An Analytical Review of the Algorithms Controlling Congestion in Vehicular Networks

IOSR Journal of Computer Engineering (IOSR-JCE)
e-ISSN: 2278-0661,p-ISSN: 2278-8727, Volume 17, Issue 3, Ver. IV (May – Jun. 2015), PP 32-41
www.iosrjournals.org
DOI: 10.9790/0661-17343241 www.iosrjournals.org 32 | Page
An Analytical Review of the Algorithms Controlling Congestion
in Vehicular Networks
Poonam Verma1
, Neeta Singh2
Research Scholar, School of ICT, Gautam Buddha University, Greater Noida, India
Assistant Professor, School of ICT,Gautam Buddha University, Greater Noida, India
Abstract: Vehicular AdhocNETworks (VANETs) relies on repetitive data exchange among vehicles and
vehicles to RoadSide Units (RSU) to facilitate road safety, route planning, etc. This may often lead to congestion
in the network. To deal with this dilemma, various congestion control schemes have been considered so far. The
basic objective of congestion control is to best utilize the available network resources while preventing
persistent overloads of network nodes and links. Suitable congestion control mechanisms are essential to
maintain the competent operation of a network. This paper highlights attributes of some of the proposed
congestion control algorithms and compares their qualities and limits.
Keywords: Congestion Control, Control Channel, DSRC, IEEE 802.11p, VANETs, WAVE.
I. Introduction
Vehicular AdhocNETworks(VANETs) have set a new example for wireless communications that aim
to exploit the recent advances in wireless device's technology to enable intelligent inter-vehicle communication,
in particular, and road safety as a whole. It has been envisaged from Intelligent Transportation System (ITS).
The US Federal Communications Commission (FCC) has allocated Dedicated Short Range Communications
(DSRC) spectrum at 5.9 GHz for VANETs. To be precise, VANET is a form of Mobile Ad hoc Network
(MANET), in which vehicles form a decentralized network of communicating via On-Board Units (OBUs).
VANET is different from MANET in numerous perspectives such as nodes in VANET are characterized by
high dynamic and mobility, high rate of topology changes and density variability along with the challenging
characteristics of MANETs such as lack of established infrastructure, wireless links, multi-hop broadcast
communications. One major difference between the MANET and VANETs is that in MANETs nodes move
randomly whereas in VANETs nodes mainly follow a predefined path as the movement is expected on roads
only.
VANETs communication can be broadly classified into two categories; Vehicles communicating with
Roadside infrastructure (V2R) and with nearby Vehicles (V2V) and is generally described as
V2Xcommunication. A RSU is an intelligent device deployed across the road network that provides an external
interface to the vehicle. VANET applications can further be divided into two major classes; safety and non-
safety applications. Applications that are critical to human life are placed under safety application category, e.g.,
pre-crash sensing, post-crash warning, pedestrian/children warning etc. and non-safety applications include toll
collection, mobile internet, infotainment and many more. Nodes in VANETs broadcast safety and non-safety
messages to support these applications. In fact, the Society for Automotive Engineers (SAE) [23] and the IEEE
Wireless Access to Vehicular Environment (WAVE) standard [18] have defined a special type of “heartbeat”
message that should be periodically broadcast by vehicles to inform one-hop neighbors of their locations,
directions, travel and speeds, etc.
The rest of the paper is structured as follows: Section 2 gives an overview of congestion control issue
within VANETs along with a brief introduction to traffic flow theory. Section 3 comprises of a detailed
overview of DSRC along with WAVE and IEEE 802.11p standards. Section 4 summarizes some typical
congestion control algorithm proposed in recent years. Section 5 provides a tabular overview of the functions
and characteristics of proposed congestion control algorithms for comparisons. Section 6 concludes paper along
with an outlook to the future work.
II. Congestion Control In VANETs
Researches in VANETs have highlighted several multifaceted issues to be focused on, including
rapidly changing topology, lack of connectivity redundancy, robust message delivery and so on. Congestion
control is one of the major challenging issue within VANETs. It should take into account the characteristics of
VANET while ensuring the quality of service, required by the applicative level. As discussed earlier, VANETs
differs from MANETs in numerous ways, therefore, typical MANET protocols e.g. table driven routing
protocols are not appropriate for VANETs as they suffer from outdated neighbor information. The dominant

An Analytical Review of the Algorithms Controlling Congestion in Vehicular Networks
form of communication on the wire-line Internet and conventional MANETs is unicast end-to-end
communication. In VANETs, the prevailing form of communication is broadcast/geocast. Most applications in
VANETs aim to provide information on the local vicinity, which has been sensed by vehicles nearby, and
hence, VANETs are more prone to congestion as compared to other wireless networks due to the broadcasting
nature of VANETs. Accidents, construction work, weather condition, increase in traffic volume and poor traffic
signal timing are some reasons for vehicle traffic congestion.
