ROUTING
IN
OPPORTUNISTIC NETWORKS
Chapter 13:
Routing Protocols in Infrastructureless Opportunistic Networks
Sanjay Kumar Dhurandher1, Deepak Kumar Sharma2, Isaac
Woungang3,and Shruti Bhati1
1University
of Delhi
2University of Delhi
3 Ryerson University
Opportunistic Networks(OppNets)
Characteristics & Challenges
 Opportunistic Network [1] is one of the most
interesting and recent evolutions of Mobile Ad-hoc
Networks (MANETs).
 The traditional routing algorithms used for MANETs
and Internet are not applicable here as they first
establish a path between the source and the
destination before the actual message transfer which
is not possible in case of OppNets [2,3].
 They exhibit a store-carry and forward approach. If
a suitable node is not found, the node simply stores
the message and carries it through the network until
a better node or destination is found [4,5].
Opportunistic Networks(OppNets)
Characteristics & Challenges (Contd.)
 OppNets are enabled to deliver messages even when
there is no connected path between the source and
the destination.
 One key characteristic of opportunistic networks is
that they are essentially delay tolerant in nature as
they can handle large delays in message delivery from
the source to the destination.
 OppNets share similar routing algorithms as used in
Delay Tolerant Networks [6,7].
 If a suitable node is not found, the node simply
stores the message and carries it through the
network until a better node or destination is found
[5].
Types of protocols for routing in
OppNets
 The routing protocols in OppNets are divided into two
categories namely the infrastructure based and the
infrastructure-less protocols [8]
 Infrastructure based protocols: These protocols make use of




some form of infrastructure to opportunistically forward
messages.
Base stations and access points are often involved in the
routing and forwarding of the messages.
Infrastructure-less protocols: These protocols are best
suited for the flat ad-hoc networks.
They only make use of the mobility of the nodes and the
contact opportunity between them in order to route the
messages.
They make no previous assumptions about the network
topology and all the nodes behave same in the network and
are given the same priority
OppNets Routing Protocols
Direct Transmission [9]:
 The source node does not forward the message to the intermediate
nodes, but stores it in the buffer until it comes in direct contact
with the destination node.
 On encountering the destination node, the message is directly given
to the destination.
 Advantages
– This protocol utilizes minimum network resources, and cannot
suffer from the problems of network clogging.
– The protocol is very simple and fairly easy to deploy.
 Disadvantages
– It is likely to suffer from heavy delays as source node may not
encounter the destination node for longer period of times.
– If a node failure occurs, the message can be lost since there is
only one cope available in the network.
Example scenario of Direct Transmission
OppNets Routing Protocols (Contd.)
First Contact [10]:
 It is a routing scheme[10] that does not predict, utilize or
assume any properties of the network or the nodes.
 The carrier node forwards the message to any node that
comes into contact with it.
 Advantages
– It does not make any assumptions about the network
and thus can be implemented easily.
– This scheme can be used for multicast messages.
 Disadvantages
– The scheme can lead to huge message delivery delays.
– Indiscriminate spreading of messaging can lead to
network clogging as well as packet dropping which are
highly unacceptable
Example Scenario of First Contact
OppNets Routing Protocols (Contd.)
Epidemic Protocol [11]:
 This protocol [11] makes minimal assumptions about the network
and is guaranteed to deliver the message to the destination.
 It aims to distribute messages to other nodes within connected
portions of the network.
 These nodes then come into contact with another portion of the
network and the message spreads like a disease (epidemic).
 Advantages
– The protocol makes minimum assumptions about the network
topology and it is fairly easy to deploy and understand.
– Out of all the opportunistic network protocols, epidemic has
the least overhead in terms of calculations for determining
the next hop.
– The message delivery probability is very high in this protocol.
OppNets Routing Protocols (Contd.)
Epidemic Protocol [11]:
 Disadvantages
– The memory and resource consumption is very high in this
protocol, as the message is passed to all the nodes
indiscriminately.
– Considerable amount of computation occurs at every node
before exchanging the messages even in the case of nodes
that might have the same messages. Hence some amount of
memory is wasted.
– Even when a message is received at the destination, some
nodes still continue passing on the messages which wastes
resources.
Example Scenario of Epidemic Routing
OppNets Routing Protocols (Contd.)
