NETWORK CONVERGENCE AND MODELING

Design of Interconnecting SW for Intranets and Fieldbuses

Miroslav Sveda

Faculty of Information Technology, Brno University of Technology, Bozetechova 2, Brno, Czech Republic

Keywords: Network Intermediate System, IP Routing, IEEE 1451, Network Convergence, Dynamic Model.

Abstract: The paper deals with the current software architectures for intermediate system for Intranet and small-range

wireless interconnections. This article brings two case studies founded on real-world applications that

demonstrate another input to network convergence and network modeling in software architecture

development stemming from design experience based on industrial network applications and on

metropolitan networking. The first case study focuses on IEEE 1451 family of standards that provides a

design framework for creating applications based not only on IP/Ethernet profile but also on ZigBee. Next

case study explores how security and safety properties of Intranets can be verified under every network

configuration using model checking.

1 INTRODUCTION

This paper focuses on software architectures for

intermediate system control plane in frame of

Intranet and ZigBee, and then presents new

contributions to network convergence and network

modeling in software architecture development. The

next section corroborates the basic concepts of

supporting resources, namely (1) IP routers as the

most important means forming the Internet,

(2) industrial network couplers that enable to create

hierarchical communication systems as a basis of

various -- not only industrial -- applications, and (3)

design experience collected by our team in this

domain, which influence unsurprisingly the current

research. The section 3 dealing with network

convergence aims at Ethernet and IP-based

industrial networking that offer an application

development environment compatible with common

TCP/IP setting. It stems from IEEE 1451 family of

standards and provides a design framework for

creating applications based not only on

TCP/IP/Ethernet profile but also on ZigBee. The

second part of this section reviews the first case

study based on an appication dealing with pressure

and temperature measurement and safety and

security management along gas pipes. In the section

4, the presented network modeling approach

provides a unifying model suitable for description of

relevant aspects of real IP computer networks

including dynamic routing and filtering. The rest of

this section reviews the second case study based on

an application exploring how security and safety

properties can be verified under every network

configuration using model checking.

2 STATE OF THE ART

2.1 IP Routers

Internet/Intranet router architectures have

experienced three generations, see e.g. (Keshav,

1997) or (Nguyen and Jaumard, 2009). The first

generaion router architecture, sometimes called also

as software router, which is based on a monolitic (or

centralized) routing engine, appears just as a simple

PC equiped with multiple line cards. Such a router is

build with one CPU on a control card handling all

basic modules such as Routing Engine, Packet

Forwarding and Service Engines. The Routing

Engine handles a set of routing protocols like IS-IS,

OSPF, BGP and MPLS that run all together and

interchange routing and switching information.

Routing Table Manager is responsible for retrieving

the information learned from the different routing

protocol modules, making decisions for selecting the

best routes and generating accordingly the Best

Route Table, which can be used later in forwarding

173

Sveda M. (2010).

NETWORK CONVERGENCE AND MODELING - Design of Interconnecting SW for Intranets and Fieldbuses.

In Proceedings of the 5th International Conference on Software and Data Technologies, pages 173-178

DOI: 10.5220/0002863201730178

 SciTePress

the packets to the corresponding destinations.

In a cluster-based architecture, often called as the

second generation, the Routing Engine modules are

distributed on several network communication cards

that share an interconnection, usually through a

system bus, to operation memory and processor on

the control card. Moreover, the network

communication cards are equipped with

communication controllers implementing physical

and data-link layer (L1 and L2) protocols and

controlling input and output buffers.

Many current Internet routers, which can provide

high speed switching capacity, are built with

switching fabrics based on a Banyan or analogous

self-routing topology. The Banyan switch fabric

transports data from input line controllers to output

line buffers according to binary labels derived by a

proper trie data structure and related simple rules. In

this case, routers are called as of the third

generation. More detailed information, namely

about the virtual output queued router architecture

that appears common nowadays for ISP backbone

networks, is provided e.g. by (Nucci and

Papagiannaki, 2009).

