Mobile Ad Hoc Networks: Routing and · PDF fileMobile Ad Hoc Networks: Routing and Clustering ... Bandwidth and Capacity Link ... infrastructure is destroyed. MANET can set up the

��

Mobile Ad Hoc Networks: Routing and Clustering

Asst. Prof. Peter H J Chong, PhD (UBC)School of EEE

Nanyang Technological UniversityE-mail: [email protected]

��

MANET - 2

��

Outline1. Introduction to MANET

� What is MANET� Characteristics of MANET� What are the applications

2. Routing Protocols in MANETs� Introduction� Types of Routing

� Flat Routing: Proactive and On-demand� Hybrid Routing� Hierarchical Routing� GPS-assisted Routing� Energy-aware Routing

��

MANET - 3

��

Outline

3. Clustering MANETs� Introduction � Classification of Clustering� Examples

��

MANET - 4

��

1 Introduction to MANET

��

MANET - 5

��

1.1 - What is MANET

� Two types of wireless network architectures.� Infrastructured network – a network with fixed

and wired access point. E.g., base station in cellular network

� Infrastructureless network – no fixed access points; all nodes can be connected with each other in an arbitrary manner, such as MANET.

��

MANET - 6

��

� Mobile Ad Hoc Network (MANET)� Infrastructureless network� A number of mobile wireless nodes to form a network

without any support from any fixed access point.� All nodes can be communicated from each other.� Source node will send message to the destination node

if they are within the communication range.� If not, source node will send message to the destination

node via the intermediate node (relay node).

��

MANET - 7

��

Example of a MANET

Source DestinationRelay

��

MANET - 8

��

Challenges in MANETs

� Connectivity � Connectivity among nodes is changed due to

radio channel condition, movement of the nodes, and battery.

� Frequent network topology update is required.� Efficient Routing

� How to select a efficient path (intermediate node) to send a message from source to destination.

� Asymmetric/symmetric link� Due to difference transmit power and terrain.

��

MANET - 9

��

MS1

MS2

MS3

MS4

MS5

MS6

MS1

Connectivity and Routing

��

MANET - 10

��

MS2

MS3

MS4

MS5

MS6

Asymmetric/symmetric link

��

MANET - 11

��

1.2 - Characteristics� Dynamic Topologies

� Network topology changes randomly and unpredictably because nodes are free to move

� Unidirectional link may exist due to difference transmit power between two nodes

� Bandwidth and Capacity Link� Lower capacity due to wireless conditions:

multipath, interference, noise and fading� Wireless capacity is lower than fixed line

capacity� Variable wireless capacity to affect QoS

��

MANET - 12

��

� Energy-constrained� Mobile devices rely on batteries� Energy optimization needed

� Limited Security� Because of peer-to-peer communication, messages may

be sent to unknown intermediate node. Security techniques are needed to prevent from message stolen.

� Higher physical security threats than wireline networks due to open transmission medium.

� Scalability� Need to support a large network.

��

MANET - 13

��

1.3 - Applications� Defense applications

� On-the-fly communication network set-up for battle-field management

� MANET can be formed among soldiers or fighter planes� Sensors can be deployed to monitor activities in an area

� Emergency search-and-rescue operations� In a nature disasters, the entire communication

infrastructure is destroyed.� MANET can set up the communication network in

hours to provide communication capability� Conventions/Meetings

� Allow persons to share information.

��

MANET - 14

��

� Telemedicine� During accident in a rural area, MANET can be

set up to provide video conference assistance for medical treatments/operations

� Education� In remote areas, MANET can provide a

temporary Internet for children and students

��

MANET - 15

��

Issues

� Routing� Unicast and Multicast

� Medium Access Control� Mobility Model� Security� Applications

��

MANET - 16

��

2 Routing Protocols in MANETs

��

MANET - 17

��

2.1 Introduction

��

MANET - 18

��

What is Routing?

� MANET is a self-organizing and self-configuring multihop wireless network.

� It does not relay on a fixed infrastructure.� Any node, in principle, can send data

packets to any other node through intermediate nodes in the network.

� All nodes cooperate in a friendly manner to engage in multihop forwarding.

� Each node functions not only host but also as a router for data packet forwarding.

��

MANET - 19

��

� Routing protocol is to find an efficientrouting path to send data packets from source node to destination node.

� Extremely challenges due to node mobility, large number of nodes, limited resources.

� Must adapt quickly to frequent and unpredictable topology changes and efficiently use of the limited communication resources.

��

MANET - 20

��

Efficient Routing Path

MS1

MS2

MS3

MS7

MS5

MS6

MS4

Efficient?- Hops- Energy- Congestion- Reliability

��

MANET - 21

��

Major Goals for a Routing Protocol

� Select alternative reliable routes fast and efficiently if a node connectivity fails.

� Select an efficient path with least cost; e.g., the least number of intermediate nodes from source node to destination node.

� Provide the best response time, short delay and high throughput.

��

MANET - 22

��

Major Challenges� A node needs to know the connectivity from its

neighbors to determine a packet route� Require data exchange for routing

selection/maintenance� Need a routing table to store this information

� Network topology changes frequently� More data exchange for routing selection/maintenance

� Large number of nodes have more potential destinations� Cause large and frequent data exchange

� The update traffic for data exchange is very high and degrades the performance.

