Schedule Based MAC Protocol

SCHEDULE BASED MAC
PROTOCOLS
Darwin Nesakumar A, M.E, (P.hD)
Assistant Professor
Department of ECE
R.M.K. Engineering College

Agenda
• Review of previous session
• Scheduled based protocols in WSN
• LEACH
• SPIN
• S-MACS
• TRAMA
• Quizzes
2Schedule based protocolsFriday, 28August 2020

Review of previous session
• Joinmyquiz.com

Question
MAC stands for
Schedule based protocols 4Friday, 28August 2020

Answer for the Question
Medium Access Control

Question
MAC is the part of which layer?
Physical Layer
Data Link Layer
Application Layer

Data Link Layer

Question
There are trade offs between energy expenditure and
__________ , throughput
Delay
Data
Distance

Delay

Question
What is the energy saving approach?

Switch the transceiver into sleep mode

Question
What is the main issue in MAC Protocol?

Energy Conservation

Question
Energy waste due to

Overhead
Overhearing
Collisions
Idle listening

Question
What are the two responsibilities of Data link Layer

Error Control
Flow Control

Question
What are the two types of MAC Protocols?

Contention based
Schedule based

Question
LLC stands for

Logical Link Control layer

Question
Provides a fraction of the frequency range to each
user for all the time
TDMA
CDMA
FDMA

FDMA

Question
Provides every user a portion of bandwidth for a
fraction of time
TDMA
CDMA
FDMA

CDMA

Question
MAC allows multiple users to share a ________ channel
Common
Single

Common

Question
What are the types of MAC protocols

Fixed assignment protocols
Demand assignment protocols
Random access protocols

Question
What are the methods to spread the bandwidth

Direct Sequence (DS)
Frequency Hoping (FH)

Question
Random access protocols are
Partially distributed
Fully distributed
No distributed

Fully distributed

Question
If the central node is bleached, the protocol is called
BLEACH
LEACH
COACH

LEACH

IMPORTANT POINTS TO BE REMEMBER
MAC Protocols
• MAC – Medium Access Control
• They coordinate the times where a
number of nodes access a shared
communication medium.
• Main requirement – Energy efficiency
• Energy waste due to – Overhead,
Overhearing, Collisions and idle
listening
• Switch the transceiver into Sleep
Mode – Energy saving approach
• There are trade offs between energy
expenditure and delay, throughput
• MAC is first protocol above the Physical
layer (PHY)
• Fundamental task is to regulate the
access of number of nodes to a shared
medium
• Few traditional criteria are delay,
throughput, fairness
• Energy conservation is an issue in MAC
• MAC is apart of Data Link Layer (DLL) –
OSI reference model
• MAC protocol determines for a node the
points in time when it accesses the
medium to try to transmit a data,
control, or management packet to
another node (unicast) or to a set of
nodes (multicast, broadcast). 36Schedule based protocolsFriday, 28August 2020

IMPORTANT POINTS TO BE REMEMBER
MAC Protocols
• MAC is a part of Data Link Layer (DLL)
• DLL Responsibilities are
• Error Control – used to ensure
correctness of transmission and to
take appropriate actions in case of
transmission errors
• Flow control - regulates the rate of
transmission to protect a slow receiver
from being overwhelmed with data
• Main approach to conserve energy –
Put nodes in sleep state whenever
possible
• Low duty cycle, Wake up concepts
• Two types of MAC Protocols are
Contention based and schedule
based
• Contention based – It is a
communication protocol for
operating wireless
telecommunication equipment that
allows many users to use same radio
channel without pre coordination
• Schedule based - A schedule exists,
regulating which participant may use
which resource at which time

Schedule- vs. contention-based MACs
• Schedule-based MAC
– A schedule exists, regulating which participant may use which resource
at which time (TDMA component)
– Typical resource: frequency band in a given physical space (with a given
code, CDMA)
– Schedule can be fixed or computed on demand
• Usually: mixed – difference fixed/on demand is one of time scales
– Usually, collisions, overhearing, idle listening no issues
– Needed: time synchronization!
• Contention-based protocols
– Risk of colliding packets is deliberately taken
– Hope: coordination overhead can be saved, resulting in overall improved
efficiency
– Mechanisms to handle/reduce probability/impact of collisions required
– Usually, randomization used somehow

