topology management ad hoc and sensor networks

Topology Management

Ad hoc and Sensor Networks

– What is it?What is it?

o The physical or logical interconnection pattern of a networkThe physical or logical interconnection pattern of a network

– Topology schemes in wired networks:Topology schemes in wired networks:

o BusBus

o StarStar

o RingRing

– Why do we need different schemes in sensor networks?Why do we need different schemes in sensor networks?

o location of sensors is not deterministiclocation of sensors is not deterministic

o resource constraints resource constraints

The Need for Topology Management

– Energy/Power consumptionEnergy/Power consumption

– InterferenceInterference

– ThroughputThroughput

– ConnectivityConnectivity

The Need for Topology Management

Motivation for Backbone Architecture

essential for management of large ad hoc networksessential for management of large ad hoc networks

helps generate the minimum possible overhead for construction helps generate the minimum possible overhead for construction

and maintenance of the backbone networkand maintenance of the backbone network

can provide efficient solution for mobility and node/link failures in can provide efficient solution for mobility and node/link failures in

very large ad hoc networksvery large ad hoc networks

Mobility-Adaptive Protocols for Managing Large Ad hoc Networks[Basagni+ 2001]

Proposed B-Protocol Description

B-ProtocolB-Protocol

• Also known as Also known as backbonebackbone protocols protocols

• Sets up and maintains a connected network (Sets up and maintains a connected network (B-networkB-network))

• B-network convey the time-sensitive network management informationB-network convey the time-sensitive network management information

• from every node in the network with minor overhead and in a from every node in the network with minor overhead and in a timely mannertimely manner

• Comprises two major tasks:Comprises two major tasks:

(a) B-nodes selection(a) B-nodes selection

(b) B-links establishment(b) B-links establishment

Nodes that are not selected as B-nodes are termed Nodes that are not selected as B-nodes are termed F- nodesF- nodes that belong to the that belong to the flat networkflat network

Mobility-Adaptive Protocols for Managing Large Ad hoc Networks

Executed at each node based on a node’s Executed at each node based on a node’s own weightown weight

Weight Weight is computed based on what is most critical to that node for the is computed based on what is most critical to that node for the

specific network applicationspecific network application

The highest weight of a node is more suitable to be a B-nodeThe highest weight of a node is more suitable to be a B-node

A node knows A node knows

Its own identifier (ID) and weightIts own identifier (ID) and weight

Ids, weights and roles (B-node or F-node) of one-hop neighborsIds, weights and roles (B-node or F-node) of one-hop neighbors

Once a node Once a node bb determines its role as B-node, all its neighbors may determines its role as B-node, all its neighbors may

become the F-nodes served under become the F-nodes served under bb unless they have decided to join unless they have decided to join

another nodeanother node

B-nodes selection B-nodes selection is adaptive to node mobility and changes in its local is adaptive to node mobility and changes in its local

statusstatus

B-nodes Selection


4(9)

5(8)

7(5)

6(1)

2(3)

1(6)

8(1)

3(2)

Numbers represent node IDs and numbers within parentheses represent the node weights

Illustrative Example:

B-nodes Selection


4(9)

5(8)

7(5)

6(1)

2(3)

1(6)

8(1)

3(2)

B-node B-node

B-node

Illustrative Example:

B-nodes Selection


Determines the inter-B-nodes links to be established in order for the Determines the inter-B-nodes links to be established in order for the

network to be connectednetwork to be connected

Two types of B-links:Two types of B-links:

PhysicalPhysical – when a direct link between B-nodes at most three hops – when a direct link between B-nodes at most three hops

away can be established without involving intermediate F-nodes away can be established without involving intermediate F-nodes

(via power control or directional antenna)(via power control or directional antenna)

VirtualVirtual – when a direct link between B-nodes at most three hops – when a direct link between B-nodes at most three hops

away away cannotcannot be established. In this case, virtual link is implemented be established. In this case, virtual link is implemented

among two B-nodes by a corresponding physical path with at most among two B-nodes by a corresponding physical path with at most

three linksthree links

The rules stated follow the theorem proven in [Chlamtac ’96]The rules stated follow the theorem proven in [Chlamtac ’96]

B-links Establishment


Theorem 1 [Chlamtac ’96]:

Given a set B of network nodes such that no two of them are neighbors Given a set B of network nodes such that no two of them are neighbors

and every other node has a link to a node in B, then a connected and every other node has a link to a node in B, then a connected

backbone is guaranteed to arise if each node in B establishes links to all backbone is guaranteed to arise if each node in B establishes links to all

other nodes in B that are other nodes in B that are at most three hops awayat most three hops away. Moreover, these links . Moreover, these links

are all needed for the deterministic guarantee in the worst case, in the are all needed for the deterministic guarantee in the worst case, in the

sense that if any of them is left out then it is not true anymore that the sense that if any of them is left out then it is not true anymore that the

arising backbone is connected for any underlying flat network.arising backbone is connected for any underlying flat network.

B-links Establishment


1.1. Each node in flat network knows Each node in flat network knows onlyonly its one-hop neighbors. This its one-hop neighbors. This

induces the minimum possible overheadinduces the minimum possible overhead

2.2. B-link establishment is run at each B-node B-link establishment is run at each B-node onlyonly with no knowledge of with no knowledge of

the surrounding B-nodes. Again, this induces the minimum overheadthe surrounding B-nodes. Again, this induces the minimum overhead

3.3. Every B-node serves a number of F-nodes each of which is Every B-node serves a number of F-nodes each of which is at mostat most

three-hops away. B-node selection protocol guarantees that all the F-three-hops away. B-node selection protocol guarantees that all the F-

nodes are served by only one neighboring B-nodenodes are served by only one neighboring B-node

4.4. There are no two B-nodes that are neighbors in the flat network. This There are no two B-nodes that are neighbors in the flat network. This

guarantees that B-nodes are evenly distributed in the networkguarantees that B-nodes are evenly distributed in the network

5.5. B-node selection is based on the node’s current status (weight)B-node selection is based on the node’s current status (weight)

