INTERNET-BASED EMBEDDED SYSTEM ARCHITECTURES

End-User Development Support for Embedded System Applications

Miroslav Sveda

Faculty of Information Technology, Brno University of Technology, Brno, Czech Republic

Radimir Vrba

Faculty of Electrical Engineering & Communication, Brno University of Technology, Brno, Czech Republic

Keywords: Smart sensors, IEEE 1451, Internet, Publish/subscribe m

essaging, IP multicast.

Abstract: This paper presents an approach to industrial embedded system networking that offers a reusable design

pattern for the class of Internet-based applications. It deals with an integrated networking framework

stemming (1) from the IEEE 1451.1 smart transducer interface standard, which is an object-based

networking model supporting among others publish-subscribe approach to group messaging, and (2) from

the Internet Protocol (IP) multicast communication, mediating efficient and unified access to smart sensors

through Internet. The kernel of this paper focuses on adaptations and tuning of those concepts and on their

utilization for a gas pipes pressure measurement system as an application example. Furthermore, the

contribution brings this scheme in form suitable not only for framework builders, but also for end-user

developers.

1 INTRODUCTION

The design framework, presented in this paper as a

flexible design environment stemming from meta-

design conception, is rooted in the IEEE 1451.1

standard specifying smart transducer interface

architecture. This framework enables to unify not

only interconnecting smart sensors with various

Fieldbuses but also their direct coupling to Ethernet-

based Intranets, which are currently replacing

various special-purpose Field busses in industrial

applications (Sveda, et al., 2005). That standard

provides an object-oriented information model

targeting software-based, network independent,

transducer application environments.

Two additional technologies, namely publisher-

subscri

ber messaging and IP multicasting, which

offer scalable and traffic-saving solution important

in the context of contemporary Internet, complement

the framework providing design patterns reusable

for various sensor-based networked systems. The

schemes discussed can properly interplay with each

other and can provide suitable support for Internet-

based sensor systems design. The kernel of this

paper focuses on adaptations and tuning of

introduced concepts and on their utilization for a

network-based pressure measurement system as a

real-world project. This pilot application implements

a distributed, gas-pipe’s measurement arrangement.

It comprises groups of smart pressure and

temperature sensors that clients can access

effectively through Internet. Each sensor group is

supported by an active web page with Java applets

that, after downloading, provide clients with

transparent and efficient access to pressure

measurement services over such geographically

distributed objects as the large-scale systems of gas

pipes or similar industrial applications.

The paper discusses in the following section

meta-d

esign basic principles utilizable for creating

flexible design environment reusable for various

application domains of sensor systems. Next three

sections introduce subsequently IEEE 1451 package

of communication standards, client-server and

publisher-subscriber communication concepts, and

Internet Protocol (IP) multicasting as main abstract

components of the design pattern forming the heart

of the generic development environment. The

section 6 presents in more detail an example of

employment of this framework for designing

networked distributed embedded systems for

pressure measurement along gas pipes. The example

covers design of network configuration,

Sveda M. and Vrba R. (2006).

INTERNET-BASED EMBEDDED SYSTEM ARCHITECTURES - End-User Development Support for Embedded System Applications.

In Proceedings of the International Conference on e-Business, pages 63-68

DOI: 10.5220/0001424300630068

 SciTePress

implementation concepts developed, node

configuration, and smart sensor implementation.

2 META-DESIGN

Component-based development involves multiple

roles (Morch, et al., 2004). Framework builders

create the infrastructure for components to interact;

developers identify suitable domains and develop

new components for them; application assemblers

select domain-specific components and assemble

them into applications; and end users employ

component-based applications to perform daily

tasks. There is room for a fifth role in this pipe-line:

end-user developers positioned between application

assemblers and end users. These end-user developers

are able to tailor applications at runtime because

they have both domain expertise and technical

know-how. They would interact with applications to

adjust individual components, and modify existing

assemblies of components to create new

functionality. Furthermore, they can play a critical

role when component-based systems have to be

redesigned for new requirements. End-user

development activities can range from customization

to component configuration and programming.

Meta-design characterizes objectives, techniques,

and processes for creating new environments

allowing end users to act as designers (Fischer, et

al., 2004). In all design processes, two basic stages

can be differentiated: design time and use time. At

design time, system developers create environments

and tools. In conventional design they create

complete systems. Because the needs, objectives,

and situational contexts of users can only be

anticipated at design time, users often find the

system unfit for their tasks at use time. Thus, they

require adaptation of the existing environment and

tools for new applications. Meta-design extends the

traditional notion of system development to include

users in an ongoing process as co-designers, not only

at design time but throughout the entire life-cycle of

the development system. Rather than presenting

users with closed systems, meta-design provides

them with concepts and tools to extend the system to

fit their needs. Hence, meta-design promotes

designing the design process.

