ngvn: a framework for next generation vehicular

NGVN: A Framework for Next Generation Vehicular Networks Sławomir Kukliński

Adrian Matei

Grzegorz Wolny

Telekomunikacja Polska – Orange Labs Warsaw University of Technology Warsaw, Poland [email protected]

POLITEHNICA University of Bucharest Orange Romania Bucharest, Romania [email protected]

Telekomunikacja Polska – Orange Labs University of Warsaw Warsaw, Poland [email protected]

proposals for solving VANET specific problems, there is no open architecture able to deal with incremental improvements or upgrades of the existing mechanisms while keeping the overall design intact.

Abstract — Vehicular communications is an important research area. Unfortunately, the proposed Vehicular Ad-Hoc Networks (VANET) solutions are either extremely complex, making them impractical for implementation, or they focus on a limited service scenario only. In this paper, we are defining a new, “clean-slate” framework for Next Generation Vehicular Networks (NGVN), which is able to cope with multiple service scenarios. The layered structure of the framework is relatively simple and is able to accommodate many of the existing VANET concepts. It is based on the context-awareness paradigm which is implemented in all framework layers and it focuses on enabling disruption-tolerant networking to improve connection reliability and content dissemination. The contexts are exchanged in a cross-layer fashion, allowing the system to adapt its behavior in order to increase the overall performance. This paper presents the fundamental concepts of the proposed framework.

In this paper we propose a new structure for a generic framework for Next Generation Vehicular Networks (NGVNs) supporting concepts like context-awareness and disruptiontolerant communications, in order to obtain reliable, adaptive and scalable architecture. This framework supports interoperability across heterogeneous networks which tolerate long delays. Mobility patterns play an important role in the communication scheme, as vital context information used for the improvement of the overall network performance and content delivery. The rest of the paper is organized as follows. Section II presents some significant work in the field of VANET. In Section III, the new framework for Next Generation Vehicular Networks is described. Finally, we conclude the work in Section IV.

Keywords: VANET, disruption-tolerant networking, contextawareness, cross-layer design

I.

INTRODUCTION

II.

Nowadays the field of Intelligent Transportation Systems (ITS) is a challenging research area due to the potential of new vehicular applications. Research efforts in Vehicular Ad-hoc Networks (VANETs) are in fact split between industrial consortia and the academic community. Unfortunately, there is no general consensus with respect to fundamental service models and the universal platform architecture. The first generation of vehicular platforms is a result of international projects and standardization activities: IEEE 802.11p (WAVE), Vehicle Safety Consortium (VSC), Car-2-Car Communication Consortium (C2C-CC), ETSI-ITS, Advanced Safety Vehicle Program (ASV) and Vehicle Infrastructure Integration Program (VII). Many recent projects, like CarTALK2000, FleetNet, NoW, CVIS, SAFESPOT, COOPERS, GeoNet and GST are focusing on the usage of the existing communications technologies like WiFi, DSRC or UMTS (see [1]).

There have been many papers (e.g. [3] – [6]) focusing on new routing protocols or data dissemination schemes specific to VANET, e.g. GeoDTN+Nav, OPERA, VADD and many more, in order to achieve increased communications reliability in some mobility scenarios (e.g. highway or urban areas) or particular applications. Unfortunately, these approaches still remain purely theoretical, they are not deployed in any commercial network. The diversity of the proposed solutions calls for a single, unified communications and service platform which can be used for all possible scenarios.

Out of the existing problems related to VANETs, two are the most challenging. The first one is related to communications reliability in a highly dynamic environment, while the second one deals with the definition of services. In order to cope with these issues, current contributions focus on disruption-tolerant forwarding mechanisms for intermittent communications, adaptations of the existing TCP/IP stacks, new routing protocols and many others. In spite of the several

c 978-1-4244-6363-3/10/$26.00 2010 IEEE

RELATED WORK

Core VANET research topics include nodes clustering, specific routing schemes, disruption-tolerant forwarding mechanisms and context-awareness. The clustering algorithms deal with the highly dynamic network topology which depends on the mobility of nodes (see [2]). These algorithms perform node grouping into stable clusters, in order to reduce the network size and provide reliable communication and routing among cluster members. However, due to various mobility patterns of the nodes, many of them are standalone nodes and the continuous connectivity cannot always be ensured for them.

