International Conference on Communication and Signal Processing, April 3-5, 2014, India

Effective Routing Model for Delay Tolerant

Network Applications

Sandhya A Kulkarni, Varaprasad Golla

Abstract-Delay Tolerant Networking(DTN) is an approach to

computer network architecture that seeks to address the technical

issues in heterogeneous networks that may lack continuous

network connectivity. Due to the lack of continuous

communications among mobile nodes, stability becomes major

challenge in distributed clustering in Delay Tolerant Mobile

Network(DTMN). Based on nodal contact probabilities, a set of

functions including synchronizationO, inO and outO are devised

for cluster formation and gateway selection. The gateway nodes

exchange the network information and perform inter-cluster

routing or intra clustering routing.

Index Terms-Delay tolerant mobile networks, nodal contact

probability.

I. INTRODUCTION

DTMN is a fundamentally opportunistic communication

system, where communication links exist temporally

rendering. It is not possible to connect end-to-end devices for

data delivery. The DTN is an occasionally connected network

that may suffer from frequent partitions and it may be

composed of more than one divergent set of protocol

families [ 1 ]-[2]. Examples of such networks are those operating

in mobile or extreme terrestrial environments, or planned

networks in space. DTNs span very challenging application

scenarios, where nodes move around in environments where

infrastructures cannot be installed. The characteristics of

DTNs are sparse and intermittent connectivity and lack of end­

to-end connectivity exists. Some solutions to routing have

been presented for these cases, starting from the basic

epidemic routing, where packets are stored and forwarded to

all neighbor nodes. Existing routing protocols(AODV)[2] are

must take to a store-and-forward method, here, the data

packets are incrementally transmitted and stored throughout

the network in hopes that it will eventually reach its

destination. This is feasible only on networks with large

amounts of local storage and internodes bandwidth relative to

the expected traffic. Most DTN protocols are flat where every

node plays a similar role in routing. The flat architecture is

simple and effective in small networks, but not scalable for

large size DTNs. Clustering has been considered as an

Varaprasad Golla is with the BMS College of Engineering, Bangalore, India; e-mail: varaprasad555555@yahoo.co.in.

Sandhya A Kulkam S. B. is with the BMS College of Engineering, Bangalore, India; e-mail: akulkami.sandhya@gmail.com.

978-1-4799-3358-7114/$31.00 ©2014 IEEE

518

effective approach to reduce the network overhead and

improve scalability. Clustering in the DTMN is unique

because the network is not fully connected. Due to the lack of

continuous communication among mobile nodes, convergence

and stability becomes a major problem in the DTMN. In non­

clustered DTMN, any node in the network may not able to

communicate with other neighboring node due to nodes will

not be having a correct updated information in their nodal

contact and the gateway information therefore they lack

communication. As a result, the nodes cannot provide end-to­

end delivery of the information. At same time, nodes break up

their communication, if they are move out of coverage area.

The rest of the paper is organized as follow. Section 2

reviews some of existing works on DTN. Section 3 presents a

detailed description of our proposed. Section 4 presents

simulation experiments and setup. The simulation results are

presented in section 5. Finally, we conclude our result in

Section 5.

II. LITERATURE WORK

The data is sent by applications in these networks can be

classified as either real-time or delay-tolerant. The real-time

traffic includes voice over IP, video conference, or monitoring

of critical processes. The delay-tolerant traffic does not carry

urgency and only eventual, reliable reception is important.

Examples are email, instant messages or sensor data of long­

term experiment. The real-time communication is challenging

for wireless mobile ad-hoc networks, because of inherent

variability in the wireless connections combined with changing

node positions. In the extreme case of sparsely connected,

moving nodes, some nodes may not be able to communicate

with any other nodes for a longer period of time. In this

scenario, only delay-tolerant communication is feasible. One

of the goals of DTN is to connect devices that are not served

by the traditional networks. These devices may be very small

and similarly processing capability in terms of CPU and

memory. These mobile nodes will not be able capable to

compute complex functions. As a natural significance of

intermittent connectivity among nodes, particularly at low

density and low transmission range, the DTN has been

familiarized[3]-[4] to mobile wireless communications such as

Zebra Net[5], Shared Wireless Info-Station(SWIM)[6]-[7],

Delay/Fault-Tolerant Mobile Sensor Network(DFT-MSN) and

Mobile Internet and peer-to-peer mobile ad hoc networks[8]-

+-IEEE Advancing Technology

for Humanity

[10]. Routing in DTNs is largely based on nodal contact

probabilities.