Spray and wait [12]:
 This protocol[12] is an extension to the epidemic routing protocol.
 It aims to reduce the overhead of flooding which often causes
network congestions and indiscriminate usage of the network
resources.
 One way of doing so is to only forward a copy with some probability.
 The probability is the utility of every node based on the timer
indicating the time elapsed since the two nodes last encountered
the node maintaining the record. These are indirectly the relative
node locations
 There are two phases in the forwarding process –
 Spray phase – Every message generated is spread randomly to L
relay nodes i.e. L copies of message are created.
 Wait phase – If the destination is not found in spray phase, the
nodes then wait for direct transmission.
OppNets Routing Protocols (Contd.)
 Binary Spray and Wait – It is a variation of the spray
and wait protocol. The source starts initially with L copies
of the message.
 The source or any relay node that has n>1 message copies
hands over n/2 copies to any other node (without
message copy) in the network and keeps the remaining
copies n/2 with itself.
 Advantages
– The protocol reduces the memory inefficiencies of epidemic
routing by limiting the amount of flooding caused in the
network.
 Disadvantages
– Even though L is chosen to limit flooding, the protocol still
suffers from delays and resource consumption issues.
– The message delivery probability depends highly on the value
of L chosen, which is assumed on the basis of the network
parameters.
Example Scenario of Spray and Wait
OppNets Routing Protocols (Contd.)
Spray and Focus [13]:
 This protocol [13] overcomes the shortcomings of simple spraying
algorithms and is better than the flooding.
 The scheme again has two phases –
 Spray phase – When a new message is generated at the source node, it
creates L forwarding tokens for this message.
 When a node meets another node with no message copy, the first node
copies the message to the second node along with n/2 forwarding
tokens.
 When a node has only one forwarding token then it forwards the
message according to the Focus phase.
 Focus phase –Forwarding is done based on some criterion. These
decisions are based on a set of timers that record the time since the
two nodes last saw each other. Node i maintains a timer Ti(j) for every
other node j which records time elapsed since the two nodes last saw
each other.
OppNets Routing Protocols (Contd.)
Spray and Focus [13]:
 Advantages
– Owing to refined selection criterion, the protocol has higher
message delivery rates.
– Fewer copies are spread into the network as compared to the
spray and wait protocol.
 Disadvantages
– The protocol suffers from a larger overhead of resource
consumption.
– Protocol suffers in case of sparse networks as the time
taken by nodes to meet will be greater and there will be
fewer opportunities to forward the data.
OppNets Routing Protocols (Contd.)
Adaptive Fuzzy Spray and Wait [14]:
 This protocol [14] has been proposed as an improvement over the
popular spray based routing schemes.
 It smartly integrates the overheads and buffer management
policies into an adaptive protocol that includes local network
parameters estimation.
 The algorithm can be summarized in the following few steps:
 The node on encountering other nodes divides the values of L by
2 and updates it in the message before passing it on.
 The node passes on all the copies to the nodes it encounters
except the last copy which is passed on as direct transmission.
 The messages in the buffer are sorted by a priority decided by
a Fuzzy decision making function.
 When the buffer is full, the messages are dropped according to
the priority level i.e. the oldest first.
OppNets Routing Protocols (Contd.)
Adaptive Fuzzy Spray and Wait [14]:
 Forward Transmission Count and Message Size are two indicators
that help in determining the prioritization quantity. The dropping
policy used for the algorithm is random instead of drop least
priority scheme so that it remains fair to all the messages.
 Advantages
– The scheme has better delivery performance than simple spray
based techniques.
– Appropriate and fair buffer management schemes used in this
protocol avoid the clogging of the network.
 Disadvantages
– Large messages might get delayed if there are a higher number
of small messages.
– If all the messages are of approximately the same size and a
constant indicator of size is used, the size of message becomes
irrelevant to priority
OppNets Routing Protocols (Contd.)
PRoPHET [15]:
 Probabilistic Routing Protocol[15] using History of Encounters
and Transitivity (PRoPHET) , assumes that instead of moving
randomly the nodes in a network move in a predictable
fashion wherein patterns are likely to repeat themselves.
 This information can be used to improve the routing
performance.