Properties of B-protocol


6.6. The B-network is always connected provided that the underlying flat The B-network is always connected provided that the underlying flat

network is connectednetwork is connected

7.7. B-protocols takes into account different technologies and mechanisms B-protocols takes into account different technologies and mechanisms

that can be used to link the B-nodes in the network. Two types of B-that can be used to link the B-nodes in the network. Two types of B-

links are provided; namely physical and virtual links. Physical links are links are provided; namely physical and virtual links. Physical links are

used when there is a direct link between B-nodes at most three hops used when there is a direct link between B-nodes at most three hops

away and virtual links are used when there is a direct link cannot be away and virtual links are used when there is a direct link cannot be

established established

Properties of B-protocol


A simulator used for an ad hoc network of nodes ranges 100 - 1000A simulator used for an ad hoc network of nodes ranges 100 - 1000

Nodes can freely move around in a rectangular region (a grid)Nodes can freely move around in a rectangular region (a grid)

Node movements are discretized to grid units of 1 meterNode movements are discretized to grid units of 1 meter

A node determines its direction randomly by choosing between its A node determines its direction randomly by choosing between its

current direction (with 75% probability) and uniformly among all other current direction (with 75% probability) and uniformly among all other

directions (with 25% probability) directions (with 25% probability)

When a node hits a grid boundary, it bounces back into the region with When a node hits a grid boundary, it bounces back into the region with

an angle determined by the incoming directionan angle determined by the incoming direction

Fixed transmission range of each node (250 m) and the grid size have Fixed transmission range of each node (250 m) and the grid size have

been chosen to obtain a good network connectivitybeen chosen to obtain a good network connectivity

Each packet contains the time-stamped, node identified weight of the Each packet contains the time-stamped, node identified weight of the

sending node. All packets are sent for the one-hop neighbors onlysending node. All packets are sent for the one-hop neighbors only

Simulation Environment


Figure 1: Number of B-nodes (% w.r.t the number of the network nodes)

kk is the total number of F-is the total number of F-

nodes a B-node can serve nodes a B-node can serve

at any point in timeat any point in time

Three cases:Three cases: k < n k < n (where n is total (where n is total

number of nodes in number of nodes in network)network)

k < 4k < 4 k < 8k < 8

Simulation Results


Figure 2: Number of B-links (%) when a physical link between any two B-nodes can be established directly.






k < 4k < 4 k < 8k < 8

Simulation Results


Figure 3: Number of B-links (%) when a link between B-nodes is implemented by a physical path with at most three hops away






k < 4k < 4 k < 8k < 8

Simulation Results


– Describes Describes

o a topology management technique that is power efficienta topology management technique that is power efficient

o energy, Latency and Density trade-offsenergy, Latency and Density trade-offs

– Provides Provides

o a theoretical analysis of these techniques, including a a theoretical analysis of these techniques, including a

mathematical formulation that can be used to design a network mathematical formulation that can be used to design a network

with required energy, latency and density configurationwith required energy, latency and density configuration

o a hybrid solution with existing topology management scheme a hybrid solution with existing topology management scheme

(GAF) to provide energy saving of over two order of magnitude(GAF) to provide energy saving of over two order of magnitude

– The proposed new topology management scheme is calledThe proposed new topology management scheme is called

STEMSTEM (Sparse Topology and Energy Management) (Sparse Topology and Energy Management)

Optimizing Sensor Networks in the Energy-Latency-Density Design Space

[Schurgers+ 2002]

– Two states for sensor nodes:Two states for sensor nodes:

o Monitoring StateMonitoring State

o Transfer StateTransfer State

– Most of the time a sensor remains in monitoring state (i.e. sensing Most of the time a sensor remains in monitoring state (i.e. sensing

environment)environment)

– When an event occurs, nodes come into transfer mode and transfer When an event occurs, nodes come into transfer mode and transfer

their datatheir data


[Schurgers+ 2002]

Issues:Issues:

– Nodes must listen periodically for call to duty (i.e transfer)Nodes must listen periodically for call to duty (i.e transfer)

– But if they poll periodically on the same frequency, it will collide with But if they poll periodically on the same frequency, it will collide with

other data transferother data transfer

Solution:Solution:

– Use two radios, one for polling while the other for data transferUse two radios, one for polling while the other for data transfer

STEM-B (Beacon Approach):STEM-B (Beacon Approach):

– Initiator sends a stream of beacon packets to poll a target with initiator Initiator sends a stream of beacon packets to poll a target with initiator

and target MAC addressesand target MAC addresses

– Target node sends acknowledgement on receiving the packetTarget node sends acknowledgement on receiving the packet

– Target node turns its transfer radio onTarget node turns its transfer radio on


[Schurgers+ 2002]

STEM-T (Tone Approach)STEM-T (Tone Approach)

– Initiator sends a wake up toneInitiator sends a wake up tone

– Every node receiving that tone starts its data transfer radioEvery node receiving that tone starts its data transfer radio

– No need to send acknowledgementNo need to send acknowledgement

– Every node in the neighborhood of initiator wakes upEvery node in the neighborhood of initiator wakes up

STEM/GAF HybridSTEM/GAF Hybrid

– GAF proposes a scheme in which a sensor network is divided in a gridGAF proposes a scheme in which a sensor network is divided in a grid

– One node in a region has its radio on, others have it turned offOne node in a region has its radio on, others have it turned off

– Nodes alternate the responsibility of being the active nodeNodes alternate the responsibility of being the active node

– GAF uses network density to conserve energyGAF uses network density to conserve energy

– Assuming the active node to be the virtual node, STEM can be used Assuming the active node to be the virtual node, STEM can be used

on the virtual node to manage whole networkon the virtual node to manage whole network


[Schurgers+ 2002]

Advantages:

– Highly efficient in environments where events are rareHighly efficient in environments where events are rare

– Flexible in term of design trade-off for energy, latency and densityFlexible in term of design trade-off for energy, latency and density

