw-CCM via:
introduction of an extensible CCM container able to support real-time features
introduction of a framework to integrate custom components interactions
confrontation with a communication system example
inspired from UMTS protocols layering at user equipment side
allows to assess and validate the developed approach.
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Presentation outline
Review of CORBA Component Model aspectsingredients, role, process
Presentation of CCM extension strategyi.e how it can be opened to handle some real-time aspectsand integrate connector notions to allow custom interactions
Confrontation with communication applicationbrief descriptionconnectors to capture and factorize recurring mechanisms for protocols inter-layers interactions
Conclusions and future work
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Review of CCM features
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Review of CCM features
a component modeldescription of components
provided/required services
events published/consumed
an execution environmentContainers
provide a templated usage of CORBAshield component developers from middleware technical concerns
underlying CORBA middleware support
a packaging modelsoftware-package formatself-descriptive : contents, dependencies
a deployment infrastructurecomponents assembly descriptors + runtime support
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CCM features review : development process / roles
different separated rolescomponent providerprovides implementationprovides packaged compnt
container providerprovides container with
adequate non-func support
integrator i.e provides assembly
description, configuration and use deployment tools to set up whole system.
8 Aug
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CCM extension strategy : on customizable interactions support
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Answering the need for CCM interactions improvement
Only basic interactions natively supported by CCMsynchronous method invocation(1,n) push-push typed events propagation
Wide variety of architectural styles in RT-systemsExamples are:pipes and filters
very classical in the communication protocols domain
variants of publish-subscribepush/pull, typed / untyped events
blackboard pattern
Goal: allow these kinds of architectural styles (and others) in CCM
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Answering the needs for CCM interaction improvements
ADLs presently introduce the concept of connectorsseparation between components and connectors
Components : functional entities
Connectors : interaction entities
We follow these ideas and introduce connectors in CCMto realize the interactions needed
behind well-defined interfaces, with suitable configuration mechanisms
in a reusable manneri.e do packaging of connectors
including : connector binaries, description, and code generation plugins for particular connectors that need it.
we are also lead to define new kinds of components' portswill correspond to “connector” interface for component role in a particular interaction.
goal : have a reusable Connector / Port types library.may be engineering domain specific (example : protocol domain)
11 Aug
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Analysis of main interaction patterns in real-time systems
Analysis :goal was to list main interaction mechanisms familiesBroad review of technologies
RTOSes, real-time middlewares, design platforms
classification follows spirit of paper :“Towards a taxonomy of software connectors”, by N.R Mehta, N. Medvidovic, S. Phadke, ICSE 2000but differs in some points
Results :Characterization of an interaction is done via:
the participants in the interaction (roles and cardinalities),
the type of service (communication or/and synchronization, ...)
QoS features (synchronicity, dynamic behavior, ...)
Three primitive connector typesMessage, Event, Procedure call
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Analysis of main interaction patterns in real-time systems
Characterization of a Message Connector (subsetted)
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CCM Extension strategy : custom interactions
Integration of connectors solution involvesprovision of description mechanisms for connectors for new kinds of ports, for usage of them
provision of framework for implementation of connectorsor for code generation plugins (in case of type-specialized conn.)
extension of CCM runtime to install / setup / configure bind connectors instances to components
extension of CCM assembly descriptors to let appear the connector notion in it and specify binding to components
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Impact on software engineering process
description of ports affected to components
done via extended IDL3 uses_port new keyword inside
“component” type declarations refers to Port collection
CIF is derived from port types definitions codegen
Assembly descriptordefines connector instances
in addition to comp instances
defines binding of components to connectors configuration of connectors
Connector instantiationadditional code generation step for “typed” connectors
15 Aug
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Illustration : basic Connectors Examples
Event Bus
Push/Pull pub-sub
publishers / subscribers
are associated to collection of char strings
event delivered to subscribers whose tag collection is a subset of the emitter one
Event channel plays particular role
Delayed procedure call
poll-based version
connector naturally parameterized by type of target interface
More relevant connectors examples in some of the next slides.