 Each node before sending a message, calculates a
probabilistic metric called Delivery Predictability for each
known destination in form of vectors.
 This Delivery Predictability is assumed to be P(a,b) {0,1} i.e.
the probability of every node a to meet any other node b in
the network.
OppNets Routing Protocols (Contd.)
PRoPHET [15]:
 Advantages
– Simulation results of this protocol show that it has less
message exchanges, less communication overhead, less delay,
and higher delivery success rate as compared to the
epidemic routing.
– The protocol is highly suited to human mobility scenarios.
 Disadvantages
– Resource consumption occurs in terms of calculations
occurring at each node.
– Memory is needed to store the probability tables generated
by the protocol.
– Packets may be dropped consistently when forwarded to a
few concentrated nodes due to FIFO queuing nature of
PRoPHET.
OppNets Routing Protocols (Contd.)
PRoPHET+ [16]:
 This protocol [16] is an extension to the PRoPHET protocol that
uses only delivery predictabilities of the nodes to decide the next
best carrier for the message.
 This scheme uses several other parameters such as Buffer, Power,
Bandwidth, Location and Popularity into consideration to reduce the
packet loss and transmission delay.
 Advantages
– Packet dropping and loss are significantly reduced as compared
to PRoPHET by monitoring the power and popularity of the node.
– The protocol takes into account several parameters other than
delivery predictability which strengthens the best node
probability.
 Disadvantages
– Too many calculations need to be done at each node.
– Uncooperative nodes can cause a problem for the sender
OppNets Routing Protocols (Contd.)
HiBOp [17]:
 The History Based Routing Protocol for Opportunistic
Networks (HiBOp) [17] aims at effectively utilizing the
context information of the node in order to decrease the
overhead of flooding.
 The Current Context (CC) of a user is a snapshot of the
local environment of the user.
 It is stored in the form of Identity Tables (ITs).
 Every node also stores a History table that stores values
from the ITs seen by the node in the past.
 Every value has a Continuity Probability (Pc),
Heterogeneity (H) and Redundancy (R) counters associated
with them.
OppNets Routing Protocols (Contd.)
HiBOp [17]:
 The forwarding process in HiBOp is made of three phases:
 Emission Phase: HiBOp injects the message into the network through
flooding to an appropriate number of nodes by creating message
replicas for reliability.
– The number of neighbors (K) to which the message is forwarded by the
sender is calculated using a formula that takes into account the
probability of delivering the message to the destination.
– The value of K should be minimized in order to minimize the joint loss
probability below a certain threshold.
 Forwarding Phase: It uses the node’s mobility and contacts to take the
message closer to the destination.
– It uses two quantities .The forwarding of message to a certain node
during its journey in the network is determined by the match between
the sender information and the context information of the nodes.
– Delivery predictability of a node is also taken into account before
passing on the message. At each node the delivery probability is
calculated using node IT, its CC and its History table.
OppNets Routing Protocols (Contd.)
HiBOp [17]:
 Delivery Phase: When an intermediate node finds the
destination, the message is delivered to it and the process
stops.
 Advantages
– This protocol stores the largest amount of context
information among all context base protocols, so it can fully
exploit the advantages of context information.
– The protocol is very suitable for human mobility models that
generally follow a particular pattern.
– The protocol reduces network clogging by drastically limiting
the number of copies spread in the network.
 Disadvantages
– The IT, CC, History table and Repository table require a
large amount of memory space on every node.
– The calculations done every time at every node can
significantly reduce the amount of time left for message
exchange.
OppNets Routing Protocols (Contd.)
CEPMF [18]:
 This protocol [18] uses the content of the messages to
relay and deliver them to their destination.
 The node that generates the messages is called the
publisher and the node that wants a message similar in
content to the message being sent is called subscriber.
 If subscribers demand a message of a particular type of
content, they spray the network with their interests all
over the network in the form of predicates.
 The entire protocol can be divided into two steps– Predicate propagation: The subscriber spreads its interests into
the network by spraying predicates. The Spray and Wait scheme is
used for sending the predicates.
– Message Forwarding: Each node has a table carrying the message
and tagged to it ep value. At source node the value is zero.
– When a node transfers message to a node carrying the message’s ep
value in its table, the acknowledgement tells the source to stop
sending until it is out of its range.
