Besides, PBNM proposes that high-level enterprize business policies could be mapped into network devices configuration by the management system, reducing.
Policy-Based Dynamic Reconfiguration of Mobile Ad Hoc Networks Marcos A. de Siqueira, Fabricio L. Figueiredo, Flavia M. F. Rocha, Jose A. Martins, and Marcel C. de Castro CPqD Telecommunications Research and Development Center, Rodovia Campinas Mogi-Mirim, km 118, 5 - 13086-902 Campinas - SP- Brazil {siqueira, fabricio, flavia, martins, mcastro}@cpqd.com.br
Abstract. Ad hoc networks are intrinsically dynamic with respect to mobility, traffic patterns, node density, number of nodes, physical topology, and others. This scenario imposes several challenges to the ad hoc routing protocols, and there is no single solution for all scenarios. This paper proposes the application of Policy-Based Network Management (PBNM) for dynamic reconfiguration of ad hoc networks. PBNM uses the concept of policies formed by events, conditions and actions. The occurrence of an event triggers conditions evaluation, and if evaluated to true, a set of actions should be performed. The paper contribution comprises the proposal of an ad hoc policy information model based on DEN-ng policy model for the implementation of a policy manager prototype to be integrated in the NS-2 simulator allowing dynamic reconfiguration of routing protocol parameters in simulation time; and the proposal of policies for dynamically adjusting the ad hoc routing protocol behavior.
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Introduction
Currently, telephony and Internet access services in the majority of the developing countries are mainly provided over the old cooper plant. In fact, fixed wireless (WLL - Wireless Local Loop) has failed in reaching a high number of subscribers around the world, due to poor service coverage, terminal cost and the lack of enough speed for Internet access (limited to 9.600bps). Mobile Ad Hoc Networks (MANETs) are being widely studied by the academy and industry, and promises to be a quite suitable technology for the provision of network access services, including of voice services in uncovered areas. The main advantage of MANETs for this scenario is that there is no need of high cost infrastructure, which dramatically reduces the network deployment costs. One of the challenges of building MANETs is the design of a suitable ad hoc routing
The research that resulted in this work was performed at CPqD and was funded by FUNTTEL.
P. Lorenz and P. Dini (Eds.): ICN 2005, LNCS 3421, pp. 116–124, 2005. c Springer-Verlag Berlin Heidelberg 2005
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protocol, each one suggested with a specific goal, such as low battery consumption, scalability, robustness and others. Besides a routing protocol, a MANET needs additional mechanisms, such as a suitable addressing scheme and a distributed algorithm for hierarchical address distribution; efficient physical and MAC (Media Access Control) layers and a distributed management system. All these mechanisms may need to be dynamically adjusted, according to dynamics of topology, traffic and node state conditions. For instance, depending on the overall battery energy stored, the routing protocol could be changed from a ”performance optimized protocol” to a ”power consumption optimized” one. In this context, an important goal of a network management system designed for ad hoc network is to set up network configuration according to several policies, thus allowing dynamic and optimized network configuration and adapting parameters, such as the routing protocol operation, addressing scheme and QoS mechanisms, to network conditions, which includes node density, signal propagation conditions, traffic patterns, and others. Moreover, the management system shall guarantee the uniformity of network configuration parameters throughout the network nodes, avoiding undesired scenarios, such as network loops and route instability, dynamic configuration of these parameters. MANET management has not been a prioritized problem so far. The wellknown proposed solutions for ad hoc network management, Ad Hoc Network Management Protocol (ANMP) [1] and Guerrilla Management Architecture [2] don’t focus on QoS, neither on mechanisms for dynamic reconfiguration of routing protocol. The ANMP is the result of a secure message efficient protocol design focused on the development of a lightweight protocol that is compatible with SNMP. The Guerrilla Management Architecture envisions ad hoc networks to be self-organized and self-managed with the collaboration of autonomous nodes. It supports dynamic agent grouping and collaborative management in order to adapt to network dynamics and to minimize management overhead. Recently, technologies such as the Policy-Based Network Management Architecture (PBNM) are emerging and allowing the operation of networks in a more automated way, adapting network devices configuration providing, for instance, suitable Quality of Service (QoS) for the different traffic flows or classes. Besides, PBNM proposes that high-level enterprize business policies could be mapped into network devices configuration by the management system, reducing network operation complexity, independently of the type, manufacturer model and operating system version of the network devices. The policy model DEN-ng [3] represents policies as a set of events, conditions and actions. This paper proposes PBNM as a solution for ad hoc network management, which consists of extending DEN-ng abstract classes (PolicyEvent, PolicyCondition and PolicyEvent) for definition of ad hoc specific policies focusing dynamic routing protocol parameters configuration management. This paper is organized as follows: section 2 presents a background in mobile ad hoc routing protocol requirements, section 3 proposes a policy information model for ad hoc networks, section 4 describes the design of a policy manager
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prototype for managing ad hoc nodes in the NS2 network simulator, section 5 presents the conclusion and future works.
