A comparative study&nb…

A comparative study of RoutingProtocols in VANET

Sandhaya Kohli,Bandanjot Kaur, SabinaBindra

 

车载自组网选路协议的比较学习(中英文)

 

中文翻译

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摘要

车载自组网是移动自组网的一类，而移动自组网为实现智能交通系统（ITS）提供了出色的方法。所以，为了获得更聪明的智能交通系统来说，研究各种路由协议不仅重要的，而且必要的。这篇文章讨论了这些路由协议的优缺点，同时探讨了这些设计背后的动机，并且回顾了这些选路协议的演变。最后，文章总结比较了各种选路协议。

 

关键词：鱼眼状态路由协议(FSR)，按需距离矢量路由协议(AODV)，动态资源路由选择(DSR)，首选组广播(PGB)，临时按序路由算法(TORA)，BROADCOMM，地域性群播(Geocast)，车载自组网络(VANET)

 

1.简介

车载自组网是移动自组网的一种形式，是为了给临近的汽车之间，或者汽车与固定设备等一些路边设备提供通信的。车载自组网的主要目的就是为乘客带来安全而舒适的服务。每个配备了车载自组网络设备的汽车，都是自组网络中的一个节点，并且能通过无线网络接收和发送信息。碰撞预警，交通信号灯以及及时的路况将成为司机选择最佳的路线的重要工具。车载自组网络或者智能车载网络提供了一种使用车载网络的智能的方式。

随着近年来在路上车辆数目的剧增，开车越来越具挑战性和危险性。道路趋于饱和，导致安全距离车距和适宜的速度难以遵守。主要的汽车制造厂商决定与政府机构合作，提出一种解决方案，旨在通过预测危险事件或者堵车地区来帮助司机。一种研究成果就是新型的无线网络接入方式，这种方式被称作车载环境的无线网接入方式，被用作车辆与车辆以及车辆与路边的通信。

车载自组网络集成了各种自组网络的技术，比如WiFiIEEE802.11b/g，WiMAX802.16，蓝牙，IRA，ZigBee，这些技术为动态移动的汽车之间提供了方便、精确、有效并且简单的通信。车载自组网络为汽车之间的流媒体通信，信息娱乐和远程信息服务界定了安全的通信方式。

2.应用

车载自组网络的应用可以分为以下几类：

（1）车载自组网为路途中的移动用户提供随处可及的连接服务；

（2）提供有效的车与车之间的通信，这使得智能交通系统成为可能。智能交通系统包含多种多样的应用，如交通协同监控，交通流量控制，碍视交叉口以及碰撞避免等等。

（3）舒适应用是指那些让乘客能够与其他车辆或者联网主机通信的应用，这些应用增加了乘客的舒适度。例如，因为车载自组网络为移动汽车的节点提供英特网连接，所以乘客可以下载音乐，发送邮件看在线视频等等。

3.网络体系结构和特点

无线自组网络并不依赖于固定的设备进行通信以及发送信息。车载自组网络的体系结构由三类构成：纯移动网络/无线局域网，纯自组网以及两者的混合。车载自组网络使用固定的移动网关，并且无线局域网/无线城域网接入点位于交叉路口，并与英特网相连接，同时车载自组网络用于收集交通信息以及完成路由选择。这种网络体系结构就是纯移动网或者称为无线局域网。车载自组网可以通过结合移动网络和无线局域网来形成网络。在道路两旁的基站或者固定的网关也可以提供与车辆的连通。在这种情形下，所有的汽车和路边设备形成了一个纯移动自组网络。混合体系由设备网络以及自组网络共同构成。每个处于车载自组网络中的节点能以没有任何中央集权的分布式的形式进行自组织和自我管理信息。因为节点是移动的，因此数据的传送是较不可靠以，并且缺乏优化。车载自组网络的一些显著的特征使得它成为移动自组网络中更具挑战性的一类，这些特征是：高动态拓扑：因为车辆总在高速行驶，所以车载自组网络形成的拓扑结构总是在变化。频繁断开连接的网络：高动态拓扑导致了频繁断开连接的网络。这个问题也源于变化的节点密度。无限的电池电源和存储空间：在车载自组网络中的节点并不像传感器网络，受限于电源和存储空间。各个节点具有充足的能源以及计算能力。车载传感器：节点由传感器构成，它们为路由提供了有用的信息。很多车载自组网络路由协议包含了GPS单元，并靠它们来提供位置信息。

