Information Dissemination in VANETs using
Zone Based Forwarding
Rayman Preet Singh
Arobinda Gupta
Dept. of Computer Sc. & Engg.
Indian Institute of Technology, Kharagpur
Dept. of Computer Sc. & Engg.
Indian Institute of Technology, Kharagpur
Abstract—Several VANET-based safety applications require
information dissemination to all vehicles within a certain area
for a certain time. Among the existing information dissemination
protocols for VANETs, only Stored Geocast provides retention
of information within a pre-determined area of the road for
a duration of time. However, the overhead incurred by it is
large. In this paper, we propose and evaluate ZBF, a zone based
forwarding scheme for information dissemination which provides
both a spatial and temporal retention of information and incurs
less overhead than Stored Geocast.
I. I NTRODUCTION
A vehicular ad hoc network (VANET) is an ad hoc wireless
communication system setup between multiple vehicles (V2V)
or between a vehicle and some roadside infrastructures (V2I).
Avoiding accidents and traffic congestions are two primary
goals of building VANETs. A VANET can enable drivers
to exchange information about current road conditions and
potentially dangerous situations to warn other drivers about
upcoming dangers, reducing the chance of accidents and traffic
congestions. Any vehicle can initiate dissemination of such
warning information. Usually, any such information has a
specified area of interest and a fixed time period within which
it is considered valid and usable. We will refer to these as the
effect-area and the effect-time of the information respectively.
For example, an information about an accident blocking a lane
of a highway is of importance to vehicles only over a few
kms from the accident site, for the duration of persistence
of the lane blockage. An information dissemination protocol
for VANETs that propagate such warning information should
aim to deliver the message to maximum number of vehicles
that pass through the effect-area during the effect-time, while
incurring low message overhead.
Using a flooding based approach in which all vehicles
that receive the message broadcast it again causes too many
messages to be sent. Several strategies for information dissemination in VANETs have been suggested that improve on
simple flooding [1][2][3]. However, all these approaches are
vulnerable to network partition during propagation. Fathy et al.
in [4] propose a scheme which can handle network partitions.
However, none of these works retain the message in the effectarea for the duration of the effect-time.
The only existing information dissemination protocol in
VANET that addresses message delivery within an effect area
c 2011 IEEE
978-1-4577-2028-4/11/$26.00 ⃝
and time is Stored Geocast [5]. In this protocol, a leader
vehicle is elected in the region of interest to store messages and
handover of messages is done when this vehicle leaves the region. The elected vehicle broadcasts periodic GATE messages
that also carry the warning information to be disseminated. A
grid based approach is used for leader election which elects
the node closest to the center of a region (grid box) as the
leader. BID messages are used within each grid to exchange
position information for electing a leader.
In this paper, we present ZBF (Zone Based Forwarding), an
information dissemination protocol for VANETs that delivers
a message to a large number of vehicles passing a predefined
effect-area during a predefined effect-time, while incurring
very little message overhead compared to other protocols.
Detailed simulation results are provided on realistic scenarios
to show that ZBF outperforms Stored Geocast and other
information dissmination protocols. An extension of ZBF is
also proposed that can tolerate high network congestion.
II. ZBF: Z ONE BASED F ORWARDING
We assume that the transmission range of all vehicles are
the same and is equal to 𝑅. The roads considered have twoway traffic with lower and upper speed limits as 0 and 𝑣𝑚𝑎𝑥
respectively. Also, each vehicle 𝑖 knows its current position
(𝑃𝑖 ), velocity (𝑣𝑖 ), acceleration (𝑎𝑖 ), and direction (𝑑ˆ𝑖 ) at any
instant of time.
ZBF divides the entire effect-area of the warning information into segments of length 𝑅, each of which is referred to
as a zone. One vehicle in each zone is assigned the task of
periodically broadcasting the warning information to notify
other vehicles in that zone. This vehicle is referred to as
a forwarder for that zone. Note that any broadcast by the
forwarder will be received by all vehicles in a zone as long
as the frequency 𝑓 of periodic broadcast is sufficiently large
(≥ 𝑣𝑚𝑎𝑥
𝑅 ). Whenever a forwarder exits a zone, a new forwarder
is elected from amongst the vehicles present in the zone and
the task of periodic broadcasting is then handed over to the
new forwarder. At the end of the effect-time duration, all
forwarders stop their periodic broadcast.