One of the main reasons for vehicular congestion is the increase in traffic volume above the road
capacity. Interestingly, the basic concept of congestion in VANETs remains the same as used in the computer
communication network wherein a network node gets congested when there is demand for more bandwidth than
available capacity. As a result of congestion, a queue starts filling up and sooner or later, as the buffer is finite,
there will be no room for newly arrived packets. The same concept is pertinent to VANETs in which, if we
consider the road as a queue and each vehicle as a packet in the queue, once the road capacity is reached, there
will be no room for any more vehicles. On the contrary, Congestion control schemes in Internet are based on an
end-to-end paradigm, for instances, the Transport Control Protocol (TCP) at the endpoints detects overload
conditions at intermediate nodes. In case, when congestion is sensed, the source reduces its data rate. However,
in VANETs the topology fluctuates within seconds and a congested node used for forwarding a few seconds ago
might not be used at all, at the point in time, when the source reacts to the congestion.
2.1 Traffic flow theory
Traffic flow is the study of interactions between vehicles, drivers, and infrastructure (including
highways, signage, and traffic control devices), with the aim of understanding and developing an optimal road
network with efficient movement of traffic and minimal traffic congestion problems. A number of traffic flow
theory has been proposed in recent years. Hence, there is a large interest in understanding the relation between
traffic flow J (typically measured in vehicles per hour and lane) and vehicle density ρ (vehicles per kilometer)
both from a theoretical and from a practical point of view [25]. This relation can be expressed in the form of the
fundamental diagram, as in Fig. 1. Here ρmin
free
denotes the minimum numbers of vehicles that can travel at their
desired speed and ρmax
free
defines the maximum amount of vehicles that can travel at their desired speed. For low
and high densities, its shape is easy to understand. At low densities, ρ <ρmin
free
vehicles can travel at their desired
speed, and additional vehicles linearly increase the total flow. At high densities, ρ >ρmax
free
, on the other hand,
vehicles hinder each other and force others to slow down. For these two regions, the functional relation between
flow and density can be expressed by the linear equation J = vρ, where v stands for the average velocity of
vehicles on the considered road segment. Between these two regions, nevertheless, there exists a metastable
range ρmin
free
< ρ <ρmax
free
where a driver’s desire to travel at maximum velocity and the tendency to hinder each
other compete and where flow can take two values depending on the system’s history.
Fig.1 Schematic of a flow-density diagram showing a metastable region between ρmin
free
and ρmax
free
[25].
The flow can spontaneously switch from free (upper branch) to congested (lower branch) traffic in this
density range for no obvious reason. Therefore, this occurrence is also referred to as “phantom jam”.
In the recent years, researches on traffic flow theory have drawn two major conclusions:
 Traffic dynamics assessed solely by vehicle density may fail in a certain density range.
 Traffic congestion can be eased by reducing disruption of traffic flow and by keeping density below ρmin
free
.

III. Dedicated Short Range Communications (DSRC)
This section provides an overview of DSRC, the wireless communication channel allocated for
VANETs. DSRC [22] was developed with a primary goal of enabling vehicular safety applications. DSRC
operates in a licensed frequency band that take place over a dedicated 75 MHz spectrum band approximately 5.9
GHz, allocated by the US FCC [21] for vehicle safety applications. It provides a secure wireless interface and
supports high speed, low latency and limited-range wireless communications for vehicles. Its performance is
immune to extreme weather conditions (rain, fog, snow, etc.). The DSRC physical layer is adapted from the
IEEE 802.11a standard using Orthogonal Frequency Division Multiplexing (OFDM) modulation, and the DSRC
medium access control layer is adapted, in part, from the introductory IEEE 802.11 and IEEE 802.11e (QoS).