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Mobile Ad Hoc Networks Requirements
A real world ad hoc routing protocol must support continuous, efficient, secure connectivity, as well as assuring QoS parameters for the applications in MANETs. Nevertheless, this kind of network has characteristics that represent serious obstacles to the operation of routing protocols, such as dynamic topology, throughput limitation, route instability, battery limitations, broadcast difficulties mainly due to hidden node problem, lack of efficient dynamic and hierarchical addressing mechanisms and others. CPqD has proposed a system based on ad hoc wireless network, aiming at providing voice and data services [4]. The main requirements of the system based on ad hoc wireless network being developed are; user data transmission rate greater that 64kbps, low cost terminal with connection to PSTN and IP networks, ability to identify system faults and to provide external visualization of them, operation at frequency bands according Brazilian spectrum regulation in multihop scenarios with quality of service. In order to fulfill these requirements, ad hoc routing protocols shall support a large number of functionalities, including fully distributed operation; loop prevention; on demand, proactive or hybrid operation; security; sleep period support; unidirectional links support; link failure detection; ingress node buffering (while discovering routes), discovery and usage of multiple routes for load balancing; fast recovery; adoption of advanced metrics, such as path longevity, battery level, node processing power and others. The success of a given routing protocol in a given network scenario can be measured in terms of a set of performance metrics achieved in the routes discovered by the protocol. Some of these metrics are: end-to-end throughput and latency, packet loss, rate of out of order packets delivered, routing efficiency - reflecting the rate of delivered payload versus routing protocol signaling overhead. From Quality of Service point of view, the ad hoc routing protocol shall be able to measure and propagate available bandwidth as an additional metric, perform distributed admission control and resource reservation, fast route recovery and reliable route establishment. We have performed an extensive research on ad hoc routing protocols and haven’t found a single solution for satisfying all the requirements described above. Each routing protocol attends on a specific set of requirements and presents a limited set of functionalities. Indeed, some protocols are focused on node energy economy, others are focused on reduced overhead and others in reducing processing power requirements, and so on. This is the main motivation for designing a policy-based auto-adaptation mechanism. It represents a feasible approach to dynamically modify ad hoc routing protocol behavior, aiming ate keeping the compliance to the network performance requirements.
