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MANAGEMENT GENERATION
~ WIRELESS NETWORKS SERVICES
AND
MANNA: A Management Architecture for
Wireless Sensor Networks
Linnyer Beatrys Ruiz, Federal University of Minas Gerais and Pontifical Catholic University of Parand
Jose Marcos Nogueira and Antonio A. F. Loureiro, Federal University of Minas Gerais
ABSTRACT military [l- 41. A WSN combines micro elec-
tromcchanical systems (MEMS) technology, new
Wireless sensor networks (WSNs) are bewm- sensor materials, low-power signal processing,
ing an increasingly important technology that computation, and low-cost wireless networking in
will be used in a variety of applications such as a compact system. Currently, it is possible to find
environmental monitoring, infrastructure man- sensor nodes varying from a few millimeters to 2
agement, public safety, medical, home and office m. Advances during the last decade in integrated
security, transportation, and militaq. WSNs will circuit technology have enabled the manufactur-
also play a key role in pervasive computing ing of far more powerful but inexpensive sensors,
where computing devices and people are con- radios, and processors, allowing mass production
nected to the Internet. Until now, WSNs and of sophisticated systems connccting the physical
their applications have been developed without world to computer networks
considering a management solution. This is a The large use of WSNs depcnds on the design
critical problem sincc nctworks comprising tens and development of a scalablc, low-cost scnsor
of thousands of nodes are expected to be used in network architecture. Such applications necd to
some of the applications above. This article pro- send sensor information to users o r network
poses the MANNA managemcnt architccture for entities at a l o w bit r a t e using low-power
WSNs. In particular, it prescnts the functional, transceivers. Continuous scnsor signal processing
information, and.physical management architec- . enables the constant monitoring of events in an
tures that take into account specific characteris- environment in which possibly a few.data bytes
tics of this type of network. Some of them are would suffice. Some of the applications foreseen
restrict physical resources such as energy and for WSNs will require a large number of devices
computing power, frequent reconfiguration and on the order of tens of thousands of nodes. Tra-
adaptation, and faults caused by nodes unavail- ditional methods of sensor networking represent
able. The MANNA architecture considers three an impractical demand on cable installation and
management dimensions: functional areas, man- network bandwidth. Performing thc processing
agement.levels, and WSN functionalities. These at the source can drastically reduce the compu-
dimensions are specified to the management of a tational burden on application, network, and
WSN and are the basis for a list of management management. On the other hand,, any solution
functions, The article also proposes WSN mod- must take into account-specific charactcristics of
els to guide the management activities and the this type of network.
use of correlation in the WSN management. Until now, WSNs and their applications have
This is a first step into a largely uncxplored been developed without considering a manage-
research area. ment solution. This may not be a problem for
small networks, but will definitcly be when appli-
INTRODUCTION cations, in order to work properly, will need to
reconfigure and adapt themselves hased o n
Wireless sensor networks (WSNs) provide dis- information scattered over the network. This
tributed network access to sensors, actuators, and article proposes a management architecture for
processors embedded in a variety of equipment, WSNs. In particular, it presents an information
facilities, and the environment. A WSN repre- architecture and a functional management archi-
Thir work irponioliysup- sents a new monitoring and control capability for tecture that take into account-specific character-
poned by National applications such as environmental monitoring, istics of this type of network.
Research Council CNPq, infrastructure management, public safety, medi- Management of WSNs is a new research area
Brazil. cal, home and office security, transportation, and that only recently started to receive attention
116 0163-6804/03/$17.00 0 2003 IEEE IEEE Communications Magazinc - February 2003
from the research community. In this sense, this collect data according to conditions defined by
work presents a contribution to the field, since it the application. A WSN is hybrid when it has at A wireless sensor
proposes a WSN management architecture. We least two of the above characteristics concerning
present a separation between both sets of func- dissemination of information. node comprises
tionalities (i.e., application and management) WSNs have other important characteristics
through a management architecture for WSN.
one or more
depending on the application. Some of them are
This will make possible the intcgration of orga- coverage, accuracy, fidelity, density, self-organi- sensor elements,
nizational, administrative, and maintenance zation, adaptation, and location. However, the
activities for this kind of network. points described above will play an important battery, memory,
The rest of this article is organized as follows. role in the definition of the functional architec- processor, and
We present the main characteristics and metrics ture presented in this article.
of WSNs. We then discuss the important aspects When designing and evaluating WSNs for dif- transceiver.
in the management of WSNs. We present and ferent applications, some of the metrics that Programs
discuss the MANNA management architecture should be considered, depending on the environ-
for WSNs, as well as a possible management sit- ment, are described below. developed to
uation and how the MANNA architecture works. Longevity/energy: Energy is a critical resource
Finally, we present our conclusions. in a WSN. Thus, all operations performed in the execute In a
network should be energy-efficient. Network wireless sensor
availability can be measured as the amount of
SENSOR NETWORKS
WIRELESS time some or all sensor nodes in the network node must take
continue to obtain sensing data and pass them to
Sensor nodes in WSNs are spread over a region the application.
and communicate among themselves using point- Latency: This refers to the time interval
to-point wireless communication, possibly form- between the instant the sensor gets the data and
ing an ad hoc network. Sensors collect, process, the moment they are delivered to the destina-
and send data observed from the environment to tion, and it has two components: inside the net-
other nodes. Basically there are three types of work, from sensor to sink node, and from sink
nodes: common nodes responsible for collecting node to observer. Depending on the kind of
sensing data, sink nodes responsible for receiv- application and network latency, the data
ing, storing, and processing data from common received by the observer may be of no value and
nodes, and gateway nodes that connect sink should be discarded.