– Transition from monitoring state to transfer state is easily achievedTransition from monitoring state to transfer state is easily achieved

– No synchronization requiredNo synchronization required

– Can be use with other topology management schemes like GAFCan be use with other topology management schemes like GAF

Disadvantages:

– Continuous polling consumes energyContinuous polling consumes energy

– Not suitable for highly reactive environmentsNot suitable for highly reactive environments

– Requires extra radio on sensor nodesRequires extra radio on sensor nodes

Suggestions/Improvements/Future Work:

– Analysis of STEM with clustered networksAnalysis of STEM with clustered networks


[Schurgers+ 2002]

– In In ASCENTASCENT, the nodes coordinate to exploit the redundancy provided by , the nodes coordinate to exploit the redundancy provided by

high density to extend the overall system lifetimehigh density to extend the overall system lifetime

– Nodes achieve self-configuration to establish a topology that provides Nodes achieve self-configuration to establish a topology that provides

communication and sensing coverage under energy constraintscommunication and sensing coverage under energy constraints

– Each node examines its connectivity and adapts its participation in the Each node examines its connectivity and adapts its participation in the

multi-hop network topology based on the operating regionmulti-hop network topology based on the operating region

– The nodeThe node

o Signals when it detects high message loss, requesting additional nodes to Signals when it detects high message loss, requesting additional nodes to

join the network to continue relaying messagesjoin the network to continue relaying messages

o Reduces its duty cycle if high messages losses are detected due to Reduces its duty cycle if high messages losses are detected due to

collisionscollisions

o Probes local communication environment and only joins to the multi-hop Probes local communication environment and only joins to the multi-hop

routing infrastructure if it is usefulrouting infrastructure if it is useful

ASCENT: Adaptive Self-Configuring sEnsor Networks Topologies

[Cerpa+ 2002]

– Sensor nodes do local processing to reduce communication and energy costsSensor nodes do local processing to reduce communication and energy costs

– Challenges arises from the increased level of Challenges arises from the increased level of dynamicsdynamics (systems and (systems and

environmental)environmental)

– One of the most important challenge arises from One of the most important challenge arises from energy constraintsenergy constraints imposed imposed

by by unattended systemsunattended systems

o These systems must be long-lived and operate without manual intervention These systems must be long-lived and operate without manual intervention

o They need to self-configure and adapt to environmental dynamics and some They need to self-configure and adapt to environmental dynamics and some

terrain conditions may result regions with non-uniform communication densityterrain conditions may result regions with non-uniform communication density

o These issues can be addressed by deploying redundant nodes and designing These issues can be addressed by deploying redundant nodes and designing

algorithms to use redundancy to extend the system lifetimealgorithms to use redundancy to extend the system lifetime

o Scaling challenges are associated with spatial coverage and robustnessScaling challenges are associated with spatial coverage and robustness

Central vs. DistributedCentral vs. Distributed

– When energy is constraint and environment is dynamic, distributed approaches are When energy is constraint and environment is dynamic, distributed approaches are

preferable and practicalpreferable and practical


[Cerpa+ 2002]

– Scalable wireless sensor networks require to avoid large amounts of data Scalable wireless sensor networks require to avoid large amounts of data

being transmitted over long distancesbeing transmitted over long distances

– ASCENT applies well-known techniques from MAC layer protocols to the ASCENT applies well-known techniques from MAC layer protocols to the

problem of distributed topology formationproblem of distributed topology formation

– Imagine a habitat monitoring sensor network that is deployed in remote forestImagine a habitat monitoring sensor network that is deployed in remote forest

– The deployed systems must confer with the following conditions The deployed systems must confer with the following conditions

o Ad-hoc deploymentAd-hoc deployment

o Energy constraintsEnergy constraints

o Unattended operation under dynamicsUnattended operation under dynamics

– If we use too few nodes initially:If we use too few nodes initially:

o the distance between neighboring nodes will be too farthe distance between neighboring nodes will be too far

o packet loss rate may increasepacket loss rate may increase

o energy required to transmit over larger distances may be prohibitiveenergy required to transmit over larger distances may be prohibitive


[Cerpa+ 2002]

– If we use all deployed nodes simultaneously:If we use all deployed nodes simultaneously:

o system will expand unnecessary energysystem will expand unnecessary energy

o nodes interfere with each other by congesting the channelnodes interfere with each other by congesting the channel

– ASCENT does not use localized distributed algorithm to find a single solutionASCENT does not use localized distributed algorithm to find a single solution

– Adaptive self-configuration using localized is suited to problem spaces which Adaptive self-configuration using localized is suited to problem spaces which

have a vast number of possible solutions (in this case, large solution spaces have a vast number of possible solutions (in this case, large solution spaces

means dense node deployment)means dense node deployment)

– ASCENT has the following two assumptions:ASCENT has the following two assumptions:

o Carrier Sense Multiple Access (CSMA) MAC protocolCarrier Sense Multiple Access (CSMA) MAC protocol

Possibilities for resource contention when too many neighboring Possibilities for resource contention when too many neighboring

nodes participate in the multi-hop networknodes participate in the multi-hop network

o Reacts when links have high packet lossReacts when links have high packet loss

Does not detect or repair network partitions and assumes that there Does not detect or repair network partitions and assumes that there

is enough node density to connect the entire regionis enough node density to connect the entire region


[Cerpa+ 2002]

– Two essential contributions of ASCENT design are:Two essential contributions of ASCENT design are:

1.1. Adaptive techniques that allow applications to Adaptive techniques that allow applications to configureconfigure the topology the topology

based on the needs while saving energy to extend network lifetime. The based on the needs while saving energy to extend network lifetime. The

techniques do not assume a specific model or fairness, degree of techniques do not assume a specific model or fairness, degree of

connectivity, or capacity requiredconnectivity, or capacity required

2.2. Self-configuring techniques that react to operating conditions are Self-configuring techniques that react to operating conditions are

measured locallymeasured locally. It does not assume any specific radio propagation . It does not assume any specific radio propagation

model, geographical distribution of nodes, or routing mechanisms usedmodel, geographical distribution of nodes, or routing mechanisms used