Question
What is needed in schedule based MACs
Frequency Synchronization
Time Synchronization
Code Synchronization

Question
Risk of packet collisions occur in
Schedule based MACs
Contention based MACs

Schedule based protocols
A B C D
Distributed, contention-based MAC
• Basic ideas for a distributed MAC
– ALOHA – no good in most cases
– Listen before talk (Carrier Sense Multiple Access, CSMA) – better, but suffers
from sender not knowing what is going on at receiver, might destroy packets
despite first listening for a hidden terminal scenario
43Friday, 28August 2020

Receiver informs interferers before transmission
• Sender B asks receiver C
whether C is able to receive a
transmission
Request to Send (RTS)
• Receiver C agrees, sends out a
Clear to Send (CTS)
• Potential interferers overhear
either RTS / CTS and know
about impending transmission
and for how long it will last
• Store this information in a Network
Allocation Vector
• B sends, C acks
• MACA protocol (used e.g. in IEEE 802.11)
A B C D
RTS
CTS
Data
Ack
NAV indicates
busy medium
NAV indicates
busy medium

Main options to shut up senders
• Receiver informs potential interferers while a reception is on-going
– By sending out a signal indication
– Problem: Cannot use same channel on which actual reception takes
place
! Use separate channel for signaling
– Busy tone protocol
• Receiver informs potential interferers before a reception is on-going
– Can use same channel
– Receiver itself needs to be informed, by sender, about impending
transmission
– Potential interferers need to be aware of such information, need to
store it

Question
The two options to shut up senders are to inform
potential interferers while a reception is on-going
and before a reception is on-going
TRUE
FALSE

TRUE

RTS/CTS
• RTS/CTS ameliorate, but do not solve hidden/exposed terminal problems
• Example problem cases:
A B C D
RTS
CTS
Data
A B C D
RTS
RTS
CTS
RTS
RTS
CTS
CTSData
Data
Ack

Schedule-based MAC Protocols

Requirements for energy-efficient MAC
protocols
• Recall
– Transmissions are costly
– Receiving about as expensive as transmitting
– Idling can be cheaper but is still expensive
• Energy problems
– Collisions – wasted effort when two packets collide
– Overhearing – waste effort in receiving a packet destined for
another node
– Idle listening – sitting idly and trying to receive when nobody is
sending
– Protocol overhead
• Always nice: Low complexity solution

Schedule-based protocols
 Schedule-based protocols that do not explicitly address idle listening
avoidance but do so implicitly.
 For example, by employing TDMA schemes, which explicitly assign
transmission and reception opportunities to nodes and let them sleep
at all other times.
 A second fundamental advantage of schedule-based protocols is that
transmission schedules can be computed such that no collisions occur
at receivers and hence no special mechanisms are needed to avoid
hidden-terminal situations.

However, these schemes also have downsides.
 First, the setup and maintenance of schedules involves signaling
traffic.
 Second, if a TDMA variant is employed, time is divided into
comparably small slots
 A third drawback is that such schedules are not easily adapted to
different load situations on small timescales.
 A further disadvantage is that the schedule of a node (and possibly
those of its neighbors) may require a significant amount of memory,
which is a scarce resource in several sensor node designs.

Low-Energy Adaptive Clustering
Hierarchy (LEACH)
• Given: Dense network of nodes, reporting to a central sink, each node can
reach sink directly
• Idea: Group nodes into “clusters”, controlled by clusterhead
– About 5% of nodes become clusterhead (depends on scenario)
– Role of clusterhead is rotated to share the burden
– Clusterheads advertise themselves, ordinary nodes join CH with
strongest signal
– Clusterheads organize
• CDMA code for all member transmissions
• TDMA schedule to be used within a cluster
• In steady state operation
– CHs collect & aggregate data from all cluster members
– Report aggregated data to sink using CDMA

Question
Clusterhead uses FDMA
TRUE
FALSE

FALSE

Question
Role of clusterhead is _____________ to share
the burden
Distributed
Rotated
Converged

Rotated

Question
What is the percentage of nodes to become
clusterhead?