nodes to external entities called observers. WSNs Accuracy: This indicates the reliability or
can also include actuators that enable control or exactness of a result. It can also be defined as
actuation on a monitored area. the fraction of valid results from all results
The observer is a network entity or final user obtained. Factors such as environmental-condi-
that wants to have information about data collect- tions when the data are obtained and communi-
ed by sensor nodes. Depending on the type of cation range of the sensor node may also
application, the observer may send a query to the degrade accuracy. The application plays an
WSN and receive a response from it. A sensor ele- important role in this metric since it is responsi-
ment generates data about a given phenomenon. ble for establishing the amount of energy to be
A WSN may collect different sensor data such as spent in obtaining data. As a consequence, the
temperature, pressure, electromagnetic field, and network should adapt to the accuracy metric
chemical agents since it can comprise different defined by the application and according to an
sensor elements. A wireless sensor node comprises upper limit of latency.
one or more sensor elements, battery, memory, Fault tolerance: In a WSN, nodes may fail
processor, and transceiver. Programs developed to due to energy, physical destruction, communica-
execute in a wireless sensor node must take into tion problems, or inactivity (a node becomes sus-
account its hardware restrictions. pended). Even if these situations occur, it may be
A WSN is said to be homogeneous when all desirable for the network to continue to operate
nodes have the same hardware; otherwise, it is properly.
heterogeneous. The nodes are autonomous when Goodput: This is the ratio of the total number
they are able to execute self-configuration tasks of packets received by the observer to the total
without human intervention. A WSN is hierarchi- number of packets sent by all the sensors over a
cal when nodes are grouped for the purpose of period of time.
communication and flat otherwise. In a hierar-
chical network, it is common to have a base sta-
tion that works as a bridge to external entities. A MANAGEMENT OF
WSN is static when nodes are stationary and SENSOR NETWORKS
WIRELESS
dynamic otherwise. Note that the topology may
be dynamic even when nodes are stationary since Traditional computer networks are designed to
new ones can be added to the network or exist- accommodate a diversity of applications. Net-
ing nodes become unavailable. A WSN is sym- work elements are installed, configured, and
metric when each transceiver has the same connected in a network in a way to provide dif-
transmission range and asymmetric otherwise. A ferent kinds of services. In general, management
WSN is continuous when sensor nodes collect aspects are clearly separated from network com-
data and send them to an ObSeNer continuously mon activities (i.e., the services they provide to
along time and on demand when they answer to their users). Therefore, it is said that there exists
observer's queries. A WSN is reactive when sen- an overlapping of management and network
sor nodes send data referring to events occurring functionalities, but the implementation can be
in the environment and programmed when nodes thought of independently. In the following we
IEEE Communications Magazine February 2003 117
discuss important characteristics of WSNs that Adapt protocols, algorithms, and mecha-
make their management different from a tradi- nisms already developed for wired and wire-
tional computer network. less networks.
Hence, the approach used in this develop-
MANAGEMENT REQUIREMENTS ment deals with complex management situations
of a WSN can be In computer networks, replacement of faulty by decomposing a problem into smaller subprob-
components or resources by technicians is a nor- lems, in successive refinement steps. We work
mal fact. The network tends to with each functional area, each management
lished planning of resources av level, and propose a new abstraction level of
location of each network element WSN functionalities described later. As a result,
In a WSN this is often not th we present a list of management functions next,
in the case o f network is planned to have unattended opera- independent of technology and functional archi-
tion and nodes can be discarded, lost, and out of tecture adopted.
operation temporarily or permanently. In this
scenario, faults are a common fact, what it is not SERVICE MANAGEMENT COMPONENTS
expected in a traditional network. In fact, the The definition of management services consists
ocean, forest, initial configuration of a WSN can be quite dif- of finding which activities or functions must be
and other remote ferent from what was supposed to be in the case executed, when, and with which data. Manage-
of throwing the nodes in the ment services are executed by a set of functions.
other remote regions. In un They need to succeed to conclude a given ser-
tions, a configuration error (e vice.
may cause the loss of the entire network even Management functions represent the lowest
before it starts to operate. granularity of functional portions of a manage-
Depending on the WSN application, it may ment service, as perceived by users. This means
be interesting to uniquely identify each node in that the management architecture must exhibit a
the network. Furthermore, we may be interested function list to deal with the integrated function-
in a value associated with a given region and not ing of a WSN, applications, and users. There-
a particular node. For instance, we may be inter- fore, management functionalities will be
ested in the temperature at the top of a moun- independent of network target activities, even
tain. A WSN is typically data-centric, which is when this is not apparent in the implementation.
not common in traditional networks. The MANNA architecture establishes that
The objective of a WSN is to monitor and, the WSN management does not end in its func-
eventually, control a remote environment. The tions, though. It is necessary to go further. Policy
objective of WSN management is to define a set management will be dependent on network
of functions that intend to promote productivity, states. A network state, o r part of it, can be
as well as to integrate in an organized way func- viewed from different perspectives and varies
tions of configuration, operation, administra- with the moment. The MANNA architecture
tion, and maintenance of all’elements and defines WSN models that represent aspects of
services of a sensor network. Nodes execute a the network, and serves as a reference to the
common application in a cooperative way (i.e., management functions. These models provide an
there is clearly a common goal in the overall abstract vision of the system through which it is
network), which may not be the case in a tradi- possible to hide all nonrelevarit aspects of a cer-
tional network. tain objective.
