END-TO-END DELAY ANALYSIS OF DELAY-TOLERANT NETWORK
Delay Tolerant Networks, DTNs, are basically ad-hoc networks where end-to-end connectivity is not available for the transmission of a message, application of the DTN would be a high latency application where message transmission on time is not important, that can be hours or weeks.
A delay-tolerant network is a network designed to operate effectively over extreme distances such as those encountered in space communications or on an interplanetary scale. The main approach used by DTN is a store and forward approach where the message is stored when the transmission is not available, as soon as the transmission is available message is forwarded. And also this article will discuss different issues occurs in DTN This article discusses the delay of end-to-end (E2E) transmission and discusses the closed topologies system of end-to-end delay, to calculate E2E delay the model incorporates the impact of traffic load(amount of data moving across), arrival rate(number of arrivals during a time rate), service rate, link connectivity, and the underlying routing algorithm.
Internet connects almost all of the devices in world using TCP/IP protocol, so every device that comprise the internet makes use of this protocol for communication purpose, but in so many areas in world does not have internet connectivity or having intermittent (irregular connection) connectivity, where TCP/IP protocol will not work due to this new type of infrastructure network has evolved called Delay Tolerant Network(DTN)
This aims to address technical issues in heterogeneous networks which are occurred because of harshness in the environment, mobility of nodes, connectivity issues due to the battery life of the nodes, and range between nodes. Some of the issues in DTN include,
Wireless Sensor Networks are deployed in regions where human intervention is not possible like wildlife sanctuaries.
Rural areas and regions where the population of humans is less (less developed), connect that world using GPS, or via ad-hoc networks.
Interconnecting extra-terrestrial nodes such as satellite and deep space communication.
ARCHITECTURE OF DTN
DTN is a technique to resolve the technical issue related to a heterogeneous network where the connection between the sender or receiver will not have regular connectivity or we say infrequent connectivity.
Applications operate properly when the network ensures that transmission of the packets will be delivered successfully, 2 broad transport layer protocol TCP and UDP helps achieve transmission successfully if there is no harshness in the environment, but TCP will not work in a harsh environment where connectivity is the main issue.
Basically, DTN is the technique to resolve failures of transmission in an intermittent network, the greatest challenge in DTN is to avoid such major issues as delay in transmission, link, connectivity, and bandwidth, properties of DTN are mentioned below,
- Opportunistic Network: Where part of the network does not necessarily have to be connected fully at one time, the connection should be established whenever it is possible to connect with the entire network, this type of network is called an opportunistic network or intermittent network.
- Variable Length of packets: This network is intermittent so it is not possible to have a regular connection where we can send regular data packets, so one other method whenever is possible to have a connection we send the data in one go (longer packet architecture).
- Store and Carry approach: Major problems like delay, disconnection, and retransmission are regular in DTN, so DTN uses the store and Carry approach to store the data in intermediate nodes, and when communication opportunity will available it forwards the packet to the next available node as mentioned in fig 2.
- Bundle Layer: This is the new layer implemented between the application layer and transport layer, where its main mechanism is to store the packet, and whenever the transmission is possible forward it to the other nodes.
- Security: In a harsh environment where human intervention is hardly possible, it is right to have security over data, so DTN provides security over these areas, by quickly discarding them whenever some unauthorized access occurs.
CONCEPT OF BUNDLE LAYER PROTOCOL:
Here we can see the bundle layer resides between the application layer and the transport layer, the main work of the bundle layer is to store the messages when the connection is not possible and when a connection is made available it forwards it to the next node whenever it is possible.
Bundle layer consists of 3 types of information,
- Source node information
- Control information (source node id, destination node id, etc.)
- Bundle layer header
ISSUES IN DTN
Major issues related to DTN to be addressed are the following.
1. Low data rate, high latency: continuous connection is not there, so whenever some data comes store mechanism should be there in order to store the data and forward it whenever the next hop is possible.
2. Discontinuity: DTN’s main problem is continuous disconnection of the network, so it’s DTN’s job to transmit data successfully to the destination node.
3. Storage: Networks use DTN architecture where end-to-end connectivity is not available every time, most of the time network is in a disconnected state, so it is needed to have much storage to be able to store the packets.
4. Environment Disruption: DTN is mainly designed for underwater networks, interplanetary networks, deep space communication, and military ad-hoc network.
IMPLEMENTATION AND ANALYSIS:
In remote systems there exists a class of systems, known as Mobile Ad Hoc Networks (MANETs) in which two gadgets are connected in the event that they are inside the correspondence scope of each other.
It is likewise connected that between any two gadgets, there may exist various transitional correspondence links (connections) what’s more, a connection may turn between ON and OFF periods. This may occur in control-constrained cell phones because of planned ON and OFF periods, or because of the versatility of MANETs that comprise cell phones.
In MANETs the gadgets refresh their correspondence ways, otherwise called directing ways, in light of topological changes and accessible ways. Mobility changes topology dynamically but also provides new connection opportunities due to which eventually there is a path between a source and destination pair over a long time.
This section will explain end to end delay of closed systems; the model consists of traffic load, arrival rate, service rate, link connectivity, and underlying routing algorithm
A link with probability αi = α and comes back on with probability βi = β, according to the state transition diagram in Figure 3, Yellow nodes correspond to disconnected states and blue nodes correspond to connected states and the table shows connected and disconnected states,
The result obtained from the model in Fig 3 and Fig 4 under various conditions, comparison of connected states(Sc) and all states (Sc U Sd), This simulation is tested on logisim simulator, and this experiment is slightly greater when we increase the number of nodes and for higher loads, the analytical results show better performance than simulation. Still, the E2E delay approximation is very close to the simulation results.
APPLICATION:
DTN is mainly used in a rural area where Internet connectivity is less, where deep space communication occurs, and wildlife sanctuaries where the work of DTN is to deploy sensors and store the data, and whenever available it sends it to the sink or base station, some of the basic application of DTN follow,
1. Interplanetary Internet: International space station communication, deep space communication, future space debris monitoring.
2. Military and Intelligence: mobile ad-hoc network for communication and monitoring cargo tracking, enemy movement, and unmanned area vehicle (UAV).
3. Commercial Purpose: monitoring of vehicles by road, air, water, agricultural crop monitoring, monitoring underground mines.
4. Environmental monitoring: Crops monitoring. Wildlife sanctuaries for Wireless Sensor Network. Atmosphere and Oceanography conditions, seismological events.
5. Public service and Safety: monitoring using CCTV cameras, and global airplane traffic control.
6. Underwater acoustic: Underwater sea-based analysis, taking continuous photos until some time and then sending them to the base station.
7. Terrestrial Mobile Networks: These networks connect mobile devices and do not necessarily maintain end-to-end connectivity, where an unexpected failure of the network occurs most of the time due to signal strength etc.
CONCLUSION:
DTN is the most important facet in terms of connectivity where TCP does not work because this protocol is based on end-to-end transmission and a low error rate, but DTN does not have any. In areas where Internet connectivity is the main problem, DTN mainly solves this problem by store and forward approach where it stores data and forwards next time when connectivity is available. DTN proposed bundle layer protocol where it implements a store and forward approach, DTN consists of so many unsolved issues like low data rate, high latency, discontinuity, and Environmental disruption, storage issues, lastly paper talked about end-to-end delay in DTN with respect to load and delay. There are so many applications of DTN like Terrestrial Mobile Networks, Underwater Acoustic, Wildlife sanctuaries, and so on.
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