MANET: Mobile Ad hoc Network
MANET stands for Mobile adhoc Network also called as wireless adhoc
network or adhoc wireless network that usually has a routable networking
environment on top of a Link Layer ad hoc network.. They consist of set of
mobile nodes connected wirelessly in a self configured, self healing network
without having a fixed infrastructure. MANET nodes are free to move randomly
as the network topology changes frequently. Each node behave as a router as
they forward traffic to other specified node in the network.
MANET may operate as standalone fashion or they can be the part of larger
internet. They form highly dynamic autonomous topology with the presence of
one or multiple different transceivers between nodes. The main challenge for
the MANET is to equipped each devices to continuously maintain the
information required to properly route traffic. MANETs consist of a peer-to-
peer, self-forming, self-healing network MANET’s circa 2000-2015 typically
communicate at radio frequencies (30MHz-5GHz). This can be used in road
safety, ranging from sensors for environment, home, health, disaster rescue
operations, air/land/navy defense, weapons, robots, etc.
Characteristics of MANET –
Dynamic Topologies: Network topology which is typically multihops,
may change randomly and rapidly with time, it can form unidirectional or
bi-directional links.
Bandwidth constrained, variable capacity links: Wireless links usually
have lower reliability, efficiency, stability and capacity as compared to
wired network.The throughput of wireless communication is even less
than a radio’s maximum transmission rate after dealing with the
constraints like multiple access, noise, interference conditions, etc.
Autonomous Behavior: Each nodes can act as a host and router, which
shows its autonomous behavior.
Energy Constrained Operation: As some or all the nodes rely on
batteries or other exhaustible means for their energy.Mobile nodes are
characterized with less memory, power and light weight features.
Limited Security: Wireless network are more prone to security threats. A
centralized firewall is absent due to its destributed nature of operation for
security, routing and host configuration.
Less Human Intervention: They require minimum human intervention to
configure the network, therefore they are dynamically autonomous in
nature.
Pros and Cons of MANET –
Pros:
1. Seperation from central network administration.
2. Each nodes can play both the roles ie. of router and host showing
autonomous nature.
3. Self configuring and self healing nodes, does not require human
intervention.
Cons:
1. Resources are limited due to various constraints like noise, interference
conditions, etc.
2. Lack of authorization facilities.
3. More prone to attacks due to limited physical security.
4. Routing (pg-132)
Routing is the primary element of an ad-hoc
network. It takes routing software in each network
node to manage the transfer of IP packets. The
simplest solution is obviously to have a direct
routing, as illustrated in Figure, in which each
network station can directly reach another station,
without going through an intermediary. The
simplest case corresponds to a small cell, with a
diameter less than 100 m, as in an 802.11 network
in ad-hoc mode.
5. The classic case of routing in an ad-hoc network
is to pass through intermediate nodes. They
must have a routing table adapted to direct the
packet to the recipient. The whole strategy of an
ad hoc network is to optimize the routing tables
for updates more or less regular. If the updates
are too regular, it can overload the network.
However, this solution has the advantage of
maintaining updated tables and therefore allow
rapid packet routing. An update only when the
arrival of a new wave restricted load circulating
in the network, but unloads the many streams
supervision network.
6. It should happen in this case to set up routing
tables may make the delivery within an
acceptable time.
7.
8. Figure illustrates the case of an ad-hoc network
in which, to get from one node to another, it
may be necessary to traverse the intermediate
nodes. Many pitfalls can be on the road to
building the routing table. For example, signal
for transmission, it is possible that the
connection is not symmetrical, a sense of
communication are acceptable and not the
other. The routing table should reflect this. The
radio signals are susceptible to interference;
asymmetric links can also be complicated by
possible fainting links.
9.
DSDV PG NO: 133
Destination Sequenced Distance Vector (DSDV) is
a hop-by-hop vector routing protocol requiring each
node to periodically broadcast routing updates. This
is a table driven algorithm based on modifications
made to the Bellman-Ford routing mechanism. Each
node in the network maintains a routing table that
has entries for each of the destinations in the
network and the number of hops required to reach
each of them. Each entry has a sequence number
associated with it that helps in identifying stale
entries. This mechanism allows the protocol to avoid
the formation of routing loops. Each node
periodically sends updates tagged throughout the
network with a monotonically increasing even
sequence number to advertise its location. New
route broadcasts contain the address of the
destination, the number of hops to reach the
destination, the sequence number of the information
received regarding the destination, as well as a new
sequence number unique to the broadcast. The
route labeled with the most recent sequence
number is always used. When the neighbors of the
transmitting node receive this update, they
recognize that they are one hop away from the
source node and include this information in their
distance vectors. Every node stores the “next
routing hop” for every reachable destination in their
routing table. The route used is the one with the
highest sequence number
Routing table updates in DSDV are distributed
by two different types of update packets:
Full dump: This type of update packet
contains all the routing information available
at a node. As a consequence, it may require
several Network Protocol Data Units
(NPDUs) to be transferred if the routing table
is large. Full dump packets are transmitted
infrequently if the node only experiences
occasional movement.
Incremental: This type of update packet
contains only the information that has
changed since the latest full dump was sent
out by the node. Hence, incremental packets
only consume a fraction of the network
resources compared to a full dump.
Destination Sequenced Distance Vector Routing protocol is a modified
version of Bellman Ford Algorithm and is based upon the concepts of
Distance Vector Routing.
In Distance Vector Routing(DVR), each node broadcasts a table
containing its distance from nodes which are directly connected and
based upon this, other nodes broadcasts the updated routing. Those
nodes which are unreachable directly are labelled as “infinite”.
But, this updation of routing tables keeps on happening and an infinite
loop is generated which is commonly known as Count-To-Infinity
problem.
To overcome this problem of count to infinity by generating sequence
number in the routing table, every time the routing table is updated. The
process of DSDV is same as that of Distance Vector Routing but an extra
attribute of sequence number is added.
Destination Sequenced Distance Vector Routing : Concept
DSDV protocol uses and maintains a single table only, for every node
individually. The table contains the following attributes.
o Routing Table : It contains the distance of a node from all
the neighboring nodes along with the sequence number( SEQ No
means the time at which table is updated).
Destination Sequenced Distance Vector Routing : Format
This table is updated on every step and ensures that each node
broadcast as well as receives correct information about all the nodes
including their distance and sequence number.
Destination Sequenced Distance Vector Routing Protocol : Working
In DSDV, nodes broadcasts their routing tables to
immediate neighbors with the sequence number. Every time any
broadcasting occurs, the sequence number is also updated along with
distances of nodes.
Consider a network of 3 nodes having distances of “1” on each of the
edges respectively. Below mentioned steps will let you know how DSDV
works and routing tables are updated.
Destination Sequenced Distance Vector Routing : Sample Network
Step-1: Draw separate tables for all the nodes “X”, “Y” & “ Z” along with
the distance and sequence number.
If “Y” wants to broadcast the routing table. Then updated routing tables
of all the nodes in the network will look like as depicted in the below
tables where red marked cell denotes the change in sequence number.
Advantages : Destination Sequenced Distance Vector Routing Protocol
Can’t be implemented commercially or on larger scale.
Efficient results will be produced if applied on small networks.
Disadvantages : Destination Sequenced Distance Vector Routing Protocol
Slower protocol processing time.
Less bandwidth.
Not suitable for large number of networks which are dynamic in nature.
