## 1 Introduction
They are suitable for non-real time applications where delay and reliability can be compromised up to some extent [15, 16]. Efficient and reliable information distribution is one of the most challenging tasks in VANETs due to their highly dynamic network environment [17, 18]. Recently, various geographic routing protocols have been suggested in the literature [19, 20, 21, 22, 23, 24]. Geographic routing is also known as geocast routing or position based routing. The idea of geocast routing came from the Unix-to-Unix Copy (UUCP) Mapping project [25], which aimed at relating IP addresses with geographic locations by maintaining a database of geographic locations of each Internet hosts. The projects, Domain Name Server (DNS) encoding of geographic locations [26] and Internet Message Access Protocol Uniform Resource Locator (IMAP-URL) scheme [27], were also aimed at associating geographical locations of each host with host name. The above three projects made it possible to identify the geographical locations of in-coming data flows but directing out-going data flows to geographical locations was not possible. Geographic Routing was first suggested in [28] through the Cartesian routing that uses longitude and latitude information of node as address. In Cartesian routing, greedy forwarding technique has been used to forward packets to the neighbor nearest to the destination using geographical information of neighboring nodes. Geographic routing or geocast routing is a variant of multicast routing. Information forwarding from a single source node to a group of destination nodes is known as multicast routing. In geographic routing, information is forwarded from single source node to a group of destination nodes within a specified geographical region that is known as Zone of Relevance (ZOR) [29]. In multihop forwarding of geographic routing, the concept of Zone of Forwarding (ZOF) has been used to improve reliability in forwarding. All the nodes within the area specified by ZOF are considered as next hop nodes of the current forwarder node [30]. Geographic routing is one of the most preferred choices for information dissemination in vehicular traffic environment. The preference can be attributed to the fact that the on-road vehicles can be grouped into geographical regions and traffic information can be shared considering the groups as geocast regions. The other benefits of geographic routing are as follows. It is not restricted to infrastructure support. It is flexible for most ITS applications. The three most preferred and recent geographic routing protocols are Voronoi diagram-based Geographic Distance Routing (V-GEDIR) [31], Junction-based Geographic Distance Routing (J-GEDIR) [32] and Peripheral node-based Geographic Distance Routing (P-GEDIR) [33]. These state-of-the-art protocols have been investigated and considered for comparative analysis in this paper. V-GEDIR selects the next hop nodes in a Voronoi region towards the destination and J-GEDIR selects junction nodes within the transmission range as next hop vehicles. P-GEDIR vertically divides the circular coverage region into two half-circular sections and selects all the border nodes as next hop vehicles from the half-circular section towards the destination. These protocols reduce the size of the forwarding region for selecting a smaller number of next hop vehicles. The performance of these protocols starts degrading with higher vehicle density and speed in the reduced forwarding region. Further, these protocols select border vehicles as next hop vehicle to minimize the number of hop count from source to destination, but the border vehicles have higher outage probability during forwarding due to the high vehicle speed in vehicular traffic environment. In urban environments, the quality of links is highly affected by obstacles such as buildings, trees, _etc_. These protocols ignore the link quality consideration in next hop vehicle selection.