DSRC is preferred over Wireless-Fidelity (Wi-Fi) because the proliferation of Wi-Fi handheld and hands-free
devices (e.g. Bluetooth) that dwell in the 2.4 GHz and 5 GHz bands, along with the anticipated increase in Wi-Fi
hotspots and wireless mesh extensions, could cause excruciating and unmanageable levels of interference that
could hamper the reliability and effectiveness of active safety applications. The normal Wi-Fi means of
recognizing nearby stations and associating with them (establishing a link between two or more devices) cannot
be used for active safety applications because it can take multiple seconds to complete this association. Active
safety applications necessitate instant establishment of communication. A number of modifications over the
basic technology (Wi-Fi) were required to achieve this goal. One of the major change is to accommodate an
enormously short time in which devices must recognize each other and transmit messages to each other. Most of
these safety applications require response times measured in milliseconds. As a result of which periodic
transmission of safety messages is used so that vehicles receiving the safety messages can immediately
determine if they should respond or not.
DSRC is similar to IEEE 802.11a, except for the major differences [24] recapitulated below:
 Operating Frequency Band: DSRC is targeted to operate on a 75 MHz licensed spectrum around 5.9 GHz,
as contrasting to IEEE 802.11a that is allowed to utilize only the unlicensed portions in the frequency band.
 Application Environment: DSRC is meant for outdoor high-speed vehicle (up to 120 mph) applications, as
opposed to IEEE 802.11a initially intended for indoor WLAN (walking speed) applications. In IEEE 802.11a,
each and every PHY {physical) parameters are optimized for the indoor low-mobility propagation environment.
 Medium Access Control (MAC) Layer: The DSRC band plan consists of seven channels which include one
control channel to support high priority safety messages and six service channels to support non-safety
applications. Prioritizing safety over non-safety applications is an open problem that started to receive attention
in the literature and is closely related to the problem of multi-channel coordination.
 Physical Layer: The bandwidth of each DSRC channel is 10 MHz, contrast to the 20 MHz IEEE 802.11a
channel bandwidth. This provides better wireless channel propagation with respect to multi-path delay spread
and Doppler effects caused by high mobility and roadway environments.
3.1 Standards
The key point of VANETs is facilitating the wireless communication among vehicles, so there is a need
for developing a set of communication protocol. In view of that, IEEE defined WAVE [19] standard intended to
promote wireless communication in a vehicular environment which consists of IEEE 802.11p and IEEE 1609
protocol family.
The physical and MAC layers of WAVE are based on IEEE 802.11p which covers the characteristics
of vehicular ad hoc network: high dynamic mobility, high change of network topology, and low latency. The
physical layer of IEEE 802.11p WAVE consists of seven channels of 10 MHz bandwidth for each channel.
The physical layer of IEEE 802.11p is related to IEEE 802.11a design, but the main difference is that the IEEE
802.11p utilizes 10MHz bandwidth for each channel instead of 20MHz bandwidth in IEEE 802.11a. The
physical layer of 802.11p uses OFDM technology which is used for increasing data transmission rate and
overcoming signal fading in wireless communication. One of the stipulations of IEEE 802.11p is that the
management functions are connected with the physical and MAC layers which are called Physical Layer
Management Entity (PLME) and MAC Layer Management Entity (MLME), respectively.
3.2 Multichannel operation
IEEE 802.11p’s MAC layer is enhanced by one of the standards of IEEE.1609 depicted as IEEE 1609.4
which supports multichannel operation [19]. This standard describes seven different channels with different
features and usage. In addition, these channels use different frequencies and powers of transmutation.

Fig.2 Frequency spectrum of DSCR[19]
As shown in fig. 2, there are six Service CHannels (SCH) and one Control CHannel (CCH) with
different characteristics. Each device can alternate between the control channel and one of the service channels,
but both the channels cannot be used simultaneously. The control channel is used for system control and safety
data transmission. On the other hand, non-safety messages are exchanged by the six service channels. The period
containing one CCH interval and one SCH interval shall last no more than 100 ms.The IEEE 802.11p MAC
layer also relies on 802.11e Enhanced Distributed Channel Access (EDCA). The EDCA mechanism supports
Quality Of Service (QOS) and prioritizing important safety messages.