��

MANET - 23

��

2.2 Types of Routing Protocols

��

MANET - 24

��

General Classification

� Flat routing� Hierarchical Routing� Hybrid Routing� Global Positioning System (GPS) Assisted

Routing� Energy-aware Routing

��

MANET - 25

��

A. Flat routing

� Table-driven (Proactive) and On-demand (Reactive)

� Adopt a flat addressing scheme� Each node in routing have an equal role,

functionality, and capability. � As network size increases, flat routing

schemes become infeasible due to link and processing overhead

� Solution is to use Hierarchical Routing

��

MANET - 26

��

1 - Table-driven Routing (Proactive)� Attempts to maintain consistent, up-to-date

routing information from each node to every other node.

� Each node is required to maintain one or more routing tables to store the routing information.

� Proactive in nature to response to changes in network topology by propagating the updates throughout the network to maintain a consistent network view

� Background routing information exchange regardless of communication requests.

� Good for real-time application and QoS guarantees due to low-latency.

� Bad for high overhead for route update regularly.

��

MANET - 27

��

Examples

� DSDV� Destination-Sequenced Distance-Vector

� WRP� Wireless Routing Protocol

� FSR� Fisheye State Routing

��

MANET - 28

��

Destination-Sequenced Distance-Vector (DSDV)

� Based on Bellman-Ford (distance vector) routing mechanism� A distributed shortest path (SPF) algorithm is

used.� Each router sends its neighbors a list of nodes it

can reach with the distance (hop)� Then, its neighbors update its routing table

��

MANET - 29

��

Example of Bellman-Ford Routing

Node 202Node 5

Node 115Node 4

Node 74Node 3

Direct0Node 1

Next HopNo. of hop

Destination

Node 122Node 9

Node 145Node 8

Node 61Node 3

Direct0Node 0

Next HopDistanceDestination

Routing Table of Node 0

Node 202Node 5

Node 13Node 9

Node 16Node 8

Node 115Node 4

Node 12Node 3

NIL0Node 1

Next HopDistanceDestination

Node 0 receives Routing Update Message of Node 1

Latest Routing Table of Node 0

��

MANET - 30

��

� In DSDV, every mobile node has a routing table including� All possible destination nodes in the network� Number of hops to each destination� Next hop� Sequence number assigned by the destination

� To keep using the latest route� Avoid the routing loops

��

MANET - 31

��

MS1

MS2

MS3

MS7

MS5

MS6

MS4

S101_MS7MS22MS7

S301_MS6S305_MS6

MS2MS3

23

MS6MS6

S011_MS5MS32MS5

S031_MS4MS41MS4

S001_MS3MS31MS3

S001_MS2MS21MS2

Sequence number

Next HopNo. of Hops

Destination

MS1 routing table

MS6

��

MANET - 32

��

� Every node sends the routing table updates to its neighbors periodically

� Two types of update packets: � Full Dump Packets carry all routing

information and require several data units. For less moving mobile nodes, these packets are sent less frequently.

��

MANET - 33

��

� Incremental Packets is smaller and requires a single data unit. It contains the information which has changed since last full dump sent.� Nodes need to have an additional table to store

the incremental packets information.� For example, MS 6 moves to MS5, the only

change in MS1’s routing table is for MS 6’s entry. Thus, MS1 will send MS6’s entry in its incremental packet.

��

MANET - 34

��

2 - On-demand Routing (Reactive)� Reactive in nature, unlike table-driven.� Creates routes only when a source node initiates.� When a node requires a route to a destination, it

initiates a route discovery process. � The source sends a route request (RREQ) packet.� The RREQ packets are broadcast/flooded into the

network.� Once a route is found or all possible routes have been

tried, the process is completed.� If route found, the destination sends back a route reply

(RREP) to the source. The RREP packets include the selected route.

��

MANET - 35

��

� A route maintenance process is needed to maintain the established route.� If there is any link change or broken, a route

error (RERR) packet is sent to the source to perform route re-discovery.

� It takes longer time to find a route.� It reduces the overhead by exchange route

information as in table-driven routing.

��

MANET - 36

��

Examples

� DSR� Dynamic Source Routing

� AODV� Ad-Hoc On-Demand Vector Routing

� DSR and AODV are Included in the Internet-Draft

� TORA� Temporally Ordered Routing Algorithm

� ABR� Associativity-Based Routing

��

MANET - 37

��

A-Dynamic Source Routing (DSR)

� In DSR, mobile nodes maintains route caches (RC) that contain the routes to the destination nodes.� RC may contain several routes for different

destination nodes.

� Two mechanisms: route discovery and route maintenance� To allow nodes to discover and maintain source

routes to any destinations

��

MANET - 38

��

Route Discovery - RREQ� When a node has a packet to send to a destination, it

checks its RC if there is an unexpired route to the destination.

� If not, the node will initiate route discovery to broadcast the RREQ packet.� The RREQ contains the source’s address, destination’s address and

a unique ID.

� When an intermediate node receives RREQ, it checks if it knows the route to the destination by checking the its RC.

� If not, the intermediate will add its address to the route record of the RREQ packet and broadcast the RREQ to other nodes.

� To limit the number of broadcast, the node will broadcast the RREQ if it has not seen the RREQ, such as source’s address or its address is not in the route record.