To model the computing aspect of the man-
PRINCIPLES FOR DEFINING
A agement service, a MANNA architecture pro-
MANAGEMENT ARCHITECTURE vides policy-based management. In the
specification of these policies there are condi-
We propose that the WSN management be sim- tions that should be satisfied so specific func-
ple, adherent to network idiosyncrasies, includ- tions are executed and thus provide the desired
ing its dynamic behavior, as well as efficient in management service.
its use of scarce resources. In this work we con- The conditions for executing a function are
sider the following principles: obtained from the WSN models. For example, a
Try to resolve in an extensive way specific maintenance service of the coverage area obtains
problems derived from the dependencies the energy and sensing range conditions of the
WSNs have on applications and energy nodes in the network. making use of some WSN
restrictions. For example, location mecha- models such as energy map and topology map.
nisms can be different among them depend- T o find out sensing areas that are not moni-
ing on environment and network tored, the service executes the coverage area
organization. supervision function. In this way it obtains the
Build a generic management function list information that allows it to choose the most
, from abstractions of different functional appropriate policy to tackle this problem.
areas, management levels, and network The relationship among services, functions,
functionalities. and WSN models is illustrated in Fig. 1. The fig-
Establish an open and documented informa- ure represents a scheme to construct the man-
tion model that allows reuse of objects, and agement, starting at the definition of both
syntax and semantic uniformity of manage- services and functions that use models to achieve
ment information. their goals. A service can use one or more man-
Provide a functional architecture that con- agement functions. Different services can specify
siders generic configuration of a wireless common functions that use models to retrieve a
sensor network. network state concerning a given aspect.
118 IEEE CommunicationsMagazine February 2003
MANAGEMENT FUNCTIONS
Management functions can he automatic, when
executed by some software invoked as a result of
information acquired from a model; semi-auto-
malic, when executed by a human operator
assisted by a software system that provides a net-
work model o r invoked by a management sys-
Function 1 Function 2 I Function 3 I I Function 4 I
tem; and manual, when executed outside of the Uses Uses
managcment system.
Five possible states are defined for a func-
tion: ready, when the necessary conditions to. WSN model WSN model
execute a function are satisfied; not-ready, when
the necessary conditions to execute a function
are not met; executing, when the function is W Figure 1. Relationship among sewices,functions and WSN models in
being executed; done, when,the function has suc- MANNA management.
cessfully exccuted; and failed, when a failure
occurs during the execution of the function:
A partial list of the management functions, in the network clement. It is mapped to object classes.
no particular order, is given below: The MANNA architecture defines an infomation
Environmental monitoring function model for representing static information. Dynamic
* Monitored area definition function management information is described by WSN
Coverage area supervision function models and needs to he obtained frequently. The
. Node deployment definition function
Node deployment function (51
* Environmental requirements acquisition
acquisition of this information has a cost in terms
of energy consumption. Therefore, an important
aspect is to determine thc adequate moment, fre-
- function
Network operating parameters configura-
quency, and fidelity for updating that information.
Furthermore, the information collected may he not
- tion function
Topology map discovery function
valid at the moment it is processed by the managc-
mcnt entity due to delays, omissions, and uncertain-
- * Network connectivity discovery function
Aggregation discovery function
Node dcnsity control function
ty prcsent in WSNs.
The dynamic information represented in the
network models could or could not be stored in
- * Priority of action definition function
Management operation schedule function
MIBs. Examples of dynamic models are given
below:
- * Cooperation discovery function
Synchronization function
Sensing coverage area map: Describes the
actual sensing coverage map of the sensor ele-
--* Energy map gencration function
Network coverage area definition function
ments.
Communication coverage a r e a map:
- User intcrface function
Self-test function
* Node localization discovery function
Describes the present communication coverage
map from the range of transceivers.
Behavioral model: Represcnts the hchdvior of
* Node operating state control function a WSN. Statistical and probabilistic models may
* Energy level discovery function he much more efficient in estimating network
We define some functions, listed below, that behavior than deterministic models.
allow one to obtain characteristics related to the Dependence model: Represents the functional
efficiency and effectivcness of a WSN. Some of dependency that exists between the nodes. The
these quantitativc functions are defined to obtain network is modeled as a graph, whcre the nodes
--
parameters presented in [6]: in the graph correspond to nodes in the WSN,
Network settling time function and the edges between them represent the exist-
Network join time function ing dependency relations (e.g., the connectivity
* Network depart time between the nodes). In order to represent the
-
'* Network recovery time function
Frequency of updates (overhcad) function
depcndencies, Bayesian or Markovian models,
for instance, may he used.
- * Memory requirement function
Network scalability function
Encrgy consumption function
Network topology: Represents t h e actual
topology map and thc reachability of the net-
work. It may he uscd t o obtain information
about the necessity of adding new nodes [SI.
WSN MODELS FOR DYNAMIC REPRESENTATION Residual energy: Represents the remaining
In a WSN, the network conditions can vary dra- energy in a node or network. This information
matically in time. In this case, the utilization of may also he available considering a region or
models estahlishcd by MANNA is of fundamen- time interval. Using this information, together
tal importance for managcment, although its with the data generated by the network topology
updating cycle can he extrcmely dynamic and model, it is possible to identify thc areas that
complex. Based on the information obtained will have shorter lifetimcs [SI.
with these models, scrvices and functions are Usage standard: Reprcsents the activity of
executed according to management policies. the network. It can be delimited for a period of
There are two kinds of management informa- time, quantity of data transmitted for each sen-
dynamic. Static information describes
tion: sratic~and sor unit, or by the number of movemcnts madc
the sewice configuration, and both the network and by the target [SI.