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Ad Hoc Policy Management
J. Strassner [3] proposed a policy architecture called DEN-ng that employs an UML (Unified Modelling Language) meta-model for granting that a set of building blocks (objects representing the network policies) are used in the model construction. The model is composed of three components: textual use cases, UML models and a data dictionary defining relationship semantics. Besides, DEN-ng defines a finite state machine for controlling policies life cycle. DEN-ng defines policy rules as containers composed of four components: Meta data, event clause, condition clause and action clause. It is mandatory that the event, condition and action clause are present in a given policy rule. This approach provides a consistent rule structure. Each clause has OCL (Object Constraint Language) constraints, thus allowing the clarifications of the policy evaluation semantics, avoiding ambiguity and interoperability problems. 3.1
Ad Hoc Policy Events
As described in the previous sections, in the DEN-ng model a policy is represented as an association of a set of events, conditions and actions. This section proposes the modelling of events, conditions and actions for ad hoc networks. We have modelled events as occurrences within the network domain. Table 1 illustrates some events that should lead to reconfiguration of network parameters. These events represent an indication that network characteristics are changing and reconfiguration may be necessary. For instance, if the average dynamicity degree increases, it may lead to a rise of route breakages. A Policy Rule can be associated with one or more events and the execution of this policy (condition analysis) can be initiated by the occurrence of a particular event or by a set of events. We propose to associate each event to a parameter measured in the network, as shown at table 1. The right column presents an illustrative default value for the thresholds, but these values could be used only initially and then they can be adapted according to dynamics of the system. Table 1. Ad hoc events Event variable Operator and variable Default value Network availability (NA) NA < Nai NAi=97% Avg packet loss (APL) APL > APLi APLi=8% for a sample of connections ”N” failures on connection CEF > CEFi in Ti CEFi = 3, Ti=10s establishment (CEF) in a time interval (Ti) ”N” route breaks (RB) in a RB > RBi in Ti RBi =3, Ti=10s time interval (Ti)
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M.A. de Siqueira et al. Table 2. Ad hoc conditions Variable Code and operator Average node density ANDE > ANDEi Average Dynamicity Degree (ADD) ADD > ADDi Ratio between the number of Source DSD > DSDi /Destination pairs and the total number Existence of real time applications (RTA) RTA = RTAi Energy saving mode ESM(ESM) = ESMi Number of nodes(NON) NON > NONi Physical topology clustering degree (PTC) PTC < PTCi
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Default value 5 0.2 events/s 10% 0 - no, 1- yes 0 - no, 1- yes 300 40%
Ad Hoc Policy Conditions
The policy conditions are defined as parameters that allow the mapping of the adaptability of the routing protocol to current network state. In order to define network states that have influence on the routing protocol, seven network features are considered, according to Table 2. The Average node density (ANDE) is calculated by counting the average number of directed connected neighbors for each node at the network. Some protocols such as DSDV don’t operate adequately in these scenarios. Others such as DLAR operate optimally with many paths for load balancing. The Average Dynamicity Degree (ADD) is defined as the average number of ticks each node can measure for the set of neighbors. It can be measured using the ”number of ticks” defined by Toh [5]. Protocols such as ABR that use the path stability as a metric present better performance with high degree of mobility. The Degree of source-destination pairs (DSD) is related to the application communication patterns. Client-server applications tend to concentrate all communications to the server. On the other hand, peer-to-peer applications tend to distribute communications uniformly between most of the nodes. Proactive protocols tend to obtain better results with many-to-many communication, while reactive protocols that use route caching are better with many-to-one communication patterns. Networks that provide services with QoS requirements such as real time applications (RTA) need a QoS aware routing protocol such as AQOR [6], INSIGNIA[7] or SWAN (Stateless Wireless Ad hoc Networks)[8]. The condition Energy Saving Mode (ESM) should influence routing protocol parameters such as route update times and routing protocol choice for a ”sleep period aware”. The number of nodes (NON) influences on the routing protocol choice. For instance, in a network with more than 300 nodes a scalable routing protocol such as ZRP should be configured. The Physical topology clustering degree (PTC) is defined as the ratio between the average number of nodes per cluster and total number of nodes in a hierarchical ad hoc network. This parameter is difficult to measure and indicates
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Fig. 1. Ad hoc condition policy variables Table 3. Ad hoc actions Type Possible values Enum, int DSDV (1), DSR (2), ABR (3), TDR (4), DLAR (5), OLSR (6), CBRP (7), ZRP (8). Cluster or zone radius int < 10 Maximum number of paths per route int 5s Action Variable Routing protocol (RP)
a tendency that a cluster-based routing protocol would provide better network performance. Figure 1 presents the PIM (Policy Information Model) mapping for the proposed policy conditions. The conditions are created as VariableCustom classes. For policy evaluation, the PolicyVariables created should be matched against PolicyValues using PolicyOperators. 3.3
Ad Hoc Policy Actions
After the detection of an event and analysis of possible root causes, the Policy Manager performs a reactive action with the goal of re-adapting the system configuration. Some possible actions are shown at Table 3. The main action proposed is the reconfiguration of the current routing protocol. This action should be executed in scenarios where overall network behavior has changed, such as mobility degree modification, communication pattern modification, power electricity company failure (nodes operating with battery), high modification in node density and others. The above actions implies in the reconfiguration of all network nodes, which is a very costly procedure.