The protocol uses three types of messages. An Info message
is sent by a forwarder vehicle 𝑖 to broadcast the actual warning
information, and contains, other than a type field identifying
it as an Info message, the fields <ID, Warning-Info, EffectTime, Effect-Area, 𝑃 , 𝑑ˆ > where 𝐼𝐷 is the sender’s id, and
Note that 𝑃𝑖 and 𝑑ˆ𝑖 are available at 𝑗 as the contents of Info
message are also piggybacked in the Query message sent by
𝑖. Using 𝑣𝑗 , 𝑎𝑗 , and 𝑑ˆ𝑗 , vehicle 𝑗 computes the approximate
time 𝑡𝑠 it will take to travel the distance 𝑠 as 𝑡𝑠 = 𝑣𝑠𝑗 . Time 𝑡𝑠
√
𝑢2 + 𝑎𝑖 .𝑠 − 𝑢
can also be computed as
for more accuracy.
𝑎𝑖
Since our aim is just to approximately estimate which vehicle
will be present in a zone for the longest duration, we prefer
𝑠
to use ( ) for simplicity. Vehicle 𝑗 then waits for a time
𝑣𝑗
𝑁
𝑡𝑤𝑎𝑖𝑡 , which is calculated as 𝑡𝑤𝑎𝑖𝑡 = max ( , 𝑇 ) where 𝑁 is
𝑡𝑠
a suitable normalizing factor. Thus, vehicles which will stay
in the zone for a longer time will wait for a smaller time and
vice-versa. If the 𝑡𝑤𝑎𝑖𝑡 period expires without 𝑗 receiving any
other Reply message, 𝑗 broadcasts a Reply message, changes
its mode to Forward, and starts functioning as a forwarder.
However, if a Reply message, broadcast from another vehicle
𝑘, is received during the wait period 𝑡𝑤𝑎𝑖𝑡 , vehicle 𝑗 cancels its
transmission of the Reply message if both 𝑗 and 𝑘 are on the
same side of the current forwarder 𝑖. If 𝑗 and 𝑘 are on different
sides of 𝑖, 𝑗 ignores the Reply message and continues to wait.
On becoming the forwarder, vehicle 𝑗 records its current
position 𝑃𝑗 as 𝑅𝐸𝐶𝑋𝑌 in order to compute the zone boundaries. The forwarder 𝑗 uses 𝑅𝐸𝐶𝑋𝑌 to detect when it reaches
the zone border, at which point it broadcasts a Query message.
As described earlier, of all the vehicles in the zone, the one
whose 𝑡𝑤𝑎𝑖𝑡 expires first sends a Reply message and gets
200
No. of vehicles
𝑃 and 𝑑ˆ are the sender’s position and direction respectively.
A Query and a Reply message contain a type field identifying
them, plus all fields of the Info message (i.e., the contents of
the Info message are also piggybacked on all Query and Reply
messages sent).
At any point of time, a vehicle can be in one of three modes,
Receive, Forward, or Relay. The Forward mode signifies that
the vehicle is a forwarder. Whenever a forwarder is about to
leave a zone it changes its mode to Relay. During the Relay
mode, a vehicle initiates election of a new forwarder while
still continuing to function as a forwarder. All other vehicles,
which are also the recipients of the periodic Info messages are
in Receive mode.
Before start of dissemination, all vehicles are in Receive
mode. A vehicle 𝑖 initiating the dissemination changes its
mode to Relay, broadcasts a Query message, and waits for
a predefined time 𝑇 for receiving a Reply message.
Any vehicle 𝑗 at position 𝑃𝑗 , on receiving a Query message
from a forwarder 𝑖, computes its distance 𝑠 from its current
position 𝑃𝑗 to the current position 𝑃𝑖 of the sender of the
Query message if vehicle 𝑗 is headed towards 𝑃𝑖 . In case
𝑗 is headed away from 𝑃𝑖 , 𝑠 is calculated as the distance
vehicle 𝑗 needs to travel to reach the position 𝑃𝑖 − 𝑅, i.e., the
boundary of 𝑖’s transmission range from 𝑖’s current position.
