2. DELAY TOLERANT
represent a different and unique wireless network which provides communication
to mobile nodes in environment where no continuous route is present between the
end nodes. In these types of networks, relay nodes are used to carry and
forward messages and make communication possible. DTNs use store carry and
forward technique. It has bundle layer which is used for store carry and
forwarding the message.
2.1 DTN APPLICATIONS
networks are required due to mobility of host and router. Another reason of
irregular connectivity is due to interferences and power management. DTN has
applications in areas where no end to end connection is possible between the
source and destination network. DTN make it possible to send data when end to
end connectivity is absent .Some of the examples of DTN are as follows:
2.1.1 EXOTIC MEDIA NETWORKS
communication includes long distance radio links, transmission in water and air,
near earth satellite communication, space communication and nanotechnology
networks31. Due to different environmental conditions(weather) these systems
may suffer occasional interruptions and have high latency. And even provide
store and forward network that is available occasionally (satellites).
2.1.2 WIRELESS SENSOR NETWORKS
have limited end node resources which
includes memory, energy and CPU power. Communication in these networks is to
make limited use of these resources. In WSNs opportunistic communication becomes very
important. Because of lack of infrastructure in sensor network, gateways are
irregularly connected to operators’ network 43.
2.1.3 MILITARY BATTLEFIELD NETWORKS
military battlefield networks DTN should be able to send message to multiple
–hop networks which is made up of different sub-networks on the basis of
parameters like delay and losses. Because these types of systems have to operate
in environment of high noise, high temperature, jamming can easily result in
disconnections and data transmission may have to wait for few seconds to be
delivered to destination node.1,12
2.1.4 SPARSE MOBILE AD-HOC NETWORKS
to node mobility intermittent connections are present in these networks. Sometimes
irregular connectivity in the network can predictable and periodic. For
example, if a bus is carrying a computer then it can act as a store and forward
switch with communication capability.12.
2.1.5 DTN IN
from earth to any space mission is one the biggest challenge for scientists.
When data is received thousands of miles away it get lost. So NASA’s solution
to this data lost is DTN. When a message is sent so far somehow or the other
the data which is sent is not received exactly the same , it is lost somewhere
in the way. So Delay Tolerant Networking (DTN)
is NASA’s solution to reliable internetworking for space missions4.
2.2 DTN CHARACTERISTICS
part explores the characteristics of DTN and focus and main concentration is on
those that produces impact on forwarding and flooding routing protocol
No end-to-end connection is present between the
nodes. These disconnections may be
due to partition of networks or faults which are not expected. Non faulty
disconnections are present due to wireless environment present which is due to
mobility of source or destination.
Delivery latency is the
amount of time taken to send the message from source to reception at the
destination. The end to end delay between the nodes is called latency. And
latency is high in this network because of presence of number of disconnections
between the nodes. Latency is one of the
important performance matrix of DTN.
and Low data rate
The end-to-end delay is
basically the total delay of each hop on the same
route. The delay is high due to
the intermittent connections in DTN. This also results in low data rate. Data rate is
the rate which tells the number of messages delivered in given time frame.
2.4 Resource limitations
DTN nodes have very limited resources because of node’s
mobility3. It needs protocol designs to be efficient. Many processes like
receiving, sending , storing and forwarding needs route discovery. In some
applications nodes have very limited memory and low processing capability15.
are unsafe to many pernicious actions and bring new challenges for security.
Intermediate nodes which are used as relay nodes offers extra opportunities
for system performance , user privacy
and security attacks. Research on DTN security is more challenging than other
mobile ad-hoc networks due to its unique security characteristics30,19.