2.2 Industrial Networks Coupling

Contemporary industrial distributed computer-based

systems encompass, at their lowest level, various

wired or wireless digital actuator/sensor to controller

connections. Those connections usually constitute

the bottom segments of hierarchical communication

systems that typically include higher-level fieldbus

or Intranet backbones. Hence, the systems must

comprise suitable interconnections of incident higher

and lower fieldbus segments, which mediate top-

down commands and bottom-up responses. While

interconnecting devices for such wide-spread

fieldbuses as CAN, Profibus, or WorldFIP are

currently commercially available, some real-world

applications can demand also to develop various

couplers either dedicated to special-purpose

protocols or fitting particular operational

requirements, see (Sveda, et al., 2005).

The following taxonomy of industrial

communication and/or control network (ICN)

interconnections covers both the network topology

of an interconnected system and the structure of its

intermediate system, which is often called in the

industrial domain as coupler. On the other hand, the

term gateway sometimes denotes an accessory

connecting PC or a terminal to an ICN. For this

paper, the expression “gateway” preserves its

original meaning according to ISO-OSI terminology

as discussed above.

The first item to be classed appears the level

ordering of interconnected networks. A peer-to-peer

structure occurs when two or more interconnected

networks interchange commands and responses

through a bus coupler in both directions so that no

one of the ICNs can be distinguished as a higher

level. If two interconnected ICNs arise hierarchically

ordered, the master/slaves configuration appears

usual at least for the lower-level network.

The second classification viewpoint stems from

the protocol profiles involved. In this case, the

standard taxonomy using the general terminology

mentioned above can be employed: bridge, router,

and gateway. Also, the tunneling and backbone

networks can be distinguished in a standard manner.

The next, refining items to be classed include

internal logical architectures of the coupler, such as

source or adaptive routing scheme, routing and

relaying algorithms, and operating system services

deployed.

2.3 Design Background

We launched our coupling development initiatives in

the Fieldbus and Internet domains almost

concurrently. Fieldbus coupling was studied by our

research team originally from the viewpoint of

network architecture of low-level fieldbuses (Sveda,

1993), (Sveda, et al., 2000). Next interest was

focused on real-world applications based on network

coupling, such as data acquissition appliance (Sajdl

et al., 2003), or wireless smart sensors (Vrba, et al.,

2004). And also, the role of Ethernet and TCP/IP

attracted our attention as a means of network

convergence (Cach, et al., 2003), (Sveda, et al.,

2005).

The other branch of our network interconnection

initiative covers IP routing. In this case we launched

with software router design based on a simple Unix

machine (Cernohlavek, et al., 1994) and with

creation of a routing domain for academic

metropolitan networking (Kania, et al., 1995). The

current research initiatives deal with modeling of

dynamically routed IP networks and exploration of

their properties such as reachability-based safety and

security (Matousek, et al., 2008).

3 NETWORK CONVERGENCE

This section deals with network convergence aiming

at Ethernet and IP-based industrial networking that

offer an application development environment

ICSOFT 2010 - 5th International Conference on Software and Data Technologies

174

compatible with the common TCP/IP setting. It

stems from IEEE 1451 family of standards,

mentioned in the subsection 3.2 and provides a

design framework for creating applications based

not only on TCP/IP/Ethernet profile but also on

ZigBee. The last part of this section reviews the first

case study based on an appication dealing with

pressure and temperature measurement and safety

and security management along gas pipes.

3.1 IP/Ethernet Profile

The attractiveness of Ethernet as an industrial

communication bus is constantly increasing.

However the original concept of the Ethernet, which

was developed during seventies of the last century as

communication technology for office applications,

has to face some issues specific for industrial

applications. The concept of the Ethernet proved to

be very successful and encountered issues are being

addressed by modifications and extensions of the

most popular 10/100 BaseT standard. In fact, the

switched Ethernet with constraint collision domains

proved to be efficient real-time networking

environment also for time-critical applications.

Similarly, IP networking support appears as a

rapidly dominating tendency in current industrial

system designs. Namely, when layered over a real-

time concerning data-link protocol, it seams as a best

choice for future applications because of a simple

interfacing within the Internet.

3.2 IEEE 1451

The design framework, presented in this paper as a

flexible design environment kernel, is rooted in the

IEEE 1451.1 standard specifying smart transducer

interface architecture. That standard provides an

object-oriented information model targeting

software-based, network independent, transducer

application environments. The framework enables to

unify interconnections of embedded system

components through wireless networks and

Ethernet-based intranets, which are replacing

various special-purpose Fieldbuses in industrial

applications (Sveda, et al., 2005).

