ad-hoc networks

Ad-Hoc NetworksEng. Mshari Alabdulkarim

Ad-Hoc Networks

Outline: Introduction. Advantages and Applications. Cellular VS Ad-Hoc Networks. Technical Challenges and Issues. Ad-Hoc Wireless Media Access Protocols. Ad-Hoc Routing Protocols. Providing Quality of Service in Ad-Hoc Networks.

Introduction (1):

Multi-hop Wireless Networks (MHWNs): It is defined as a collection of nodes that communicate with each other wirelessly by using radio signals with a shared common channel.

Host Switching Unit

Hop

Path, chain or route

Ad-Hoc Networks

Introduction (2): There are several names for MHWNs; it could be called packet

radio network, Ad-Hoc network or mobile network.

The nodes here could be named stations or radio transmitters and receivers.

MHWNs

Ad-Hoc Networks Mesh Networks

Wireless Sensor

Networks

Ad-Hoc Networks

Introduction (3):

Ad-Hoc Networks:

It is a type of MHWNs. Nodes in the network are mobile in general. The wireless hosts in such networks, communicate with each

other without the existing of a fixed infrastructure and without a central control.

A mobile ad-hoc network can be connected to other fixed networks or to the Internet.

Most of the Ad-Hoc networks use the allocated frequencies for the Industrial, Scientific and Medical (ISM) band.

Ad-Hoc Networks

Advantages and Applications (1):Ad-hoc networks have several advantages over the traditional networks, like:

Ad-hoc networks can have more flexibility. It is better in mobility. It can be turn up and turn down in a very short time. It can be more economical. It considered a robust network because of its non-hierarchical

distributed control and management mechanisms.

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Advantages and Applications (2):There are lots of applications for Ad-Hoc networks, like:

Group of people with laptops and they want to exchange files and data without having an access point.

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Connected to the internet

Sharing the internet

Advantages and Applications (2): Incase if we need to exchange information and the network's

infrastructure has been destroyed.

It is suitable for military communications at battlefield where there is no network infrastructure.

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Cellular VS Ad-Hoc Networks:

Cellular Ad-Hoc Networks

Ad-Hoc Networks

Infrastructure networks. Fixed, pre-located cell sites and

base station. Static backbone network topology. Relatively caring environment and

stable connectivity. Detailed planning before base

station can be installed. High setup costs. Large setup time.

Infrastructureless networks. No base station, and rapid

deployment. Highly dynamic network topologies. Hostile environment and irregular

connectivity. Ad-Hoc network automatically

forms and adapts to changes. Cost-effective. Less setup time.

Technical Challenges and Issues (1):There are several challenges that Ad-Hoc network faces such as:• Limited wireless range.• Hidden terminals.• Packet losses.• Routes changes.• Devices heterogeneity.• Battery power constraints.

Ad-Hoc Networks

Technical Challenges and Issues (2):The main challenges face the Ad-Hoc networks are the following:

Energy conservation: Nodes in Ad-Hoc networks are equipped with limited batteries.

Unstructured and/or time-varying network topology: Because of the nodes mobility, that makes the network topology usually unstructured and makes the optimizing process a difficult task.

Scalability: In some cases, there will be a huge number of nodes.

Ad-Hoc Networks

Technical Challenges and Issues (3): Low-quality communications: In general, wireless networks are

less reliable than the wired networks. In addition to that, the quality of the network can be affected by the environmental factors.

Resource-constrained computation: The resources in Ad-Hoc networks such as energy and network bandwidth are available in limited amounts.

Ad-Hoc Networks

Technical Challenges and Issues (4):In addition to that, Ad-Hoc networks inherit some of the issues which are faced by the traditional wireless networks, like:

There are no known boundaries for the maximum range that nodes will be able to receive network frames.

The wireless channel is weak, unreliable, and unprotected from outside interferences.

The wireless channel has time-varying and asymmetric propagation properties.

Hidden-node and exposed-node problems may occur.