5%

• Set-up phase
• Cluster heads assign a TDMA schedule for their members where
each node is assigned a time slot when it can transmit.
• Each cluster communications using different CDMA codes to
reduce interference from nodes belonging to other clusters.
• TDMA intra-cluster
• CDMA inter-cluster
• Spreading codes determined randomly
• Broadcast during advertisement phase
• In steady state operation
– CHs collect & aggregate data from all cluster members
– Report aggregated data to sink using CDMA

LEACH rounds
Setup phase Steady-state phase
Fixed-length round
……….. ………..
Advertisement phase Cluster setup phase Broadcast schedule
Time slot
1
Time slot
2
Time slot
n
Time slot
1
…..….. …..
Clusterheads
compete with
CSMA
Members
compete
with CSMA
Self-election of
clusterheads

Question
Inter cluster uses
TDMA
CDMA

CDMA

Question
Which transmission is used in advertisement phase?
Unicast
Multicast
Broadcast

Broadcast

Question
TDMA is being used for
Intra Cluster
Inter Cluster

Intra Cluster

The LEACH protocol (Low-energy
Adaptive Clustering Hierarchy)
 The LEACH protocol (Low-energy Adaptive Clustering Hierarchy)
assumes a dense sensor network of homogeneous, energy-
constrained nodes, which shall report their data to a sink node.
 The reason we need network protocol such as LEACH is due to the
fact that a node in the network is no longer useful when its battery
dies
 This protocol allows us to space out the lifespan of the nodes,
allowing it to do only the minimum work it needs to transmit data

Question
LEACH stands for

Low-energy Adaptive Clustering Hierarchy

 In LEACH, a TDMA-based MAC protocol is integrated with
clustering and a simple “routing” protocol.
 LEACH partitions the nodes into clusters and in each cluster a
dedicated node,
 the cluster head, is responsible for creating and maintaining a
TDMA schedule; all the other nodes of a cluster are member
nodes.

• To all member nodes, TDMA slots are assigned, which can be
used to exchange data between the member and the
clusterhead.
• There is no peer-to-peer communication.
• With the exception of their time slots, the members can spend
their time in sleep state.
• The clusterhead aggregates the data of its members and
transmits it to the sink node or to other nodes for further
relaying.
• Since the sink is often far away, the clusterhead must spend
significant energy for this transmission.
• For a member, it is typically much cheaper to reach the
clusterhead than to transmit directly to the sink

 The protocol is organized in rounds and each round is
subdivided into a
 The Set-Up Phase
Where cluster-heads are chosen
 The Steady-State phase
The cluster-head is maintained
When data is transmitted between nodes
The LEACH protocol (Low-energy Adaptive
Clustering Hierarchy)

• Advantages
• Increases the lifetime of the network
• Even drain of energy
• Distributed, no global knowledge required
• Energy saving due to aggregation by CHs
• Disadvantages
• LEACH assumes all nodes can transmit with enough power to reach BS if
necessary (e.g., elected as CHs)
• Each node should support both TDMA & CDMA
• Need to do time synchronization
• Nodes use single-hop communication
• LEACH would not be able to cover large geographical areas of some
square miles or more, because a clusterhead two miles away from the
sink likely does not have enough energy to reach the sink at all,

• Sensor Protocols for Information via Negotiation (SPIN)
• A Negotiation-Based Protocols for Disseminating Information in
Wireless Sensor Networks.
• Dissemination is the process of distributing individual sensor
observations to the whole network, treating all sensors as sink
nodes
• Replicate complete view of the environment
• Enhance fault tolerance
• Broadcast critical piece of information
SPIN -Sensor Protocols for Information
via Negotiation

• Flooding is the classic approach for dissemination
• Source node sends data to all neighbors
• Receiving node stores and sends data to all its neighbors
• Disseminate data quickly
• Deficiencies
• Implosion
• Overlap
• Resource blindness
SPIN