4.路由协议的概述

在车载自组网络中，路由协议被分为五类：基于拓扑学的，基于位置的，基于群集的，地域性群播，广播。

4.1基于拓扑学的路由协议

这些路由协议利用存在在网络中的连接的信息来进行数据包转发。这些协议被更近一步的分为主动型和被动型。

4.1.1.主动型路由协议

主动型路由协议意味着，像下一个转发的路由之类的路由信息被保存在了后台无关的通信请求中。数据包不断地广播，并在各个节点中流动以此来维护路径，接着在节点中建立一张表格，它指出了到达目的地所需的下一跳的节点。主动路由协议的优点是其不需要路由发现，因为目的路由已经被保存在后台，但是它的缺点是对于实时应用程序有较低的延时，它也增加了对一些不需要的数据通道的维护，这降低了可用带宽。各种类型的主动型路由协议是：

4.1.2鱼眼状态路由协议(FSR)

鱼眼状态路由协议与标签交换路由(LSR)相似，在鱼眼状态路由协议中的节点保存着一张基于最近从临节点接收到的信息的拓扑表(TT)，并且持续与本地的临节点交换信息。在大型网络中，为了减小数据包大小，FSR对不同的路由表条目采用了不同的交换周期。对于给定目的地的路由表条目，它完美地与其具有低频率的邻居更新，这个频率随着到目的地的距离增加而减小。FSR路由协议的问题在于其路由表随着网络规模的增加也同样增加。同时，随着移动性增加，到达远程的目的地的路径变得不精确。如果目标节点在源节点范围之外，路由发现将会失败。

4.1.2.1临时按序路由算法（TROA）

临时按序路由算法属于链路反转路由的家庭，这类路由管理着一个环形图表，它被建立用来管理数据包流，并确保每个节点的可到达性。每个节点通过广播查询数据包来建立有向图。一个节点收到查询包，如果其有到达目的地的下行链路，它将广播一个回复包，否则其只是丢弃这个数据包。一个节点收到回复包时，仅在回复包的高度小于其他回复包的高度时，更新自己的高度。临时按序路由算法优点是它给出了到达所有在网络中节点的路径，但是在车载自组网络中维护所有这些路径是很困难的。

4.2基于位置的路由协议

基于位置的路由协议算法由一系列的路由算法构成。他们的共同特征是利用地理位置信息来选择下一跳。在没有任何地理信息的情况，数据包被发送到一个与目的地相近的邻居节点。基于位置的路由协议优点在于不需要创建和维护从源节点到目的节点的全局道路。基于位置的路由协议一般被分为两类：基于位置的车与车的贪婪协议，允许延时协议。

4.2.1基于位置的车与车的贪婪协议

路径中的节点利用贪婪策略和中间媒介，往下一个目标方向上最远的邻节点传递信息。贪婪算法要求中间节点需要掌握自己的位置，邻居的位置以及目的地的位置。这些协议的目的在于尽快的转发数据包，因此它们也被称作最小延时路由协议。不同种类的基于位置的车与车贪婪协议有：地理源路由(GSR)，贪婪周边无状态路由(GPSR)，有序分配路由(sequential assignment routing,SAR)，贪婪周边协调路由(GreedyPerimeter Coordinator Routing ,GPCR)，ASTAR，STBR，CBF，DIR，ROMSGP

4.2.1.1地理源路由

早期的地理源路由被用于移动自组织网络。然后它通过并入贪婪的向目的地转发信息而得到优化，以用于车载自组网络。如果在任意一跳中，没有指向目的地的节点，那么GPSR将运用一个被称为边界模式的恢复策略。边界模式包含两个部分，一个是分布式平面化算法，这个算法通过移除冗余的边界，将本地的连接图转化成平面图。第二个部分是在线路由算法，这个算法在平面图上操作。

因此，GPSR的边界模式在车载自组网络中得以使用。在GPSR中，如果有任何障碍或者无效出现，那么算法将进入边界模式，同时启动平面图路由算法，它致力于向中间媒介的邻居而不是向更远的节点发送信息，但是这个方法因为增加了路由跳的次数因此有较长的延时。因为汽车的高速移动，路由圈由此形成，这会导致信息发送到更长的路径上。GSR采用了静态街道地图和以及每个节点的位置信息，因此GPSR并没有考虑街道上车辆的密度，所以其对于车载自组网络来说，不是一个高效的方法。