This paper discusses a deployment of meta-

design principles for creating a flexible design

environment focused on sensor systems

interconnected by Internet aiming namely at

industrial applications. Necessarily under-designed

open source tools and techniques create design

spaces for end-user developers in such application

domains as pressure measurement along gas pipes,

which is used as a case study demonstrating the

principles of such environment exploitation.

3 IEEE 1451 SET OF STANDARDS

The IEEE 1451 package consists of the family of

standards for a networked smart transducer interface

that include namely (see Figure 1) (i) a smart

transducer software architecture, 1451.1 (IEEE,

2000), targeting software-based, network

independent, transducer applications, and (ii) a

standard digital interface and communication

protocol, IEEE 1451.2, for accessing the transducer

or the group of transducers via a microprocessor

modeled by the 1451.1 standard. The next three

standard proposals extend the original hard-wired

parallel interface 1451.2 to serial multi-drop 1451.3,

mixed-mode (i.e. both digital and analogue) 1451.4,

and wireless 1451.5 interfaces.

NCAP

Smart Transducer

Object Model (1451.1)

Smart Transducer

Interface Model (STIM)

Network

Network hardware + drivers

Transducer interface

Specification (1451.2)

sensors and actuators

Transducer driver hardware

Figure 1: IEEE 1451 configuration example.

The 1451.1 software architecture provides three

models of the transducer device environment: (i) the

object model of a network capable application

processor (NCAP), which is the object-oriented

embodiment of a smart networked device; (ii) the

data model, which specifies information encoding

rules for transmitting information across both local

and remote object interfaces; and (iii) the network

communication model, which supports client/server

and publish/subscribe paradigms for communicating

information between NCAPs. The standard defines a

network and transducer hardware neutral

environment in which a concrete sensor/actuator

application can be developed.

The object model definition encompasses the set

of object classes, attributes, methods, and behaviors

that specify a transducer and a network environment

to which it may connect. This model uses block and

base classes offering patterns for one Physical

Block, one or more Transducer Blocks, Function

Blocks, and Network Blocks. Each block class may

include specific base classes from the model. The

base classes include Parameters, Actions, Events,

and Files, and provide component classes.

All classes in the model have an abstract or root

class from which they are derived. This abstract

ICE-B 2006 - INTERNATIONAL CONFERENCE ON E-BUSINESS

class includes several attributes and methods that are

common to all classes in the model and provide a

definition facility for the instantiation and deletion

of concrete classes including attributes.

Block classes form the major blocks of

functionality that can be plugged into an abstract

card-cage to create various types of devices. One

Physical Block is mandatory as it defines the card-

cage and abstracts the hardware and software

resources that are used by the device. All other block

and base classes can be referenced from the Physical

Block.

The Transducer Block abstracts all the

capabilities of each transducer that is physically

connected to the NCAP I/O system. During the

device configuration phase, the description is read

from the hardware device what kind of sensors and

actuators are connected to the system. The

Transducer Block includes an I/O device driver style

interface for communication with the hardware. The

I/O interface includes methods for reading and

writing to the transducer from the application-based

Function Block using a standardized interface. The

I/O device driver provides both plug-and-play

capability and hot-swap feature for transducers.

The Function Block provides a skeletal area in

which to place application-specific code. The

interface does not specify any restrictions on how an

application is developed. In addition to a State

variable that all block classes maintain, the Function

Block contains several lists of parameters that are

typically used to access network-visible data or to

make internal data available remotely.

The Network Block abstracts all access to a

network employing network-neutral, object-based

programming interface supporting both client-server

and publisher-subscriber patterns for configuration

and data distribution.

4 CLIENT-SERVER AND

PUBLISHER-SUBSCRIBER

PATTERNS

The majority of communication protocols provide a

client-server style of communication. In case of

sensor communications, the client-server pattern

covers both configuration of transducers and

initialization actions. If the client wants to call some

function on server side, it uses a command execute.

On server side, this request is decoded and used by

the function perform. That function evaluates the

requested function with the given arguments and,

after that, it returns the resulting values to the client.