ASCENT DesignASCENT Design

– Adaptively elects Adaptively elects activeactive nodes from all the nodes nodes from all the nodes

– Active nodes stay awake always and participate in routing while the other Active nodes stay awake always and participate in routing while the other

nodes remain nodes remain passivepassive and periodically checks if they should become active and periodically checks if they should become active


[Cerpa+ 2002]


– Initially, only some nodes are active while other are passively listening to Initially, only some nodes are active while other are passively listening to

packets but not transmittingpackets but not transmitting

– When source starts transmitting data packets towards the sink, the sink gets When source starts transmitting data packets towards the sink, the sink gets

high message loss from the source due to limited radio range, called high message loss from the source due to limited radio range, called

communication holecommunication hole

– The receiver gets high packet loss due to poor connectivity with the senderThe receiver gets high packet loss due to poor connectivity with the sender


[Cerpa+ 2002]

Help Messages

Data Message

SinkSource

Active NeighborPassive Neighbor

Figure 2(a): Communication HoleFigure 2(a): Communication Hole


– Sink start sending Sink start sending help messageshelp messages to neighbors that are in listen-only mode, to neighbors that are in listen-only mode,

called called passive neighborspassive neighbors, to join the network, to join the network

– When a neighbor receive a When a neighbor receive a help messagehelp message, it decides to join the network or not, it decides to join the network or not

– If the node joins, it becomes an If the node joins, it becomes an active neighboractive neighbor and signals the existence of a and signals the existence of a

new active neighbor to other passive neighbors by sending a new active neighbor to other passive neighbors by sending a neighbor neighbor

announcement messageannouncement message

– It continues until the number of active nodes stabilizes on a certain value and It continues until the number of active nodes stabilizes on a certain value and

the cycle stopsthe cycle stops


[Cerpa+ 2002]


– When the process is completed, the newly joined nodes participate in the data When the process is completed, the newly joined nodes participate in the data

delivery process from source to sink more reliablydelivery process from source to sink more reliably

– The process will be repeated in the case of network event (e.g., node failure) The process will be repeated in the case of network event (e.g., node failure)

or environmental effect (e.g., new obstacle) causes message lossor environmental effect (e.g., new obstacle) causes message loss

Sink

SinkSource

Neighbor AnnouncementsMessages

Data Message

Source


[Cerpa+ 2002]

Figure 2(b-c): Self-configuration transition and final stateFigure 2(b-c): Self-configuration transition and final state

NT: neighbor threshold

LT: loss threshold

T?: state timer values (p: passive, s: sleep, t: test)

DL: Data loss rate

Test

Passive Sleep

Activeafter Tt

after Tp

after Ts

neighbors < NT and• loss > LT• loss < LT & help

neighbors > NT (high ID for ties); orloss > loss T0

ASCENT State TransactionsASCENT State Transactions


[Cerpa+ 2002]


– Initially, a random timer turns on the nodes to avoid synchronizationInitially, a random timer turns on the nodes to avoid synchronization

– Node initializes to test state:Node initializes to test state:

Sends data and routing control messagesSends data and routing control messages

Sets up a timer, Tt and sends neighbor announcement messagesSets up a timer, Tt and sends neighbor announcement messages

Moves into passive state if the conditions are met before Tt expiresMoves into passive state if the conditions are met before Tt expires

When Tt expires, it enters to active stateWhen Tt expires, it enters to active state

– The reasoning behind theThe reasoning behind the test test state is to probe the network to decide whether state is to probe the network to decide whether

the addition of a new node would improve connectivitythe addition of a new node would improve connectivity

– On entering the passive state, node:On entering the passive state, node:

Sets up a timer Tp and when Tp expires, it enters to sleep stateSets up a timer Tp and when Tp expires, it enters to sleep state

If before Tp expires, it enters to test state only if the conditions are metIf before Tp expires, it enters to test state only if the conditions are met

Nodes in passive state can hear all packets transmitted, but no routing Nodes in passive state can hear all packets transmitted, but no routing

or data packets are forwarded in this state since this is listen-only stateor data packets are forwarded in this state since this is listen-only state


[Cerpa+ 2002]


– The reasoning behind theThe reasoning behind the passive passive state is to gather information about the state is to gather information about the

state of the network without causing interference with other nodesstate of the network without causing interference with other nodes

– Nodes in passive and test states update the number of active neighbors and Nodes in passive and test states update the number of active neighbors and

data loss ratesdata loss rates

– In passive states, the nodes still consume energy since the radio is on In passive states, the nodes still consume energy since the radio is on

– The nodes in sleep state turns the radio off, sets up timer Ts and goes to The nodes in sleep state turns the radio off, sets up timer Ts and goes to

sleepsleep

– When Ts expires, the nodes moves into passive stateWhen Ts expires, the nodes moves into passive state

– A node in the active state continuous to forward data and routing packets A node in the active state continuous to forward data and routing packets

until it runs out of energyuntil it runs out of energy


[Cerpa+ 2002]

ASCENT Parameters TuningASCENT Parameters Tuning

– ASCENT has many parameters and the choices are left to the applications ASCENT has many parameters and the choices are left to the applications

such as a particular application may trade energy savings for greater sensing such as a particular application may trade energy savings for greater sensing

coveragecoverage

Neighbor Threshold (NT):Neighbor Threshold (NT):

Determines the average connectivity if the networkDetermines the average connectivity if the network

Tradeoff between energy consumed and/or level of interference (packet Tradeoff between energy consumed and/or level of interference (packet

loss) vs. desired sensing coverageloss) vs. desired sensing coverage

Loss Threshold (LT):Loss Threshold (LT):

Determines the maximum amount of data loss an application can tolerate Determines the maximum amount of data loss an application can tolerate

before requesting help to improve network connectivitybefore requesting help to improve network connectivity

This value is highly application dependentThis value is highly application dependent


[Cerpa+ 2002]

