# Improved Road Segment-Based Geographical Routing Protocol for Vehicular Ad-hoc Networks
## 2 Related Works  
In the literature, different routing protocols have been suggested for information dissemination in VANETs. Due to the unique and challenging network characteristics of VANETs, including rapid changes in network topologies and the high mobility of nodes, most of the protocols in the literature are not so feasible for dealing with each type of network constraints. Therefore, various improvements of existing routing protocols have been taken into consideration for information dissemination [16]. There are five main categories of routing protocols: topology-based routing, geographical routing, cluster-based routing, broadcast routing, and geocast routing protocols. Topology-based routing protocols are based on a neighbor node receiving information and updating routing tables. It is further classified into reactive and proactive types of routing. Geographical routing refers to transferring the data packet by using the position information of vehicle nodes. Geographical routing needs additional resources like GPS to get the node's position information of neighbors and its own for routing. Cluster-based routing protocols create a virtual arrangement of nodes known as on-road vehicle groups. Each group has one group leader that is responsible for data communication between different other groups. Intra-node data communication is done via local links. A reactive routing protocol has been suggested as a Modified version of Location-Aided Routing scheme 1 (MLAR1) [17]. This protocol uses three packets to send data and maintain connections including route request, route reply, and route error packets. Route request packets are further classified into two types. They get information about the destination as modified route request packets. In addition, when a route breaks during communication, the original route-request packet is used for alternative route establishment. To reduce the size of the modified route request packet, this protocol removes the redundant fields, flooding the variable field and zone-centric non-variable field. Authors have claimed that due to this modified request strategy, the protocol has less overhead and better performance. However, this type of protocol strategy might have a lesser overhead but involves complex route request processes that result in network processing delays in vehicular traffic environment. An enhanced bandwidth efficient acknowledgment-based multicast (EBEAM) protocol has been suggested for VANETs [18]. This protocol is an enhanced version of variant of the BEAM protocol that was not performing well for emergency application messages, as the protocol was experiencing multicar chain collision issues. The enhanced protocol has overcome the BEAM limitations. In this enhanced protocol, all messages could be shared between the cluster head (CH) and the RSU to deliver information among all vehicle nodes. In the previous protocol, only a multicasting group member vehicle node got emergency messages. However, in the enhanced protocol, all vehicle nodes can get messages whether that are group members or not. However, the protocol has extra overhead due to its complex dissemination process where every node gets emergency messages. A perception-based geographical routing protocol (PGRP) has been explored for VANETs [19]. To select the next hop, this protocol considers routing parameters including the central node and the distance and direction of the vehicle nodes. In this protocol, each vehicle continuously broadcasts a beacon message to get the information of other vehicles. It considers the central vehicle for forwarding data packets rather than selecting the outermost vehicle with a higher chance to exit from the transmission range. It uses a carry and forward approach to address the dis-connectivityproblem. It has been claimed that the PGRP has better results than exiting routing protocols. However, it considers the central node as an assumption to test the routing protocol, which does not support real scenarios in VANETs' traffic environments.