More formally, the distance 𝑠 can be computed as follows:
{
if 𝑑ˆ𝑖 = 𝑑ˆ𝑗
∣𝑃𝑗 − 𝑃𝑖 ∣
𝑠=
𝑅 − ∣𝑃𝑗 − 𝑃𝑖 ∣ if 𝑑ˆ𝑖 = −𝑑ˆ𝑗 .
150
100
50
Total no. of vehicles in zone
ZBF
Torrent-Moreno
Stored Geocast
0
0
0.015
0.03
0.045
0.06
0.075
0.09
0.105
0.12
f
Fig. 1.
Total no. of vehicles informed v/s 𝑓 .
elected as the new forwarder for the zone. The task of periodic
rebroadcast of Info messages is hence, handed over to the new
forwarder.
The frequency of periodic re-transmissions of Info messages
𝑣𝑚𝑎𝑥
. The wait time 𝑇 is empirically
𝑓 is upper bounded by
𝑅
selected such that 𝑇 > 2 × (𝑚𝑒𝑠𝑠𝑎𝑔𝑒 𝑝𝑟𝑜𝑝𝑎𝑔𝑎𝑡𝑖𝑜𝑛 𝑑𝑒𝑙𝑎𝑦).
III. S IMULATION R ESULTS
The performance of ZBF is evaluated through simulation
using an integrated traffic-cum-network simulator that couples
ns-2 with the traffic sumulator VanetMobiSim for realistic
VANET simulation. We measure (i) Coverage, The total number of vehicles passing through the effect-area during the entire
effect-time which receive the information, (ii) total number of
message broadcasts, and (iii) the distance a vehicle travels
inside the effect-area before it gets the warning information
for the first time.
The performance of ZBF is compared with that of Stored
Geocast [5], Torrent-Moreno’s algorithm [2], and Fathy et al.’s
algorithm [4]. [2] and [4] are chosen after a detailed evaluation by simulation (not shown here) of several information
dissemination protocols, in which these two protocols were
found to outperform all others.
A highway scenario of length 10 Km is used, with two lanes
per driving direction, and a total of 500 vehicles with speed
raging between 0 and 30 m/sec. The values of 𝑁 and 𝑇 are 0.1
and 1 second respectively. The zone length and the grid length
respectively in the two approaches are set to the transmission
range (=250 m). The performance is measured by varying the
frequency 𝑓 of the periodic Info message broadcasts in ZBF
and GATE message broadcasts in Stored Geocast respectively
𝑣𝑚𝑎𝑥
= 0.12). The results are sampled
(𝑓 is upper bound by
𝑅
at 5 random instances for a period of 5 minutes for each of
the three cases of one, two, and three zones or grids existing
in the scenario, and then averaged over all these cases.
Figure 1 shows the coverage achieved by both the algorithms with varying frequency 𝑓 . The coverage of Stored
Geocast increases as 𝑓 increases. However it is surpassed by
ZBF when 𝑓 attains its maximum value of 0.12. At that value
of 𝑓 , ZBF ensures that the warning information is delivered
to all the vehicles which are present in the zone during the
No. of vehicles/messages
No. of messages
ZBF
Torrent-Moreno
Stored Geocast
200
150
100
50
0
0
0.015
0.03
0.045
0.06
0.075
0.09
0.105
0.12
Fig. 4.
effect-time. Note that Torrent-Moreno’s algorithm delivers the
warning information to a far less number of vehicles as it does
not retain the information within the area of interest.
Figure 2 shows the total number of message broadcasts by
each of the strategies. As 𝑓 increases the number of GATE
and Info messages increases. We observe that the number of
message broadcasts by Stored Geocast far exceeds those by
ZBF. A further analysis shows that the increased message
broadcasts in Stored Geocast is due to the large number of
BID messages broadcast by it.