4.3广播路由

在车载自组网络中，广播路由经常用于车辆之间的共享，交通信息，天气信息，紧急情况以及道路状况的发送，发送广告和公告。广播被用于向超出范围的车辆发送消息，比如多跳的使用。广播向所有在网络中的节点发送数据包，一般采用的是泛洪。这样确保了数据包的发送，但是浪费了带宽，并且节点会收到重复包。在车载自组网络中，它在节点数量较少的情况下，表现出色。各种广播路由协议包括BROADCOMM,UMB,V-TRADE以及DV-CAST。

4.3.1BROADCOMM路由协议

BROADCOMM是基于高速网络的层次结构的。在BROADCOMM中，高速通道被分成分成很多虚拟存储单元，这些单元像车辆一样移动。在高速通道中的节点由两个层次组成：第一层次包含了所有在一个单元格的节点，第二层次以单元反射器为代表，单元反射器是少数的位置上接近单元格地理中心的节点。单元格会在单元格的相同成员或相邻单元格发出簇头和紧急信息的情况下定期，不间断地作出反应。这个协议在消息广播以及路由开销方面，与基于泛洪的路由协议具有类似的表现。

4.3.2城市多跳广播协议（UMB）

UMB的设计源于解决在多跳广播中分发信息时，出现的干扰、包冲突以及隐藏节点的问题。在UMB中，发送节点尝试选择广播路径上更远的节点，并确认数据包没有任何之前的拓扑信息。在高数据包负载以及高车辆密度的时候，UMB协议表现出色。

4.3.3基于矢量跟踪检测（V-TRADE）

这是一个基于GPS的信息广播协议。它最基本的想法与单播路由协议中的区域路由协议（ZRP）相似。V-TRADE根据位置和移动信息，将临节点分为不同的转发组。对于每个组，只有一小部分的汽车被选来再次广播信息。V-TRADE提高了带宽利用率，但是一些路由开销与在每一跳中下一个转发节点的选择相关。

4.3.4位置辅助路由

位置辅助路由主要是一个基于位置的多播路由。其目标是从源节点向所有其他在特定地理区域(ZOR)的节点发送数据包。在位置辅助路由中，在相关区域之外的车辆不会受到被警告，从而避免了不必要的匆忙反应。位置辅助被认为是一种在特定地理区域内的多播服务。它一般指定了转发区域，这也指出了数据包泛洪的区域，这样是为了降低信息开销和网络拥塞，这一般是因为简单的随处转发的泛洪数据包而引起的。在目的区域，单播路由将被用于数据包的转发。位置辅助的缺陷有网络划分，也有不支持的临节点可能会隐藏合适的转发信息。各种位置辅助路由协议有IVG，DG-CASTOR和DRG。

5.结论和未来展望

在这篇文章中，我们回顾了已有的路由协议。表格1中给出了这些协议的比较。优先转发方法描述了当有数据包转发时，协议中第一个路由的选择。在延迟约束协议中，应用了优先转发的方法，然后在其他所的路由协议中，使用了无线多跳的转发方法。数字地图提供了街道层次的地图，以及交通统计数据，例如交通密度，不同时间车辆在路面上的速度。在一些基于簇群的路由协议中，数字地图被强制使用。为了提供可扩展性，虚拟设备通过集群节点而创建。每个集群可以有其簇头，这些簇头负责集群间的安全通信，和群内的网络协调。恢复策略将被用于从一个不利情形恢复。恢复策略是一个判断协议性能的标准。

协议

主动型协议

被动型协议

基于位置的贪婪协议

延时约束协议

基于集群协议

广播协议

地域性群播协议

优先转发方法

无线多跳转发

无线多跳转发

启发式方法

储存和转发

无线多跳转发

无线多跳转发

无线多跳转发

是否要求数字地图

否

否

否

否

是

否

否

是否要求虚拟设备

否

否

否

否

是

否

否

是否真实交通流

是

是

是

否

否

是

是

恢复策略

多跳转发

储存和转发

储存和转发

多跳转发

储存和转发

储存和转发

泛洪

适应场景

城市

城市

城市

稀疏道路

城市

高速公路

高速公路

表1 不同协议的比较

 