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Technical Challenges and Issues (5):Hidden-node problem:

Sender 1 Sender 2Receiver

Collision

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Technical Challenges and Issues (6):Exposed-node problem:

TransmitterReceiver Exposed Node

BlockedBy The

Transmitter

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Ad-Hoc Wireless Media Access Protocols (1):Why do we need for a media access protocol?

The medium is shared by all of the nodes.

If we give the node the freedom to send at any time, then that could result in a contention.

We can't have a central controller to manage the transmission process, because every node can move at any time.

Therefore, we will choose from the medium access control (MAC) protocols in order to use the shred medium in the most efficient way.

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Ad-Hoc Wireless Media Access Protocols (2):

MAC Protocols

Synchronous Asynchronous

MAC Protocols

Sender-Initiated Receiver-Initiated

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Ad-Hoc Wireless Media Access Protocols (3):Sender-Initiated MAC Protocols:

Sender Receiver

RTS1

2 CTS

3 Data

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Ad-Hoc Wireless Media Access Protocols (4):Receiver-Initiated MAC Protocols:

Sender Receiver

RTR1

2 Data

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Ad-Hoc Wireless Media Access Protocols (5):Existing Ad-Hoc MAC Protocols:

1. Multiple Access with Collision Avoidance (MACA):

It was proposed as a solution for both hidden terminal and exposed node problems.

It has the ability to control the transmitter power for each packet.

It uses a three-way handshake, RTS-CTS-Data. Collisions could occur in MCSA, because there is no carrier

sensing in it.

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Sender Receiver

RTSCTS

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2. MACA-BI (By Invitation):

MACS-BI is considered as Receiver-Initiated MAC Protocol.

In MACA-BI, there is no way that the receiver will know whether the transmitter has a data to transmit or not, which will affect the communication performance, because of the waiting time for the RTR messages.

MACA-BI is less likely to have a control packets collision because it uses half as many control packets as MACA.

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Ad-Hoc Wireless Media Access Protocols (8):3. Power-Aware Multi-Access Protocol with Signaling (PAMAS): PAMAS is based on the MACA protocol with an extra separated

signaling channel where RTS-CTS handshake occurs. It reduces the power consumption by turning off all nodes that

are not actively transmitting or receiving. In PAMAS, each node has the ability to shout down its

transceiver. There are two conditions where the node has to turn off its

transceiver:• If it doesn't have data to transmit.• If one of its neighbors is transmitting data and another is

receiving.

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4. Dual Busy Tone Multiple Access (DBTMA):

It has been proposed to solve the hidden terminal problem. In BTMA, when node is receiving data, it sends a busy tone

signal to its neighbors. After the hidden terminals sense the busy tone they refrain from transmitting.

The DBTMA (Dual Busy Tone Multiple Access) is a customization of BTMA for the Ad-Hoc networks.

In DBTMA, there are two out of band busy tones, one use to signify transmit busy and the other use to signify receive busy.

Ad-Hoc Networks


Sender Receiver

RTS

RBT - CTS

Dual Busy Tone Multiple Access (DBTMA) Process

TBT

Prohibited Prohibited

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Ad-Hoc Routing Protocols (1):

There are lots of routing protocols which have been developed for Ad-Hoc networks. When these protocols have been developed, it has been taken in the consideration the limitations of this type of network.

Ad-Hoc Mobile Routing Protocols

Table Driven / Proactive Hybrid On-Demand-

Driven / Reactive

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1. Table-Driven Approaches:

Table-driven routing protocols try to keep the last updated and stable routing information from each node to the rest of the nodes in the network.

In this type of routing protocol, each node should maintain at least one table to store the routing information.

In case of any change in the network topology, the nodes will propagate the route updates throughout the network in order to maintain a stable network view.

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1.1. Destination Sequenced Distance Vector (DSDV):

The main feature in this protocol is the avoidance of the routing loops.

Each node here maintains a routing table of all destinations within the non-partitioned network and the number of hops to these destinations.

A sequence numbering system is used in order to be able to distinguish between the old and bad routes from the new ones.