ASCENT Parameters TuningASCENT Parameters Tuning

Test timer (Tt), Passive timer (Tp), Sleep timer (Ts):Test timer (Tt), Passive timer (Tp), Sleep timer (Ts):

Determines the maximum time a node remains in test, passive, sleep statesDetermines the maximum time a node remains in test, passive, sleep states

Tradeoff between power consumption vs. decision qualityTradeoff between power consumption vs. decision quality


[Cerpa+ 2002]

– SPANSPAN is a power is a power saving technique for multi-hop ad hoc networks that saving technique for multi-hop ad hoc networks that

reduces energy consumption with the consideration of maintaining the reduces energy consumption with the consideration of maintaining the

capacity or connectivity of the networkcapacity or connectivity of the network

– It is distributed and randomized algorithm in which the nodes make It is distributed and randomized algorithm in which the nodes make

local decisions on whether to sleep or join to the backbonelocal decisions on whether to sleep or join to the backbone

– Each node decides based on an estimate of how many neighbors will Each node decides based on an estimate of how many neighbors will

benefit from it being awake and the energy available to itbenefit from it being awake and the energy available to it

– Improvement in the system lifetime increases along with the ratio of Improvement in the system lifetime increases along with the ratio of

idle-to-sleep energy consumptionsidle-to-sleep energy consumptions

– Non-coordinators remain in power saving mode and periodically check Non-coordinators remain in power saving mode and periodically check

to see if they should wake up and become coordinatorsto see if they should wake up and become coordinators

SPAN: An Energy-Efficient Coordination Algorithm for Topology Maintenance in Ad hoc Wireless Networks[Chen+ 2002]

– A good power saving technique for ad hoc networks should have the following:A good power saving technique for ad hoc networks should have the following:

1.1. Allow as many as nodes to turn their radios off most of the timeAllow as many as nodes to turn their radios off most of the time

2.2. Forward packets between any source and destination with the minimum Forward packets between any source and destination with the minimum

possible delay than if all nodes were awakepossible delay than if all nodes were awake

3.3. Distributed algorithm where having each node making local decisionsDistributed algorithm where having each node making local decisions

4.4. Backbone formed by the awake nodes should provide close to total capacity as Backbone formed by the awake nodes should provide close to total capacity as

the original networks such that congestion can be avoidedthe original networks such that congestion can be avoided

5.5. Do not make many assumptions about the link layer’s facilities for sleeping and Do not make many assumptions about the link layer’s facilities for sleeping and

work with any link layer that provides sleeping and periodic pollingwork with any link layer that provides sleeping and periodic polling

6.6. Inter-operate correctly with any routing algorithm being usedInter-operate correctly with any routing algorithm being used

– SPAN fulfills all the above requirementsSPAN fulfills all the above requirements

– Each node makes periodic local decisions to sleep or stay awake as a Each node makes periodic local decisions to sleep or stay awake as a coordinatorcoordinator

and participate in the forwarding backbone topologyand participate in the forwarding backbone topology

SPAN

– In order to keep the same level of capacity of the original network, a node may In order to keep the same level of capacity of the original network, a node may

volunteer to become a coordinator if it figures out from the local information volunteer to become a coordinator if it figures out from the local information

gathering that two of its neighbors cannot communicate directly or through one or gathering that two of its neighbors cannot communicate directly or through one or

two existing coordinatorstwo existing coordinators

– In order to keep the number of coordinators low and rotate this role amongst all In order to keep the number of coordinators low and rotate this role amongst all

nodes, each node delays sending message about its desire to become a nodes, each node delays sending message about its desire to become a

coordinator by a random time intervalcoordinator by a random time interval

– The decision is based on two factors:The decision is based on two factors:

1.1. the remaining battery energythe remaining battery energy

2.2. the number of pairs of neighbors it can connect togetherthe number of pairs of neighbors it can connect together

– This allows SPAN to maintain capacity-preserving backbone at any time with the This allows SPAN to maintain capacity-preserving backbone at any time with the

nodes consuming about the same level of energynodes consuming about the same level of energy

– SPAN also scales well with the number of nodesSPAN also scales well with the number of nodes

SPAN

SPAN DesignSPAN Design

– The goals of SPAN includes:The goals of SPAN includes:

1.1. Ensures enough coordinators to be elected such that each node is in radio Ensures enough coordinators to be elected such that each node is in radio

range of at least one coordinatorrange of at least one coordinator

2.2. Rotates coordinators to ensure that all nodes provides equal support to Rotates coordinators to ensure that all nodes provides equal support to

achieve global connectivityachieve global connectivity

3.3. Increases the network lifetime, preserves the capacity with minimum latency by Increases the network lifetime, preserves the capacity with minimum latency by

minimizing the number of elected coordinatorsminimizing the number of elected coordinators

4.4. Coordinators are elected based on local available informationCoordinators are elected based on local available information

– SPAN is proactive such that each node periodically broadcasts HELLO messages SPAN is proactive such that each node periodically broadcasts HELLO messages

which contains the node’s status (coordinator or not), its current coordinators, and which contains the node’s status (coordinator or not), its current coordinators, and

its current neighborsits current neighbors

– From these HELLO messages, each node keeps tracks of a list of the node’s From these HELLO messages, each node keeps tracks of a list of the node’s

neighbors and coordinators, and for each neighbor, a list of its neighbors and neighbors and coordinators, and for each neighbor, a list of its neighbors and

coordinatorscoordinators

SPAN

Coordinator AnnouncementCoordinator Announcement

– Each non-coordinator node periodically determines whether it should become a Each non-coordinator node periodically determines whether it should become a

coordinator or notcoordinator or not

– The coordinator eligibility rules ensures that the network is covered with sufficient The coordinator eligibility rules ensures that the network is covered with sufficient

number of coordinatorsnumber of coordinators

Coordinator Eligibility RuleCoordinator Eligibility Rule

A non-coordinator node should become a coordinator if it figures out from the local A non-coordinator node should become a coordinator if it figures out from the local

information gathering that two of its neighbors cannot communicate directly or throughinformation gathering that two of its neighbors cannot communicate directly or through

one or two existing coordinatorsone or two existing coordinators

– If many nodes are willing to become coordinators, SPAN solves this contention by If many nodes are willing to become coordinators, SPAN solves this contention by

delaying coordinator announcement with a randomized backoff delaydelaying coordinator announcement with a randomized backoff delay

