NCO_yhlee_ 1

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Real-time SOA

• Yann-Hang Lee, Wei-Tek Tsai, and Yinong Chen
• Computer Science and Engineering Department
• Arizona State University
• yhlee_at_asu.edu

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Future Combat Systems
A large-scale distributed real-time embedded
system which is dynamic, survivable, verifiable,
reusable, maintainable
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Trends of Real-time Embedded Systems

• Wide-spreading
• Distributed, connected, and heterogeneous
• Mission and safety critical
• Quality of the products
• portable/reusable, reliable/dependable,
  interoperable, predictable (schedulable), and
  secured
• Software extensive
• Examples
• Home and factory automation, transportation
• Communication (PCS, wire and wireless) and sensor
  networks
• Medical devices monitoring and implantable
• Defense applications Network centric warfare
  and future combat system

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Building RT Embedded Systems

• Advances in general-purpose computers
• PCs are powerful, cheap, and versatile
• Information processing is ubiquitous
• Thanks for the increase in productivity

Process technology Hardware design
productivity Software productivity
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Distributed Embedded Software

• Characteristics
• Network centric, concurrent operations, time and
  environment dependent
• Embedded software development
• 80 programs in embedded system is with C/C
  and15 in assembly
• the same thing that has been done more than 30
  years (Ada?)
• Software complexities
• inherent and cannot be eliminated, i.e.
  algorithm, concurrency, etc.
• accidental (due to technology or methods used),
  i.e. memory leaks
• What can we do?
• abstraction (e.g. modeling)
• automation (e.g. code generation, composition)

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Service-Oriented Architecture

• Service as an abstraction for
• discovery
• composition
• invocation
• SOA represents a paradigm shift away from the
  software application to the software-as-a-servi
  ce model
• Based on connectivity of the sites that provide
  services

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Real-time Perspectives in SOA

• Invocations of services must be completed within
  specific timing constraints
• should include network delay, and data
  marshalling overhead.
• How about the semantics of embedded applications
• Never-ending operation periodic or aperiodic
• Event-driven or time-driven
• Asynchrony - signals, events, transfer of
  control
• Concurrency invoke more than one services at
  the same time
• Must be based on a distributed real-time
  architecture

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Service Model of RTSOA

• Passive and active services

App_1
App_1
Periodic Service _1
invoke/request
Service _1
send(msg)
receive
result
Periodic Service_2
App_2
App_2
send(msg)
Periodic Service_3
Service_2
Service_3
send(msg)
App_3
App_3
control/conf.
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Service Model of RTSOA

• Basic functional service model
• Real-time properties of services
• Quality of service
• Minimum and maximal response times
• Service capacity (such as a number of service
  invocations that can be accepted per unit of
  time)
• Degree of concurrency (the maximal number of
  service consumers that the service provider can
  be bounded to simultaneously)
• Cost and required resource
• Communication as a service
• guaranteed message delay or bandwidth reservation

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Execution Model of Real-time SOA

• System model services are distributed in
  multiple nodes which are connected by networks
• Task model a sequence of services executed in
  several nodes
• Possible precedence constraint between consequent
  services
• Service allocation and scheduling
• End-to-end delay execution times of services and
  message delays
• Jitter control when a service can be released

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Schedule Services in RT SOA
Service Binding
traffic volume msg routing
utilization
msg ready time
service scheduling at each node
message scheduling
service ready time
computation delay
msg delay
end-to-end delay
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Generalized RMS for Distributed Scheduling

• Assign periodic execution for each required
  service at its host node
• Partition end-to-end deadlines to each service
  and communication
• Synchronized period for each service
• Rate-monotonic or deadline monotonic scheduling
  to determine priorities at each node
• Bandwidth allocation to ensure bounded message
  delays.
• Schedulability test

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Cyclic Scheduling (Time-based)

• Time triggering in TMO
• A synchronized clock
• Tasks are scheduled in cyclic manner at each node
• Control the jitter (earliest and latest instants)
• Pinwheel scheduling
• A task set with harmonic periods can have 100
  schedulability utilization
• Transfer the periods into harmonic numbers
• Use pinwheel scheduling at each node
• Distance constraints at each pipelined stage
• Pinwheel phase alignment to minimize end-to-end
  delay

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Real-Time Communication

• To achieve an end-to-end delay bound for messages
• Difficulties
• distributed queueing --- distributed scheduler
• efficient use of bandwidth
• non-preemptable
• buffer requirement
• interaction between consecutive link servers
• Typical approaches scheduling based on assigned
  priority or reserved bandwidth
• Reserve a suitable bandwidth during admission
  control
• Packet-by-packet generalized processor sharing
  (PGPS) to schedule packets according to the
  simulated finishing time

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Optimal Composition

• Following discovery, determine how a plan should
  be realized if multiple services exist.
• A typical optimization problem with
• Objectives minimize cost (resource usage,
  vulnerability)
• Constraints deadlines, jitters, number of
  service nodes.
• Global or local optimization
• How practical of the approaches
• scalability
• dynamic composition due to mission requirement,
  external event, and mobility
• effectiveness
• the availability of information

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A Practical Approach

• Levels of service quality
• service threads from a fixed pool
• invocation frequency or periodicity
• resolution, bandwidth, and resource allocation
• Restriction of accessing to various levels
• When compositing a plan,
• a partial search (breath or depth first) while
  reserving the resources the requestor is allowed
• basically, a greedy approach
• Cached and canned services
• Backup and duplicated services

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Ontology for RTSOA

• Consider smart home applications
• All houses are different with different appliance
  and residence
• Can plans be developed for each house and its
  residence
• Ontology a knowledge base for the specific
  application domain
• generic services and application templates
• key words and relations
• Based on registration information, plans can be
• generated and composited
• re-evaluated for service mobility

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Summary

• Software development is a tough job, it is more
  difficult for RTES
• many emerging requirements
• it is the design of the systems
• what else other than C C, or Ada
• Is SOA ready for distributed real-time embedded
  applications
• the goals abstraction and automation
• SOA overhead, optimization and real-time issues
  can be solved to certain degrees
• how effective depends upon the application
  domains
• service semantics and models can be tailored to
  specific application domains
• SOSE service-oriented system engineering

Real-time Embedded System Lab, ASU
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• Thanks.
• Questions and Comments

Real-time Embedded System Lab, ASU