فایل ورد کامل بررسی آدرس تکراری بین لایه ای توزیع شده برای ارتباطات بحرانی و ایمن VANET

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تعداد صفحات این فایل: ۱۸ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Distributed cross layer duplicate address handling for safety critical VANET communication~~en~~

Abstract

Vehicular ad-hoc networks are in the wake of mass deployment within upcoming years. This dedicated kind of mobile ad-hoc networks in the automotive domain is of high interest to increase safety of driving. We find that prior approaches for duplicate address detection in such networks fail to cover significant use cases. Low available bandwidth and limited communication radius together with high node mobility lead to reduced presence of meta data, like routing tables. This, holds especially for non IP-based safety critical message exchange using dedicated VANET protocols. However, common address duplicate handing mechanisms rely on such meta data. We show that this can lead to failure of duplicate address detection for ETSI ITS and WAVE in safety critical use cases. This is caused by a variant of the well known hidden station problem. To overcome this weakness, we propose a cross layer aware duplicate address detection scheme in combination with active address change requests to resolve the duplicates. An evaluation within a simulation environment shows the feasibility of the approach.

۱ Introduction

Mobile ad-hoc networks (MANETs) are an important topic in both research and practice. Vehicular ad-hoc networks (VANETs) are an important subset of MANETs, whose mass roll out is predicted within upcoming years. VANET standardization is mainly performed within US wireless access in vehicular environments (WAVE) and European ETSI intelligent transport systems (ITS) frameworks [1–۳]. A rigid security system is required for VANETs, due to wireless data exchange and safety critical use cases.

Safety critical communication within a VANET is typically stateless, i.e., each message should be usable on its own. Dedicated communication protocols have been developed for this kind of data exchange. Their requirements arise from robustness against package loss, highly mobile participants and tough realtime requirements of use cases. Thus, each message is digitally signed to ensure authenticity and integrity. Required cryptographic parameters are contained in a security envelope, which embeds the message’s payload at the network layer level. It holds per message parameters (e.g., the signature) and per node parameters (e.g., the public key), which are packed into certificates. These certificates are only sporadically piggybacked on messages to reduce average message size [4,5].

Duplicate address detection (DAD) is a well known problem in communication protocols. It arises from independent (i.e., uncoordinated) selection of addresses at individual nodes, as used within VANETs. Countermeasures typically rely on meta data like routing tables, which are not present in many VANET specific protocol stacks, e.g., in the WAVE system without support for multi-hop communication [1,6]. We find that this leads to a variant of the well known hidden station problem, which occurs on various protocol layers. VANET protocol stacks use node identifiers (i.e., addresses) on many protocol layers. Thus, DAD has to be performed on all these layers, too. However, this is not done by current standards. Only the ETSI ITS network layer uses DAD so far, but the applied mechanism only covers the case in which the own node is causing the duplication. A detailed problem definition is given in Section 2.

The need for DAD in regard to certificate IDs is specific to VANETs. Low communication bandwidth and high numbers of highly mobile nodes require frequent on the fly certificate distribution among nodes. This is done by piggybacking certificates on beacon messages. A-priori certificate distribution is infeasible, due to high numbers of nodes and frequent certificate changes by each node caused by privacy requirements [3,7]. To limit channel load, most messages do not carry their signer’s certificate, but only an ID of it [4,5]. Such an ID is typically determined by using a hash function on the certificate. To further limit message size, IDs are limited in length, e.g., to eight bytes for WAVE and ETSI ITS. This leads to the risk of duplicate certificate IDs within communication range of a node, especially in scenarios with high node density.

The further outline is as follows. Section 2 gives a detailed problem statement. A review of related work is provided in Section 3. Section 4 describes the impact of duplicate addresses on functionality of various protocol layers of VANETs together with mechanisms to detect such duplicates. A decentralized scheme for fast DAD and duplicate resolution requiring only low overhead is proposed in Section 5. Moreover, an evaluation of the introduced mechanism is provided. Finally, Section 6 gives a conclusion about achieved results and possible subjects of future work.

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