��

MANET - 39

��

Building of the Route

MS1

MS2

MS3

MS7 MS5

MS8

MS4

MS6

MS10

MS9

MS1

MS1

MS1

MS1-MS3

MS1-MS2

MS1-MS10

MS1-MS3-MS7

MS1-MS2-MS4

MS1-MS10-MS6

MS1-MS10-MS8

MS1-MS2-MS4-MS9

MS1-MS2

��

MANET - 40

��

Route Discovery - RREP� When the RREQ reaches the destination or

an intermediate node find an unexpired route to destination from its RC, a RREP is generated.

� The RREP includes the route to reach destination.� If the destination generates the RREP, it puts its

address in route record in the RREP. � If the intermediate node generates the RREP, it

will append its RC to the route record in RREP.

��

MANET - 41

��

Route Discovery - RREP� To return the RREP to the source, the destination /

intermediate must have a route to go to source.� If the destination / intermediate has a route from

its RC to return to the source, it will use its own route. Otherwise,� Support symmetric link: the RREP is sent back to the

source by reversing the route in the route record.� Not support symmetric link: the destination /

intermediate initiates the route discovery to send a RREQ and piggyback the RREP on the new RREQ.

� No matter what, the route obtained from source to destination in the RREP is used to send data packet from source to destination.

��

MANET - 42

��

Propagation of RREP - symmetric link

MS1

MS2

MS3

MS7 MS5

MS8

MS4

MS6

MS10

MS9

MS1-MS3-MS7-MS5

Destination

MS1-MS3-MS7-MS5MS1-MS3-MS7-MS5

��

MANET - 43

��

Route Maintenance� RERR (Route Error)

� A node generates a RERR packet when the packet transmission is failed to the downstream node. Then, the RERR is sent back to the source node.

� When the source node receives this RERR, the hop in error is removed from its RC. Then, the source node initiates the route discovery starting from that upstream node.

� Acknowledgment� When a node receives a data packet, it send an ACK to

its upstream node.� To verify the correct operation of the links.

��

MANET - 44

��

B - Ad-Hoc On-Demand Vector Routing (AODV)

� Builds on DSR� Different from DSDV, AODV broadcasts

the routing messages on a demand basis to reduce the routing overhead.

� Nodes that are not selected on a route do not maintain routing information or exchange the routing table information.

��

MANET - 45

��

� Each node has a routing table to store the route information to some nodes.

� When a source does not find a route to the destination from its routing table, it initiates a route discovery process.

� The source node broadcasts a RREQ packet to its neighbors.

� Then the neighbors forward the RREQ to their neighbors until the destination is found or the intermediate node has a route to the destination from its routing table. � Then, the RREP including the selected route is sent

back to the source.

Route Discovery

��

MANET - 46

��

MS1

MS2

MS3

MS7 MS5

MS8

MS4

MS6

MS10

MS9

RREQ

RREQ

RREQ

��

MANET - 47

��

� RREQ packet contains� Source node’s IP address� Destination node’s IP address� Recent sequence number for the destination

� Each node maintains its sequence number for each RREQ to ensure loop-free for all routes

� Broadcast ID� It is incremented each time the source node initiates

a RREQ� The broadcast ID and the source node make a

unique identifier for the RREQ

RREQ

��

MANET - 48

��

� When a node receives a RREQ, it checks if it has seen the RREQ by checking the broadcast ID and source node’s IP

� Each node will keep the broadcast ID and source node’s IP address for a specified time

� If the node has seen it, it discards the RREQ. Otherwise, it broadcasts the RREQ

� During RREQ forwarding, the intermediate nodes record the neighbor node, where they receives the RREQ packet, in their route table, in case, to establish the reverse path later

� The intermediate node replies to the RREQ if it has a route with the sequence number greater than the one in the received RREQ

��

MANET - 49

��

RREP

� If the RREQ reaches the destination or the intermediate has a route to the destination, the destination/intermediate node sends an unicastRREP to the source from which it first receives the RREQ.

� The RREP sends back along the reverse path.� When the intermediate receives the RREP, it will

check its route table and unicast the RREP to the next downstream node

� Since AODV forwards the RREP along the path established by RREQ, it supports symmetric links.

��

MANET - 50

��

RREP along the Reverse path

MS1

MS2

MS3

MS7 MS5

MS8

MS4

MS6

MS10

MS9

RREP

��

MANET - 51

��

Route Maintenance

� If source node moves, it will reinitiate the route discovery.

� If an intermediate node moves, the upstream node will send a link failure notification message to its upstream node.

� The nodes receiving this link failure notification will propagate its to their upstream until the source node is reached. Then, the source will reinitiate the route discovery.

� An option in AODV is to send periodic ‘Hello’messages to maintain the local connectivity.

��

MANET - 52

��

RERR (Route Error)

MS1

MS2

MS7

MS5

MS9

MS7

RERRRERR

��

MANET - 53

��

B. Hybrid Routing

� Combines both proactive and on-demand routing strategies.

� Short distance destination nodes use proactive routing to maintain routing information:� Shorten the routing discovery time.� Reduce the memory size

� Long distance destination nodes do not maintain routing information due to large overhead.� Use on-demand routing to reduce the size of the routing

table and overhead

��

MANET - 54

��

Examples

� ZRP� Zone Routing Protocol

� LANMAR� Landmark Ad Hoc Routing Protocol

��

MANET - 55

��

Zone Routing Protocol (ZRP)

� Combines both proactive and on-demand routing strategies to benefit from advantages of both.

� Each node defines its own zone in terms of number of hops.