车载自组网络路由协议的未来展望包含以下几点：

1.在车载自组网络中，协议设计的主要挑战是提高协议的可靠性，降低发送延时和数据包的重新转发次数。

2．在进行延时约束路由协议的设计时，应当考虑驾驶员的行为，因为携带和转发都是发送数据包的主要方法。

3.应该考虑研究提供舒适应用的位置辅助路由。舒适信息一般是允许延时的。一般为紧急信息预留了网络带宽。因此一个有效的位置辅助路由协议是值得开发的，其使用最小的带宽提供了具有允许延时能力的舒适应用。

引用文献

1.      James Bernsen, D. Mnivannan, Department of

Computer Science, University ofKentucky, Lexington, USA “Unicast routing protocols for vechicularad hoc 

2.      networks: A critical comparison and classification”,in  journalhomepage: www.elsevier.com/locate/pmc Pervasive andMobile Computing 5 (2009) 1-18

3.      Sascha Schnaufer, Holger Fuisler, Matthias Transier, WolfgangEffelsberg, “Unicast Ad-hoc Routing in

Vehicular City Scnarios“ in “Network on wheels“ project undercontract no. 01AK064F and Matthias Transier.

4.      Kevin,Uichin Lee, Mario Gerla, “Survey of Routing Protocolsin Vehicular Ad Hoc Networks in Car 2 Car communicationconsortium

5.      Yu Wang and Fan Li, “Vehicular Ad Hoc Networks” in Guide toWireless Ad Hoc Networks, Computer communication and Networks, DOI10.1007/978-1-

84800-328-6_20

6.      Maxim Raya and Jean-Pierre Hubaux  “Securing vehicular adhoc networks”, Journal of Computer security, IOS Press Amsterdam,The Netherlands, Volume 15, Issue 1(January 2007), pages39-68

7.      Maxim Raya, Panos Papadimitratos and Jean-Pierre Hubaux“Securing Vehicular Communication”, IEEE Wireless CommunicationsMagazine, Special Issue on Inter-Vehicular communication, Vol 13,num. 5, 2006, p. 8-15

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Verita/Ascona, March 9-11,2005 

英文原文

A comparative study of Routing Protocols in VANET

 

Sandhaya Kohli, Bandanjot Kaur, Sabina Bindra

Dept. of CSE, RIMT-IMT, Dept. of CSE, RIMT-IET

 

 

Abstract

Vehicular Ad Hoc Networks (VANET) is a subclass of Mobile ad hocnetworks which provides a distinguish approach for intelligenttransport system (ITS).  The survey of routingprotocols in vanet is important and necessary issue for smartITS.  Thechapter discusses the advantages and disadvantages of these routingprotocols, it explores the motivation behind the designed and tracethe evolution of these routing protocols.  Finally it concludesthe chapter by comparing the various routing protocols.

 

Keywords:FSR, AODV, DSR, PGB, TORA, BROADCOMM, Geocast, VANET

 

1. Introduction

A Vehicular Ad-Hoc network is a form of Mobile ad-hoc Networks, toprovide communication among nearby vehicles and between vehiclesand nearby fixed equipment i.e. roadside equipment. The main goalof VANET is providing safety and comfort for passengers. Eachvehicle equipped with VANET device will be a node in the Ad-hocnetwork and can receive & relay other messagesthrough the wireless network. Collision warning, Road signal armsand in place traffic view will give the driver essential tool todecide the best path along the way. VANET or Intelligent VehicularAd-Hoc Networking provides an intelligent way of using vehicularNetworking.

With the sharp increase of vehicles on roads in the recent years,driving becomes more challenging and dangerous.  Roads are saturated,safety distance and reasonable speeds are hardlyrespected.   Theleading car manufacturer decided to jointly work with govt.agencies to develop solution aimed at helping drivers on the roadsby anticipating hazardous events or bad traffic areas.  One of the outcomeshas been a novel type of wireless access called wireless access forvehicular environment (WAVE) used for vehicle to vehicle andvehicle to road side communication.