A recent work[ll] proposes a DTN Hierarchical

Routing(DHR) protocol to improve routing scalability. The

DHR is based on a detenninistic mobility model, where all

mobile nodes move accordingly, which are known by the

routing and clustering algorithms. It cannot be generalized to

such networks with unknown mobility as DTN-based peer-to­

peer mobile ad hoc networks. In community-based mobility

model, each node has its own home location that it visits most

frequently along with several elsewhere locations. Obviously,

if two mobile nodes share the same home location, then they

will have more chance to meet each other. The real life

mobility patterns logically grouped mobile nodes into the

clusters. In this work, it investigates distributed clustering and

cluster-based routing protocols for DTMNs. Clustering in the

DTMN are unique and non-trivial because the network is not

fully connected. Due to the lack of constant communications,

the mobile nodes will have inconsistent infonnation and

therefore respond differently. Although it is largely understood

by the research community that clustering helps to improve the

network scalability. The ability to transport or route data from

a source to a destination is a fundamental ability of

communication networks. The DTNs are characterized by their

lack of connectivity resulting in lack of instantaneous end-to­

end paths. The AODV and DSR protocols fail to establish the

routes. This is due to these protocols trying to first establish a

complete route and then forward the actual data to the

destination.

The DTN is an occasionally connected network that may

suffer from frequent partitions and that may be composed of

more than one divergent set of protocol families[12]. The main

objective of DTN is to provide communication for the

interplanetary Internet. It is primarily focused on the deep

space communication in high-delay environments. The inter­

operability between different networks deployed in extreme

environments lacking continuous connectivity[13]. An overall

design of DTN has been proposed in and functions as an

overlay above the transport layer to provide services. In[I3],

Burleigh et aI., identify several fundamental principles that

would underlie DTN architecture and propose a new end-to­

end overlay network protocol. In[14], Fallet et aI., investigate

the custody transfer mechanism to ensure reliable hop-by-hop

data transmission, thus enhancing the reliability of DTN. The

basic routing paradigm of effective routing in DTNs is to use

the store-and-forward approach, where intermediate nodes

keep the messages until new links come up in the path to the

destination. One general class of proposed DTN routing

algorithms assume that some level of knowledge regarding

node mobility and connectivity fonnulates the DTN routing in

terms of directed multi-graph, where more than one edge may

exist between a pair of nodes[15]-[16]. Such multiple edges

exist because there may be more than one distinct physical

connection or different network links may only be available at

different time intervals. By using different levels of

infonnation regarding connectivity and/or mobility, routing

decisions can be made at individual nodes. However, in many

cases, no such information may be known to the nodes in the

network. Under such conditions, different routing approaches

are necessary for effective message delivery.

III. PROPOSED WORK

A. DTN Network Model

The DTN graph is a directed multi-graph in which more

than one edge may exist between a pair of nodes as shown in

fig. I. Nodes may be connected by multiple edges representing

different physical links. Each mobile node executes store and

forward procedure and has a fmite storage capacity(bj). An

edge is parameterized by its source and destination nodes plus

a capacity(c(t)) and delay function(d(t)). The reason for using

multi-graph is straightforward. It may be possible to select

between the two distinct (physical) connections to move data

between the same pair of nodes. Furthennore, the link

capacities (and to a lesser extent, propagation delay) are time­

dependent(capacity is zero at times, when link is unavailable).

The set of edges in the graph must capture time-varying

capacity and propagation delay as well as multiple parallel

edges. A simple example of an edge captured by this

description involves a ground station and a LEO satellite

rising, passing directly overhead, and setting at the opposite

horizon. As it rises, its channel capacity will generally increase

until it is directly overhead and will decrease for the remaining

time of the pass. This is because noise is minimal when the

satellite is directly overhead but increases at lower elevations.

Another example is a bus passing by a village. The throughput

of the wireless link depends upon the distance of the bus from

the village. If the edge is assigned with "0" capacity, then there

is no communication.

Source Destination

bu Storag e capaci ty

Fig.I. Edges in DTN graph.