The client-server pattern corresponds to remote

procedure call (RPC), which is the remote

invocation of operations in a distributed context

(Eugster, et al., 2003). To be more precise, the RPC

interaction considered in this paper provides a

synchronous client-server communication, i.e. the

client is waiting for a server’s response before

completion the RPC actions related to the current

call. Evidently, the client-server communication

style relates to point-to-point message passing called

as unicast.

The subscriber-publisher style of communication

(Eugster, et al., 2003) can provide the efficient

distribution of measured data. All clients, wishing to

receive messages from a transducer, register

themselves to the group of its subscribers using the

function subscribe. After that, when this transducer

generates a message using the function publish, this

message is effectively delivered to all members of

its subscribing group. Transducers in the role of

publishers have also the ability to advertise the

nature of their future events through an advertise

function.

The interaction publish-subscribe relates to point-

to-multipoint or multipoint-to-multipoint

asynchronous message passing. Of course, it can be

implemented using multiple unicast communication

transactions. On the other hand, to satisfy the

requirement of efficiency, it is necessary to utilize

elaborate multicast techniques encompassing

multicast addressing and, namely, multicast routing.

The basic principles of the network layer multicast

in the Internet environment are discussed in the

following section.

5 MULTICASTING

Traditional network computing paradigm involves

communication between two network nodes.

However, emerging Internet applications require

simultaneous group communication based on

multipoint configuration propped e.g. by multicast

IP, which saves bandwidth by forcing the network to

replicate packets only when necessary. Multicast

improves the efficiency of multipoint data

distribution by building distribution trees from

senders to sets of receivers (Miller, 1999).

The functions that provide the Standard Internet

Multicast Service can be separated into host and

network components. The interface between these

components is provided by IP multicast addressing

and Internet Group Management Protocol (IGMP)

group membership functions, as well as standard IP

packet transmission and reception. The network

functions are principally concerned with multicast

INTERNET-BASED EMBEDDED SYSTEM ARCHITECTURES - End-User Development Support for Embedded System

Applications

routing, while host functions can also include

higher-layer tasks such as the addition of reliability

facilities in a transport-layer protocol.

IP multicasting is the transmission of an IP

datagram to a host group, a set of zero or more hosts

identified by the single IP destination address of

class D. Multicast groups are maintained by IGMP

(IETF RFC 1112, RFC 2236). Multicast routing

considers multicasting routers equipped with

multicast routing protocols such as DVMRP (RFC

1075), MOSPF (RFC 1584), CBT (RFC 2189),

PIM-DM (RFC 2117), PIM-SM (RFC 2362), or

MBGP (RFC 2283). For Ethernet-based Intranets,

the Address Resolution Protocol provides the last-

hop routing by mapping class D addresses on

multicast Ethernet addresses.

6 CASE STUDY

The presented case study, used to demonstrate the

introduced concepts, includes several groups of

smart pressure and temperature sensors that clients

can access effectively through Internet. Each sensors

group is supported by an active web page with Java

applets that, after downloading, provide clients with

transparent and efficient access to pressure

measurement services over such geographically

distributed objects as the considered large systems of

gas pipes. The complete system comprises several

groups of smart pressure sensors complemented by

temperature sensors that enable computing of

temperature corrections (Sveda and Vrba, 2003).

6.1 Network Configuration

Each sensor group is supported by an active web

page with Java applets that, after downloading,

provide clients with transparent and efficient access

to pressure measurement services. This section

demonstrates the above-introduced concepts and

tools adapted and applied to the development of

such a gas-pipes pressure analyzer

In this case, clients communicate to transducers

using a messaging protocol defined by client-server

and subscriber-publisher patterns employing 1451.1

Network Block functions. A typical configuration

includes a set of smart pressure sensors generating

pressure values for the users of those values. To

user — playing the role of either subscriber or client

— opens the related server’s web page with the

relevant Java applet. This applet is, after uploading

to the subscriber/client site, started on

subscriber/client’s computer, which launches

communications with a group of transducers

allowing Java clients to connect and subscribe to the

smart sensors. Java can directly support both client-

server and subscriber-publisher application

architectures as the core Java specifications include

TCP/IP and UDP/IP networking APIs.

The developed Java applet uses the core java.net

package to implement both client-server and

subscriber-publisher application distribution

allowing to access smart sensors and supporting

nodes. The applet consists of a series of object

classes, including multi-threaded applet

environment, animation, and UDP/IP-based

subscriber and TCP/IP-based client communications.

The subscriber/client software implemented in Java

enables applets to be included in a web server

HTML page, and run under a regular web browser

on subscriber/client side. The subscriber/client

communicates with the transducer by standard

UDP/TCP sockets employing IP multicast.