-
IEEE CommunicationsMagazine February 2003 119
' In WSnls, a//
operational,
administrative
0 Management
function -
WSN functionalities
Configuration
Maintenance
Sensing
and maintenance Processing
Communication
characteristics of
the network Business management
Service management Management
-I
Fault IeYelS
elements, the c",",:gyt
Configuration
Network management
Network element management
network, the areas Performance Network element
Security
services, and Accounting
business, as well ~
W Figure 2 . Monagementfunctronal,~
abstractions
as the adequate
execution in the
Cost: Represents the cost of equipment, ener- The concepts involved with the functional
activities of gy, and personnel necessary to maintain the areas of WSNs differ from established defini-
configuration, desired performance levels. tions for traditional networks or even other wire-
In telecommunication networks and distrihut- less networks. T h e M A N N A architecture
maintenance, ed systems, there arc two categories of relations: considers that the fault, security, performance
sensing, process- structural and cooperational, which may be repre- and accounting functional areas are extremely
sented through these models: dependent on the configuration functional area.
ing and Structural, models: Represent the relations of I n WSNs, all operational, administrative and
communication aggregation and connectivity between network maintenance characteristics of the network ele-
elements, as well as the description of the same ments, the network, the scrviccs, and business,
are dependent on network elements. as well as the adequate execution in the activi-
Cooperational models: Represent relations of ties of configuration, maintenancc, sensing, pro-
the configuration interaction between network entities. For exam- cessing, and communication are dependent on
of the WSN. ple, there is a service-user relation. The relations t h e configuration of the WSN. This idea is
of cooperation are created, activated, and termi- depicted in Fig. 3 where the configuration func-
nated (normally; abnormally, aborted, etc.) tional area plays a central role.
between the network components and distrihut- Configuration management is a functional
ed systems. The components involved may, by area of high relevance in WSN management.
their own initiative or activated by foreign actors, Since the objective o f a sensor network is to
adjust their behavior or share resources, con- monitor (acquisition, processing, and delivcry of
tributing to a common objective. In sensor net- data) and, eventually, to control an environment,
works, cooperation between the sensors, i n any problem or situation not anticipated in the
general, is peer to peer. Only two sensor nodes configuration phase can affect the offered ser-
cooperate with each other at a given moment. vice. Some management functions we have
defined for network-level configuration manage-
WSN FUNCTIONALITIESA
AS ment are requirements specification of the net-
NEW DIMENSION MANAGEMENT
TO work operational environment; monitoring of
environmental variations; size and shape defini-
Traditional network management is organized over tion of the region to be monitored; node deploy-
two planes, management functional areas and ment, random o r deterministic; operational
management levels. The MANNA architecture network parameters determination; network
defines a new dimension to management. It is state discovery; topology discovery; network con-
another abstraction level where thcnetwork func- nectivity discovery; control of node density; syn-
tionalities are also considered. In this way, WSN chronization; network energy map evaluation;
management will have an organization that eomcs coverage area determinati0n;and integration
from abstractions offered by management func- with thc ohserver. Some managcment functions
tional areas, management levels, and network fnnc- we have defined for network-element-level con-
tionalities (configuration, maintenance, sensing, figuration management arc, node programming,
processing, and communication). The MANNA node self-test, node location, node operational
architectnrc considers the three abstraction planes state, node administrative state, node usage
in the definition of a management function. state, and node energy Icvel.
Figure 2 presents the existing relationships in Faults in wireless sensor networks are.not an
the definition and utilization of managcment exception and tend to occur frequently. This is
functions. The new dimension introduced can be one of the things that make management of
observed in the upper part of the figure. WSNs different from traditional network man-
agement. Faults happen all the time due to encr-
MANAGEMENT AREAS
FUNCTIONAL gy shortages, connectivity interruptions,
In the following, we present a contribution to environmental variations, and so on. In general,
WSN management technology from the perspec- sensor networks must he fault-tolerant and
tive of functional areas. robust, and must survive despite occurrences of
120 IEEE Communications Magazine Fehruary 2003
faults in individual nodes, the network, or even
services provided, In addition to events caused
by energy problems, other events can happen in
a WSN related to communication, quality of ser-
vice, data processing, physical equipment fault,
environment, integrity violation, operational vio-
-- In the logical
layer architecture,
management
-
lation, security, and time domain violation. functionalities
Therefore, even if a node has an adequate ener-
gy level to execute its function, it may decide not depend,on the
to do that because of other reasons. management
Security functionalities for WSNs are difficult
to provide because of their ad hoc organization, level. Many
intermittent connectivity, wireless communica-
tion, and resource limitations. A WSN is subject traditional
to different safety threats: internal, external, management
accidental, and malicious. Information or
resources can he destroyed, modified, stolen, W Figure 3. The role of configuration mnnage- systems use this
removed, lost, or disclosed, and service can be ment. model in a
interrupted. Even if the WSN is secure, the envi-
ronment can turn it insecure or vulnerable. bottom-up
Sensor networks have inherited the typical work setup, maintenance, sensing, processing,
problems of wirelcss networks, including a high and communication.
approach. ln the
percentage of communication data loss and diffi- The management of the services provided is MANNA
culty in controlling energy consumption. Two of the re.sponsibility of the MANNA architecture.