IV. Some Proposed Congestion Control Algorithm
In recent years, VANETs have drawn attention of many researchers. The prime goal of VANETs is to
provide life security on the roads. To achieve this, vehicles make use of two types of messages; i) Periodic
safety messages (beacons) to exchange status information e.g. location, speed, velocities etc. ii) Event-driven
messages which are broadcasted in case of an emergency situations e.g. accidents, stiff-braking etc. As both
types of messages shares same Control Channel, in opaque traffic, periodic beacons may consume the entire
channel bandwidth leading to a drenched/congested channel. In a congested channel, event-driven messages
may not be able to access the channel at all, consequently providing no safety.
A number of algorithms have been proposed to control congestion in the vehicular adhoc network that
aims at controlling the load of traffic conditions and enhancing the performance of vehicular network.
Congestion control approaches are basically classified as: end-to-end or hop-by-hop approach. End-to-
end congestion control approaches are not suitable for VANETs as relay node's context are not considered in
these approaches, and thus, interferences, collisions and transmission problems are not considered [16].
However, the required quality of service of a transmission can be defined by the sender with end-to-end
congestion control approaches.
On the contrary, hop-by-hop congestion control approaches suffer from lack of scalability, when the
amount of transmitted flows rises within the network. However, it is known that the size of the transmitted data
within VANET is not considerable, due to the dynamic nature of this network, and to the node limitations in
terms of storage and computation competences. Consequently, hop-by-hop congestion control approaches are
the most suitable for VANET, while considering the required quality of service of the transmitted data, as for
the end-to-end approaches. However, hop-by-hop congestion control approaches present some leaks to e.g.
generation of communication and computation overheads, reactive congestion control techniques.
Utility-based congestion control and packet forwarding in VANETs:
L. Wischhof et al. [20] provided a concept for utility-based congestion control and packet forwarding
in VANETs. The control algorithm used an application-specific utility function and encodes the quantitative
utility information in each transmitted data packet in a transparent way for all users within a confined
environment. A decentralized algorithm then calculates the "average utility value" of each individual node based
on the utility of its data packets and assigns a share of the available data rate proportional to the relative priority.
In order to achieve a large information range, a combination of broadcast data transmissions and a store-and-
forward approach is used in this approach.
The algorithm in [20] totally relies on GPS receiver equipped onboard the vehicle within VANETs in
order to provide the utility information required. Since GPS is not always available i.e. GPS signals cannot be
received under tunnels, area characterized by high buildings, etc. accurate information of vehicles at their
current road segment cannot be provided. Moreover this algorithm did not take into account the behavior of
neighborhood to choose the next packet to be transmitted.

Neighborhood evaluation of vehicular ad-hoc networks:
To evaluate the role of neighborhood in VANETS, Stibor et al. [15] approximates the neighborhood
nature of VANETs within a four highway lanes context (two lanes for each direction). Their simulations and
analysis that show that the average number of potential communication neighbors is approximately four. In
addition, in 50% of all occurrences, the maximum potential communication duration is 1 sec; in 90% of the
occurrences, the upper boundary for the communication time is 5 sec.
Cooperative Collision Warning Using Dedicated Short Range Wireless Communications:
Tamer ElBatt et al. [17] directs towards periodically broadcasting short messages for the purpose of
driver situational awareness and warning via vehicles. They explored two design issues that are highly relevant
to Cooperative Collision Warning (CCW) applications, specific performance trends with distance and potential
avenues for broadcast enhancements. The ultimate goal of CCW is to realize the concept of .360 degrees driver
situation awareness, whereby vehicles alert drivers of impending threats without expensive equipment.
Furthermore, instead of end-to-end per-packet latency, they introduced a novel latency metric that
reflects the critical role played by successive packet collisions in degrading the performance of periodic safety
applications [17]. Moreover, they employed DGPS instead of ordinary GPS receiver to increase the range of the
sensor. But here, periodic broadcast messages indicating velocities, speed and direction of vehicles within
VANETs were not separated from unusual disaster messages like an accident, sudden breakdown or any mishap.
On the Congestion Control within VANET:
Mohamed Salah et al. [14] presented a congestion control algorithm that relies on the concept of
dynamic priorities-based scheduling, to ensure a reliable and safe communications architecture within VANETs.
Messages priorities, under this scheme, are dynamically evaluated according to their types, the network context
and the neighborhood. They used UPPAAL to verify and validate their congestion control technique. UPPAAL
is a tool box for validation (via graphical simulation) and verification (via automatic model-checking) of real-
time systems.
