DOI 10.4010/2015.309
ISSN-2321 -3361 © 2015 IJESC
Research Article
March 2015 Issue
Multipath Routing under Connectivity Behaviour in VANET’s
R.Hema
M.E (CSE)
A.R.J College of Engineering And Technology
ABSTRACT
Vehicular ad hoc networks (VANETs) are going to be an important communication infrastructure in our moving life. The
design of routing protocols in VANETs is a significant and necessary issue for supporting VANET-based applications. However,
due to high mobility, frequent link disconnection, and uneven distribution of vehicles, it becomes quite challenging to establish a
robust route for delivering packets. This paper presents a connectivity-aware intersection based routing (CAIR) protocol to
address these problems by selecting an optimal route with higher probability of connectivity and lower experienced delay; then,
geographical forwarding based on position prediction is used to transfer packets between any two intersections along the route.
Simulation results show that the proposed protocol outperforms existing routing protocols in terms of data delivery ratio and
average transmission delay in typical urban scenarios.
Index terms: Routing protocols, Route maintenance, Transportation system, Destination address.
1.
parallel roads separated by irregularly spaced buildings, the
channel conditions for transmissions between both nodes
might quickly alternate between a near perfect, lossless
channel and strong (but predictable) shadowing.
Consequently, in order to address the influences
from the above issues, a well-designed routing protocol
often consists of two steps:
(1) select an optimal route, consisting of a
sequence of passed road intersections.
(2) select the next hop, usually through greedy
forwarding.
Although the existing routing protocols can ensure
the inter-vehicle communication in most cases, these
protocols are generally designed with the assumption that
vehicles are uniformly or randomly distributed on the roads.
Under such an assumption, the vehicle density in hand is
actually averaged over the discussed area, which is
sometimes not consistent with the actual case. An urban
VANET snapshot is depicted in Figure as an example
where average vehicle density in Figure 1a is higher than
that in Figure 1b, whereas the road segment in Figure 1a
has the temporal network disconnection problem.
The reason is that vehicles are frequently interrupted due to
the traffic signals and often slow down or stop in front of
the intersections. In addition, traffic statistics indicate that
more than 70% of the vehicles travelling in a platoon form
in urban areas, which may further increase the
disconnection probability considering the possible gap
between clusters.
INTRODUCTION
Vehicular ad hoc networks (VANETs) represent a particular
subclass of mobile ad hoc networks (MANETs), used for
communication and cooperation driving between cars on the
road. VANETs are one of the influencing areas for the
improvement of intelligent transportation system (ITS) in
order to provide safety and comfort to the road users.
VANETs assist vehicle drivers to communicate and
coordinate among themselves in order to avoid any critical
situation through vehicle to vehicle information exchanges,
e.g., road accidents, traffic jams, speed violation, and
unseen obstacles, etc. Besides safety applications, VANETs
also provide entertainment-related applications among
drivers.
For example, weather information, mobile ecommerce, Internet access, and other multimedia services.
Although being a subclass of MANETs, VANETs have
many unique characters different from traditional MANETs.
The most significant differences are the special mobility
pattern and rapid changing topology, so it might not be
effective to apply the existing routing protocols from
MANETs to VANETs.
In urban VANETs, more issues should be
considered in the design of routing protocols such as the
large number of vehicles, various traffic signals, the
restricted movement area, uneven vehicle distributions, no
transmitting power constraints, obstacles such as
skyscrapers and big trees, etc. Among these factors, the
impact of obstacles on the communication quality is a more
representative characteristic in urban scenario. As an
example, when considering two vehicles that are driving on
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1.1 OVERVIEW OF VANETS
Vehicular adhoc networks (VANETs) represent a
particular subclass of mobile ad hoc networks (MANETs),
used for communication and cooperation driving between
cars on the road. VANETs are one of the influencing areas
for the improvement of intelligent transportation system
(ITS) in order to provide safety and comfort to the road
users. VANETs assist vehicle drivers to communicate and
coordinate among themselves in order to avoid any critical
situation through vehicle to vehicle information exchanges,
e.g., road accidents, traffic jams, speed violation, and
unseen obstacles, etc. Besides safety applications, VANETs
also provide entertainment-related applications among
drivers.
2. LITERATURE SURVEY
DSDV use two types of packet to transfer routing
information: full dump and incremental packet. The first
time two DSDV nodes meet, they exchange all of their
available routing information in full dump packet. From that
time, they only use routing. Incremental packets to notice
about change in the routing table to reduce the packet size.
Every node in DSDV has to send update routing
information periodically. When two routes are discovered,
route with larger sequence number will be chosen. If two
routes have the same sequence number, route with smaller
hop count to destination will be chosen. DSDV has
advantages of simple routing table format, simple routing
operation and guarantee loop-freedom. The disadvantages
are (i) a large overhead caused by periodical update (ii)
waste resource for finding all possible routes between each
pair, but only one route is used.
Select an optimal route, consisting of a sequence of passed
road intersections. The nodes maintain a table of routes to
every destination in the network, for this reason they
periodically exchange messages. At all times the routes to
all destinations are ready to use and as a consequence initial
delays before sending data are small. Keeping routes to all
destinations up-to-date, even if they are not used, is a
disadvantage with regard to the usage of bandwidth and of
network resources.
2.1.1 On-Demand (or Reactive)
These protocols were designed to overcome the wasted
effort in maintaining unused routes. Routing information is
acquired only when there is a need for it. The needed routes
are calculated on demand. This saves the overhead of
maintaining unused routes at each node, but on the other
hand the latency for sending data packets will considerably
increase.
