1 university of delhi 2 university of delhi 3 ryerson university

Chapter 13:Routing Protocols in

Infrastructure-less Opportunistic Networks

Sanjay Kumar Dhurandher1, Deepak Kumar Sharma2, Isaac Woungang3,and Shruti Bhati1

1University of Delhi2University of Delhi

3 Ryerson University

ROUTING IN OPPORTUNISTIC NETWORKS

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 ProtocolsDirect 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


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.


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


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.


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


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.


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.


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.


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


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.


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.


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


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.


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.


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.


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.


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


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.


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.


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.


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


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.


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.


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


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.


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.


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 high-quality 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.


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.


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 Assumptions Simulation Model

Number of Message copies

Next hop selection method

Drawbacks DeliveryDelay

Delivery Ack

Buffer Size

Available

BandwidthCapacity

Simulator Used

Mobility Model Used

Direct Trans-

mission [9]Single

The destination of the message

itself

High Delays and low delivery latency

High None Limited Not Men-tioned

Custom discrete

event driven

Random Waypoint

(RWP) [27]

First Contact

[10]Single The next node

encounteredHigh amount of clogging in the network

High due to path loops

None Not men-tioned

Not men-tioned

Own for DTN environment

[28]

Own Remote village city bus N/W

Epidemic Routing

[11]

Un- limited Flooding

High resource (bandwidth,

buffer) usageLow Not men-

tioned Limited Not men-tioned Monarch[29] RWP

Spray and Wait [12] Limited (L) Randomness

Random decision making

Medium Not men-tioned Sufficient Sufficient Own RWP,

RD,RW

Spray and Focus [13] Limited (L)

Timer based probabilities calculation

High resource consumption Medium Not men-

tioned Sufficient Sufficient OwnRWP,

Random Walk(RW)

Adaptive Spray and Wait [14]

Limited FloodingDistinction

made in size of messages

Medium Not men-tioned

Limited. Buffer man-

agement used

extensively

Sufficient ONE[30] RWP

Tabular Comparison of various protocols (contd.)

Protocol Algorithm Assumptions Simulation ModelNumber of Message copies



Delivery Ack

Buffer Size

Available

BandwidthCapacity

Simulator Used

Mobility Model Used

PRoPHET [15] Single

Probability obtained from

previous meetings

Too much calculation overhead at each node

Medium Not mentioned Limited Not men-

tioned Own Own

PRoPHET+ [16] Single

Probability of previous

meetings, buffer, power,

bandwidth and popularity

parameters

Un-cooperative nodes can

cause security & forwarding

problems

Medium Not men-tioned

Limited. Managed

extensively

Sufficient and evaluated

before transferring

message

DTNSIM [31] iMote trace [32]

HiBOp [17] SingleIdentity tables

and history table used to find

context of nodes

High overhead of storing

tablesMedium Not men-

tionedLimited and managed

Assumed infinite Own Community

Based (CB)

CEMPF [18] Limited Flooding

Content of the message and

predicatesPrivacy and risk issues

High as content of messages

are matched

Relay to relay as well as

source to destination ack used

Limited Sufficient OMNET++ [33]

A hybrid of RWP and CB

Robust Proactive Routing Protocol

[19]

SinglePredictability

and connected-ness information

Overhead of exchanging, storing and updating

tables

Medium Not men-tioned Limited Sufficient Jist/SWANS

[34]Not

mentioned

RFP [20] Single Type of node Failure of fixed nodes Medium Used Limited Sufficient Own

Human Mobility Model

Tabular Comparison of various protocols (contd.)

Protocol Algorithm Assumptions Simulation Model

Number of

Message copies



Delivery Ack

Buffer Size

Available

BandwidthCapacity

Simulator Used

Mobility Model Used

MaxProp [21] Single

Previous node meetings and finding best path using

likelihood of meetings

In case of sparse

network the no of

available paths might

decrease drastically

Medium Used

Unlimited (own)

Limited (others). Buffer

management Used

Sufficient OwnSynthetic models of real data

CAR [22] Single

DSDV and Delivery

probability using context information

Overhead of table

management and

exchange

Medium Not men-tioned Sufficient Sufficient OMNET++

[33]

Own Group based

mobility model [35]

MV

Routing [23]

SingleProbability of visiting the

region of thedestination

Overhead in storing the

mobility pattern of a node at regular intervals

Medium more than

Epidemic

Not men-tioned

Unlimited (own)

Limited (others). managed by FIFO.

Sufficient NS-2[36]

Synthetic traces of

node move-

ment in geographic

area

Network

Coding [24]

Limited Flooding to the neighbors

Overhead in encoding

and decoding of

message and

reassembling at

destination

Not Men-

tionedNot men-

tionedNot men-

tionedNot men-

tioned

Own (custom

time based simulator)

RWP

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.

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