A Cooperative Congestion Control Approach within VANETs: Formal Verification and Performance
Evaluation:
A cooperative and fully distributed congestion control technique, based on dynamic scheduling and
transmission of priority-based messages, to guarantee reliable and safe communication architecture within
VANETs was proposed by Mohamed Salah et al. [9]. Considering the context of high reliability and real-time
response required for inter-vehicular communications (including emergency breaking notification for example),
they proposed a complete validation method of their congestion control algorithms, considering reliability,
temporal, and operational facets.
Congestion Control to Achieve Optimal Broadcast Efficiency in VANETs:
In VANETs, every vehicle broadcasts update messages that contain location and speed information
periodically to its one hop neighbors. Thus, broadcast efficiency measures the average rate at which a vehicle
receives these packets from any of its neighbors. As the node density increases, keen interference lowers
broadcast efficiency if congestion control mechanism is not used. Fei Ye et al. [10] scrutinize the broadcast
efficiency under Rayleigh fading channel, and provides a congestion control and power control strategies that
maximize the efficiency. A worst-case assured strategy achieving at least 95% of the optimal is also provided
for cases when the network nodes have high mobility. NS-2 simulations show that their analytical results
accurately predict the system dynamic.
Efficient Congestion Control in VANET for Safety Messaging:
A conceptual view of a congestion control scheme using transmission rate and transmission power
control techniques simultaneously for optimal congestion control within VANETs was proposed by Bilal Munir
Mughal et al. [11]. The algorithm reveals that only power control techniques do not satisfy the requirements of
envisioning beacon-dependent safety applications and also methods used for measuring channel usage level in
transmission rate control technique may not be as effective under real world conditions.
A Review of Congestion Control Algorithm for Event-Driven Safety Messages in Vehicular Networks:
Assigning uni-priority for event-driven messages to secure life is proposed by Mohamad Yusof Doris
et al. [5]. They summarized the weaknesses and advantages of some congestion control algorithms to assist
researchers to tackle the inherent problems of congestions in VANETs.

A Robust Congestion Control Scheme for Fast and Reliable Dissemination of Safety Messages in
VANETs:
The periodic beacon broadcast consumes a large part of the available bandwidth leading to an
escalating number of collisions among MAC frames, particularly in case of high vehicular density. This severely
affect the performance of the ITS safety based applications that require timely and reliable dissemination of the
event-driven warning messages. To deal with this dilemma, SoufieneDjahel et al. [4] proposed an algorithm
that included three phases as mentioned: priority assignment to the messages to be transmitted / forwarded
according to two special metrics, congestion detection phase, and finally transmit power and beacon
transmission rate adjustment to aid emergency messages spread within VANETs. Moreover, this algorithm
ensures that the most critical and nearest dangers are advertised prior to the remote and less damaging events.
Vehicle Traffic Congestion Management in Vehicular ad-hoc networks:
A pioneering approach to deal with the problem of traffic congestion using the characteristics of
VANETs was proposed by BrijeshKadriet al. [13] that used the Adaptive Proportional Integral (PI) rate
controller, a congestion control technique, intended for the Internet, to deal with the problem of vehicle traffic
congestion in vehicular networks. They proposed that the adaptive PI rate controller is a potential algorithm to
deal with the problem of vehicle traffic congestion as seen when the traffic volume exceeds the road capacity. In
practice, the average waiting time could be calculated using the information provided by the algorithm and some
intelligence that can calculate the current number of vehicles waiting to use the road segment. Using VANETs,
this information can be transmitted to prospective drivers before they reach the intersection in order to assist
them to choose a congestion free route. Using this algorithm, if all the routes ahead are congested, waiting for a
free route may cause congestion in that particular lane too and consequently no further information regarding
choice of route would be able to propagate.
An Optimal Strategy: Interplay Between TVWS and DSRC for QoS of Safety Message Dissemination
For vehicular communications, Dedicated Short-Range Communication (DSRC), the de facto standard,
has normally been used. However, the one-hop transmission range of the DSRC is so short that a multi-hop
dissemination is required in order to cover a large dissemination area of ESM. The multi-hop dissemination with
the limited number of DSRC channels induces channel collision and network congestion. Moreover, the
coexistence with PBMs aggravates collision and congestion of DSRC channels, which makes it hard to satisfy
the requirements of the ESM dissemination. To overcome the limitation of the DSRC, [1] utilize an extra TV
White Space (TVWS) band that has a large communication range for ESM disseminations, and exploit a DSRC
band as a control channel for TV channel rendezvous.