2.2.2 Proactive
2.2.2.1 DSDV
DSDV has one routing table, each entry in
the table contains: destination address, number of hops
toward destination, next hop address. Routing table contains
all the destinations that one node can communicate. When a
source A communicates with a destination B, it looks up
routing table for the entry which contains destination
address as B. Next hop address C was taken from that entry.
A then sends its packets to C and asks C to forward to B. C
and other intermediate nodes will work in a similar way
until the packets reach B. DSDV marks each entry by
sequence number to distinguish between old and new route
for preventing loop.
2.2.3 Reactive
2.2.3.1 On-demand Routing Protocols
In on-demand trend, routing information is only created
to requested destination. Link is also monitored by
periodical Hello messages. If a link in the path is broken, the
source needs to rediscovery the path. On-demand strategy
causes less overhead and easier to scalability. However,
there is more delay because the path is not always ready.
The following part will present AODV, DSR, TORA and
ABR as characteristic protocols of on-demand trend.
2.2.3.2 AODV Routing
Ad hoc on demand distance vector routing (AODV) is the
combination of DSDV and DSR. In AODV, each node
maintains one routing table. Each routing table entry
contains. For two RREPs with the same sequence number,
the one will less number of hops to destination will be
chosen. When a route is found, it is maintained by Route
Maintenance mechanism: Each node periodically send Hello
packet to its neighbours for proving its availability. When
Hello packet is not received from a node in a time, link to
that node is considered to be broken. The node which does
not
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receive Hello message will invalidate all of its related routes
to the failed node and inform other neighbour using this
node by Route Error packet. The source if still want to
transmit data to the destination should restart Route
Discovery to get a new path. AODV has advantages of
decreasing the overhead control messages, low processing,
quick adapt to net work topology change, more scalable up
to 10000 mobile nodes. However, the disadvantages are that
AODV only accepts bi-directional link and has much delay
when it initiates a route and repairs the broken link.
Compared to other reactive routing protocols like ABR
or SSA, DSR is beacon-less which means that there are no
hello-messages used between the nodes to notify their
neighbours about her presence.
DSR was developed for MANETs with a small
diameter between 5 and 10 hops. DSR is based on the LinkState-Algorithms which mean that each node is capable to
save the best way to a destination. Also if a change appears
in the network topology, then the whole network will get
this information by flooding.
In urban VANETs, more issues should be considered
in the design of routing protocols such as the large number
of vehicles, various traffic signals, the restricted movement
area, uneven vehicle distributions, no transmitting power
constraints, obstacles such as skyscrapers and big trees, etc.
Among these factors, the impact of obstacles on the
communication quality is a more representative
characteristic in urban scenario.
DSR contains 2 phase
2.
Once the link in the entry is broken, neighbour
nodes in this list will be informed.
Destination address.
4.
Next-hop address toward that destination.
Route Discovery (find a path)
2.
Route Maintenance (maintain a path)
2.3.1 ROUTE DISCOVERY
Route discovery If node A has in his Route Cache a
route to the destination E, this route is immediately used. If
not, the Route Discovery protocol is started Node A
(initiator) sends a RouteRequest packet by flooding the
network If node B has recently seen another RouteRequest
from the same target or if the address of node B is already
listed in the Route Record, Then node B discards the
request!
If node B is the target of the Route Discovery, it
returns a RouteReply to the initiator. The RouteReply
contains a list of the “best” path from the initiator to the
target. When the initiator receives this RouteReply, it caches
this route in its Route Cache for use in sending subsequent
packets to this destination. Otherwise node B isn’t the target
and it forwards the Route Request to his neighbours (except
to the initiator).
1.
Active neighbour list: a list of neighbour nodes that
are actively using this route entry.
3.
1.
5.
Routing in AODV consists of two phases: Route
Discovery and Route Maintenance. When a node wants to
communicate with a destination, it looks up in the routing
table. If the destination is found, node transmits data in
the same way as in DSDV. If not, it starts Route
Discovery mechanism: Source node broadcast.
2.3.2 Route Maintenance
6.
Route Request packet to its neighbour nodes,
which in turns rebroadcast this request to their neighbour
nodes until finding possible way to the destination.
In DSR every node is responsible for confirming that the
next hop in the Source Route receives the packet. Also each
packet is only forwarded once by a node (hop-by-hop
routing). If a packet can’t be received by a node, it is
retransmitted up to some maximum number of times until a
confirmation is received from the next hop.
2.3 DSR PROTOCOL
DSR is a reactive routing protocol which is able to
manage a MANET without using periodic table-update
messages like table-driven routing protocols do. DSR was
specifically designed for use in multi-hop wireless ad hoc
networks. Ad-hoc protocol allows the network to be
completely self-organizing and self-configuring which
means that there is no need for an existing network
infrastructure or administration.
For restricting the bandwidth, the process to find a path
is only executed when a path is required by a node (OnDemand-Routing). In DSR the sender (source, initiator)
determines the whole path from the source to the destination
node (Source-Routing) and deposits the addresses of the
intermediate nodes of the route in the packets.
Only if retransmission results then in a failure, a
RouteError message is sent to the initiator that can remove
that Source Route from its Route Cache. So the initiator can
check his Route Cache for another route to the target. If
there is no route in the cache, a RouteRequest packet is
broadcasted.
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2.5 DISADVANGES OF DSR
Path-finding-process: Route Request & Route Reply
The Route Maintenance protocol does not locally repair a
broken link. The broken link is only communicated to the
initiator. The DSR protocol is only efficient in MANETs
with less than 200 nodes. Problems appear by fast moving
of more hosts, so that the nodes can only move around in
this case with a moderate speed. Flooding the network can
cause collusions between the packets. Also there is always a
small time delay at begin of a new connection because the
initiator must first find the route to the target.
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