The IEEE 1451 package consists of the family of

standards for a networked smart transducer interface.

It includes namely (1) a smart transducer software

architecture, 1451.1 (IEEE 1451.1, 2000), targeting

software-based, network independent, transducer

applications, and (2) a standard digital interface and

communication protocols for accessing the

transducer or the group of transducers via a

microprocessor modeled by the 1451.1. One of

them, wireless 1451.5, is used in frame of the first

application case study.

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.

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.

3.3 ZigBee

The ZigBee/IEEE 802.15.4 protocol profile (ZigBee,

2006) is intended as a specification for low-powered

wireless networks. ZigBee is a published

specification set of higher level communication

protocols designed to use small low power digital

radios based on the IEEE 802.15.4 standard for

wireless personal area networks. The document

802.15.4 specifies two lower layers: physical layer

and medium access control sub-layer. The ZigBee

Alliance builds on this foundation by providing a

network layer and a framework for application layer,

which includes application support sub-layer

covering ZigBee device objects and manufacturer-

defined application objects.

Responsibilities of the ZigBee network layer

include mechanisms used to join and leave a

network, to apply security to frames and to route

frames to their intended destinations. In addition to

discovery and maintenance of routes between

NETWORK CONVERGENCE AND MODELING - Design of Interconnecting SW for Intranets and Fieldbuses

175

devices including discovery of one-hop neighbors, it

stores pertinent neighbor information. The ZigBee

network layer supports star, tree and mesh

topologies. Star topology network is controlled by

one single device called ZigBee coordinator, which

is responsible for initiating and maintaining devices

on the network. Those devices, known as end

devices, directly communicate with the ZigBee

coordinator. In mesh and tree topologies, the ZigBee

coordinator is responsible for starting the network

and for choosing key network parameters.

The ZigBee application layer includes

application support sub-layer, ZigBee device objects

and manufacturer-defined application objects. The

application support sub-layer maintains tables for

binding, which is the ability to match two devices

together based on their services and their needs, and

forwards messages between bound devices. The

responsibilities of the ZigBee device objects include

defining the role of the device within the network

(e.g., ZigBee coordinator or end device), initiating

and/or responding to binding requests and

establishing a secure relationship between network

devices. The ZigBee device object is also

responsible for discovering devices on the network

and determining which application services they

provide.

3.4 Application Case Study I

This section describes a case study that demonstrates

utilization of the introduced design framework. The

application deals with pressure and temperature

measurement and safety and security management

along gas pipes. The related implementation stems

from the IEEE 1451.1 model with Internet and the

IEEE 1451.5 wireless communication based on

ZigBee running over the IEEE 802.15.4.

The interconnection of TCP/IP and ZigBee is

depicted on Figure 1. It provides an interface

between ZigBee and IP devices through an abstracted

interface on IP side.

Each wireless sensor group is supported by its

controller providing Internet-based clients with

secure and efficient access to application-related

services over the associated part of gas pipes. In this

case, clients communi-cate to controllers using a

messaging protocol based on client-server and

subscribe-publish patterns employing 1451.1

Network Block functions. A typical configuration

includes a set of sensors generating pressure and

temperature values for the related controller that

computes profiles and checks limits for users of

those or derived values. When a limit is reached, the

safety procedure closes valves in charge depending

on safety service specifications.

Figure 1: Network gateway.

Security configurations in this case can follow the

tiered architecture discussed above. To keep the

system maintenance simple, all wireless

communication uses standard ZigBee hop-by-hop

encryption based on single network-wide key

because separate pressure and/or temperature values,

which can be even-dropped, appear useless without

the overall context. Security in frame of Intranet

subnets stems from current virtual private network

concepts. The discussed application utilizes ciphered

channels based on tunneling between a client and a

group of safety valve controllers. The tunnels are

created with the support of associated

authentications of each client.