VANET integrates multiple Ad-Hoc networking technologies such asWiFi IEEE 802.11 b/g, WiMAX 802.16, Bluetooth, IRA, ZigBee for easyaccurate effective and simple communication between vehicles ondynamic mobility.  VANET helps indefining safety measures in ehicles, streaming communicationbetween vehicles, infotainment and telematics 

2. Applications

VANET application can be categorized into following categories (a)VANET provide ubiquitous connectivity on the road to mobile users(b) It provides efficient vehicle to vehicle communications thatenables the Intelligent Transport System(ITS). ITS includes varietyof applications like cooperative traffic monitoring, control oftraffic flows, blind crossing and collision prevention. (c) Comfortapplication are the application to allow the passenger tocommunicate with other vehicles and with internet hosts, whichimproves passengers comfort.  For example VANETprovides internet connectivity to vehicular nodes while on themovement so that passenger can download music, send emails, watchonline movies etc.

 

3. Network Architecture andcharacteristics

Wireless ad hoc networks do not depend on fixed infrastructure forcommunication and dissemination of information. The architecture ofVANET consists of three categories: Pure cellular/WLAN, Pure Ad hocand hybrid. 

VANET may use fixed cellular gateways and

WLAN/WiMax access points at traffic intersections to connect to theinternet, gather traffic information or for routingpurposes. This network architecture is pure cellular or WLAN.  VANET can compile bothcellular network and WLAN to form the network.  Stationery or fixedgateways around the road sides also provides connectivity tovehicles. In such a scenario all vehicles and road sides devices form a puremobile ad hoc networks.  Hybrid architectureconsists of both infrastructure networks and ad hoc networkstogether. Nodes in VANET can self organized and self manage the informationin a distributed fashion without any centralizedauthority. Since the nodes are mobile so data transmission is less reliableand sub optimal.  Some of thedistinguishing feature of VANET which make it more challengingclass of Manet are: High Dynamic Topology: Since vehicles aremoving at high speed, Topology formed by VANET is alwayschanging. Frequently disconnected network: The highly dynamic topologyresults in frequently disconnected network. This problem is alsocaused by changing node density. Unlimited Battery Power andStorage: Nodes in VANET are not subject to power and storagelimitation as in sensor networks.  Nodes have ampleamount of energy and computing power.  On Board Sensors:Nodes consists of sensors which provide useful information forrouting. Many VANET routing protocols consists of GPS unit which provideslocation information.

 

4. Overview of RoutingProtocols

In VANET, the routing protocols are classified into fivecategories: Topology based, Position based, Cluster based, Geocast,Broadcast.

4.1 Topology based  routingprotocols

These routing protocols use links information that exist in thenetwork to perform packet forwarding. They are further divided intoProactive and Reactive.

4.1.1 Proactive  routingprotocols

The proactive routing means that the routing information like nextforwarding hope is maintained in the background irrespective ofcommunication requests. The packets are constantly broadcast andflooded among nodes to maintain the path, then a table isconstructed within a node which indicates next hop node towards adestination.  The advantage ofproactive routing protocols is that there is no route discovery isrequired since the destination route is stored in the background,but the disadvantage of this protocol is that it provides lowlatency for real time application, it also leads to the maintenanceof unused data paths, which causes the reduction in the availablebandwidth. The various types of proactive routing protocols are:

4.1.2 Fisheye state routing(FSR)

FSR is similar to LSR, in FSR node maintains a topology table (TT)based upon the latest information received from neighboring andperiodically exchange it with local neighbors.  For large networks toreduce the size of message the FSR uses the different exchangeperiod for different entries in routing tables.  Routing table entriesfor a given destination are updated preferably with the neighborshaving low frequency, as the distance to destinationincreases. The problem with the FSR routing is that with the increase innetwork size the routing table also increases.  As the mobilityincreases route to remote destination become lessaccurate. If the target node lies out of scope of source node then routediscovery fails.

4.1.2.1 Temporally Ordered Routing Algorithm(TORA)

TORA belongs to the family of link reversal routing in whichdirected a cyclic graph is built which directs the flow of packetsand ensures its reachability to all nodes. 

A node would construct the directed graph by broadcasting querypackets.  Onreceiving a query packet, if node has a downward link todestination it will broadcast a reply packet; otherwise it simplydrops the packet.  A node on receiving areply packet will update its height only if the height of repliedpacket is minimum of other reply packets.  TORA Algorithm has theadvantage that it gives a route to all the nodes in the network,but the maintenance of all these routes is difficult inVANET.

4.2position based routingprotocol

Position based routing consists of class of routingalgorithm. They share the property of using geographic positioning informationin order to select the next forwarding hops.  The packet is sendwithout any map knowledge to the one hop neighbor which is closestto destination. Position based routing is beneficial since noglobal route from source node to destination node need to becreated and maintained.  Position based routingis broadly divided in two types: Position based greedy V2Vprotocols, Delay Tolerant Protocols.