– Each node selects a delay value and delays sending HELLO message indicating Each node selects a delay value and delays sending HELLO message indicating

the desire to become coordinator for that amount of timethe desire to become coordinator for that amount of time

– At the end of the delay, the node reevaluates its eligibility based on the HELLO At the end of the delay, the node reevaluates its eligibility based on the HELLO

messages received from neighbors and if it is still eligible, it makes announcementmessages received from neighbors and if it is still eligible, it makes announcement

SPAN


– At the end of the delay, the node reevaluates its eligibility based on the HELLO At the end of the delay, the node reevaluates its eligibility based on the HELLO

messages received from neighbors and if it is still eligible, it makes announcementmessages received from neighbors and if it is still eligible, it makes announcement

– Consider a case where all the nodes have the same level of energy which means Consider a case where all the nodes have the same level of energy which means

that only topology is considered in the decision of becoming a coordinatorthat only topology is considered in the decision of becoming a coordinator

– Consider a case where the nodes have unequal energy leftConsider a case where the nodes have unequal energy left

EErr = energy remaining at node = energy remaining at node NNii = number of neighbors for node i = number of neighbors for node i

EEmm = maximum amount of energy = maximum amount of energy T = round-trip delay for packetT = round-trip delay for packet

CCii = number of new connections through node i = number of new connections through node i R = random number in [0, 1]R = random number in [0, 1]

Eq. 2

Eq. 1

SPAN


– In Eq. 1, if nodes with high CIn Eq. 1, if nodes with high C ii become coordinators, total number of coordinators become coordinators, total number of coordinators

needed would be less to ensure that every node in the network is coveredneeded would be less to ensure that every node in the network is covered

– Therefore, the nodes with a high CTherefore, the nodes with a high C ii values should volunteer for coordinator position values should volunteer for coordinator position

quicker than those with smaller Cquicker than those with smaller C ii

– In Eq. 2, the node with large value of (EIn Eq. 2, the node with large value of (Err/E/Emm) is expected to volunteer quicker to ) is expected to volunteer quicker to

become a coordinator than the nodes with smaller ratio in order to assure the become a coordinator than the nodes with smaller ratio in order to assure the

fairnessfairness

SPAN

Coordinator WithdrawalCoordinator Withdrawal

– Each node periodically checks whether it should withdraw as a coordinator Each node periodically checks whether it should withdraw as a coordinator

– A node withdraws if all of its neighbors can reach each other directly or with one or A node withdraws if all of its neighbors can reach each other directly or with one or

more coordinatorsmore coordinators

– For fairness, after some period of time, a coordinator withdraws and declares itself For fairness, after some period of time, a coordinator withdraws and declares itself

as a tentative coordinator if all neighbors can reach each other via other neighbors, as a tentative coordinator if all neighbors can reach each other via other neighbors,

even if these are not coordinators (allows neighbors to act as coordinators)even if these are not coordinators (allows neighbors to act as coordinators)

– A tentative coordinator is still used to forward packets and described coordinator A tentative coordinator is still used to forward packets and described coordinator

announcement algorithm treats tentative coordinators as non-coordinator nodesannouncement algorithm treats tentative coordinators as non-coordinator nodes

– A coordinator nodes gives its neighbors the opportunity to become coordinators by A coordinator nodes gives its neighbors the opportunity to become coordinators by

declaring itself as tentative coordinatordeclaring itself as tentative coordinator

– A coordinator maintains its position as tentative for WA coordinator maintains its position as tentative for WTT time, where W time, where WTT is the is the

maximum value of Eq. 2 which is maximum value of Eq. 2 which is

WWTT = 3 x N = 3 x Nii x T x T

SPAN

Coordinator WithdrawalCoordinator Withdrawal

– If the coordinator has not withdrawn within WIf the coordinator has not withdrawn within WTT time period, it clears its tentative bit time period, it clears its tentative bit

– In order to prevent node to drain its battery completely, the amount time a node acts In order to prevent node to drain its battery completely, the amount time a node acts

as a coordinator before turning on its tentative bit is proportional to the amount of as a coordinator before turning on its tentative bit is proportional to the amount of

energy it has, indicated as (Eenergy it has, indicated as (Err/E/Emm) )

SPAN

Simulation Results

SPAN

– Topology Control Topology Control

o Does not describe a new topologyDoes not describe a new topology

o Provides a mechanism to build certain topologyProvides a mechanism to build certain topology

– DistributedDistributed

o No central control or central source of informationNo central control or central source of information

– Asymmetric LinksAsymmetric Links

o Due to the presence of heterogeneous devicesDue to the presence of heterogeneous devices

Distributed Topology Control in Wireless Sensor Networks with Asymmetric Links

[Liu+ 2003]

Objective

– Reachability between any two nodes is guaranteed to be like initial Reachability between any two nodes is guaranteed to be like initial

topologytopology

– Nodal power consumption is minimizedNodal power consumption is minimized


[Liu+ 2003]

Model

– Network of heterogeneous sensors (called nodes)Network of heterogeneous sensors (called nodes)

– Nodes deployed in a two dimensional planeNodes deployed in a two dimensional plane

– Each node equipped with omni-directional antenna with adjustable Each node equipped with omni-directional antenna with adjustable

transmission powertransmission power

– Nodes have different maximum powerNodes have different maximum power

o PPii = Transmission Power of Node i = Transmission Power of Node i

o PPiimaxmax = Maximum Transmission Power of Node i = Maximum Transmission Power of Node i

o PPijij = Transmission Power required for node i to reach j = Transmission Power required for node i to reach j

o LLijij = Asymmetric link from i to j = Asymmetric link from i to j

o G = (V, L) : directed graph of topology with max powerG = (V, L) : directed graph of topology with max power

o G is strongly connectedG is strongly connected


[Liu+ 2003]