A reliable communication has to deal with intermittent connectivity of VANET nodes. Adapting Disruption Tolerant Networking (DTN) to VANET provides a way to cope with

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CROSS‐LAYER CONTEXT

Figure 1. NGVN layers

temporary disconnections. The combination of DTN with node mobility information can be used for advanced content dissemination (the store-carry-forward paradigm). In the existing approaches (see [7] and [8]), disruption-tolerant forwarding is a part of a convergence layer which enables dynamic address binding and data rate adaptation.

III.

FRAMEWORK DEFINITION

In this paper, we focus on the definition of a framework for Next Generation Vehicular Networks, driven by the context data exchange and decisions based on it. In the proposed framework, there is an internal separation into three functional layers (see Figure 1), namely the Mobility Layer (ML), the Connectivity Layer (CL) and the Application Layer (AL), representing basic functionality related to mobility, connectivity and application. Each layer is described by a set of key parameters, which can be represented as context information. This information can be exchanged between layers to optimize their internal behavior (e.g. the selection a routing/forwarding mechanism which is the best matched to a certain mobility context), but not by direct transfer between them. The context is not only referring to a set of external constraints on the system for a given instance, but in this case it relates to any piece of information regarding the network and services – it can include internal or external control data or can be instance related. The advantage of using important parameters as contexts is the possibility to identify the most significant data related to the intra-layer mechanisms, which can be described in a unified way and to use the context information to enable the cross-layer transversal interaction. There is no direct context transfer between layers in the framework. The context information is exchanged bidirectionally only after applying the cross-layer adaptation mechanisms to it. This also assures functional separation between the layers.

Until now, there have been several, mostly theoretical approaches to context-awareness, which deal with context at the service level in next generation networks (see [9] – [10]). In the MIDAS project (see [11]), the approach was to develop a secure middleware platform for context-aware MANET services, which includes a context engine implementing mechanisms to retrieve, model, synthesize and distribute the context information in a mobile distributed environment. It is also worth to notice an attempt to use the existing infrastructure of a telecom operator for the creation of vehicle-to-vehicle services. In [12], the authors are proposing the m:Vía system, a practical approach which combines advanced concepts of ITS with the IP Multimedia Subsystem (IMS). Although IMS integration is an advantage, the local context is ignored and the scalability can be an issue. Despite the significant research efforts in VANET, most of the proposed contributions are assuming ‘closed architectures’, which are not mutually compatible. In order to deal with this issue, we have developed a framework which is able to integrate the existing concepts related to communications protocols and service definitions. One possible usage of this framework combines VANET with disruption-tolerant networking and context-awareness, in a unique approach which ensures the flexibility of the system, able to adapt to the changing context information.

The NGVN framework is based on the importance of mobility context information and the relations between neighboring nodes. The mobility context refers to GPS

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generate the movement prediction context data. This context can be cross-layered and used to shape the behavior of the other AN components.

position, node velocity (both instantaneous and average), direction and neighbor movement data. This information is analyzed inside the ML according to an algorithm (e.g. nodes clustering) and as a result the stable node structures are identified, together with some nodes which are potential candidates to be assigned to such structures. Some important mobility information can be passed in a cross-layer manner to the CL or the AL. Inside the CL the network topology is build and the most appropriate routing and forwarding schemes are applied (including DTN).

B. Connectivity Context component The overall structure of the Connectivity Context component, responsible for the routing and forwarding functions, is presented in Figure 3. Based on cross-layer mobility and application contexts, the connectivity component finds the path to the destination, whenever it is possible, updates the local routing table and takes the best forwarding decision. Connectivity context includes some performance metrics related to standard routing, as well as disruptiontolerant forwarding.

The definition of the framework and the exchange of the cross-layer information in a unified format enables possible improvements and extensions in order to integrate many of the existing VANET algorithms. These improvements especially concern the specific intra-layer mechanisms and algorithms (e.g. a new clustering algorithm, a new routing or forwarding scheme, a new information dissemination mechanism, etc.). However, the framework does not allow changes in the internal structure. Based on the interactions and dependencies between the nodes in the network at each of the three layers of the framework, a node internal architecture can be defined on the idea of context transfer in a component-based approach. This generic architecture defined for Abstract Nodes (AN) is depicted in Figure 2. It emphasizes the three key components – mobility, connectivity and application, which correspond to the three previously defined framework layers. This AN concept is applied to all types of entities, such as clusters, un-clustered nodes and roadside infrastructure nodes.