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Other actions are related to routing protocol optimization, such as variation of cluster or zone radius, variation of the maximum number of paths for multi-path protocols, optimization of the cache entry expiration time for reactive protocols and route update message time for proactive routing protocols.
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Policy Manager Implementation
This section describes the architecture and implementation of a Policy Manager (PM) for dynamic reconfiguration of ad hoc networks. The main goal is to integrate the PM in the NS2 network simulator for experimentations of dynamic policy-based network reconfiguration evaluation in a simulation scenario. The main purpose of the Policy Manager is to allow the creation, modification and removal of policies, as well as the evaluation of these policies and configurations at network device level. The PDP architecture is shown in Figure 2, and the PM interfaces and components used are described below: – I-PMT (Policy Management Tool Interface): provides access for network administrators, allowing them to insert, edit and delete policies; – I-PR (Policy Repository Interface): provides access to the policies (events, conditions, actions and its relationships) stored at the policy repository; – I-PSMR (Policy State Machine Repository Interface): provides access to the policies state repository; – I-NELC (Network Element Layer Configuration Interface): provides access to the different network devices for configuration. This interface may translate policy actions into protocols and specific commands from the devices being managed; – I-NELM (Network Element Layer Monitoring Interface): provides access to device for monitoring network and traffic state; – PE (Policy Editor): implements the server side presentation logic of the policy editor. Policy edition encompasses a user friendly interface, policy translation to the adopted PIM (Policy Information Model), and policy conflict detection;
Fig. 2. Policy Manager internal architecture
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– EG (Event Generator): provides generation of specific pre-configured events, mainly obtained through the I-NELM interface, subsequently triggering the analysis of the set of conditions from the policies associated with the given event; – CA (Condition Analyzer): provides simple condition analysis based on PolicyVariables, PolicyOperators and PolicyValues; – AG (Actions Generator): sends specific actions to the I-NELC interface after condition evaluation to TRUE or FALSE; – SMC (State Machine Controller): communicate with EG, CA and AG modules for updating and providing up to date policy state, allowing the system to run free of policy evaluation errors and helping the network administrator to monitor the QoS levels applied through the policies.
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Conclusion and Future Works
In this paper we have described the implementation architecture of a PBNM system designed specifically for dynamic configuration of wireless ad hoc routers. The paper contribution comprises the proposal of an ad hoc policy information model based on DEN-ng policy model for the implementation of a policy manager prototype to be integrated in the NS-2 simulator allowing dynamic reconfiguration of routing protocol parameters in simulation time; and the proposal of policies for dynamically adjusting the ad hoc routing protocol behavior. As far as the policy-based management of ad hoc networks proves to be effective, not causing network instability (through simulation), the strategy shall be applied to the project proposed by CPqD of a system based on ad hoc wireless network, aiming at providing voice and data services. Other future works includes the integration of the Policy Manager within NS2 network simulator, validation of the applicability of policy-based reconfiguration of ad hoc network parameters and the development of a policy conflict detector and a policy pluggable Policy Manager. This means that new kinds of events, conditions and actions could become available on the Policy Editor and Policy Manager without new generation of code. This task should be performed using mechanisms based on XML.
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5. Toh, C.K.: Ad Hoc Mobile Wireless Networks: Protocols and Systems. Prentice Hall; 1st edition December 3, (2001). 6. Xue, Q., Ganz, A.: Ad Hoc on-demand routing (AQOR) in mobile ad hoc networks. Journal of Parallel Distributed Computing (2003). 7. Ahn, G-S., et al.: INSIGNIA, IETF Internet Draft, draft-ietf-manet-insignia-01.txt, October (1999), expired. 8. Ahn, G.S., Campbell, A.T., Veres, A., Sun, L.H.: Supporting Service Differentiation for Real-Time and Best-Effort Traffic in Stateless Wireless Ad Hoc Networks (SWAN). IEEE Transactions on Mobile Computing, Vol. 1, No. 3, July (2002).