• Negotiation
• Before transmitting data, nodes negotiate with each other to
overcome implosion and overlap
• Only useful information will be transferred
• Observed data must be described by meta-data
• Resource adaptation
• Each sensor node has resource manager
• Applications probe manager before transmitting or processing
data
• Sensors may reduce certain activities when energy is low
SPIN

• SPIN : A three-stage handshake protocol for point-to-point media
• ADV – data advertisement
• Node that has data to share can advertise this by transmitting
an ADV with meta-data attached
• REQ – request for data
• Node sends a request when it wishes to receive some actual
data
• DATA – data message
• Contain actual sensor data with a meta-data header
• Usually much bigger than ADV or REQ messages
SPIN (cont.)

SPIN Protocol

The mediation device protocol
 It is compatible with the peer-to-peer communication mode
 It allows each node to go into sleep mode periodically and to wake up
only for short times
 There is no global time reference, each node has its own sleeping
schedule, and does not take care of its neighbors sleep schedules.

 Upon each periodic wakeup, a node transmits a short query beacon,
indicating its node address and its willingness to accept packets from
other nodes.
 When a node wants to transmit a packet to a neighbor, it has to
synchronize with it.
 The dynamic synchronization approach achieves this synchronization
without requiring the transmitter to be awake permanently to detect the
destinations query beacon.
 To achieve this, a mediation device (MD) is used. We first discuss the
case where the mediation device is not energy constrained and can be
active all the time.
The mediation device protocol

• Because of its full duty cycle, the mediation device can receive the query beacons from
all nodes in its vicinity and learn their wakeup period
Protocol
• Sender A sends RTS to MD
• MD stores this information
• Receiver B sends query to MD
• MD tells reciever B when to
wake up
• B sends CTS to A (now in sync)
• A sends data
• B acknowledges
• B returns to old timing

Advantages
 First, it does not require any time synchronization between
the nodes, only the mediation device has to learn the periods
of the nodes.
 Second, the protocol is asymmetric in the sense that most of
the energy burden is shifted to the mediation device, which
so far is assumed to be power unconstrained.

Disadvantages
 The nodes transmit their query beacons without checking for ongoing
transmissions
 If the wakeup periods are properly randomized and the node density is
sufficiently low, this collision probability can be low too.
 However, in case of higher node densities or unwanted synchronization
between the nodes, the number of collisions can be significant.
 A possible solution to this is the following: When the MD registers
collisions, it might start to emit a dedicated reschedule control frame.

Disadvantages
 All colliding nodes can hear this frame as long as the MD repeats it often
enough.
 Reception of this frame causes each node to randomly pick a new period
from a certain interval [a, b] indicated in the reschedule frame.
 If the MD continues to perceive collisions, it can enlarge the interval
accordingly

Main Drawbacks
The mediation device is energy unconstrained, which does not
conform to the idea of a “simply thrown out” wireless sensor network
There are sufficient mediation devices to cover all nodes. The
distributed mediation device protocol deals with these problems in a
probabilistic manner.

• MACA’s idle listening is particularly unsuitable if average data rate is low
• Most of the time, nothing happens
• Idea: Switch nodes off, ensure that neighboring nodes turn on simultaneously to
allow packet exchange
Sensor-MAC (S-MAC)
• Only in these active periods, packet
exchanges happen
• Need to also exchange wakeup schedule
between neighbors
• When awake, essentially perform RTS/CTS
• Use SYNCH, RTS, CTS phases
Wakeup period
Active period
Sleep period
For SYNCH For RTS For CTS

S-MAC Synchronized islands
• Nodes try to pick up schedule synchronization from neighboring nodes
• If no neighbor found, nodes pick some schedule to start with
• If additional nodes join, some node might learn about two different schedules from
different nodes
– “Synchronized islands”
• To bridge this gap, it has to follow both schemes
Time
A A A A
C C C C
A
B B B B
D D D
A
C
B
D
E E E EE E E