connector EvtBus { provides PushInterface for_publishers; provides PullInterface for_consumers;};
connector RPC_Poll<I> { provides trsf(I) for_poll_client; uses I for_server; };
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More insight on connectors for CCM (runtime setting)
connectors realizations are fragmentedsome fragments co-localized with components
implement interface between component and connector
some fragments in a priori unknown in advance placeexample : event channel
collaboration modalities between fragments is connector specific fragments created and configured via local factories
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Relations between components, ports, and connectors
Ports definitionscan be parameterizedrefer to IDL interfaces
not only syntactical contracts
Componentsdeclare Ports usage
Connectorsrefer to port typesor directly to interfaces if the mapping is 1 to 1
Exampleinterface PushEventInterface { void push( in any evt );};
Port_type PushPublisher { uses PushEventInterface pe;};
Port_type PushConsumer { provides PushEventInterface pe;};
component C { uses_port PushPublisher pub_port;};
component D {uses_port PushConsumer cons_port;
};
connector PushPushEvent { provides_port PushPublisher for_pubs; provides_port PushConsumer for_cons;};
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Extension of configuration and deployment for CCM
Extensions
of assembly file format (XML Schema)
for ability to refer to connector package
for ability to install, instantiate and configure connector instance
local fragments as well as non-localization constrained ones
configuration : per connector instance, or associated to particular components bound to connector instance
for ability to define bindings between components ports to connector slots (i.e between matching ports)
of CCM runtime
to support interaction with deployment tool
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CCM Extension strategy :how to build custom containers supporting real-time
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CCM Containers general facts
CCM containers: provide predefined lifecycle for components, some non-functional features (not the good ones for RT),come in four (fixed) categories
Extension approach :provide extensible container construction facilities to embed predefined / custom services in it
to apply on hosted componentsand obtain the container fitting the needs for particular application
how this is done : framework to develop container modules (interfaces to implement) container uses this framework base interfaces at particular points:
interceptioncreation of POA with particular policies, activation of servants services explicitly provided to component via context interface
21 Aug
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Extensible container overview / examples for services
Basic RT services as possible container ingredientsusage of an RT-CORBA ORB
with selected prio models / Policies (example : CLIENT_PROPAGATED)
Threadpools
scheduling mechanisms
clocks
time triggers
for periodic activities combined with associated defined priority
...
22 Aug
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Communication applicationSimplified UMTS radio protocol stack
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Overall description of use-case : UMTS protocol layers at UE
• Notions :• TTI: transmission time interval• TFC: transport format
combination• BO : buffer occupancy• SAP : service access point
in each TTI : - RLC submits info about BOs to MAC - MAC informs RLC of PDUs nb to submit to log channels SAPs - RLC submits PDUs to MAC - MAC processes RLC PDUs and submits transport blocks sets to PHY according to TFC selection - ...
Note: only uplink shown
24 Aug
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Connectors examples 1
Intent : capture recurring inter protocol layers interactions upper layers to RLC entity interaction in uplink
Message type connectorBuffering of RLC SDUsDiscarding policies for SDUs
based on : TTI index, if Buffer full, discard-timers
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Connectors examples 2
Intent : capture recurring inter-layers interactions
control of access to RACH (random access channel)
selection of TTI to initiate access on RACHdone randomly with probability P_iuntil success or nb_retries > N_maxadditional timing delay in case of Negative ACK by PHY
26 Aug
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Conclusions
Presented extensions of CCM to supportmultiple kinds of software interactionsextensible component framework construction supporting real-time
parts of this work are in progress
Assessment and validation of proposal:forthcoming with prototyping of presented radio-protocol stack use-case.Could lead to CCM extensions proposal in the future in case of good evaluation.
Acknowledgements:CARROLL-ICE : THALES/SC2 – CEA/LIST Collaborative project IST-Compare and ITEA-Merced European projects