Algorithm

– Fully distributed with no synchronization requiredFully distributed with no synchronization required

– Takes G as input and produces G’ where G’ has:Takes G as input and produces G’ where G’ has:

o Same bi-directional reachabilitySame bi-directional reachability

o Consumes minimum powerConsumes minimum power

– PhasesPhases

o Establishing the vicinity topologyEstablishing the vicinity topology

o Deriving the minimum power vicinity treeDeriving the minimum power vicinity tree

o Propagation of transmission powersPropagation of transmission powers

o OptimizationsOptimizations


[Liu+ 2003]

Establishing the vicinity topology

– Node i broadcasts initialization request (IRQ) with PNode i broadcasts initialization request (IRQ) with P iimaxmax

– VVii is the set of nodes that receive the message {i.e. location is the set of nodes that receive the message {i.e. location ii, P, Piimaxmax}}

– Each node j in VEach node j in Vii sends initialization reply (IRP) message {i.e. location sends initialization reply (IRP) message {i.e. location jj, P, Pjjmaxmax}}

o If PIf Pjjmax max > P > Pij , ij , j can reach I with single hop Lj can reach I with single hop L jiji

o Otherwise find a multi-hop path to reach iOtherwise find a multi-hop path to reach i

– Given the knowledge of location and max power of itself and all vicinity Given the knowledge of location and max power of itself and all vicinity

nodes, node i can determine the vicinity edgesnodes, node i can determine the vicinity edges

– Node i establishes a vicinity topology , GNode i establishes a vicinity topology , Gii =(V =(Vii, E, Eii))


[Liu+ 2003]

Deriving Minimum Power Vicinity Tree

– Derive Minimum power path in GDerive Minimum power path in Gii, to reach from a node i to node j using , to reach from a node i to node j using

Dijkstra or Bellman-Ford algortihms based on sum of power consumption on Dijkstra or Bellman-Ford algortihms based on sum of power consumption on

that path.that path.

– Compute it for each node in VCompute it for each node in Vii to obtain minimum-power vicinity tree, to obtain minimum-power vicinity tree,

GGisis = (V = (Vii, E, Eisis))


[Liu+ 2003]


[Liu+ 2003]

Propagation of transmission powers

– Node i computes minimum power requirement for itself and others nodes in VNode i computes minimum power requirement for itself and others nodes in V ii

– Node i sends a power request (PR) message to each node in VNode i sends a power request (PR) message to each node in V ii, describing the , describing the

minimum power required for that node to reach farthest hopminimum power required for that node to reach farthest hop

– A node j in VA node j in Vii, receiving the PR message increases its power requirement if the , receiving the PR message increases its power requirement if the

requested power in PR is greater than current onerequested power in PR is greater than current one

– Otherwise, it discards the PR messageOtherwise, it discards the PR message

Optimizations

– Achieved via discarding PR messages whenAchieved via discarding PR messages when

o A node already has run the algorithm to find its shortest vicinity treeA node already has run the algorithm to find its shortest vicinity tree

o A node receives a PR message for a node in its vicinityA node receives a PR message for a node in its vicinity

– Example: A asks B for PExample: A asks B for PBCBC while B already has P while B already has PBD BD to reach node Cto reach node C


[Liu+ 2003]

Figure 1: A scenario of further optimized nodal transmission rangeFigure 1: A scenario of further optimized nodal transmission range

Advantages:

– Guarantees same bi-directional interconnection while reducing per node Guarantees same bi-directional interconnection while reducing per node

power consumptionpower consumption

– Distributed algorithm:Distributed algorithm:

o No synchronization requiredNo synchronization required

o No central control node with network informationNo central control node with network information

o Easy to add/remove nodes from the networkEasy to add/remove nodes from the network

– Uses existing well known algorithms to obtain minimum power consumptionUses existing well known algorithms to obtain minimum power consumption

– Works on network with asymmetric links, which seem more realisticWorks on network with asymmetric links, which seem more realistic

– Assumption of asymmetric links, makes it possible to obtain minimum power Assumption of asymmetric links, makes it possible to obtain minimum power

path via multi-hop rather than using a single hop high power linkpath via multi-hop rather than using a single hop high power link


[Liu+ 2003]

Disadvantages:

– Computationally expensive to be run on network with mobile sensorsComputationally expensive to be run on network with mobile sensors

– Overhead of sending IRQ, IRP and RP in a large network of sensorsOverhead of sending IRQ, IRP and RP in a large network of sensors

– Time to converge for the algorithm is largeTime to converge for the algorithm is large


– More details on how multi-hop paths will be discoveredMore details on how multi-hop paths will be discovered

– Detailed example covering more complex scenariosDetailed example covering more complex scenarios


[Liu+ 2003]

– The primary design constraints of the sensor network algorithms and The primary design constraints of the sensor network algorithms and

protocols are: protocols are: energy-efficiencyenergy-efficiency, , scalabilityscalability and and localizationlocalization

– The improved energy efficiency can be achieved by designing protocols The improved energy efficiency can be achieved by designing protocols

and algorithms with and algorithms with cross-layer approachcross-layer approach, i.e., considering interactions , i.e., considering interactions

between different layers of the communication process such that overall between different layers of the communication process such that overall

energy consumption is minimizedenergy consumption is minimized

– A A scalablescalable algorithm algorithm performs well in a large network

– The scalability for an algorithm is related to that of localization: in a scalable algorithm each node exchanges information only with its neighbors (localized information exchange) in a very large wireless network

Optimal Local Topology for Energy Efficient Geographical Routing in Sensor Networks

[Melodia+ 2004]

– This paper considers the interaction between topology control and This paper considers the interaction between topology control and

energy efficient geographical routingenergy efficient geographical routing

– The question to answer is: The question to answer is: ““How extensive should be the Local Knowledge of the global topology in each sensor node, so that an energy efficient geographical routing can be guaranteed?”