Timeout-MAC (T-MAC)
• In S-MAC, active period is of constant
length
• What if no traffic actually happens?
• Nodes stay awake needlessly long
• Idea: Prematurely go back to sleep mode
when no traffic has happened for a certain
time (=timeout) ! T-MAC
• Adaptive duty cycle!
• One ensuing problem: Early sleeping
• C wants to send to D, but is hindered by
transmission A! B
A B C D
CTS
May not
send
Timeout,
go back to
sleep as
nothing
happened

SMACS
• Given: Many radio channels, superframes of known length (not
necessarily in phase, but still time synchronization required!)
• Goal: Set up directional links between neighboring nodes
– Link: radio channel + time slot at both sender and receiver
– Free of collisions at receiver
– Channel picked randomly, slot is searched greedily until a
collision-free slot is found
• Receivers sleep and only wake up in their assigned time slots, once
per superframe
• In effect: a local construction of a schedule

TRAMA
• Nodes are synchronized
• Time divided into cycles, divided into
– Random access periods
– Scheduled access periods
• Nodes exchange neighborhood information
– Learning about their two-hop neighborhood
– Using neighborhood exchange protocol: In random access
period, send small, incremental neighborhood update
information in randomly selected time slots
• Nodes exchange schedules
– Using schedule exchange protocol
– Similar to neighborhood exchange

TRAMA – possible conflicts
• When does a node have to receive?
– Easy case: one-hop neighbor has won a time slot and announced a packet
for it
– But complications exist – compare example
C
A
B
D
Prio 100 Prio 95 Prio 79 Prio 200
 What does B believe?
 A thinks it can send
 B knows that D has
higher priority in its 2-
hop neighborhood!
 Rules for resolving such
conflicts are part of
TRAMA

Comparison : TRAMA, S-MAC
• Comparison between TRAMA & S-MAC
– Energy savings in TRAMA depend on load situation
– Energy savings in S-MAC depend on duty cycle
– TRAMA (as typical for a TDMA scheme) has higher delay but
higher maximum throughput than contention-based S-MAC
• TRAMA disadvantage: substantial memory/CPU requirements for
schedule computation

• Directed diffusion consists of
– Interest - Query which specifies what a user wants
– Data - Collected information
– Gradient
• Direction and data-rate
• Events start flowing towards the originators of interests
– Reinforcement
• After the sink starts receiving events, it reinforces at least
one neighbor to draw down higher quality events
Directed Diffusion

Contention-based protocols
 If only one neighbor tries its luck, the packet goes through the channel.
 If two or more neighbors try their luck, these have to compete with each other and
in unlucky cases,
for example, due to hidden-terminal situations, a collision might occur, wasting energy
for both transmitter and receiver.
 two important contention based protocols: (slotted) ALOHA and CSMA, along with
mechanisms to solve the hidden-terminal problem.
 In the following sections, we discuss variations of these protocols with the goal to
conserve energy. As opposed to some of the contention-based protocols having a
periodic wakeup scheme
 the protocols described in this section have no idle listening avoidance and make
no restrictions as to when a node can receive a packet. 96Schedule based protocolsFriday, 28August 2020

The PAMAS protocol (Power Aware
Multiaccess with Signaling)
 Originally designed for ad hoc networks.
 It provides a detailed overhearing avoidance mechanism while it does not consider the
idle listening problem.
 The protocol combines the busy-tone solution and RTS/CTS handshake similar to the
MACA protocol
 A distinctive feature of PAMAS is that it uses two channels:
 Data channel (while the data channel is reserved for data packets)
 Control channel. (All the signaling packets (RTS, CTS, busy tones) are transmitted
on the control channel. 97Schedule based protocolsFriday, 28August 2020

• first describing the main protocol operation and then discussing
the power-conservation enhancements
Node X Node y
RTS
CTS
BusyTone
• First, x sends an RTS packet on the control
channel without doing any carrier sensing.
This packet carries both x’s and y’s MAC
addresses
• If y receives this packet, it answers with a
CTS packet if y does not know of any
ongoing transmission in its vicinity.
• Upon receiving the CTS, x starts to
transmit the packet to y on the data
channel. When y starts to receive the data,
it sends out a busy-tone packet on the
control channel.
• If x fails to receive a CTS packet within
some time window, it enters the backoff
mode, where a binary exponential backoff
scheme is used (i.e., the backoff time is
uniformly chosen from a time interval that
is doubled after each failure to receive a
CTS)