Updates in the routing table are sent periodically to keep the routing table up-to-date and consistent.

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Ad-Hoc Routing Protocols (4): The broadcasts of the new route will contain:• Destination address.• Number of hops to the destination.• Sequence number of the information received regarding the

destination.• New sequence number unique to the broadcast.

Each route is labeled with a sequence number and the route with the highest sequence number will be used.

If there are two updates have the same sequence number, then the route with the smaller hop count will be used.

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1.2. Wireless Routing Protocol (WRP):

Each routing node in WRP communicates the distance and second-to-last hop information for all destinations in the network.

The WRP is classified as one of the path-finding algorithms, but here the count-to-infinity problem has been avoided by making each node check the consistency of the predecessor information reported by its neighbors.

In WRP, each nodes learns about its neighbors from the acknowledgments and the other messages it's receives.

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In case if the node does not have any data to send, it should send a HELLO message in a specified periodic time to make sure that the connectivity information is properly reflected.

Existing NodeNew Node

HelloRouting Table

Routing Table

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Each node here should maintain four tables: • Distance table: contains the number of hops from the node to

all possible destinations.• Routing table: specifies the next hop.• Link-cost table: tells about the delay for each link.• Message retransmission list table: contains information such as

the sequence number of the update message, the retransmission counter, the list of all the sent updates, … etc.

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Each node sends a periodic update messages to its neighbors to ensure that the routing information is accurate.

The update message indicates:• The destination.• The distance to the destination.• The predecessor of the destination.• List of all nodes who should acknowledge the update.

The update message is sent either after the node is finished from processing the updates which it has received from its neighbors or if there is any change detected in any link.

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1.3. Cluster Switch Gateway Routing (CSGR):

Nodes in CSGR are grouped in clusters and each cluster has a cluster head which can control a group of Ad-Hoc hosts.

Each time a cluster head moves away, a new cluster head is selected.

By using the least cluster change (LCC) algorithm, the cluster head will be changed either if two cluster heads come into contact or if the node moves away from all other cluster heads.

CSGR is based on the DSDV, but with a little difference that CSGR uses a hierarchical cluster-head-to-gateway routing approach.

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Each node in CSGR maintains two tables:• Cluster member table: where it stores information about the

destination cluster head for all nodes in the networks, and it is broadcast this table periodically using the DSDV protocol.• Routing table: is used to determine the next hop to reach the

destination.

When routing packets, a node will use the previous two tables to select the nearest cluster head along the route to the destination.

Ad-Hoc Networks


2. Source-Initiated On-Demand Approaches: Here, the routing protocols create routes only when requested

by the source node. A route discovery process is initiated by the source node. This process is considered done either after:• finding a route to the destination.• after examined all the possible route permutations.

Once the route is established, it will be maintained by some form of route maintenance procedure until either the destination becomes inaccessible or the route is no longer desired.

Ad-Hoc Networks


2.1. Ad-Hoc On-Demand Distance Vector Routing (AODV):

The AODV routing protocol is based on the DSDV algorithm.

It can minimize the number of required broadcasts by creating routes on an on-demand basis.

It is considered as a pure on-demand route acquisition system.

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The source node does the discovery process by broadcasting a route request (RREQ) packet to its neighbors, which in their turn forward the request to their neighbors, and their neighbors do the same thing, and so on, until either the destination or an intermediate node with a route to the destination is located.

The RREQ is identified by using the broadcast ID and the node's IP address.

The source node adds the last sequence number it has for the destination into the RREQ packet.

The intermediate nodes reply to the RREQ only if they have a route to the destination with a sequence number equal or greater than the one included in the RREQ.

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2.2. Dynamic Source Routing (DSR):

The DSR protocol is based on the concept of source routing, where each node is required to maintain route caches that contain the source routes of which the mobile is aware.

There are two phases in this protocol: • The route discovery phase.• The route maintenance phase.

When node has data to send, it first checks its route cache to see if it already has an unexpired route to the destination.