� Each node maintain a routing table for neighboring nodes within the zone.

� For destination nodes within the zone, it uses proactive routing based on the routing table.

� For destination nodes outside the zone, it uses on-demand routing.

��

MANET - 56

��

Hybrid Routing

MS1

MS2

MS3

MS5

MS6MS4

proactive

On-demand

��

MANET - 57

��

Intrazone Routing Protocol (IARP)

� Within the zone, Intrazone Routing Protocol (IARP) can be used to maintain route.

� For the destination node within the zone, IARP is used to forward packet to the destination.

� Any proactive DV, such as DSDV, routing can be used.

��

MANET - 58

��

Interzone Routing Protocol (IERP)

� Outside the zone, it uses a reactive InterzoneRouting Protocol (IERP).

� IERP is similar to any on-demand routing based on RREQ and RREP packets to discover a route.

� The RREQ is broadcast from the border nodes to other border nodes, and it is called Bordercast Resolution Protocol (BRP).

� The RREQ is broadcast from one border node to other border until the node knows the path to the destination.

��

MANET - 59

��

Advantages and Disadvantages

� The proactive limits the proactive overhead to the size of the zone.

� The reactive search limits to the border nodes outside of the zone.

� However, it is possible that the flooding of the RREQ packets goes through the whole network.

��

MANET - 60

��

C. Hierarchical Routing

� As the network size increases, ‘flat’routing becomes infeasible due to link and routing overhead.

� One solution to solve the scalable and efficient problem is to use hierarchical routing.

��

MANET - 61

��

Hierarchical Routing

� Hierarchical routings assign different roles to nodes and require a hierarchical addressing scheme.

� Idea is to organize nodes in groups or clusters, then assign nodes with different functionalities inside and outside a group.� For example, clusterhead (CH), cluster member (CM) and

cluster gateway (CGW) in cluster-based routing.

� The simple way is group the nodes geographically close to each other.

� Routing table size and update packet size can be reduced by including only part of the network.

��

MANET - 62

��

Cluster Structure

��

MANET - 63

��

Examples

� CBRP� Cluster-based Routing Protocol

� CGSR� Clusterhead Gateway Switch Routing

� HSR� Hierarchical State Routing

��

MANET - 64

��

Cluster based Routing Protocol (CBRP)

� CBRP is a popular hierarchical routing and it has been included in the Internet-Draft.

� Cluster formation is based on lowest ID (LID).

� Cluster maintenance is based on LCC.� Each node maintain two tables: neighbor

table (NT) and cluster adjacency table (CAT).

� Each node also maintain the route cache to store the routes for some destinations.

��

MANET - 65

��

� Each mobile node periodically broadcasts “Hello” messages to its neighbors.� ‘Hello’ messages include:

� Own ID, node degree, cluster status (CH, CM, CGW or unspecified).

� 1-hop neighbors’ ID, node degree and cluster status.

� Thus, mobile node can grasp the topology information within two hops and maintains such information in its neighbor tables NTs.

Neighbor Table (NT)

��

MANET - 66

��

An Example of CBRP

��

MANET - 67

��

1-hop NT and 2-hop NTTable I. 1-hop NT of node n1

11.83CM313

11.03CH53

10.53, 4CGW32

N.A.3CM31

EntryUpdateTime(s)CIDNode Status Node Degree Node ID

Table II. 2-hop NT of node n1

9.53CM313

11.813CGW46

11.03CGW46

11.03CGW45

10.52CH44

10.52CH53

11.03CGW32

EntryUpdateTime(s)Next Hop

Node Status Node Degree Node ID

��

MANET - 68

��

Cluster Adjacency Table (CAT)

� Each mobile node also maintains a CAT, recording its neighboring CHs and corresponding CGWs to reach each neighboring CH.

� CAT records the information for the 3-hop neighboring CHs.

Table III. CAT of node n4

10.6910

11.2510

EntryUpdateTime(s)Gateway ID (GID)Cluster ID (CID)

��

MANET - 69

��

Route Discovery - RREQ� When a source node attempts to obtain a route to

its intended destination, it first check if it finds a route from the 1-hop NT, 2-hop NT, and RC.

� If not found, it broadcasts a RREQ packet. � When an intermediate CH node receives such a

RREQ for the first time, it attaches its own ID in a space called traveled cluster list (TCL) in the packet header and then broadcasts the RREQ.

� When an intermediate CGW node receives the RREQ, it unicasts the RREQ to its corresponding CH and append the CH ID in the TCL.

� Thus, when the RREQ arrives at the destination, it will include the sequence of CHs that the RREQ has traveled through.

��

MANET - 70

��

Route Discovery - RREP� A route reply (RREP) will be returned to the source with

TCL copied from the received RREQ. � With the information from TCL, the RREP packet knows

the necessary sequence of CHs to travel in order to reach the source.

� And RREP utilizes IP loose source routing to travel between neighboring clusters.

� IP loose source routing means that it does not specific the exact nodes to reach the next CH.

� TCL only records the CHs to travel, but no specific nodes is recorded to show how to reach next CH.

� Because a CH always knows how to reach its neighboring CHs based on the information from its NT and CAT.

��

MANET - 71

��

Route Maintenance� When a forwarding mobile node detects a broken link

along an active route, it will manage to salvage the data packet by utilizing the local route repair mechanism / local salvage based on its NT and CAT.