Node X Node y
RTS
CTS
BusyTone
 If y knows about an ongoing transmission in
its vicinity, it with a CTS packet and starts to
send out a busy-tone packet as soon as x’s
transmission has started. suppresses its CTS,
causing x to back off.
 Node y can obtain this knowledge by either
sensing the data channel or by checking
whether there was some noise on the control
channel immediately after receiving the RTS.
 This noise can be an RTS or CTS of another
node colliding at y. In the other case, y
answers
 Furthermore, y sends out busy-tone packets
each time it receives some noise or a valid
packet on the control channel, to prevent its
neighborhood from any activities.

When can a node put its transceivers
(control and data) into sleep mode?
Any time a node knows that it cannot transmit or receive packets because some other
node in its vicinity is already doing so.
This decision is easy if a node x knows about the length of an ongoing transmission,
for example from overhearing the RTS or CTS packets or the header of the data packets
on the data channel.
However, often this length is unknown to x, for example, because these packets are
corrupted or a foreign data transmission cycle starts when x is just sleeping.
Additional procedures are needed to resolve this

Suppose that x wakes up and finds the data channel busy.
There are two cases to distinguish:
either x has no own packet to send or x wants to transmit. In the first case, x desires
to go back into sleep mode and to wake up exactly when the ongoing transmission
ends to be able to receive an immediately following packet.
Waking up at the earliest possible time has the advantage of avoiding unwanted
delays.
However, since x may not have overheard the RTS, CTS, or data packet header
belonging to the ongoing transmission, it runs a probing protocol on the control
channel to inquire the length of the ongoing packet.

Demand Assignment Protocols
• Resources are allocated on a short term basis
• Centralized and distributed versions are possible
• Central
– Nodes request a reource (e.g. time slot) from a central server
– Waits for ACK and then transmits
– Polling by central station is possible
– Central server to be switced on always
– Central node requires a lot of energy
– Central node may be rotated (LEACH) 102Schedule based protocolsFriday, 28August 2020

Distributed Demand Assignment
Protocols
• Token passing (IEEE 802.4) may be used
• Token is passed among stations in a logical ring
• Ring management needed
– Include/exclude nodes from the ring
– Correct lost tokens
• In WSNs, maintenance is difficult
– Channel errors
– Node xceiver must be switched on all the time (energy ..) due to variable
token delivery times

Random Access Protocols
• Fully distributed
• ALOHA (more on this later)
• CSMA based
– Listen to the medium
– If idle, xmit
– If busy, wait (p persistent, non-persistent etc.)
• RTS/CTS based on MACAW protocol (more later)

Main options Wireless medium access
Centralized
Distributed
Contention-
based
Schedule-
based
Fixed
assignment
Demand
assignment
Contention-basedSchedule-based
Fixed
assignment
Demand
assignment

Centralized medium access
• Idea: Have a central station control when a node may access the medium
– Example: Polling, centralized computation of TDMA schedules
– Advantage: Simple, quite efficient (e.g., no collisions), burdens the central
station
• Not directly feasible for non-trivial wireless network sizes
• But: Can be quite useful when network is somehow divided into smaller
groups
– Clusters, in each cluster medium access can be controlled centrally –
compare Bluetooth piconets, for example
! Usually, distributed medium access is considered

• STEM
• Sparse topology and energy management
S-MAC
sensor MAC
T-MAC
B-MAC
Low duty cycle & Wakeup concepts

Preamble Sampling
• So far: Periodic sleeping supported by some means to synchronize wake up of nodes
to ensure rendez-vous between sender and receiver
• Alternative option: Don’t try to explicitly synchronize nodes
– Have receiver sleep and only periodically sample the channel
• Use long preambles to ensure that receiver stays awake to catch actual packet
– Example: WiseMAC
Check
channel
Check
channel
Check
channel
Check
channel
Start transmission:
Long preamble Actual packet
Stay awake!