the main objectives ofpefformancemanagement in WSN services are concerned with functionalities architecture, the
a WSN are the quality of information acquisition associated with application objectives.'A com- LLA model is used
and distribution services. In performance manage- mon priority for all services is to minimize ener-
ment, there is a trade-off to be considered:'the gy consumption. Examples of WSN services are in a top-down
highest the number of managed parameters, the data gathering, processing, and communication. approach.
highest the energy consumption and the lowest I n network-level management, relationships
the network lifetime. On the other hand, if param- among sensor nodes are to he considered. It is
eter values are not obtained, it may he not possi- known that individual nodes are designed to
ble to manage the network appropriately. sense, process data, and communicate, contribut-
Accounting manngement includes functions ing to a common objective. In this way, nodes
related to the use of resources and correspond- can be involved in collaboration, connectivity,
ing reports. It establishes metrics, quotes, and and aggregation relationship.
limits that can he used by functions of other The network element level of the logical layer
functional areas. Thcse functions can trace the architecture corresponds to network elements
behavior of,the network, and even make infer- that need to be managed or execute some man-
ences about the bchavior of a given node. Some agement function. Considering that applications
functions related to accounting management are may require networks with a large amount of
discovery, counting, storing, and data reporting sensor nodes, network element management can
of a parameter; network inventory; determina- deal with a group of nodes. I n such a case, a
tion of communikation costs; energy consump- 'manageable element can he a cluster of nodes or
tion; and traffic checking. a cluster head rather than an individual node.
MANAGEMENT LEVELS
In the logical layer architecture (LLA), manage-
MANAGEMENT
ARCHITECTURE
ment functionalities depend on the managcment The MANNA architecture comprises functional,
Icvel. Many traditional management systems use information, and physical architectures. They are
this model in a bottom-up approach. In the described below.
MANNA architecture, the LLA model is used in a
top-down approach. After analyzing the business FUNCTIONAL ARCHITECTURE
Icvel issues, the necessities of the lower levels The functional architecture describes t h e distri-
bccome clear. Similarly, it is only after defining the bution of management functionalities in the net-
application, including the corresponding require- work among manager, agent, and management
ments on the service layer, that we can plan the information base (MIB). In the architecture it is
network and network element management layers, possible to have a diversity of managers and
'and network element. This is a key observation agent locations. The functional architecture sug-
when reasoning about the WSN management. gests both locations for managers and agents
In the following we present a brief discussion and functions they can execute.
concerning WSN management from the perspec-
tive of management levels. WSN Manager - The WSN management can
Requirements that allow the characterization he centralized, distributed, or hierarchical. In a
of a sensor network came from the objectives centralized management network, there is a sin-
defined for the business munagement layer. Since gle manager that collects information from all
WSNs depend on applications, business manage- agents and controls thc entire network. A dis-
ment deals with service development and deter- tributed management network has several man-
mination of cost functions. It represents a sensor agerqeach responsible for a subnetwork and
network as a cost function associated with net- communicating with other managers. In a hierar-
IEEE Communications Magazine - Fcbrualy 2003 121
I I In the following we explore some possible
configurations:
Agents in flat and homogeneous WSNs: A
flat WSN has at least one sink node to provide
network access. All network nodes havc the
events ': same hardware configuration. Some possible
1 a Manager A Agent @ Sink node b Common node 1 alternatives for flat and homogeneous networks
.
considering agent location in the WSN are:
Agents T network and external manager
n
(Fig. 5a).
I
a Figure 4.Agent and manager located uternallj in the WSN.
l
-
* Agent in sink node (Fig. Sb).
Agents and manager in network. The two
possibilities for manager organization are
hierarchical (Fig. Sc) and distributed (Fig.
chical management network, there are interme- W.
diate managers to distribute the management In any of these proposals, the main concern is
tasks. The management alternative to he chosen the large amount of traffic that may he generat-
depends on the application running on the WSN. ed in response to operation requests and sending
In any solution, it may he important to have a notifications. Another alternative is to place
manager entity located externally to the WSN. managers inside the network, allowing them to
communicate among themselves. This defines
WSN Agents Location -The development of distributed management. If having agents as part
a functional architecture raises some questions of common nodes, some questions remain such
related to the location of agents. The most ade- as how to distribute the agents, how to define
quate location for an agent depends on the kind domains for the agents, and how to deal with
of WSN. nodes with more than one agent.
A first alternative for agent location is to Agents in flat and heterogeneous WSNs: In a
place it close to the manager (i.e.,.external to the heterogeneous WSN, nodcs diffcr in their hard-
network). This would cause isolation of the man- ware physical capabilities. Agents can be placed in
agement and make difficult to integrate it in the more powerful nodes, as long as they present ade-
future and even access other management sys- quate location in the network. The sink node can
tems. This configuration can be viewed in Fig. 4. host an intermediate manager or even present no
management function at all. To establish distrihut-
ed management, we can place agents in less pow-
erful nodes and managers in more powerful ones.
Agents in hierarchical homogeneous or het-
erogeneous WSNs: In this kind of network. there
is no sink node. A cluster head node is responsi-
hlc for sending data to a base station. It also com-
municates with the observer. The cluster head
may also executc correlation of management
data. This computation may decrease the infor-
mation flow and thus energy consumption. The
correlation may also allow multiresolution where
differences are filtered and higher precision is
obtained. Some possible alternatives for a hierar-
-
chical WSN considering the agent location are:
Agentsin the network and external manag-
er (Fig. 6a)
Agent in the base station (Fig. 6h)
* Agents in the network and intermediate
manager (Fig. 6c)
* Agents and distributed managers in the net-
work (Fig. 6d)
Responses, : Centralized management for WSNs, as well as
notifications j
for traditional ad hoc networks, is not always
appropriate. One main reason is the traffic con-
centration problem, caused by a central manager
that.receives and originates management traffic.
