Vehicular Adhoc Network (VANET) is an outgrowth of Mobile Adhoc Network (MANET), in which the mobile vehicles on road and the stationary roadside units (RSU) constitutes the nodes and communicate with each other on the fly (Fig. 1); Vehicle to Vehicle (V2V) and Vehicle to Roadside Unit (V2R). VANET can be categorised under hybrid architecture that consists of both infrastructure and infrastructure less features. VANET nodes are capable of self organising and managing the information in a distributed fashion with or without any centralised authority. Road Side Units (RSU) supported by DSRC standard  acts as gateways or fixed access points to vehicles in mobility and provides interim ...view middle of the document...
Figure 1. A VANET Scenario.
This research work proposes an improved version of REDEM, a reliable QoS aware routing scheme for dynamic vehicular ad hoc network ( REDEM), which focuses on identifying optimal paths. The outcome of the research work is compared with the performance of AODV, based on simulation test beds using ns2 simulator. The proposed routing scheme has been designed and implemented as per the DSRC specifications  and IEEE 802.11p MAC.
The aim of the research work focuses on:
Analysis and identify the required optimal QoS for
P.R. Subramaniam et al. / IRRIT, Vol. 1, No. 3, pp. 58-62, September 2011 59
media streaming services over VANET.
To provide an optimal QoS for highly congested VANET test bed.
To find a QoS validated route between highly “on mobile” vehicles using REDEM.
The simulated results show that REDEM protocol’s performance is better than the AODV protocol for VANET.
2. QoS issues in VANET
Most of the car manufacturers are involved in implementing wireless connectivity between vehicles and road side units and also between vehicles for the purpose of safety, driving assistance and entertainment. This vehicular network has constraints such as road type, mobility pattern, speed, number of vehicles on road, etc. Providing QoS for media streaming applications in VANET is highly challenging due to highly dynamic vehicle mobility, unpredictable driver’s behaviour which leads to frequent link breakage (short life time of node connection).
A QoS extension for AODV routing packets has been proposed by Perkins  to provide QoS. This extension specifies the service requirements which must be met by nodes whilst (re)broadcasting a route request or route reply. In particular it specifies to ensure a delay that does not exceed a maximum value or to ensure a certain amount of network capacity (bandwidth) is made available along a route between communication partners. Another QoS routing protocol based on AODV , has used only bandwidth as QoS metric for a route that is identified.
In VANETs, the support for QoS is to be thought as an inherent necessity rather adding such features as an afterthought. Following are the reasons that insist on the need for QoS enabled routing algorithms:
a) Limited bandwidth availability results in rapid fluctuation of wireless channel that severely affects multi-hop flows.
b) Very high speed node mobility may affect the network topology to change frequently that will have an impact on packets contending for the shared media.
c) Interference can affect transmission on adjacent links and nodes beyond neighbours.
3. REDEM modelling and design
REDEM is modelled as a set of high speed vehicles on a straight highway in which any vehicle can establish connectivity with any other vehicle(s) travelling in same direction or opposite direction. Vehicles within communication range can act as intermediate nodes and participate in forwarding the data packets to be transmitted between...