Jae-Han Lim et al. [1] proposed and analyzed a distributed channel usage scheme between DSRC and
TVWS bands for quality of service (QoS) of ESM disseminations under the existence of PBMs. The scheme
employs TVWS Channel Rendezvous Algorithm (TCRA) that is based on available TVWS channel map,
ensuring that vehicles within a dissemination area select the same channel with the ESM sender. To compensate
ESM reception failures in a TVWS band, the scheme adopts On-Demand Recovery Algorithm (ODRA) that
uses a DSRC band for an ESM retransmission to reception failure vehicles.
Distributed Beacon Frequency Control Algorithm for VANETs (DBFC):
LvHumeng et al. [6], proposed an adaptive congestion control scheme which adjusts the beacon
transmission frequency according to the current network condition, while considering the appropriate accuracy
of status information updating. It adaptively adjusts the frequency of beacon messages in two stages, which
correspond to the dynamic vehicular environment. [6] analyzed it theoretically and experimentally. The
algorithm detects and estimates the network load and controls the frequency of outgoing periodic beacons
according to the environment. In particular, the method of half the frequency every time was adopted to
effectively deal with the congestion caused by periodic messages.
A Markov Chain Based Model for Congestion Control in VANETs
M. A. Benatia et al. [2], proposed a novel Markov chain model that consists of four steps, namely,
priority assignment, buffer monitoring,congestion detection phase, and beacon transmission rate adjustment to
facilitate emergency packets propagation. The model responds to congestion in a proactive manner, and hence,
minimizes the loss rate of safety messages due to the proactive nature of the algorithm.
Performance Evaluation of Beacon Congestion Control Algorithms for VANETs:
Long Le et al. [7], considered three beacon congestion control algorithms: rate control, power control,
and joint power+rate control. Each of these algorithms incorporates the following three aspects. First, they
observe the channel conditions during the monitoring interval T. Second, they derive the estimated channel load

from the observed channel conditions. Third, they adjust the transmit power and/or the beacon rate to be used in
the next monitoring interval.
Power-control-based Broadcast Scheme for Emergency Messages in VANETs:
Liqi Wei et al. [8], proposed a power-control broadcast scheme based on studying the IEEE 802.11p
and IEEE 1609 WAVE standards for vehicular communications. Transmission strategy is adjusted based on
vehicles’ situation and the receive power of recently broadcastpacket from a sender node, and re-dissemination
power in short-range for reliable broadcast is adapted based on the observed channel status.
The algorithm [8] uses selected boundary nodes to relay data avoiding broadcast storm problems in the
highway scenario. Also, to ensure reliable transmission, two algorithms are executed simultaneously, Forward---
Fast dissemination and Backward---Retransmisssion for reliable 1-hop broadcast of safety messages.
Application-Based Congestion Control Policy for the Communication Channel in VANETs:
Miguel Sepulcre et al. [12] proposed a novel proactive congestion control policy for vehicular ad-hoc
networks, in which every vehicle’s communication parameters are adapted based on their individual application
requirements. Irrespective of other approaches, where transmission resources are likely to be assigned based on
system-level performance metrics, the technique proposed in this research aims to individually satisfy the target
application performance of each vehicle, while globally minimizing the channel load to prevent channel
congestion.
Reducing Traffic Jams via VANETs:
A strategy to reduce traffic congestion with the help of periodically emitted beacons to analyze traffic
flow and to warn other drivers of a possible traffic breakdown is illustrated by Florian Knorr et al. [3]. Under
this scheme, drivers who receive such a warning are informed to keep a larger gap to their precursor so that they
are less likely to be the source of perturbations, which can cause a traffic breakdown. However, this work does
not pay attention to prioritizing event driven messages above beacon messages.
V. Overview Of Functions, Parameters And Characteristics Of Congestion Control Algorithms
A comparative analyze of functions, characteristics and parameters of some of the existing algorithms
are overviewed in table 1.
Sr.
No.
Algorithm Parameter Function Attributes
1. Utility-Based
Congestion Control
and Packet
Forwarding in
VANETs
Data rate based The algorithm uses an application-specific
utility function and encodes the quantitative
utility information in each transmitted data
packet. A decentralized algorithm then
calculates the “average utility value” of each
individual node based on the utility of its
data packets and assigns a share of the
available data rate proportional to the
relative priority.