Figure 3. Connectivity Context component

The Routing Manager (RM) deals with finding routes to particular network destinations, according to an appropriately selected Routing Scheme. The Forwarding Manager (FM) is responsible for forwarding decisions, such as selecting the right forwarding scheme (either disruption-tolerant or not) and choosing the next hop. In case of disruption-tolerant forwarding, custody transfer mechanism (delivery responsibility transfer between nodes) is coordinated by the dedicated Custody Manager. C. Application Context component The Application Context component has similar functionality to the Application Layer in the OSI stack. It is close to the end user of the system and interacts with some applications. It can also be involved in the creation of new context based services. At the Application Context component, a key issue to be resolved is related to addressing of nodes and services, especially if there is the requirement of enabling disruption-tolerant communication between nodes. In the case of highly dynamic vehicular networks most applications require some type of controlled broadcast of information and there is not much need for unicast, therefore assigning a constant address to the node is irrelevant. The address of the destination is not known and bound at the source, since the destination is constantly on the move. Much more important is the context information related to the destination group, location and neighborhood.

Figure 2. Abstract Node component-based internal architecture

The functional layers are fixed in the framework and so are the components of the Abstract Node. Inside these components, new algorithms can be implemented to introduce new functionality. A. Mobility Context component The Mobility Context component is responsible for network topology discovery and the mapping of the real network into a set of Abstract Nodes (“common denominator”), characterized by a set of Mobility parameters (usually geographical position, speed and direction vector). In particular, inside this layer, the nodes clustering algorithm can reduce network size by identifying stable clusters. Communication between nodes inside a cluster is assumed to be continuously available, so in the overall network routing and forwarding, these structures can be treated as single virtual nodes (i.e. the Abstract Node). In this case AN has specific contextual description (e.g. cluster size, neighborhood information, applied intra-cluster routing etc.).

D. Cross-Layer Context component The Cross-Layer Context component (in Figure 4) has a crucial role in our design, as it implements a set of key functions:

The component also maintains movement information of the node itself and neighboring nodes, which can be used to

F1. Gathers important contexts related to mobility, connectivity and application and stores it in a local repository.

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be easily extended and upgraded, applying a context-oriented model for data exchange between components.

F2. Performs context analysis in order to make intelligent decisions related to the distribution of context to other layers. F3. Schedules DTN bundle events. F4. Provides the necessary support for inter-working with multiple communication stacks. F5. Handles security functions related to data validation and user authorization.

The implementation of the architecture is currently in progress and the preliminary results of the test platform simulations will be included in the future work. Given the complexity of the solution and the absence of a good benchmark for it, the main challenge is to further extend the fundamental concepts of the framework to cover the requirements of specific vehicular applications. ACKNOWLEDGMENT The authors gratefully acknowledge the support from France Telecom R&D – OrangeLabs. REFERENCES [1]

Figure 4. Cross-Layer Context component

The core functionality (F1 and F2) is provided by a CrossContext Manager (CCM). Scheduling (F3) is performed by the Scheduling Manager which is responsible for selecting a particular Scheduling Scheme (e.g. Deficit Weighted Round Robin) which will be applied in the case of bundle events (send or receive). By using cross-layering operations on the contexts the system is capable of behaving differently according to the given context and learn from previous experience, in order to adapt to the topology changes and service requirements. IV.

[2]

[3]

[4]

CONCLUSIONS AND FUTURE WORK

In this paper, we have defined NGVN, a new framework for VANETs, which enables disruption-tolerant communications and context-awareness. Although the framework imposes some constraints by the definition of the three layers, developers have a high degree of freedom in selecting the algorithms which will be implemented inside these layers. Enhancing VANET by using disruption-tolerant communication and context-awareness is an innovative approach to deal with the issues of a dynamic network and content delivery. This allows for basic concepts to be reused for other applications. The framework is in line with the key concept characterizing disruption-tolerant communication systems, which is content distribution by applying a storecarry-forward model.

[5]

[6]

[7]

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[9]

The framework cross-layer information exchange can optimize intra-layer mechanisms, as well as the overall system performance. The capability of selecting the best behavior according to a given context, the flexibility of the componentbased approach to integrate multiple algorithms and the unified way of interaction between the layers makes any vehicular system based on this design open for an evolution towards an autonomous, self-configuring, self-optimizing system capable of learning from its history (a cognitive approach). It is this quality that makes it a good candidate for Future Internet.

[10]

[11]

[12]

While this paper focuses on the definition of a layered network framework, further development of this concept has led to the definition of an open architecture implementation model for NGVN nodes, closer to a software-oriented approach (see [13]). The node architecture is modular, scalable and can

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