� When a route with broken links is successfully adjusted, a gratuitous RREP with the adjusted route will be returned to the source node, and thus additional RREQ for discovering new routes can be avoided.

• A RERR is generated at the upstream node of a broken link along an active route and sent back to source if the local salvage is not successful.

• Hence source can use an alternative route, if any, recorded in its RC or discover a new route for subsequent data delivery.

��

MANET - 72

��

Local Route Repair Mechanisms

[n7, n4, n5, n6] [n8, n1, n3, n5, n9]

��

MANET - 73

��

D. GPS Assisted Routing� Assume that the nodes know other nodes’

locations at the cost of the overhead by exchanging coordinates.

� Each node is assumed to have a GPS to obtain the location information.� Still realistic because GPS devices are inexpensive and

providing reasonable precision.� Routing with assistance from geographic location

information, which can be used for directional routing

� Due to mobile environment, locations may not be accurate by the time the information is provided.

��

MANET - 74

��

Examples

� LAR� Location-Aided Routing

� DREAM� Distance Routing Effect Algorithm for Mobility

� GeoCast� Geographic Addressing and Routing

��

MANET - 75

��

a - Location-Aided Routing (LAR)

� On-demand routing based on source routing. Similar to DSR.

� Based on location information, LAR performs route discovery through limited flooding within a request zone.

� Two schemes are proposed to define the request zone.

��

MANET - 76

��

Scheme 1� The source first estimates a circular area as a

expected zone for the destination.� The expected zone is calculated based on the previous

destination location, the time instant with the previous location record, and the average moving speed.

� Then, a rectangular region including the expected zone is defined as the request zone as shown in the next figure.� The coordinates of 4 corners of request zone are

attached in the RREQ.

� Only the nodes inside the request zone will broadcast the RREQ.

��

MANET - 77

��

Request Zone and Expected Zone

D

S

I J

K

Request Zone

Expected Zone

��

MANET - 78

��

Scheme 2

� The source calculates the distance to the destination.

� The distance information and the destination location are included in a RREQ.

� When a node receives a RREQ, it calculates its distance to the destination.

� If the new distance is less than or equal to the distance stored in the RREQ, that node broadcasts the RREQ and put its new distance in the RREQ.

� Otherwise, it discards the RREQ.

��

MANET - 79

��

Scheme 2

D

S

D1

I

K

D2

D3J

D3<D1

D2>D1

��

MANET - 80

��

E. Energy-aware Routing

� Mobile nodes operate using batteries.� It is important to minimize the power

consumption.� Energy-aware routing considers the energy-

related metrics in routing and route selection.� The objectives are

� Extend the nodes’ lifetime� Balance the energy consumption among nodes� Increase the throughput

��

MANET - 81

��

Classification

� Active Communication Energy Consumption Optimization� The energy-aware routing is operated when the

mobile nodes actively transmits/receives packets.

� Inactive Communication Energy Consumption Optimization� The energy-aware routing is operated when the

mobile nodes are in inactive period.

��

MANET - 82

��

a - Active Communication Energy Consumption Optimization

� Two types of protocols:� Transmission power control approach.

� It reduces the active communication energy consumption of mobile nodes by adjusting each mobile node’s radio power just enough to reach the receiving node by satisfying signal-to-noise ratio (SNR).

� Hence it obtains the optimal route that minimizes the total transmission energy required to deliver data packets between a source-destination pair.

��

MANET - 83

��

Example – Minimum Total Transmission Power Routing (MTPR)

� As the distance between two nodes decreases, the transmit power decreases.

� Thus, the transmit power can be reduced by selecting a hop with shorter distance.

� The objective of MTPR is to find a path with minimum total transmit power.

� Normally, with the consideration of minimum transmission power will likely select route with more hops because of shorter distance for each hop.

� It may not be desirable.� Thus, in MTPR, the node receive power will be also

considered in the algorithm.� Thus, it attempts to choose a node with lower receive

power for longer distance to reduce the number of of hops.

��

MANET - 84

��

a - Active Communication Energy Consumption Optimization

� Load distribution approach.� Its main goal is to avoid over-utilizing mobile

nodes serving as data relays. � Thus, the overall network performance for such

an energy-limited MANET can be improved by avoiding the network partition and communication interruption caused by the early “death” of partial mobile nodes due to energy depletion

��

MANET - 85

��

Example – Localized Energy Aware Routing (LEAR)

� LEAR is originated from DSR but modifies DSR’s route discovery procedure in order to choose mobile nodes with enough battery capacity as data relays.

� Hence it can avoid the early “death” of partial mobile nodes due to energy depletion.

� In LEAR, a mobile node decides whether to process a RREQ depending on its residual battery capacity E .

� If E is higher than the threshold Th , the mobile node forwards the RREQ packet, otherwise, it drops the RREQ.

� Hence, when the RREQ arrives at the destination, it contains a route with all intermediate nodes with satisfying energy levels.

��

MANET - 86

��

Example –LEAR

� As E for mobile nodes decreases with time, the value of Th should be adjusted adaptively to identify energy-rich mobile nodes and energy-poor ones dynamically.

� If a source node does not receive any RREP within a specified time for its out-going RREQ message, the source will send a duplicated RREQ with a different sequence number.

� When an intermediate node receives the duplicated RREQ, it adjusts (or reduces) its Th to allow forwarding to continue.