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N1

N1

N1 -N2

N1-N3

N1 -N2-N5

N1 –N3-N4

N1 –N3-N4

N1 –N3-N4

N1 –N3-N4-N6

N1 –N3-N4-N7

Propagation of the route request messages:

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N1 -N2-N5-N8

Propagation of the route replay with the route record :

N1 -N2-N5-N8N1 -N2-N5-N8

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2.3. Temporally Ordered Routing Algorithm (TORA):

TORA is a source-initiated, loop-free, distributed routing algorithm based on the concept of link reversal.

This protocol performs three basic functions: route creation, route maintenance, and route erasure.

During the phases of creating and maintaining the route, nodes will use a "height" metric to establish a DAG (directed acyclic graph) rooted at the destination.

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N5 N6

N7

Route maintenance process in TORA:

N4N1

N2 N3

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TORA has five elements:• The logical time of link failure.• The unique ID of the node that defined the new reference level.• The reflection indicator bit.• The propagation ordering parameter.• The unique ID of the node.

The invalid routes would be erased in the route erasure phase, and that is done by flooding a broadcast "clear packet" (CLR) throughout the network.

Ad-Hoc Networks


3. Location Aided Routing (LAR):

One of the LAR protocol concepts, that it uses the location information (e.g. by utilizing the GPS) to enhance the performance of the Ad-Hoc network.

There are two defined zones in LAR: • The expected zone.• The request zone.

Ad-Hoc Networks

Ad-Hoc Routing Protocols (21):Concepts of request zone and expected zone in LAR :

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There are several reasons make the location based routing suffer and fail to operate in the real field, such as: • The GPS is not yet available worldwide.• The positional information from the GPS could come with

deviation.• Some devices do not have GPS receivers.

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4. Power Aware Routing (PAR):

In this protocol, battery life is the metric for selecting the route.

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5. Zone Routing Protocol (ZRP):

The ZRP is a hybrid routing protocol.

The routing zone in ZRP is similar to the routing zone in CSGR, but in ZRP, every node acts as a cluster head and a member of other clusters, and zones can be overlapped.

The ZRP can be subdivided into three sub-protocols: • the proactive (table-driven) Intra-zone Routing Protocol (IARP).• the reactive Inter-zone Routing Protocol (IERP).• the Border-cast Resolution Protocol (BRP).

Ad-Hoc Networks


The IARP can be implemented using link state or distance vector routing.

The IARP depends on the discovery protocol to detect the neighbors, and the link connectivity to them.

The IERP depends on the border nodes to search for routing information to nodes located outside its current zone by performing on-demand routing.

Ad-Hoc Networks


6. Source Tree Adaptive Routing (STAR):

The STAR protocol is a proactive routing protocol. In STAR, each node maintains its own source tree. Each node in STAR knows about its adjacent links and the source

trees of its neighbors, and after it aggregates the adjacent links with the source trees, it will get a partial topology graph.

Each node derives the routing table from running a route selection algorithm on its own source tree, and from the routing table it can know what the successor to any destination is.

Ad-Hoc Networks

Providing Quality of Service in Ad-Hoc Networks (1):

The QoS is defined as a set of measurable pre-specified service requirements need to be met by the network while transferring packets from source to destination.

It could be defined as an agreement or a guarantee that the network will provide a set of measurable service performance such as end-to-end delay, delay variance (jitter), available bandwidth, probability of packet loss, cost of transport, total network throughput, etc.

Ad-Hoc Networks

There are lots of problems in Ad-Hoc network when providing QoS such as:

1. Routing problem: It can be defined as the process of finding a loop free route from the source to the destination which should also support the requested level of QoS.

2. Maintenance problem: It can be described as how to make sure that the network will continue support the agreed level of QoS in case if any change happened in the network topology.

3. Variable resource problem: It deals with the changes in the available resources and how to react to these changes.

Providing Quality of Service in Ad-Hoc Networks (2):

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Thank you for your attention

ad-hoc networks

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networks advantages

networks introduction

networks infrastructure

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fixed networks

traditional networks

networks outline

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