Distance travelled
80
70
60
50
40
30
20
ZBF
Stored Geocast
0
0
0.015
0.03
0.045
0.06
0.075
0.09
0.105
0.12
f
Fig. 3.
300
200
100
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
Time from start of dissemination (sec)
Total no. of messages broadcast v/s 𝑓 .
10
400
0
f
Fig. 2.
No. of messages
No. of nodes informed
500
Distance travelled inside a zone before being informed v/s 𝑓 .
Figure 3 shows the average distance any vehicle which
is inbound to a zone travels before it gets the warning
information. In case of Stored Geocast, this is the distance
travelled before receiving the first GATE message broadcast
from the leader vehicle. For both these approaches it is seen
that as 𝑓 is increased, the distance decreases. Stored Geocast
outperforms ZBF at lower 𝑓 values, but at higher values of 𝑓 ,
ZBF performs better.
Figure 4 shows the performance of Fathy et al.’s algorithm
[4] on the same highway scenario. It is seen that as time progresses, information is eventually delivered to all the vehicles
in the scenario. However, it takes 20-25 seconds to deliver
the information to the same number of vehicles as in the
case of ZBF. However, ZBF delivers the warning information
only to the vehicles for which it is relevant within a distance
of 40-80m from the zone boundary. At an average speed of
𝑣𝑚𝑎𝑥
= 15𝑚/𝑠𝑒𝑐 (𝑣𝑚𝑎𝑥 = 30𝑚/𝑠𝑒𝑐), this results in a delay
2
Result of the Fathy algorithm [4] on a sample highway scenario.
of only 2.6 − 5.3 seconds. Thus, the worst case delay is much
less for ZBF compared to that in [4].
In heavy traffic, Query messages may be lost due to collision
etc., causing the warning information to be lost permanently in
that zone. We extend ZBF as follows to address this problem.
All vehicles in the Receive mode anticipate the receipt of a
Query message in advance. On receipt of an Info message, a
receiver vehicle obtains the forwarder’s position and direction,
and uses that to compute the approximate distance 𝑠′ which
the forwarder will travel before reaching the zone boundary. If
𝑠′ is less than a threshold 𝑠′𝑇 𝐻 , the receiver vehicle schedules
the handling of the receipt of a Query message at an instant
after 𝑡𝑇 𝐻 seconds, at which the forwarder is supposed to
reach the boundary. If a Query message is actually received
by then, this scheduled execution is cancelled. However, if no
Query message is received, the receiver vehicle sends a Reply
message anyway after handling the perceived receipt of the
Query message. All other steps of the algorithm remain the
same as shown earlier. The extended protocol is simulated over
the same highway scenario but with the number of vehicles
increased to 1000 to induce heavy bumper-to-bumper traffic. It
is seen that in heavy traffic, some Query messages are dropped.
However, the proposed extension still retains the information
in a zone by electing a new forwarder and achieves a greater
vehicle coverage than ZBF. However, because Reply messages
may be sent by more than one vehicle that fail to receive
Query messages, the number of messages broadcast increases
somewhat.
R EFERENCES
[1] M. Sun, W. Feng, T. Lai, K. Yamada, and H. Okada, “GPS-Based
Message Broadcasting for Inter-vehicle Communication”, International
Conf. on Parallel Processing (ICPP), 2000.
[2] M. Torrent-Moreno, “Inter-Vehicle Communications: Assessing Information Dissemination under Safety Constraints”, 4th Annual IEEE/IFIP
Conf. on Wireless On Demand Network Systems and Services, 2007.
[3] R. Preet and A. Gupta, “Traffic Congestion Estimation in VANETs
and Its Application to Infomation Dissemination”, 12th Intl. Conf. on
Distributed Computing and Networking (ICDCN), 2011.
[4] M. Fathy and S. Khakbaz,“A Reliable Method for Disseminating Safety
Information in Vehicular Ad hoc Networks Considering Fragmentation
problem”, 4th Intl. Conf. on Wireless and Mobile Communications,
2008.
[5] C. Maihofer, W. Franz and R Eberhardt, “Stored Geocast”, Kommunikation in Verteilten Systemen (KiVS), Leipzig, Germany, 2003.