��

MANET - 87

��

b - Inactive Communication Energy Consumption Optimization

� Each mobile node can save its inactivity energy by switching the mode of operation of its radio into sleep/power-down mode or simply turns it off when there is no data traffic.

� This leads to considerable energy savings, especially when the network is with low data traffic load.

� However, it requires well-designed routing protocols to provide data delivery guarantee because partial mobile nodes turning into sleep mode may impair route diversity, route discovery time and packet delivery.

��

MANET - 88

��

Sleep / Power-down mode

� Based on statistics, a mobile node in a network is often with idle status, which means it does not transmit or receive any useful information.

� Also, the wireless network interface is usually a mobile device’s single largest consumer of power.

� It is desirable to put the radio into power save/sleep mode or simply turn it off to save energy since most radio hardware supports low power states.

��

MANET - 89

��

Sleep / Power-down mode� Sleep/power-down mode protocols manage to put partial

mobile nodes into power save mode at a time and periodically rotate this portion among all mobile nodes when possible without affecting the network performance much.

� Hence, the lifetime of individual mobile nodes as well as the network lifetime can be extended.

� This requires the cooperation between the power saving mechanism and other functionalities of a mobile node.

� In a multi-hop MANET, the coordination of power saving with routing is especially important considering that mobile nodes may depend on each other for packet forwarding.

��

MANET - 90

��

Example – Geographic Adaptive Fidelity Protocol (GAF)

� In GAF, each mobile node utilizes the location information provided by GPS to associate itself with a virtual grid so that the entire network area is divided into several square grids.

� Any mobile node insides a grid should be able to reach other mobile nodes in a neighboring grid for inter-grid communication.

� The relationship the grid size, r, is smaller than the transmission range, R, of a mobile node.� r^2+(2r)^2 R^2

��

MANET - 91

��

GAF Grids

��

MANET - 92

��


� In GAF, mobile node with the highest residual battery capacity within each grid becomes the master of the grid for the inter-grid routing and packet forwarding.

� Hence, other mobile nodes in the same grid can be released from the inter-grid routing and packet forwarding, and they can be safely put to power saving mode without affecting the routing efficiency.

� A slave node of a grid periodically becomes awake to make sure that there is a master node in its grid to stay awake and route packets.

��

MANET - 93

��


� Normally a master node continues serving its grid for a period of time, Ta, and then it changes its status to discovery to give other mobile nodes in the same grid a chance to become the grid master.

� A slave node wakes every Ts seconds, changes to discovery status, and tries to become a master by sending out discovery message including its grid ID and its residual energy.

� Such a mobile node successfully wins the master role if it does not hear any other discovery message for a predefined duration Td.

� If more than one mobile node is in the discovery status, the one with the highest energy level becomes a master.

��

MANET - 94

��

Performance Metrics� Data packet delivery ratio

� Defined as the total number of data packets received by all destination nodes over the total number of data packets sent by all source nodes in the network.

� Normalized routing overheads� Refers to the total number of non-data packets

transmitted at the IP layer over the total data packets received during the simulation.

� Each transmission of a non-data IP layer packet from one hop to another hop is counted as one packet.

� End-to-end transmission delay � Calculates the average time from a data packet is

generated at the source node till this data packet is received at the destination node.

��

MANET - 95

��

3 Clustering MANETS

��

MANET - 96

��

3.1 Introduction

��

MANET - 97

��

What is Flat MANETs?

� Flat MANET refers to that all nodes (in terms of role, hardware, functionality) in the network are equal and perform the similar functionality:� source, intermediate, and destination

� Control messages are sent to maintain the connectivity and search the routing path

��

MANET - 98

��

MS1

MS2

MS3

MS7

MS5

MS6

MS4

MS8

MS9

��

MANET - 99

��

To divide mobile nodes in a MANET into different virtual groups and to allocate mobile nodes geographically near into the same cluster based on some rules.

What is clustering MANETs?

Roles:-Clusterhead (CH)-Clustermember (CM)-Clsutergateway (CGW)

��

MANET - 100

��

�A cluster (hierarchical) structure helps better utilize the radio band resource in a MANET;

�A cluster structure facilitates routing events in a MANET;

�A cluster structure makes a MANET appear smaller and more stable in the view of each mobile node.

Why do Ad Hoc networks require clustering?

��

MANET - 101

��

Clustering Mechanisms� Every clustering algorithm consists of two

mechanisms: Cluster Formation and Cluster Maintenance.

� Cluster formation refers to how to build a cluster structure for a MANET at the very beginning. � For example, it determines how to select the CH and

the coverage of the CH for the number of CMs.� Cluster maintenance is about how to update and

maintain the cluster structure according to the underlying network topology change during the operation. � For example, after certain time the original CH may not

be suitable to be CH anyway due to its mobility, coverage or battery. Then, it needs to look for other mobile node as CH to maintain structure.

��

MANET - 102

��

Cluster Formation and Maintenance

��

MANET - 103

��

3.2 Classification of Clustering

��

MANET - 104

��

A cluster-based MANET has its side effects and drawbacks because constructing and maintaining a cluster structure usually requires additional cost compared with a flat-based MANET.

�Explicit control message for clustering

�Ripple effect of re-clustering

�Stationary assumption for cluster formation

�Communication complexity for clustering

What are the costs for clustering?

��

MANET - 105

��

How to classify clustering schemes?