The communication scheme applies multicast

both for distributing measured values from a

transducer to a group of subscribers/clients

registered by the web server for this transducer, and

for spreading commands of a client to a group of

transducers registered for this client.

6.2 Implementation Concepts

In the transducer’s 1451.1 object model, basic

Network Block functions initialize and cover

communication between a client and the transducer,

which are identified by unique unicast IP addresses.

The client-server style communication, which in this

application covers both the configurations of

transducers and initialization actions, is provided by

two basic Network Block functions: execute and

perform. The standard defines a unique ID for every

function and data item of each class. If the client

wants to call some function on server side, it uses

command execute with the following parameters: ID

of requested function, enumerated arguments, and

requested variables. On server side, this request is

decoded and used by the function perform. That

function evaluates the requested function with the

given arguments and, in addition, it returns the

resulting values to the client. Those data are

delivered by requested variables in execute

arguments.

The subscriber-publisher style of communication,

which in this application covers primarily

distribution of measured data, but also distribution

of group configuration commands, employs IP

multicasting. All clients wishing to receive messages

from a transducer, which is joined with an IP

multicast address of class D, register themselves to

this group using IGMP. After that, when this

ICE-B 2006 - INTERNATIONAL CONFERENCE ON E-BUSINESS

transducer generates a message by Block function

publish, this message is effectively delivered to all

members of this class D group, without unnecessary

replications and repeated transmissions.

The Network Block abstracts all access to a

network employing network-neutral, object-based

programming interface. The network model provides

an application interaction mechanism supporting

both client-server and publisher-subscriber

paradigms for event and message generation and

distribution.

6.3 Node Configuration

The primary communication scheme, which is based

on publish-subscribe application interface, applies

multicast both for distributing measured values from

a transducer to a group of clients registered by the

www server for this transducer, and for spreading

commands of a client to a group of transducers

registered for this client. Those commands can

specify e.g. individual subgroup’s sampling

frequencies and/or events for launching irregular

publishing such as a limit value crossing.

A typical node, depicted on Figures 2 and 3,

consists of STIM (Smart Transducer Interface

Module) connected with PSD sensor for pressure

measurements, and with auxiliary temperature

sensor for signal conditioning. Of course, NCAP can

be either embedded in a complex smart sensor, or

shared among more simple smart sensors. On the

other hand, from the viewpoint of Internet, only

NCAP is directly addressable being equipped by its

own IP address. Therefore, we can also denote as

smart sensor the device consisting of an NCAP

accessing one or more STIMs with connected

sensors. To register itself for a specified group of

sensors, the client opens a related server’s web page

with the relevant Java applet. This applet is, after

uploading to the client site, started on client’s

computer, what launches communication with the

dedicated group of transducers.

6.4 Smart Sensor Implementation

WWW SERVER

10/100Mbps TCP/IP / Etherne

INTRANET

JAVA-APPLET

CPU

[kPa]

Http

ackbone

CAP

This subsection discusses, as an example, the

pressure sensors with reflected laser beam and

diffractive lens. The sensitive pressure sensor is

based on a nitride membrane and an optoelectronic

read-out subsystem. Measured pressure values are

transformed into related thick-layer nitride

membrane deflections. The nitride membrane serves

as a mirror for laser beam, and it can move the

related reflected laser mark. The mark’s position is

sensed using position-sensing device, which is a

fotolateral diode. Diode double current signal is

amplified and conditioned digitally by the ADuC812

microcontroller. This single-chip microcontroller

provides also the IEEE 1451.2 interface.

Figure 2: Sensor node configuration example.

The sensing subsystem combines two principles

that provide both high precision and wide range

pressure measurements. Large displacements are

measured by the position of reflected focused laser

beam. Small position changes are measured by one-

side layer diffractive lens principle. Sensor output

signal is conditioned in digital by the ADuC812

single-chip microcontroller, which provides the

IEEE1451.2 interface as one of its communication

ports. This microcontroller calculates the position of

the light spot and converts that position on the

measured pressure using an internal table.

Figure 3: Sensor node implementation example.

Figure 3 depicts principles of the implementation

of that smart sensor. The STIM contains (1) a PSD

sensor with two analog differential transducers

(XDCR), (2) a microcontroller ADuC812 with

nonvolatile memory containing a TEDS field

(Transducer Electronic Data Sheet) that props IEEE

1451.2 storing sensor specifications, (3) a TII

(Transducer Independent Interface), (4) a

temperature sensor necessary for signal

conditioning, (5) an analogue-to-digital conversion

units (ADC), and (6) a logic circuitry to facilitate

communication between the STIM and the NCAP.