1.Avoids the typical starvation of some nodes
in the network.
2. Increases the efficiency of information
dissemination and fairness.
3. Combination of broadcast data
transmission and SAFE application is used.
2. Cooperative
Collision Warning
Using Dedicated
Short Range
Wireless
Communication
Cooperative
Collision
Warning
Periodic broadcasting of short messages for
the purpose of driver situational awareness
and warning via vehicles.
1.Two design issues are explored;
performance trends with distance and
potential avenues for broadcast
enhancements.
2.Vehicles alert drivers of impending threats
without expensive equipment.
3.Employs DGPS instead of ordinary GPS
receiver to increase the range of the sensor.
4.Introduces a novel latency metric that
reflects the critical role played by successive
packet collisions in degrading the
performance of periodic safety applications.
3. Dynamic priorities-
based Congestion
Control scheme
Prioritizing
messages based
Messages priorities are dynamically
evaluated according to their types, the
network context and the neighborhood.
1. Priorities are assigned based on two
factors;
a. Static Factor: deduced from application
type and consist of five priorities levels,
namely, PRIEmergency, PRIVANET, PRIHIGH,
PRIMID, and PRILOW.
b. Dynamic Factor: realized from specific
network context and depends on two
considerations, namely, Node Speed and
Message Utility Consideration.
2. Low priority message transmission is

freezed in order to send high priority packets
with minimum delay.
4. Congestion Control
to Achieve Optimal
Broadcast Efficiency
in VANETs
Transmission
power based
The algorithm provides a congestion control
and power control strategies to achieve
optimal broadcast efficiency under the
Rayleigh fading channel.
1. Provides power control policy in VANET
as node density varies.
2. Presents a complete characterization of the
optimal transmission probability as a function
of node density, transmission power, packet
length and other VANET system parameters.
3. Offers a worst-case guaranteed congestion
control strategy that achieves over 95% of the
optimal performance even when the bounds
on the node density differ by an order of
magnitude.
5. Congestion Control
approach for Event-
Driven Messages in
VANETs
Prioritizing
messages based
The algorithm focuses on uni-priority of
event-driven messages so that these
messages along with the nodes with the
same high priority packets can be scheduled
before starting the transmission process to
ensure timely and reliable delivery of event-
driven safety messages.
1. Features weaknesses and advantages of
some congestion control algorithms to assist
researchers to tackle the inherent problems of
congestions in VANETs.
2. Provides an overview of some of the
congestion detection methods, namely, Event-
Driven Detection Method, Measurement-
Based Detection Method and MAC Blocking
Detection Method.
6. Efficient Congestion
Control in VANET
for Safety Messaging
Transmission
Rate and
Transmission
Power.
The algorithm provides a conceptual view
of a congestion control scheme using
transmission rate and transmission power
control techniques simultaneously for
optimal congestion control within VANETs.
1. The algorithm reveals that only power
control techniques do not satisfy the
requirements of envisioned beacon-dependent
safety applications and also methods used for
measuring channel usage level in transmission
rate control technique may not be as effective
under real world conditions.
2. The algorithm offers a congestion
mitigation process to decide appropriate
technique to be used i.e. adjusting
transmission power or message transmission.
7. A Congestion
Control Scheme for
Fast and Reliable
Dissemination of
SafetyMessages
Priority
assignment and
Transmission
power & rate
adjustment
The algorithm consist of three phases;
priority assignment to themessages to be
forwarded, congestion detection phase, and
finally transmit power and beacon
transmission rate adjustment to facilitate
emergency messages spread within
VANETs.
1. It doesn’t alter the performance of the
running ITS applications unless a VANET
congestion state is detected.
2. It ensures that the most critical and nearest
dangers are advertised prior to the farther and
less damaging events.
3. Three priorities level are defined; high,
medium and low level.
8. Adaptive
Proportional Integral
rate controller
congestion control
algorithm
Adaptive
Proportional
Integral rate
controller
(Control
Theory)
Adaptive Proportional Integral rate
controller congestion control technique,
intended for the Internet, deals with the
problem of vehicle traffic congestion in
vehicular networks.
1. This is a potential algorithm to deal with
the problem of vehicle traffic congestion as
seen when the traffic volume exceeds the road
capacity.
2. The information evaluated can be
transmitted to prospective drivers before they
reach the intersection in order to assist them
to choose a congestion free route.