� Clustering schemes refer to how to form and maintenance a cluster such as cluster and clusterhead selection. � DS-based clustering� Low-maintenance clustering� Mobility-aware clustering� Energy-efficient clustering� Load-balancing clustering� Combined-metrics-based clustering

��

MANET - 106

��

A. DS-based Clustering

� Finding a dominating set (DS) to reduce the number of nodes participating in routing events.

� Finding a DS for a MANET is because that the routing process is only aggregated on mobile nodes in the DS.

� Objective: Reduce the DS size by finding a minimum number of mobile nodes as dominating nodes to construct a Connected DS (CDS). � Decrease the number of nodes participating in routing

and eliminate unnecessary dominating nodes without breaking the direct connection between neighboring dominating nodes.

��

MANET - 107

��

DS-based Clustering

For example, a mobile node sets itself as a dominating node if it has at least two unconnected neighbors.And each nodes connects to only 1 dominating node.

��

MANET - 108

��

B. Low-maintenance Clustering

� Clustering normally needs explicit clustering-related control messages for cluster structure formation and maintenance.

� Clustering may compete the band resource with routing and data packet delivery.

��

MANET - 109

��

B. Low-maintenance Clustering

� Low-maintenance clustering targets at maintaining a cluster structure with low maintenance cost with lower clustering control overhead.

� The typical way is to limit:� the re-affiliation (clustermember joining or

leaving a cluster)� re-clustering rate (changing of clusterhead) and � to eliminate the ripple effect of re-clustering.

��

MANET - 110

��

Clustering Maintenance

� ��

H – ClusterheadG – GatewayM - Member

��

MANET - 111

��

C. Mobility-aware Clustering• Mobile nodes’ movement is a prominent

characteristic of MANETs and is the main factor affecting topology change and route invalidation.

• Utilizing mobile nodes’ mobility behavior for cluster construction and maintenance.

• The cluster structure is determined by the mobility behavior of mobile nodes.

• By grouping mobile terminals with low-relative speed into the same cluster, the intro-cluster links are more tightly connected. The re-affiliation rate and re-clustering rate are decreased.

��

MANET - 112

��

Techniques

1. Minimizing the influence of mobile nodes’ movement on cluster topology updates depending on mobile nodes’explicit relative speed.

2. Grouping mobile nodes with low relative speed into the same cluster and forming a multi-hop cluster structure.

��

MANET - 113

��

D. Energy-efficient Clustering� Mobile nodes are normally based on battery power

supply, but clustering behavior requires mobile nodes consume extra energy.

� The early “death” of mobile nodes due to energy depletion may cause network partition and communication interruption.

� However, mobile nodes with special cluster-related status, such as clusterhead, likely consume more energy.

� Energy-efficient clustering avoids unnecessary energy consumption or balances energy consumption in the clustering events for mobile nodes in order to prolong the lifetime of mobile nodes and a network.

��

MANET - 114

��

Techniques

� Avoiding possible node failure because of excessive serving as clusterheads by limiting the time that a mobile node can serve as a clusterhead continuously.

� Guaranteeing a connected DS and avoiding unnecessary energy consumption for mobile nodes by deleting redundant mobile nodes with poor energy-level from the DS.

��

MANET - 115

��

E. Load-balancing Clustering� In a clusterhead-based cluster structure,

backbone nodes, especially cluster heads, normally bear extra work. Hence, � A too-large cluster may make the clusterhead

become network bottleneck. � A too-small cluster, however, may produce a

large number of clusters, which intends to increase backbone size and is not favorable to simplify network structure.

� Objective is to maintain a multi-hop cluster structure with optimal cluster size.

��

MANET - 116

��

Technique� Distributing the workload of a network more

evenly into clusters by limiting the number of mobile nodes in each cluster in a defined range� Sets upper and lower limits on the number of mobile

nodes that a cluster can handle to produce cluster structure with optimal cluster size.

� When a clusterhead finds its cluster size exceeds the pre-defined upper limit, it tries to explicit its cluster into two .

� When a clusterhead finds its cluster size is below the pre-defined lower limit, it tries to merge with a neighbor cluster .

��

MANET - 117

��

Combine and Divide Technique

��

MANET - 118

��

F. Combined-metrics-based Clustering

� In clusterhead-based clustering schemes, electing clusterheads to satisfy specific attributes makes the clusterhead election favors a small portion of mobile nodes, and thus makes those mobile nodes over-utilized.

� Takes a number of metrics into account for cluster configuration to elect more appropriate clusterheads� Including node degree, mobility, battery energy, cluster

size, etc., and adjusting their weighting factors catering for different application scenarios

��

MANET - 119

��

Example

� Each mobile node records several parameter for itself, including degree difference, sum of distance with all neighbors, average moving speed and clusterhead serving time. Use

� To calculate its combined weight and exchange this information with all direct neighbors. The one with the minimum weight is selected as clusterhead.� Dv is the difference between the number of neighbor

nodes and the ideal cluster size, M.� Tv is the expected serving time.

1 2 3 4v v v v vI c D c P c M c T= + + +

��

MANET - 120

��

3.3 Examples

��

MANET - 121

��

1 – High Connective Clustering (HCC)

� Based on the node degree for cluster formation and maintenance.

� Cluster Formation� Initially each mobile node obtains its node degree

information by collecting the periodic Hello messages from its neighbors.

� Then each node includes this node degree information in its following Hello message.