INTERNET-BASED EMBEDDED SYSTEM ARCHITECTURES - End-User Development Support for Embedded System

Applications

The ADuC812 microcontroller, the basic building

block of the smart pressure sensor electronics,

includes on-chip high performance multiplexers,

ADCs, DACs, FLASH program and data storage

memory, an industrial standard 8052 microcontroller

core, and supports several standard serial ports. The

microcontroller may also utilize nonvolatile memory

containing a TEDS field and ten-wire TII that prop

IEEE 1451.2.

7 CONCLUSIONS

This contribution deals with industrial, sensor-based

applications development support aiming at

distributed components interconnected by Internet

compatible intranets. The paper presents an

approach to embedded system networking that offers

a reusable design pattern for a class of Internet-

based applications. It aims at an integrated

networking framework stemming (1) from the IEEE

1451.1 smart transducer interface standard, which is

an object-based networking model supporting client-

server and publish-subscribe communication

patterns in group messaging, and (2) from the IP

multicast communication, mediating efficient access

to smart sensors through Internet.

The pilot application demonstrates that clients

can access groups of smart pressure and temperature

sensors effectively through Internet. Each sensors

group can be supported by an active web page with

Java applets that, after downloading, can provide

clients/subscribers with transparent and efficient

access to measurement services flexible enough to

satisfy various application requirements.

The newly established application domain of

industrial sensor networks brings special

requirements not only on safety and security, but

also on reuse of platforms developed originally for

different domains. This paper deals with a concrete

industrial embedded system networking design

approach that employs meta-design principles for

reuse IEEE 1451.1 smart transducer object model

with publish-subscribe messaging over IP

multicasting, which mediate efficient access from

Internet to sensors and vice versa. Such solution can

offer rapid tailoring of development environments

aiming, among others, at sufficient response times

also in frame of unpredictable Internet background

traffic.

This paper discusses a deployment of meta-

design principles for creating a flexible design

environment focused on sensor systems

interconnected by Internet aiming namely at

industrial applications. Necessarily under-designed

open source tools and techniques create design

spaces for end-user developers in such application

domains as pressure measurement along gas pipes,

which is used as a case study demonstrating the

principles of such environment exploitation. The

sensor-based embedded systems accessible via

standard Internet and based on the IEEE 1451.1

standard as described in the paper can be simply

reused, modified or redesigned to new systems not

only for industrial, but also for scientific, medical,

biological and other purposes.

ACKNOWLEDGEMENTS

This research has been partly funded by the Czech

Ministry of Education in frame of the Research

Intention No. MSM 0021630503 MIKROSYN: New

Trends in Microelectronic Systems and

Nanotechnologies; and by the Grant Agency of the

Czech Republic through the grants GACR

102/05/0723: A Framework for Formal

Specifications and Prototyping of Information

System's Network Applications, and GACR

102/05/0467: Architectures of Embedded Systems

Networks.

REFERENCES

Eugster, P.T., et al., 2003. The Many Faces of

Publish/Subscribe. ACM Computing Surveys, Vol. 35,

pp.114-131.

Fischer, G. et. al., 2004. Meta-Design: A Manifesto for

End-User Development. Communications of the ACM,

Vol.47, No.9, pp.33-37.

IEEE, 2000. IEEE 1451.1, Standard for a Smart

Transducer Interface for Sensors and Actuators --

Network Capable Application Processor (NCAP)

Information Model.

Miller, C.K., 1999. Multicast Networking and

Applications, Addison-Wesley, Reading,

Massachusetts, USA.

Morch, A.I., et. al., 2004. Component-Based Technologies

for End-User Development. Communications of the

ACM, Vol.47, No.9, pp.59-62.

Sveda, M. and R. Vrba, 2003. An Integrated Framework

for Internet-Based Applications of Smart Sensors.

IEEE Sensors Journal, Vol.3, No. 5, pp.579-586.

Sveda, M., et al., 2005. Introduction to Industrial Sensor

Networking, A book chapter in: Ilyas, M., and I.

Mahgoub, (Eds.), 2005. Handbook of Sensor

Networks: Compact Wireless and Wired Sensing

Systems, CRC Press LLC, Boca Raton, FL, USA.

ICE-B 2006 - INTERNATIONAL CONFERENCE ON E-BUSINESS