9. Application-Based
Congestion Control
Policy for the
Communication
Channel in VANETs
Vehicle’s
Communicatio
n parameter
depending
upon Dw i.e.
Warning
Distance.
The algorithm aims to individually satisfy
the target application performance of each
vehicle, while globally minimizing the
channel load to prevent channel congestion.
1. The algorithm takes into account lane
change assistance application.
10. Reducing Traffic
Jams Algorithm
Vehicle to
Vehicle
Communicatio
n
The algorithm make use of periodically
emitted beacons to analyze traffic flow and
to warn other drivers of a possible traffic
breakdown.
1. Drivers who receives warning are
informed to keep a larger gap to their
precursor so that they are less likely to be the
source of perturbations, which can cause a
traffic breakdown.
11. A Markov Chain
Based Model for
Congestion Control
Markovian
model based
transmission
rate control
A novel Markov chain model that consists
of four steps: priority assignment, buffer
monitoring,congestion detection phase, and
beacon transmission rate adjustment to
facilitate emergency packets propagation.
1. The model responds to congestion in a
proactive manner.
2. Minimizes the loss rate of safety messages
due to proactive nature.
12. An Optimal
Strategy: Interplay
Between TVWS and
DSRC for QoS of
Interplay
Between
TVWS and
DSRC
The algorithm proposes adistributed channel
usage scheme between DSRC andTVWS
bands for quality of service (QoS) of ESM
disseminationsunder the existence of PBMs.
1. To overcome the limitation of the DSRC,
the algorithm utilize an extra TV White Space
(TVWS) band that has a large communication
range for ESM disseminations, and exploit a
DSRC band as a control channel for TV

Safety Message
Dissemination
channel rendezvous.
2. The scheme employs TVWS Channel
Rendezvous Algorithm (TCRA) that is based
on available TVWS channel map, ensuring
that vehicles within a dissemination area
select the same channel with the ESM sender.
3. To compensate ESM reception failures in a
TVWS band, the scheme adopts On-Demand
Recovery Algorithm (ODRA) that uses a
DSRC band for an ESM retransmission to
reception failure vehicles.
13. Distributed Beacon
Frequency Control
Algorithm for
VANETs (DBFC)
Beacon
frequency
control
An adaptive congestion control
schemewhich adjusts the beacon
transmission frequency according tothe
current network condition, while
considering theappropriate accuracy of
status information updating.
1. Estimates the network load and controls the
frequency of outgoing periodic beacons
according to the environment.
2. The method of half the frequency every
time is adopted to effectively deal with the
congestion caused by periodic messages.
14. Power-control-based
Broadcast Scheme
for Emergency
Messages in
VANETs
Selects
boundary nodes
to relay data
Transmission strategy is adjusted based
onvehicles’ situation and the receive power
of recently broadcastpacket from a sender
node, and re-dissemination power inshort-
range for reliable broadcast is adapted based
on theobserved channel status.
1. Uses selected boundary nodes to relay data
avoiding broadcast storm problems in the
highway scenario
2. To ensure reliable transmission, two
algorithms are executed simultaneously,
 Forward---Fast dissemination
 Backward---Retransmisssion for reliable 1-
hop broadcast.
15. Performance
Evaluation of
Beacon Congestion
Control Algorithms
for VANETs
Transmit rate
and/or transmit
power control
Considers three beacon congestion control
algorithmsthat control the beacon load
below a certain threshold byadjusting the
transmit rate and/or transmit power for the
beaconmessages.
1. Rate control is adequate when all nodes
use the same transmit power and it is possible
to adjust the beacon rate without violating the
applications’ requirements.
2. Power control is appropriate when all
nodes’ beacon rate is constant and the
communication ranges corresponding to the
varying transmit power meet the applications’
requirements.
3. Power+rate control is the mostflexible
algorithm because it allows application
designer to trade off between beacon rate and
beacon transmit power.
Table 1. Function, parameters and characteristics of Congestion Control Algorithms
VI. Conclusion
This paper focuses on congestion control issue within VANETs. It provides an analytical view to some
of the proposed congestion control algorithm in recent yearsalongwith an overview to DSRC standards for
VANETs.The presented compilation can be accounted as groundwork to the study of congestion control
schemes for VANETs. The challengesemphasized in this study can be considered as future work by researchers
to develop an algorithm to control congestion within VANETs in order to utilize network resources efficiently
in various circumstances.
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