A contact is an opportunity to send data over an edge. More

precisely, it is a specific edge and a corresponding time

interval during which the edge capacity is strictly positive. A

packet is a tuple(u, v, t, m), here, u and v are source and

destination nodes, t is the time at which the message is injected

into the network and m is message size. The set of all

messages is called traffic demand. The nodes in a DTN have

finite long-tenn storage(buffers) used for holding transit-data

or data waiting to be consumed by the application at a

519

destination node. In our model, the storage is exclusively used

for holding in-transit data. The destination nodes are assumed

to have sufficient capacity to hold data to be consumed by an

application. It occurs in a store and forward fashion. The

routing algorithm is responsible for determining the next

edge(s) that a message should be forwarded along. Messages

not immediately forwarded until they are assigned to contacts

by the routing algorithm.

B. Clustering

The clustering is a process that divides the network into

interconnected substructures, called clusters. Each cluster has

a Cluster Head(CH) as coordinator within the substructure.

Every CH works as a temporary base station within its zone or

cluster and communicates with other CHs. In our protocol,

there are three possible states for each node such as normal

cluster head(manager) and gateway. In fig.2, each hexago� denotes a cluster. The mobile nodes are represented by a circle

and one will be acting as CH and other nodes will be acting as

gateway nodes and remaining nodes will be acting as normal

mobile nodes.

o

• Gateway • Cluster Head o Normal Mobile Node Fig.2. Cluster fonnation.

C. Distributed Clustering Algorithm

The distributed clustering algorithm is used to form a cluster

in the DTMN. The algorithm is event-driven where the key

part lies on meeting event between any pair of nodes. The set

of functions in the algorithm including Sync, Leave and Join is

outlined below. The methodology which is discussed in

following section will give out an idea how the algorithm

performs its functions.

D. Methodology

The synchronizationO process is invoked when two cluster

members meet. The synchronization process is necessary

because each node separately learns network parameters which

may differ from the nodes to nodes. The inO procedure are

deployed for a node with lower stability which must leave the

cluster. The stability of a mobile node is measured in terms of

connectivity with the cluster members. It indicates the

likelihood that the node will be excluded from the cluster, due

to low contact probability. The outO procedure is deployed for

a node to rejoin a cluster or to join a new cluster. Thus, the

distributed clustering algorithm is used to form a cluster in the

DTMN.

E. Cluster Based Routing

The cluster based routing protocol is used to perform a

routing in the DTMN. We consider the node i has a message to

send to node j, the cluster-based routing protocol used.

F. Intra Cluster Routing

In fig.3, nodes i, j are the mobile nodes and node I IS a

source and node j is a destination node. If nodes i and j are in

the same cluster, then they have high chance to meet each

other. Thus, node i will transmit the data message to node j

directly upon their meeting and relay node is not necessarily

involved. It is also called as direct routing.

(

i

0-__ j -- -0

Fig.3. Intra-clustering routing.

G. Inter Cluster Routing

)

In figure 4, node i looks up its gateway table. If an entry for

node j is found, then there exists a gateway, i.e., Gi, to node j's

cluster. In this scenario, node i sends the data message to its

gateway Gi. Upon receiving the data message, the gateway

node looks into its tables to find node j's( cluster ID). If the

gateway node meets any node(node k), then it forwards the

message to node k, which in turn delivers the data message to

node j via the intra-cluster routing. Since, node Gi is gateway

and has high probability to meet at least one node in node j's

cluster. Node k in fig.4 is not necessary to be gateway node.

j ,0

Fig.4. Inter clustering routing.

The gateway nodes are used for communication between the

clusters. Inter-cluster routing can happen in two ways such as

one-hop inter-cluster routing and multi-hop inter-cluster

routing. One-hop-inter-c1uster routing is chosen when a source

node present in a cluster wants to send information to a

destination node present in the adjacent clusters, i.e. data can

be sender node to receiver node by a single or one hop. Multi­

hop-inter-c1ustering routing is chosen when multiple hops are

required to send the data from the sender node presented in a

cluster to destination node presented in another cluster.

520

IV. SIMULATION SETUP

In this work, cluster-based routing is executed by using

following parameters. For intra-cluster routing, we use

following metrics:

o Transmission range is 50 m.

o A number node in a cluster is 5.

o Bandwidth is 140 bytes.

For inter-cluster routing, we use:

o Transmission range is 50m.

o Total number of clusters is 45.

o Number nodes in an each cluster are 6.

o Total number of nodes in network is 270.

o Bandwidth is 140 bytes. iii Secure Cluster Routing Analysis

1447.]11

Basic Routinll

Secllre Cluster Rot.ing

eS1l1

Path: 119-161 success

Distance' 69,Hops'1

ime:Q,858

o Cluster Head • GateWay

oOtherNOOle

Fig.5. One-hop-inter-cluster routing.