4.2.1  Position Based GreedyV2V Protocols 

In greedy strategy and intermediate node in the route forwardmessage to the farthest neighbor in the direction of the nextdestination.  Greedy approachrequires that intermediate node should possessed position ofitself, position of its neighbor and destinationposition. The goal of these protocols is to transmit data packets todestination as soon as possible that is why these are also known asmin delay routing protocols.  Various types ofposition based greedy V2V protocols are GSR, GPSR, SAR, GPCR, CAR,ASTAR, STBR,   CBF,DIR and ROMSGP

4.2.1.1 Geographic Source Routing (GSR)

Earlier GSR was used in MANET.  Then it was improvedto use in VANET scenario by incorporating in to it greedyforwarding of messages toward the destination.  If at any hop thereare no nodes in the direction of destination then GPSR utilizes arecovery strategy known as perimeter mode.  The perimeter mode hastwo components one is distributed planarization algorithm thatmakes local conversion of connectivity graph into planar graph byremoving redundant edges.  Second component isonline routing algorithm that operates on planergraphs.  

So in VANET perimeter mode of GPSR is used.  In GPSR if anyobstruction or void occurs then algorithm enter perimeter mode andplanner graph routing algorithm start operations, it involvessending the message to intermediate neighbor instead of sending tofarthest node, but this method introduces long delays due togreater no. of hop counts.  Due to rapid movementof vehicles, routing loops are introduced which causesdissemination of messages to long path.  GPSR uses staticstreet map and location information about each node, since GPSRdoes not consider vehicle density of streets so it is not anefficient method for VANET.

4.3BroadcastRouting

Broadcast routing is frequently used in VANET for sharing, traffic,weather and emergency, road conditions among vehicles anddelivering advertisements and announcements.  Broadcasting is usedwhen message needs to b disseminated to the vehicle beyond thetransmission range i.e multi hops are used. Broadcast sends apacket to all nodes in the network, typically using flooding. Thisensures the delivery of the packet but bandwidth is wasted andnodes receive duplicates. In VANET, it performs better for a smallnumber of nodes.  The various Broadcastrouting protocols are BROADCOMM, UMB, V-TRADE, andDV-CAST.

4.3.1      BROADCOMM Routing Protocol

BROADCOMM is based on hierarchal structure for highwaynetwork.  InBRAODCOMM the highway is divided into virtual cells which move likevehicles. The nodes in the highway are organized into two level of hierarchy:the first Level includes all the nodes in a cell, the second levelis represented by cell reflectors, which are few nodes locatedclosed to geographical centre of cell.  Cell reflected behavesfor certain interval of time as cluster head and handles theemergency messages coming from same members of the cell or nearbyneighbor. This protocol performs similar to flooding base routing protocolsfor message broadcasting and routing overhead.  

4.3.2 Urban Multihop Broadcastprotocol (UMB)

UMB is designed to overcome the interference, packet collision andhidden node problems during message distribution in multi hopbroadcast. In UMB the sender node tries to select the furthest node in thebroadcast direction for forwarding and acknowledging the packetwithout any prior topology information.  UMB protocol performswith much success at higher packet loads and vehicle trafficdensities.

4.3.3      Vector Based Tracing Detection (V-TRADE)

It is a GPS based message broadcasting protocols.  The basic idea issimilar to unicast routing protocols Zone Routing Protocol(ZRP). V-TRADE classifies the neighbors into different forwarding groupsdepending upon position and movement information.  For each group only asmall subset of vehicles is selected to rebroadcast themessage. V-TRADE improves the bandwidth utilization but some routingoverheads are associated with selecting the next forwarding node inevery hop.