OppNets Routing Protocols (Contd.)
CEPMF [18]:
 Advantages
– The protocol can be safely used for multicast
messaging situations.
– It does not rely on the geographic location of the
nodes and thus can be used in cases where GPS is
not enabled.
 Disadvantages
– A node may still receive a particular message which
it does not want, if its demands are partially
similar to the predicates of the message.
– There might be high privacy and rick issues
associated with the content transparency.
Example Scenario of CEPMF
OppNets Routing Protocols (Contd.)
Robust Proactive Routing Protocol [19]:
 This protocol[19] has been proposed as a proactive scheme
to deliver messages in the highly disconnected scenarios
present in OppNets.
 It is an adaptive protocol that uses the opportune
contacts between the nodes to determine the
neighborhood information for each node and use that to
deliver the messages.
 The basic principle is that a node can determine the
predictability information and connectedness information
using past history.
 The nodes do not forward data randomly instead they have
a well studied and selected next hop node.
OppNets Routing Protocols (Contd.)
Robust Proactive Routing Protocol [19]:
• Advantages
– The following protocol is suited to Human
mobility models since it can show better
results for predictable movement.
– It reduces the overhead of flooding by limiting
the next hop for node and only selects the
best candidate.
• Disadvantages
– There is considerable overhead in exchanging
and storing tables at each node.
OppNets Routing Protocols (Contd.)
Repository Based Forwarding Protocol [20]:
 This protocol [20] makes distinction between the types of
nodes in the network and uses them to deliver the
message to its destination.
 It argues that assuming all nodes to be Mobile Nodes is
not correct in a model where nodes move in a predictable
fashion (Human mobility model).
 Some nodes are likely to be in a place more often than
others. Hence commonly visited and shared location are
assigned to be Fixed Nodes.
 The Mobile Nodes are characterized by the mobility
pattern which in turn has a strong impact on their
performance.
 Each node has a character table (CT) that defines the
node’s home location, communication range, ID and type.
OppNets Routing Protocols (Contd.)
Repository Based Forwarding Protocol [20]:
 When a node meets another node, they exchange their CT tables
that describe their characteristics.
 Depending on the type one of the nodes initiates the forwarding
process. The forwarding process is further divided into two parts:
– Message Dispatch: Node initiating communication sends all
messages as type tsend either directly (to the target node
itself) or indirectly (i.e. through a Fixed Node which eventually
forwards it).
– Message Collect: Node collects all the messages that have the
target_ID set as the node itself. The status flag is checked to
prevent from the same message being collected again
 Advantages
– Fixed nodes can decrease the delivery delays considerably.
 Disadvantages
– If fixed nodes fail, the entire network will be brought down
OppNets Routing Protocols (Contd.)
MaxProp [21]:
 This protocol [21] assumes that it has no prior knowledge about
the network connectivity and uses the local information and
opportune movement to select the next best hop for the
message delivery.
 The protocol has three main components :
 Estimating Delivery Likelihood: The protocol aims to find
the optimal delivery paths by constructing a directed graph
of nodes which are connected by edges [21].
– A variation of Dijkstra’s algorithm is used to determine the
shortest path out of available paths at any given point of
time.
 Complementary Mechanisms: This step describes the
priority order in which messages are exchanged when two
nodes discover each other.
 Managing Buffer: The protocol states that there is a
difference between managing limited storage and limited
transmission in that the packets sent once can be sent again.
OppNets Routing Protocols (Contd.)
MaxProp [21]:
 Advantages
– MaxProp uses Dijkstra’s algorithm to ensure that
the lowest cost path is chosen so as to decreases
the delivery latency.
– Proper buffer management schemes lead to a
lowered rate of packet dropping.
 Disadvantages
– The overhead of table exchange can decrease the
effective time for message exchange.
– The protocol is not suited for sparse networks, as
it will not give a proper connected graph and thus
will not satisfy the protocol criteria.
OppNets Routing Protocols (Contd.)
CAR [22]:
 In this protocol[22] , the nodes are assumed to rely on their ‘logical
connectivity information’ with other nodes.
 They are not aware about the location of the nodes, which are the
recipients of the messages they are carrying with them.
 Proactive protocol such as DSDV [25] is used to deliver the
messages if the recipient node belongs in the same cloud.