V. SIMULATION RESULTS

In inter-cluster routing, the routing will happen through

mUltiple nodes. Inter-cluster routing is done by using either

one-hop-inter-cluster routing or multi-hop-inter-cluster

routing. In fig.5, it shows one-hop-inter-cluster routing and it

is chosen when the nodes presented in adjacent clusters want

to communicate with others. From the adjacency lists, we will

come to know that the clusters are adjacent to each other. Cltiffi!rRCiiltiiig-

djacencyUs1:

8110143

8111042

8112'1451920

,�� ourceNode.121

BasieROll1lng

SecureCllIstefRout�lII

ath121-172·177 success

Istance194,Hops 2

Ime 1 263

ooateW8y' OOtllerNOOle

Fig.6. Multi-hop-inter-c1uster routing.

If source and destination node are selected, then the cluster­

based routing algorithm will check in the adjacency list,

whether chosen-nodes are present in the adjacent cluster or

521

not. For example, if we select source node is 119 and

destination node is 161, then both nodes are present in

adjacent cluster. If path taken from the source to destination is

119-161, then the number of hops used is 1 and time taken to

send message is 0.858 ms. In fig.6, it shows multi-hop-inter­

cluster routing is done when nodes selected for communication

are not adjacent. The path from the source to destination takes

place through the mUltiple nodes using cluster-based-routing

algorithm. For example, if source node is 121 and destination

node is 177, then number of hops used is 2 and time taken to

send message is 1.263 ms. In intra-cluster-routing, the network

manager listens and updates the nodes that are present in the

network which are shown in figs 7 and 8. If c is source and c3

is destination, then both nodes are in same cluster. Both nodes

are not within transmission range. Hence, communication will

take place by making use of intermediate nodes.

-

.'

. . "

• •

• • :=- o -x

latno Clust.r Routiag

NETWORK MANAGER

Fig.7. Network manager listening.

latno Clust.r Routiag

NETWORK MANAGER

Fig. 8. Clients are connected to network.

In fig.9, it shows the intra-cluster-routing where source node

is sending a message to destination. Both source and

destination are present in same cluster. The mobile nodes c

and c3 are out of communication range hence the routing will

take through default c-7c4-7c3, which is the shortest path.

In fig.lO, it shows the intra-cluster routing where destination

accepts the message send by the source. Both the source and

destination nodes are present in same cluster. Suppose if c 4

moves out of range, then the message will be send to source

and destination by using alternate path c-7c2-7c 1-7c4. If both

nearer mobile nodes, c2 and c4 are out of range, then node

c(source node) will not be able to send the message to

destination. A message will be displayed that both nearer

mobiles are out of range, which is shown in fig. II . . � ."

---

. .� ® -

--

�.�.� 1 • 2- � 1- r 4_ 5_ II 5-7_ 8- II 9-. 0 II • •

+Sun �

o

Fig. 9. c is sending a message to c3 using intra-cluster routing.

4_ 6-7

o

Fig. 10. Message is received by destination using intra-cluster routing.

VI. CONCLUSIONS AND FUTURE WORK

The DTNS are a promising new development in network

research that offer hope of connecting people and devices that

hitherto were either unable to communicate, or could do so

only at great cost. Establishing end-to-end connections for data

delivery among DTMN becomes impossible as communication

links only exist temporarily. In such networks, routing is

largely based on nodal contact probabilities A set of functions

including syncO, leaveO, and joinO is devised for cluster

formation and gateway selection. Finally, the gateway nodes

522

exchange the network information and perform routing. The

simulation result shows that by using cluster-based routing

approach is an efficient and effective approach for DTNs.

Since, we are grouping the nodes based on same mobility

pattern hence routing can be done easily. In intra-cluster

routing and inter-cluster routing, as number of nodes increases,

more buffer space is needed to store the incoming messages

and forward to destination node. If there is no nearer mobile

node to accept the message, then the message will be lost and

it cannot be retrieved. The CH keeps the information about

mobile nodes present in the cluster. Hence, CH will be active

always. In future, it can include more security features and

make it a secured routing. The manager can show the current

path rather than the previous path. We can also update nodes

with the real-time information.

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