4.3.4 GeocastRouting

Geocast routing is basically a location based multicastrouting. Its objective is to deliver the packet from source node to allother nodes within a specified geographical region (Zone ofRelevance ZOR).  In Geocast routingvehicles outside the ZOR are not alerted to avoid unnecessary hastyreaction. Geocast is considered as a  multicast servicewithin a specific geographic region. It normally defines aforwarding zone where it directs the flooding of packets in orderto reduce message overhead and network congestion caused by simplyflooding packets everywhere. In the destination zone, unicastrouting can be used to forward the packet. One pitfall of Geocastis network partitioning and also unfavorable neighbors which mayhinder the proper forwarding of messages. The various Geocastrouting protocols are IVG, DG-CASTOR and DRG

5. Conclusion &Future Perspectives

In this section we have reviewed existing routing protocols. Table1 gives a Comparison of these protocols. Prior forwarding methoddescribes the first routing decision of the protocol when there arepackets to be forwarded. In case of Delay Bounded protocols theprior forwarding method is used, whereas in all other routingprotocols wireless multi hop method of forwarding isused. Digital map provides street level map and traffic statistics suchas traffic density and vehicle speed on road at different times.Digital map is mandatory in case of Some of Cluster Based RoutingProtocols. Virtual Infrastructure is created through clustering ofnodes in order to provide scalability. Each cluster can have acluster head, which is responsible for secure communication betweeninter-cluster and intra cluster coordination in thenetwork. Recovery strategy is used to recover from unfavorable situations.Recovery strategy is the criteria, which is used to judge theperformance of protocol. 

 

 

Forwarding Method

Protocols

 

Proactive

Protocols

Reactive

Protocols

Position based Greedy

Protocols

Delay

Bounded

Protocols

Cluster

Based

Protocols

Broadcast

Protocols

Geo       cast

Protocols

Prior

Wire less multi hop Forwarding

Wire less multi hop Forwarding

Heuristic method 

Carry &

Forward 

Wireless

Multi hop

Forwarding

Wire less multi hop

Forwarding

Wire less multi hop Forwarding

Digital Map

 

 

 

 

 

 

 

Requirement

No

No

No

No

Yes

No

No

Virtual

 

 

 

 

 

 

 

Infrastructure

Requirement

No

No

No

No

Yes

No

No

Realistic

 

 

 

 

 

 

 

Traffic Flow

Yes

Yes

Yes

No

No

Yes

Yes

Recovery

Strategy

 MultiHop

Forwarding

Carry   &

Forward

Carry       &

Forward

Multi       hop

Forwarding

Carry   &

Forward

Carry   &

Forward

Flooding

Scenario

Urban

Urban

Urban

Sparse

Urban

Highway

Highway

 

 

 

 

 

 

 

 

 

Table 1: Comparison of Various Protocols

The future perspectives for VANET routing protocols should includefollowing:

1.   Amajor challenge in protocol design in VANET is to improvereliability of Protocols and to reduce delivery delay time and thenumber of packet retransmission.

2.  Driver behavior should be considered for designing of delay boundedrouting protocols since carry and forward is the mainly approach todeliver packets.

3.   Geocast routing for comfort applications should also considered.Comfort messages are usually tolerant of delay, Network bandwidthis generally reserved for emergency messages. It is worth todevelop an efficient geo cast routing protocol for comfortapplications with delay tolerant capabilities with low bandwidthutilization.

References

1.   James Bernsen, D. Mnivannan, Department of

Computer Science, University of Kentucky, Lexington, USA “Unicastrouting protocols for vechicular ad hoc 

2.   networks: A critical comparison and classification”, in  journal homepage:www.elsevier.com/locate/pmc Pervasive and Mobile Computing 5 (2009)1-18

3.   Sascha Schnaufer, Holger Fuisler, Matthias Transier, WolfgangEffelsberg, “Unicast Ad-hoc Routing in

Vehicular City Scnarios“ in “Network on wheels“ project undercontract no. 01AK064F and Matthias Transier.

4.   Kevin,Uichin Lee, Mario Gerla, “Survey of Routing Protocols inVehicular Ad Hoc Networks in Car 2 Car communicationconsortium

5.   Yu Wang and Fan Li, “Vehicular Ad Hoc Networks” in Guide toWireless Ad Hoc Networks, Computer communication and Networks, DOI10.1007/978-1-

84800-328-6_20

6.   MaximRaya and Jean-Pierre Hubaux  “Securing vehicular adhoc networks”, Journal of Computer security, IOS Press Amsterdam,The Netherlands, Volume 15, Issue 1(January 2007), pages39-68

7.   Maxim Raya, Panos Papadimitratos and Jean-Pierre Hubaux “SecuringVehicular Communication”, IEEE Wireless Communications Magazine,Special Issue on Inter-Vehicular communication, Vol 13, num. 5,2006, p. 8-15

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Verita/Ascona, March 9-11, 2005