In addition, the response implosion problem may
happen when there is a high volume of incoming
replies triggered by management operations or
events. In any case, there will always he one access
point (sometimes more than one) through which
(d) data go to the observer or management applica-
a Manager A Agent Sink node Common node
tion. The access point represents a sink node or
base station that can make use of a gateway to
communicate with the external environment.
To resolve the response implosion problem,
Figure 5. Manager and agent location in flat WSNs. one possibility is to select only a subset of agents to
122 IEEE Communications Magazine - February 2003
send replies back, known asfidelity. This approach
may be suitahle for densely populated sensor net-
works with a large number of sensor nodes, where
missing information from some nodes can be
Aq:::.<.. *4
@
....._
......
...... ......
.....
ignored with acceptable accuracy. The accuracy of ...........
............ ..
...
II ....... !.. ,
the calculation might significantly degrade in a
sparse sensor network or one with a small number
of nodes not collecting enough replies. However, Responses,
notifications j
.....&.{-9.*:8..
:a'v$..,
' .'. ,'i
,& -:*; ....
9 ,............?'&, *.:.*,,
Ls
1
0
the number of replies may not he small enough to .. . ...........
be received without taking into account the .......... ...........
-
response implosion problem. One solution is to (a)
make a scheduled response approach [7J ....... ........................
M a n a g e m e n t I n f o r m a t i o n Base - The Operations p/ ..... *e-
::
: II...............,.. ../
: , ...... : ............. -'!
description of objects present in the information
model and the relationship among them are spec-
Kb 4-
+..
*'.
....
.. : ? e ,
.. ; - . . : *
...
I
j IO^,,'*.. ,b 0;;....*-L.b-,
;*;:
.
.
I
,
ified in the management information base. In the Responses, ........... ' ' ,
WSN, to update an MIB with the current network notifications :,,& 0 1
... .. . .................. ?
state may require measuring various parameters. ........
In general, the collection of these parameters may (b)
present spatial and temporal errors.
-
To have higher precision in the network state,
probabilistic measures should be made with high-
er granularity. As in any probing, this would take Operations
a finite amount of system energy and could modi-
fy the network state. This is called the probe effect
In this way, better precision of management infor- Responses,
mation requires modification of the state. notifications
This work proposes limitation of scope as a
method to reduce uncertainty and energy con-
sumption while updating the MIB. Spatial Iimitu-
lion consists of defining a physical space where
the data will be considered for management.
Temporal limitation defines a time window (fixed
or sliding) inside which the collected data are
considered. Funcfionallimitation selects the data f--
of a certain functional network segment for Responses,
management (e.g.. the data of a group of nodes notifications
Or a group leader).
PHYSICALARCHITECTURE
The physical architecture is the implementation
of the functional architecture. In doing this,
physical aspects such as the management proto-
a Manager A Agent
0 Common node
0 Cluster-head U
Base station
col, the physical location of agents, agent func-
tionalitics, management service implemcnted,
and supported interfaces for WSNs are defined. W Figure 6. Agent location in hierarchical networks.
The interface between the management enti-
ties should use a lightweight protocol stack. The
MANNA architecture does not dcfine a protocol In the model of mobile agents, data stay at
stack for thcse interfaces, but provides protocol the local place while the processing task is moved
profiles that may be adequate for each applica- to the data locations. The management functions
tion type. are executed locally, and only the resulting data
Although thc Simple Network Management are sent to the manager. By transmitting the
Protocol (SNMP), Common Management Infor- code instead of data, the mobile agent model
mation Protocol (CMIP), WBM, and Ad Hoc offers several important benefits: reduction in
Network Management Protocol (ANMP) [SI network bandwidth requirements, which is espe-
management protocols allow management in a cially important for real-time applications and
decentralized form and event-oriented, the struc- when communication uses low-bandwidth wire-
ture of the managed components is always too less channels; an agent can migrate to another
rigid. In these paradigms, the management intel- node'when the hosting node is compromised;
ligence always resides in the managing instance, network scalability is supported; an agent can
while the information is generdted.in the man- migrate to regions of interest independent of the
aged instances. An alternative method would he movement of nodes, if they are mobile; extensi-
the delegation of management functionalities to bility is supported, that is, mobile agents can be
the managed systems. A solution, for supporting programmed to carry task-adaptive processes
this feature in the implementation of the physi- that extend the capability of the system; more
cal architecture is management by delegation stability, because mobile agents can be sent
(MbD). Other alternatives are to imvlement when the network connection is alive and return
intelligemagents and mobile agents. results when the connection is reestablished
IEEE Communications Magazine * February 2003 123
along with the network data; it reduces delay in sensing, processing, and communication services.
management actions; managers are not required Examples of new attributes: localization (relative
to instruct agents all the time; the main manage- or absolute), element type (common node, sink
ment part does not resjde only in the manager; node, gateway, cluster head), minimum energy
and agent cloning offers robustness and fault tol- limit, and mobility (direction, orientation, and
erance. acceleration).