� Thus, a mobile node claims as a CH only when it finds out that it has higher node degree than all neighbors, who have not determined their clustering status yet

��

MANET - 122

��

1 – High Connective Clustering (HCC)

� Cluster Maintenance� Each CH periodically compare its own node

degree with that of each neighbor by consulting its Information Table.

� If a neighbor with higher node degree is found, the current CH then resigns its CH role to that neighbor.

� Hence, the clustering structure changes accordingly.

��

MANET - 123

��

2 – Least Cluster Change (LCC)

� Cluster Formation� Based on Lowest ID Clustering (LIC)

� Initially, each mobile node broadcast its ID via the periodic Hello message to its neighbors.

� A mobile node can claim as a CH only if it has the lowest ID compared with all neighbors with unspecified clustering status

��

MANET - 124

��

2 – Least Cluster Change (LCC)� Cluster Maintenance� Re-clustering is event-driven and invoked only in

two cases: � (1) when two CHs move into the reach range of each

other, one gives up the CH role, or � (2) when a mobile node cannot access any CH, it re-

builds the cluster structure for the network according to LIC.

� Hence, compare to HCC, LCC significantly improves the cluster stability by relinquishing the requirement that a CH should always bear some specific attributes in its local area.

��

MANET - 125

��

3 – Random Competition-based Clustering (RCC)

� Cluster Formation� A mobile node not involved in any cluster is

with “unspecified” status and any mobile node with “unspecified” status can claim as a CH.

� But before a mobile node broadcasts a CH claim message, if it receives such message from some other mobile node in its neighborhood, it aborts its own CH claim message and joins that neighbor’s cluster as a CM.

��

MANET - 126

��

3 – Random Competition-based Clustering (RCC)

� Cluster Maintenance� The cluster structure is updated accordingly

in RCC when the underlying network topology is changing.

� The cluster structure change in RCC is only invoked in several situations: � 1) When two CHs move into the reach range of

each other, one of them gives up the CH role.� 2) When a mobile node becomes disconnected

with its CH(s), it claims as a new CH in order to cover itself in some cluster.

��

MANET - 127

��

� Achieving goal:

Minimized inter-cluster connectivity;Reduce overlapping areasStable cluster structure;Less number of control packets;

� Some prevailing clustering schemes:

Lowest-ID Cluster Algorithm (LID);Highest-Connectivity Cluster Algorithm (HCC);Random Competition-based Clustering (RCC);

That’s the goal!

4 - Efficient Clustering Scheme (ECS)

��

MANET - 128

��

�Clusterguest (CG): a mobile node, which is not in the transmission range of any clusterheads, but within the range of some clustermembers;

�AP(access point): a mobile node, with which a clusterguest can access some cluster;

�HP(head priority): an attribute, which describes the possibility of a node serving as a clusterhead in the cluster formation procedures;

Some New Definition Items

��

MANET - 129

��

Cluster Formation Procedures (1)

�The cluster formation procedures attempts to provide 3-hop distance between adjacent cluterheads;

��

MANET - 130

��

Cluster Formation Procedures (2)

� When a node finds all of its neighbors are involved in formed clusters as clustermembers/clusterguests it access some cluster as a clusterguest.

��

MANET - 131

��

Cluster Maintenance Mechanisms

� A clusterhead change occurs when two heads move into the transmission range of each other;

�When a non-clusterhead node moves out of the range of any existing clusterheads, if it can still communicate with any clustermember nodes, it joins the corresponding cluster as a CG;

�When a CH finds out all its members can attach to other clusters as CM or clusterguest, it relinquishes its CH role, and joins a neighboring cluster as a CG (MERGE FUNCTION).

��

MANET - 132

��

References

� E. M. Royer, and C.-K. Toh, “A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Netwroks,” IEEE Personal Communications, pp. 46-55, April 1999.

� C.–K. Toh, “Maximum Battery Life Routing to Support Ubiquitous Mobile Computing in Wireless Ad Hoc Networks,” IEEE Communications, pp. 2-11, June 2001.

� X. Hong, K.Xu, and M. Gerla, “Scalable Routing Protocols for Mobile Ad Hoc Networks,” IEEE Networks, pp. 11-21, July/August 2002.

� C. M. Cordeiro, H. Gossain, and D. P. Agrawal, “Multicast over Wireless Mobile Ad Hoc Networks: Present and Future Directions,”IEEE Network, pp. 52-59, January/February 2003.

� J. Y. Yu and P. H. J. Chong, “A Survey of Clustering Schemes for Mobile Ad Hoc Networks,” IEEE Communications and Survey, pp. 32-48, First Quarter, 2005.

��

MANET - 133

��

References

� J. Li, D. Cordes and J. Zhang, “Power-aware Routing Protocols in Ad Hoc Wireless Networks,” IEEE Wireless Communications, pp. 69-81, December 2005.

� J. Y. Yu and P. H. J. Chong, “An Efficient Clustering Scheme for Large and Dense Mobile Ad Hoc Networks (MANETs),” Computer Communications, 30, pp. 5-16, 2006.

� S. Guo and O. W. W. Yang, “Energy-aware Multicasting in Wireless Ad Hoc Networks: A Survey and Discussion,” Computer Communications, 30, pp. 2129-2148, 2007.

Documents

Mobile Ad Hoc Networks: Routing and · PDF fileMobile Ad Hoc Networks: Routing and Clustering ... Bandwidth and Capacity Link ... infrastructure is destroyed. MANET can set up the