 Otherwise, the relay nodes are chosen in such a manner that they
present the highest delivery probabilities.
 The process of prediction and evaluation of context takes care of
following things.
– Calculation of self delivery probabilities
– Table
– Local prediction of delivery probabilities at intervals
– New message recipient
– Message exchange
OppNets Routing Protocols (Contd.)
CAR [22]:
 Advantages
– The protocol is uninfluenced by the unavailability
of GPS.
– The proactive approach highly reduces the
overhead of prediction calculation and can deliver
message faster if dense networks are present.
 Disadvantages
– The overhead of table exchange, updating and
maintenance can severely reduce the performance.
– In absence of a proper buffer management
scheme, the messages may be lost.
OppNets Routing Protocols (Contd.)
Meetings and Visits [23]:
 This routing protocol [23] uses the same pair-wise
message exchange principle as Epidemic Routing, but
improves on the method used to determine which
messages to transmit.
 Instead of flooding its neighbors, each node uses
observation data on the meetings between nodes and
visits to locations (hence the name MV) to compute a
delivery probability for every other node.
 When two nodes meet, the summary vectors contain
not only the message identifiers but also the
computed delivery probability.
 Nodes compare their own and their pair’s values, and
only request messages for which their probability is
higher.
OppNets Routing Protocols (Contd.)
Meetings and Visits [23]:
 Advantages
– The protocol is highly suited to human mobility scenarios as
mobility patterns of nodes are stored for routing of the
messages.
– It uses the techniques from robotic control to obtain highquality approximations for the optimal solution.
– It also limits the number of hops that are required, by
calculating an estimation of delivery likelihood assuming an
infinite buffer at each peer.
 Disadvantages
– As it uses FIFO for buffer management at nodes, packets may
get dropped consistently when forwarded to a concentrated
node.
– Considerable overhead occurs in storing the mobility pattern of
nodes at regular time intervals.
OppNets Routing Protocols (Contd.)
Network Coding [24]:
 This protocol[24] presents an approach in which a
message is encoded into another format before
transmission.
 The intermediate nodes not only forward but also can
combine packets using a given invertible function
before forwarding to limit the message flooding.
 At the receiver side, as compared to the replication
based schemes which rely on successful delivery of
each individual data block, this scheme consider the
successful delivery of a block only when the
necessary number of blocks is received to
reconstruct the original data.
OppNets Routing Protocols (Contd.)
Network Coding [24]:
 Advantages
– This schemes is more robust against packet losses than replication
based schemes when network connectivity is extremely poor, as it
consider the successful delivery of a block only when the necessary
number of blocks is received to reconstruct the original data.
– The number of transmissions is reduced in this approach, and
consequently the packet delivery ratio is much higher than the
probabilistic forwarding both in dense mobile networks and sparse
networks.
 Disadvantages
– When the network is well connected this schemes is less efficient
due to additional information embedded in the code blocks.
– This method leads to additional processing power and memory
requirements due to the encoding and decoding process.
Tabular Comparison of various protocols
Protocol
Algorithm
Number of
Next hop
Message
selection method
copies
Drawbacks
Assumptions
Buffer Size BandwidthCap
Available
acity
Simulation Model
DeliveryDe
lay
Delivery
Ack
Simulator
Used
Mobility
Model Used
High
None
Limited
Not Mentioned
Custom
Random
discrete event Waypoint
driven
(RWP) [27]
None
Not mentioned
Not mentioned
Own for DTN Own Remote
environment village city
[28]
bus N/W
Direct Transmission [9]
Single
The destination High Delays and
of the message
low delivery
itself
latency
First Contact
[10]
Single
The next node
encountered
Epidemic
Routing [11]
Unlimited
Flooding
High resource
(bandwidth,
buffer) usage
Low
Not mentioned
Limited
Not mentioned
Monarch[29]
RWP
Spray and
Wait [12]
Limited (L)
Randomness
Random
decision
making
Medium
Not mentioned
Sufficient
Sufficient
Own
RWP,
RD,RW
Spray and
Focus [13]
Limited (L)
Timer based
probabilities
calculation
High resource
consumption
Medium
Not mentioned
Sufficient
Sufficient
Own
RWP, Random
Walk(RW)
Flooding
Distinction
made in size of
messages
Medium
Limited.