Equipment: Represents the physical aspects
INFORMATION ARCHITECTURE of the sensor node constitution, which is com-
The MANNA information ture is based posed of memory, processor, sensor device, bat-
information on the object-oriented info model. Basi- tery, and transceiver. 'The equipment class can
cally, the system is decomposed into two cate- be specialized in object classes: battery (with the
gories of modules, which play the role of attributes of battery type, capacity, remaining
managers and agents exchanging management energy level, energy density, max current), pro-
information. cessor (clock, state of use, available memory,
The information model provides mapping of endurance, AD channel, operating voltage, I O
manageable resources and support of object pins), sensor (sensor type, current consumption,
voltage range, minmax range, accuracy, tempera-
ture dependence, version, state current), and
transceiver (type, modulation type, carrier fre-
management levels, and network functionalities. quency, operating voltage, current consumption,
The design of an information model for a throughput, receiver sensitivity, transmitter
WSN is a complex task. T h e solution of the power).
MANNA architecture to tackle this complexity is System: Represents a set o f hardware and
the abstraction represented in Fig. 2. software that constitutes an autonomous system ,
There are two types of object classes defined capable of executing information processing
in the MANNA architecture: managed objects and/or transference. Examples of new attributes:
and support objects. The managed object class operational system type, version, code length,
information. directly relates with the network components complexity, and synchronization type (mutual
and with the network itself. On the other hand, exclusion, synchronization of processes). A noti-
the support object classes play the role of sup- fication of change in an attribute value must be
porting management functions (i.e., making reported upon an event occurrence, such as soft-
available to them the necessary information). ware upgrade.
The specification of an object class is done Environment: Represents the environment
through predefined syntactic structures called where the WSN is operating. Examples of new
templates that utilize Abstract Syntax Notation. 1 attributes: environmental type (internal, exter-
(ASN.l)s to describe the objects and their char- nal, and unknown), noise ralio, atmospheric
acteristics. pressure, temperature, radiation, electromagnet-
The object classes may be inherited or reused ic field, humidity, and luminosity. The environ-
from standard objects. Reuse allows future man- ment can present static and dynamic features.
agement integration. Some object classes and Phenomenon: Represents the phenomenon
their new attributes, based on WSN characteris- behavior in the environment where the WSN is
tics, are listed below. operating. Examples of attributes: phenomenon
type, occurrence frequency, and media type.
Support Object Classes - These classes can Connection: Represents the actual connec-
be programmed in the agent or present in the tions and a r e expressed as an association
management application. These classes a r e between particular points. The direction of con-
mostly derived from Open Systems Interconnec- nectivity can be unidirectional (asymmetric) or
tion (OSI). Some support object classes are log, bidirectional (symmetric). If an instance of this
stateChangeRecord, attibuteChangeValueRe- class is unidirectional, point a will be the origin
cord, alarmRecord, eventFonvardingDiscrimina- and terminal point z will be the destination. The
tor, and managementOperationSchedule. operational state will indicate the capacity to
load a signal. An example of an attribute for this
Managed Object Classes - Observing the class is the communication type (simplex, half
functionalities of WSNs, the following object duplex, full duplex).
classes can be identified.
Network: Composed of interconnected man- PUTTING IT ALLTOGETHER
aged objects (physical or logical ones), capable
of exchanging information. Examples of new Consider that a managing entity has just received
attributes: network identifier, composition type a sensing range area rnap and detects the exis-
(homogeneous, heterogeneous), organization tence of high node density, because there are
type (flat, hierarchical), organization period, lots of intersections from the sensing range of
mobility (stationary, stationary nodes and mobile the nodes. The managing entity faces a redun-
phenomenon;mobile node, and mobile phe- dancy problem of the sensing data received. On
nomenon), data delivery (continuous, event driv- one hand redundancy provides a mechanism for
en, on demand, programmed), type of access fault-tolerance and multi-resolution, on the
point (sink node or base station), and localiza- other hand, it represents waste of resources.
tion type (relative and absolute). This redundancy problem was detected by the
Managed element: Represents the sensor and MANNA architecture using the WSN models, in
acting nodes or other WSN entities, which exe- particular, the sensing coverage area map. Based
cute functions on managed elements, providing on this map, maintenance functions may be exe-
124 IEEE Communicatians Magazine February 2003
cuted. These functions can be manual, automat-
ic, or semi-automatic, depending on the physical
architecture established for the management and
the management policy. In this case, a function
possibly invoked is the node operating state con-
cal architecture. It also establishes the communi-
cation interfaces for the management entities
according to the available protocol profiles.
REFERENCES
-In the MANNA
architecture, the
execution of
trol function. [11 S. Lindsey et al., "Data Gathering in Sensor Networks
This function represents the intersection of . Using the Energy Delay Metric," /€E€ Trans. Parallel and management
the three abstraction plans for the configuration Distrib. Syst., vol. A, no. 13, Sept. 2002, pp. 924-35.
functional area, network element management [2] D. Estrin, R. Govindan, and J . Heidemann, "Embedding services (composed
the internet," Commun. ACM, vol. 43, no. 5, May
level, and sensing functionality. The function 2000, Special I, pp. 39-41. of functions) is
allows placing the redundant nodes in the inac- [31 B. R. Badrinath et al., "Special issue on Smart Spaces
tive state. For this, the agent attributes the value and Environments," /€€E Pers. Commun., Oct 2000. dependent on the
[4] S. Meguerdichian et a/.,."Coverage Problems in Wireless
disable for the operational state of the objects AdHoc Sensor Networks," INFOCOM, 2001, pp. 1380-87. information
(present in the MIB) that represent such nodes, [5] S. B. B. Deb and B. Nath, "A Topology Discovery Algo-
acting over the nodes and removing them from rithm for Sensor Networks with Applications t o Net- obtained from
the sensing service. work Management," Tech. rep. DCSTR-441, Dept. of
In the MANNA architecture, the execution of Comp. Sci., Rutgers Univ., May 2002. the WSN models.