The application architecture comprises several

groups of wireless pressure and temperature sensors

with safety valve controllers as base stations

connected to wired intranets that dedicated clients

can access effectively through Internet. The WWW

server supports each sensor group by an active web

page with Java applets that, after downloading,

provide clients with transparent and efficient access

to pressure and temperature measurement services

through controllers. Controllers offer clients not only

secure access to measurement services over systems

of gas pipes, but also communicate to each other and

cooperate so that the system can resolve safety and

security-critical situations by shutting off some of

the valves.

Each controller communicates wirelessly with its

sensors through 1451.5 interfaces by proper

Bee Gatewa

App

lication

Bee

Gatewa

Trans

ort

TCP

UDP

802.15.4

MAC

Ethernet

Wireless

802.15.4

PHY

App

. Su

Network

Layer

DHCP

SNMP

App

lication

(

Java

…

)

802.15.4

PHY

802.15.4

MAC

App

. Su

Network

Layer

Embedded

Application

TCP/IP-ZigBee Gateway

ZigBee

ICSOFT 2010 - 5th International Conference on Software and Data Technologies

176

communication protocol. In the discussed case the

proposed P1451.5-ZigBee, which means ZigBee

over IEEE 802.15.4, protocol was selected because

it fits application requirements, namely those dealing

with power consumption, response timing, and

management. The subscriber-publisher style of

communication, which in this applica-tion covers

primarily distribution of measured data, but also

distribution of group configuration commands,

employs IP multicasting. All regular clients wishing

to receive messages from a controller, which is

joined with an IP multicast address of class D,

that, when this controller generates a message by

Block function publish, this message is delivered to

all members of this class D group, without

unnecessary replications.

4 NETWORK MODELING

The current goals of our research in frame of

Internet-level routed networks consist of i) creation

of a unifying model suitable for description of

relevant aspects of real computer networks including

routing information, ACLs (access control lists),

NAT (network address translation), dynamic routing

policy; and ii) delivering methods for automated

verification of dependable properties (e.g.

availability, security, survivability). The project

aims to merge the research on formal methods with

the research on network security to devise a new

method for network security verification.

4.1 Dynamic Network Model

The recent work has focused on studying models

and analysis techniques based on simulation and

network monitoring (Matousek, et al., 2008).

The dynamics of current network models is most

often limited to changes of actual data in time. The

other dimension of dynamics of routed networks

comes from dynamic routing protocols and topology

changes based on the availability of links and link

parameters, e.g. reliability, bandwidth or load.

4.2 Application Case Study II

Suppose a small organization running a web server

that provides information to their customers. The

server is placed in the local network equipped with

three routers. A path to the Web server goes through

router R2 that filters traffic by in its input, see

Figure 2. There is a backup line between routers R1

and R3 with higher costs (lower priority). However,

when the link between R2 and R3 goes down, the

traffic is not filtered any more and the web server

can be attacked from the outside network. In another

scenario, the priority line appears between routers

R1 and R3. This line enables to access the Web site

from the PC. When the link goes down, traffic is

redirected by routing tables trough R2. However, R2

entry interface is filtered by ACL1. The connection

from PC to Web server is filtered out and the Web

services are no longer available.

Figure 2: Network example.

These two scenarios present typical situation of a

real-world network with a dynamic behaviour. Our

approach focuses on the area of automatic analysis

of a network that consists of L3 devices (hosts,

routers, firewalls etc.) connected by links and,

optionally, with firewall rules applied on them.

In our work we explore how security and safety

properties can be verified under every network

configuration using model checking (Clarke, et al.,

1999). The model checking is a technique that

explores all reachable states and verifies if the

specified properties are satisfied over each possible

path to those states. Model checking requires

specification of a model and properties to be

verified. In our case, the model of network consists

of hosts, links, routing information and ACLs. The

network security-type properties are expressed in the

form of modal logics formulas as constraints over

states and execution paths. If those formulas are not

satisfied, the model checker generates a

counterexample that reveals a state of the network

that violates the specification. If the formulas are

satisfied, it means, that the property is valid in every

state of the systems, see more detail in (Matousek,

et al., 2008).

NETWORK CONVERGENCE AND MODELING - Design of Interconnecting SW for Intranets and Fieldbuses

177

5 CONCLUSIONS

The paper discusses software architectures for

intermediate system’s control planes belonging to

Intranets and Fieldbuses by two case studies derived

from genuine implementations. The interest is

focused both on network convergence and on

network modeling in application architecture

development.