Not men- Buffer mantioned agement used
extensively
Sufficient
ONE[30]
RWP
Adaptive
Spray and
Wait [14]
Limited
High amount of High due
clogging in the to path
network
loops
Tabular Comparison of various protocols
(contd.)
Protocol
Algorithm
Number of
Next hop
Message
selection method
copies
PRoPHET [15]
PRoPHET+
[16]
HiBOp [17]
CEMPF [18]
Assumptions
Drawbacks
DeliveryDe
lay
Delivery
Ack
Too much
calculation
overhead at
each node
Medium
Not
mentioned
Limited
Not mentioned
Limited.
Managed
extensively
Not mentioned
Limited and
managed
Assumed
infinite
Own
Community
Based (CB)
Limited
Sufficient
OMNET++
[33]
A hybrid of
RWP and CB
Not mentioned
Limited
Sufficient
Jist/SWANS
[34]
Not
mentioned
Used
Limited
Sufficient
Own
Human
Mobility
Model
Single
Probability
obtained from
previous meetings
Single
Probability of
Un-cooperative
previous meetings,
nodes can cause
buffer, power,
security &
Medium
bandwidth and
forwarding
popularity
problems
parameters
Single
Limited
Flooding
Identity tables
High overhead
and history table
of storing
used to find
tables
context of nodes
Medium
High as
Relay to
content of relay as well
Content of the
Privacy and risk
message and
messages as source to
issues
are
destination
predicates
matched
ack used
Robust
Proactive
Routing
Protocol [19]
Single
Predictability and
connected-ness
information
RFP [20]
Single
Type of node
Overhead of
exchanging,
storing and
updating tables
Medium
Failure of fixed
Medium
nodes
Buffer Size BandwidthCap
Available
acity
Simulation Model
Not mentioned
Simulator
Used
Mobility
Model Used
Own
Own
Sufficient and
evaluated
iMote trace
before
DTNSIM [31]
[32]
transferring
message
Tabular Comparison of various protocols
(contd.)
Protocol
MaxProp
[21]
CAR [22]
MV
Routing [23]
Network
Coding [24]
Algorithm
Number of
Message
copies
Next hop
selection
method
Single
Previous node
meetings and
finding best
path using
likelihood of
meetings
Single
Single
Limited
Assumptions
DeliveryD Delivery
Drawbacks
elay
Ack
In case of
sparse
network the
no of
available
paths might
decrease
drastically
Medium
Used
Simulation Model
Buffer
BandwidthCa Simulator
Mobility
Size
pacity
Used
Model Used
Available
Unlimited
(own)
Limited
(others).
Buffer
management Used
Sufficient
Own
Synthetic
models of
real data
DSDV and
Overhead of
Own Group
Delivery
table
Not menOMNET++
based
probability
Medium
Sufficient Sufficient
management
tioned
[33]
mobility
using context
and exchange
model [35]
information
Overhead in
Unlimited
Synthetic
storing the
(own)
traces of
Probability of
Medium
mobility
Not menLimited
node movevisiting the
more than
Sufficient NS-2[36]
pattern of a
tioned
(others).
ment in
region of the
Epidemic
node at regmanaged by
geographica
destination
ular intervals
FIFO.
rea
Overhead in
encoding and
Own (custom
Not MenFlooding to the decoding of
Not men- Not menNot mentime based
RWP
neighbors
message and
tioned
tioned
tioned
tioned
simulator)
reassembling
at destination
Conclusion
 In this chapter, we have given a brief outline of a number
of routing protocols for infrastructure-less OppNets.
 These protocols have been analyzed and compared on the
basis of their advantages and disadvantages with respect
to a variety of parameters.
 This study leads to the identification of some critical and
explicit characteristics of each protocol along with their
areas of application.
 A few main concerns that are reflected in almost all
protocols are delivery latency, packet dropping and packet
loss, memory management, computation and storage
overhead.
 The discussed protocols in this chapter implement
different techniques to abate the inefficiencies caused
due to these factors.
References
[1] L. Lilien, Z.H. Kamal, V. Bhuse, and A. Gupta, “Opportunistic Networks: The Concept and Research Challenges in Privacy and Security,” in
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