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A comparative study of Broadcasting Protocols in VANET
Table II: Data Forwarding Table
In ordered to forward the data packet, a vehicle selects the next hop based on the direction if the
location of destination is known. Table II represents data forwarding table maintained by every vehicle. Before
forwarding any data packet the parameters of data forwarding table associated with the data packet are stored in
the table. The vehicle searches for necessary information in data forwarding table to select the next hop
whenever a data packet is received [3].
III. STREETCAST PROTOCOL
This protocol comprises of three components: relay-node selection, MRTS handshaking, and adaptive
beacon control. It uses two units such as Roadside Unit (RSU) and OnBoard Units (OBUs). RSU can pick up
relay nodes from its one-hop neighbors and disseminate packets over specified road segments. The selected
OBRs upon receiving messages disseminate packets in their forward direction. The selected OBUs will reply
ACKs to ensure reliability [2].
A. Selection of Relay Nodes
In order to reduce redundancy, we apply the Multi-Point Relay (MPR) broadcast strategy to reduce the
number of relay nodes. Every OBU and RSU maintains the neighbor table. Each node in VANETs periodically
broadcasts a “hello” beacon, which includes the node’s Dislocation and timestamp. When a node receives a
“hello” beacon, it checks the digital street map and updates the neighbor information to its neighbor list. A
neighbor is deleted from the table if no beacons are received from it for a period of time. Then the node with the
optimal distance is picked from each neighbor list as a relay node.
B. Multicast Request to Send
We use MRTS to protect from collision. With MRTS mechanism, senders can send packets to multiple
receivers simultaneously without worrying about collision and hidden-terminal problems. A sender transmits an
MRTS and waits for CTSs from receiver. Nodes receiving MRTS frame set their NAVs (Network Allocation
Vector) if they are not the relay nodes. Only relay nodes reply CTSs to the source following the order specified
in the MRTS frame. Fig 2 illustrates the MRTS frame format [2].
2 2 6 6 6 6 6 6
FC Duration Src Ra1 Ra2 Ra3 Ra4 FCS
FC: Frame Control
Duration: NAV Duration
Src: Source Address
Ra1, Ra2, Ra3, Ra4: Receiver Address
FCS: Frame Check Sequence
Fig 2. MRTS Frame Format
If transmission may fail due to loss of CTSs or ACKs. According to the number of received ACKs, a
source can decide whether the transmission is successful or not, and re-initiate the MRTS procedure. If no CTS
are received, then the source will directly re-initiate the MRTS procedure.
C. Adaptive Beacon Control
In urban areas, there could be thousands of vehicles moving across intersections in short period of time.
If each vehicle keeps sending beacons, it will cause many collisions and failures. So, this protocol uses a beacon
control mechanism to adjust beacon generation rate. The main function of beacons in this approach is to find the
farthest neighbor in each direction for greedy forwarding. It is not necessary to let all nodes send beacons. There
should be a proper number of nodes sending beacons.
IV. ABBP PROTOCOL
It is an adaptive broadcast protocol that is suitable for a wide range of mobility conditions. The main problem that a
broadcast protocol must face is its adaptability to the very different vehicular arrangements in real scenarios. It should
achieve high coverage of the network at the expense of as few transmissions as possible, regardless on whether the network
is extremely dense or highly disconnected[1].
ABBP is localized. Vehicles are assumed to be equipped with Global Positioning System (GPS) receivers. Periodic
beacon messages are exchanged to update the vehicles’ local topology knowledge. The position of the sender is included
within the beacons, which suffices to calculate a CDS (Connected Dominating Set) backbone after each beacon message
round. The source node transmits the message. Upon receiving the message for the first time, each vehicle initializes two
lists: list R containing all nodes believed to have received the message, and list N containing those neighbors in need of the
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