From the previous discussion it is evident that

the illustrated above network convergence would

influence not only the unification of modeling

techniques, but also the fusion of development

targets such as quality of service assurance in the

same way like empowering development tools by

technology reuse for new application domains.

ACKNOWLEDGEMENTS

The research has been supported in part by the

Czech Ministry of Education in frame of the

Research Intentions MSM 0021630528, Czech

Ministry of Industry and Trade through the grant

FR-TI1/037, by the Brno University of Technology

through the grant FIT-10-S-1, and by the Grant

Agency of the Czech Republic through the grant

GACR 102/08/1429.

The author appreciates contributions to the

presented work by his colleagues Radimir Vrba,

Ondrej Rysavy and Petr Matousek.

REFERENCES

Cach P., Fiedler, P., Sveda, M., Prokop, M., Wagner M.,

2003. A Sensor with Embedded Ethernet, In WSEAS

Transactions on Circuits, Iss.1, Vol.2, pp.213-215.

Cernohlavek, I., Novotny, J., Slama, V., Zahorik, V.,

Sveda, M., 1994. Open-Box Routers with Academic

Metropolitan Networking, Technical Report, Brno

University of Technology (CVIS Department) and

Masaryk University (UIVT Department). Brno.

Clarke, E.M., Grumberg, O., Peled, D.A., 1999. Model

Checking, MIT Press, Boston, MA.

Kania, L., Smolik, S., Sveda, M., Zahorik, V., 1995. The

Brno Academic Computer Network and its Future

Development, In Proceedings INVEX-CCT'95, BVV

Press, Brno, pp.1-5.

Keshav, S., 1997. An Engineering Approach to Computer

Networking: ATM Networks, the Internet, and the

Telephone Network, Addison-Wesley, Reading, MA.

Matousek, P., Rab, J., Rysavy, O., Sveda, M.: A Formal

Model for Network-wide Security Analysis, In

Proceeding of the 15 IEEE International Symposium

and Workshop on the Engineering of Computer-based

Systems, Belfast, GB, IEEE Computer Society, Los

Alamitos, CA, 2008, pp.171-181.

Nguyen, K.-K., Jaumard, B., 2009. Routing Engine

Architecture for Next Generation Routers: Evolutional

Trends, In International Journal of Network Protocols

and Algorithms, Vol.1, No.1, Macrothink Institute,

Las Vegas, Nevada, pp.62-85.

Nucci, A., Papagiannaki, K., 2009. Design, Measurement

and Management of Large-Scale IP Networks:

Bridging the Gap between Theory and Practice,

Cambridge University Press, New York.

Sajdl, O., Bradac, Z., Vrba, R., Sveda, M., 2003. Data

Acquisition System Exploiting Bluetooth Technology,

In WSEAS Transactions on Circuits, Iss.1, Vol.2,

pp.117-119.

Sveda, M., 1993. Routers and Bridges for Small Area

Network Interconnection, In Computers in Industry,

Vol.22, No.1, Elsevier Science, Amsterdam, NL,

pp.25-29.

Sveda, M., Vrba, R., Zezulka, F., 2000. Coupling

Architectures for Low-Level Fieldbuses, In

Proceedings 7th IEEE ECBS'2000 Conference,

Edinburgh, Scotland, IEEE Comp. Soc., pp.148-155.

Sveda, M., Benes, P., Vrba, R., Zezulka, F., 2005.

Introduction to Industrial Sensor Networking. Book

Chapter in M. Ilyas, I. Mahgoub (Eds.): Handbook of

Sensor Networks: Compact Wireless and Wired

Sensing Systems, CRC Press LLC, Boca Raton, FL,

pp.10.1-10.24.

Vrba, R., Sajdl, O., Kuchta, R., Sveda, M., 2004. Wireless

Smart Sensor Network System, In Proceedings of the

Joint International Systems Engineering Conference

(ICSE) and The International Council on Systems

Engineering (INCOSE), Las Vegas, Nevada.

ZigBee, 2006. ZigBee Specification. ZigBee Alliance

Board of Directors Website http://www.zigbee.org/.

ICSOFT 2010 - 5th International Conference on Software and Data Technologies

178