[6] M.-W. Subbarao, "Ad Hoc Networking Critical Features
management services (composed of functions) is and Performance Metrics," Tech. rep., Wireless Com- The definition of
dependent on the information obtained from the mun. Technology Group, NIST, Sept. 1999.
WSN models (topology map, energy map, cover- 171 D. B Johnson and D. A. Maltz, "Dynamic Source Rout- functions that
ing in Ad Hoc Wireless Networks," lmielinski and Korth,
ing area map). The definition of functions that Eds., Mobile Comp., vol. 353, 1996. compose these
compose these services is based on the three [8] W. Chen, N. Jain; and 5 . Singh, "Anmp: Ad Hoc Net-
functional plans. work Network Management Protocol," /E€€ JSAC, vol. services is based
17,no. 8, Aug. 1999, pp. 1506-31.
on the three
CONCLUSION BIOGRAPHIES functional plans.
Wireless sensor networks represent a new fron- LINNYER BEATRYS RUIZ (linnyer@dcc.ufmg.br) has been an
tier in the development of technology to be used associate professor of computer science at the Pontifical
Catholic University of Parana (PUCPR), Brazil, since 1996.
in a variety of applications of our daily life in the She is currently working toward a Ph.D. degree in comput-
future. As a new research area, there are several er science at the Federal University of Minas Gerais (UFMG),
open problems that need to be investigated. One Brazil, She received an M.S. degree in electrical engineering
of them is management of those networks. As and industrial information from the Federal Center of Tech-
nological Education of Parana (CEFETPR), Brazil, in 1996
pointed out earlier, there are several significant and a B.S. degree in computer engineering from PUCPR.
differences in the management of traditional Her areas of interest and research include WSNs, telecom-
networks and WSNs. Therefore, we need a dif- munications and mana,gement o f computer networks,
ferent management. architecture for this kind of information theory, and software development. She is an
expert in telecommunications management network (TMN).
network. Since 1993 she has participated i n and coordinated
The task of building and deploying manage- research groups on TMN. Currently, she is coordinating the
ment systems in environments where there will WSN group in the Computer Science Department of UFMG.
be tens of thousands of network elements with She has been a member of the technical program commit-
tees of IEEE Latin American Network Operation (LANOMS
particular features and organization is very com- 2001) and a referee in other conferences.
plex. The task becomes worse due to the physi-
cal restrictions of the sensor nodes, in particular [M
NOGUEIRA I
JOSE MARCOS (jmarcos@dcc.ufmg.br) is an
energy and bandwidth restrictions. associate professor of computer science at UFMG, Brazil. His
areas of interest and research include computer networks,
This work presents and discusses the telecommunications and computer network management,
MANNA management architecture for WSNs, and software development. He received a B.S. degree i n
based on the principles presented and discussed electrical engineering, an M.S. degree in computer science
earlier. The article discusses the management from UFMG in 1979, and a Ph.D. degree in electrical engi-
neering from the University of Campinas, Brazil in 1985. He
functional areas, WSN models, WSN functionali- he1d.a post-doctoral position at the University of British
ties, and management levels. It presents the Columbia, Canada, 1988-1 989. He headed the Department
technical basis to the evolution of such a tech- of Computer Science at UFMG from 1998 t o 2000. Current-
nology from the management point of view. ly, he heads the computer network group at UFMG [PBI I
and was technical coordinator of the System for the Inte-
As mentioned before, a WSN is application- gration of Supervision (SIS) [PB2] Project where a complex
dependent, which implies that the management and distributed system for the management of telecommu-
requirements also change among sensor net- nications networks was developed. He has served in various
works. Nevertheless, the MANNA architecture roles, including General Chair (1985) and TPC Chair (1999)
of the Brazilian Symposium on Computer Networks (SBRC),
provides flexibility when defining the three and General Chair o f LANOMS 2001. He has been a TPC
architectures: functional, information, and physi- member in IEEE/IFIP NOMS (2000 and 2002). IEEE/IFIP IM
cal. The coordination among the three planes is 2003, IEEE LANOMS (1999 and 2001), IEEE/IFIP MMNS
based solely on policy-based management. The (2000, 2001, 2002, 2003), IPOM 2002, IFIP/IEEE IM (2003),
SBRC(from 1990 t o 2003). and iEEE/IFIP DSOM 2003.
functional architecture allows the establishment
of all possible configurations for the manage- ANTONIO F. LOUREIRO
A. (loureiro@dcc.ufmg.br) is an associ-
ment entities (manager, agent, and MIB). The ate professor of computer science at UFMG, Brazil..His
areas of interest and research include computer networks,
information architecture specifies object classes network management, distributed algorithms, mobile com-
and the syntax and semantics of the information puting, and wireless communication. He received B.S. and
exchanged among the entities. The physical M.S. degrees in computer science from the UFMG. and a
architecture reflects the flexibility provided by Ph.D. degree i n computer science from the University of
British Columbia, Canada, in 1995. He has served in various
the functional architecture by allowing different roles, including General Chair of the Brazilian Symposium
locations of managers and agents, and the defi- on Computer Networks - SBRC 2000 and TPC Chair of
nition of a centralized, distributed, or hierarchi- LANOMS 2001.
IEEE Communications Magazine February 2003 125
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