– This question is related to the degree of localization of the routing scheme

– If each sensor node have the complete knowledge of the topology, it could compute the “global” optimal next hop to minimize the energy consumption

– However, the knowledge of complete topology information has an associated cost, i.e., energy used to exchange the signaling traffic


[Melodia+ 2004]

– An analytical framework is developed to capture the tradeoff between the topology information cost, which increases with the Knowledge Range of each node, and the communication cost, which decreases when the knowledge becomes more complete

– This analytical framework is then applied to different position based forwarding schemes and demonstrated by using Monte Carlo simulations that a limited knowledge is sufficient to make energy efficient routing decisions

– A “neighbor” for a certain sensor node is another node which falls into its topology Knowledge Range, denoted as KR


[Melodia+ 2004]

– The contributions of this work are:

o Introduction of a novel analytical framework to evaluate the energy consumption of geographical routing algorithms for sensor networks

o Integer Linear Programming (ILP) formulation of the topology Knowledge Range optimization problem

o Detailed comparison of the leading existing forwarding schemes [Takagi+ 1984, Hou+ , Finn 1987, Kranakis+ 1999, Nelson+ 1984] and introduced a new scheme called Partial Topology Knowledge Forwarding (PTKF)

o Introduction of PRobe-bAsed Distributed protocol for knowledge rAnge adjustment (PRADA) for the on-line solution of the problem that allows nodes to select near-optimal Knowledge Ranges in a distributed way


[Melodia+ 2004]

Advantages:

– No need for knowing the global topology of the networkNo need for knowing the global topology of the network

– PRADA can be run independently in the nodes, thus the nodes do not PRADA can be run independently in the nodes, thus the nodes do not

require time synchronizationrequire time synchronization

– Demonstrates a limited amount of topology knowledge is sufficient in Demonstrates a limited amount of topology knowledge is sufficient in

order for energy conserving routing protocols to be implementedorder for energy conserving routing protocols to be implemented

– The nodes periodically update their knowledge range, thus the The nodes periodically update their knowledge range, thus the

algorithm could be implemented in sensor networks where the nodes algorithm could be implemented in sensor networks where the nodes

are mobileare mobile

– Draws a fine line between topology information cost and communication Draws a fine line between topology information cost and communication

costcost


[Melodia+ 2004]

Disadvantages:

– No mentioning about the sensitivity towards location error of their No mentioning about the sensitivity towards location error of their

proposed protocolproposed protocol

– For a pair of source-destination path, the most optimal path is always For a pair of source-destination path, the most optimal path is always

chosen; however, this would lead to a starvation of some of the nodes chosen; however, this would lead to a starvation of some of the nodes

that would not get any trafficthat would not get any traffic

– The performance evaluation of protocol does not consider the lower The performance evaluation of protocol does not consider the lower

layers, such as MAClayers, such as MAC


[Melodia+ 2004]


– Extending the optimization objectives to include not only power but also Extending the optimization objectives to include not only power but also

battery level of each node (thus improving network lifetime)battery level of each node (thus improving network lifetime)

– Implementing the proposed routing protocol within a simulator which Implementing the proposed routing protocol within a simulator which

considers routing and MAC layer together to draw a more convincible considers routing and MAC layer together to draw a more convincible

conclusionconclusion


[Melodia+ 2004]

[Basagni+ 2001] S. Basagni, D. Turgut, and S.K. Das, Mobility-Adaptive Protocols for Managing Large Ad hoc Networks, Proceedings of IEEE International Conference on Communications (ICC), Helsinki, Finland, June 11-14, 2001, pp. 1539-1543.

[Chen+ 2002] B. Chen, K. Jamieson, R. Morris, and H. Balakrishnan, SPAN: An Energy-Efficient Coordination Algorithm for Maintenance in Ad hoc Wireless Networks, To appear in ACM Wireless Networks Journal, Vol. 8, No. 5, September 2002.

[Cerpa+ 2002] A. Cerpa and D. Estrin, ASCENT: Adaptive Self-Configuring Sensor Networks Topologies, Proceedings of the Twenty First International Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2002), New York, NY, USA, June 23-27 2002.

[Finn 1987] G.G. Finn, Routing and Addressing Problems in Large Metropolitan-Scale Internetworks, ISI res. rep ISU/RR- 87-180, Mar. 1987.

[Hou+ ] T.C. Hou and V.O.K. Li, Transmission Range Control in multihop packet radio networks, IEEE Transactions on Communications, Vol. 34, No.1, pp. 38-44.

[Kranakis+ 1999] E. Kranakis, H. Singh, and J. Urrutia, Compass routing on geometric networks, Proceedings of the 11th Canadian Conference on Computational Geometry, Vancouver, Canada, August 1999.

[Liu+ 2003] J. Liu and B. Li, Distributed Topology Control in Wireless Sensor Networks with Asymmetric Links, GLOBECOM 2003.

References

[Melodia+ 2004] T. Melodia, D. Pompili, and I.F. Akyildiz, Optimal Topology Knowledge for Energy Efficient Geographical Routing in Sensor Networks, Proceedings of the Twenty First International Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2004), Hong Kong, P.R., China, March 2004.

[Nelson+ 1984] R. Nelson and L. Kleinrock, The spatial capacity of a slotted ALOHA multihop packet radio network with capture, IEEE Transactions on Communications, Vol. 32, No.6, pp. 684-694, 1984.

[Takagi+ 1984] H. Takagi and L. Kleinrock, Optimal Transmission Ranges for Randomly Distributed Packet Radio Terminals, IEEE Transactions on Communications, Vol. 32, No.3, pp. 246-57, 1984.

[Schurgers+ 2002] C. Schurgers, V. Tsiatsis, S. Ganeriwal, and M.B, Srivastava, Optimizing Sensor Networks in the Energy-Latency-Density Design Space, IEEE Transactions on Mobile Computing, Vol. 1, No.1, pp. 70-80, January-March 2002.

References

topology management ad hoc and sensor networks

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