B-MAC
• Combines several of the above discussed ideas
– Takes care to provide practically relevant solutions
• Clear Channel Assessment
– Adapts to noise floor by sampling channel when it is assumed to be free
– Samples are exponentially averaged, result used in gain control
– For actual assessment when sending a packet, look at five channel samples
– channel is free if even a single one of them is significantly below noise
– Optional: random backoff if channel is found busy
• Optional: Immediate link layer acknowledgements for received packets

B-MAC II
• Low Power Listening (= preamble sampling)
– Uses the clear channel assessment techniques to decide whether there is
a packet arriving when node wakes up
– Timeout puts node back to sleep if no packet arrived
• B-MAC does not have
– Synchronization
– RTS/CTS
– Results in simpler, leaner implementation
– Clean and simple interface
• Currently: Often considered as the default WSN MAC protocol

CONTENTION BASED PROTOCOLS

PAMAS - Power Aware Multi access with
Signaling
• Idea: combine busy tone with RTS/CTS
– Results in detailed overhearing avoidance, does not address idle listening
– Uses separate data and control channels
• Procedure
– Node A transmits RTS on control channel, does not sense channel
– Node B receives RTS, sends CTS on control channel if it can receive and does not
know about ongoing transmissions
– B sends busy tone as it starts to receive data
Time
Control
channel
Data
channel
RTS
A ! B
CTS
B ! A
Data
A ! B
Busy tone
sent by B

PAMAS – Already ongoing transmission
• Suppose a node C in vicinity of A is already receiving a packet when A initiates RTS
• Procedure
– A sends RTS to B
– C is sending busy tone (as it receives data)
– CTS and busy tone collide, A receives no CTS, does not send data
A
B
C
?
Time
Control
channel
Data
channel
RTS
A ! B
CTS
B ! A
No data!
Busy tone by C
Similarly:Ongoing
transmission near B destroys
RTS by busy tone

Three categories
• Data-centric
• Hierarchical
• Location based routing
Classification of WSN
routing protocols

Classification of routing protocols

• Natural information gradient
• Gradient is known as fingerprint
f ( d ) = t / d2.
Regions
• Flat region
• Gradient region
RoUting on finGerprint Gradient in sEnsor
networks (RUGGED)

• there could be multiple gradient regions active
• A query may be initiated at any arbitrary node
• If the node is in a flat region,
• It uses flooding to forward the query
• It sets the query mode to flat region mode
• The query doesn’t switch to the gradient mode unless gradient information
is found
RoUting on finGerprint Gradient in
sEnsor networks (RUGGED)-con

• If the node is in gradient information region
• Uses a greedy forwarding approach
• well suited for broad range of applications
• time gradient based target tracking, event boundary detection.
RoUting on finGerprint Gradient in sEnsor
networks (RUGGED)-con

• Active query routed
• Resolves query partially in each node
• Next node can be selected randomly or selected intelligently based on other
information
• Query gets resolved as quickly as possible
• Last active node answers the last remaining piece of the original query
ACtive QUery forwarding In sensoR nEtworks
(ACQUIRE)

• Routing protocol is based on ANT colony
• highly adaptive, efficient and scalable
• ANTS travel through the WSN looking for path between sensor nodes and a
destination node
• that are both short in length and energy efficient
An Energy Efficient ANT Based Routing algorithm
(EEABR)

• Forward (FANT) and backward ANTS (BANT).
• A forward ANT is launched periodically from every node
• ANT stores the identifiers of all the nodes it visits
• selection probability is a trade-off between visibility(Energy) and actual trail
intensity
• BANT sent back along the path stored
An Energy Efficient ANT Based Routing algorithm
(EEABR)-con

EECDA (Energy Efficient Clustering and Data
Aggregation) Protocol
 After the CHs election, a path with maximum sum of residual energy would
be selected for data communication instead of the path with minimum
energy consumption.
 Therefore, each CH first aggregates the received data and then transmits
the aggregated data to the Base Station (BS).
 The main contributions of EECDA protocol is to provide longest stability
and improves the network lifetime

Energy-Aware Unequal Clustering with Fuzzy
(EAUCF)
• EAUCF is a distributed competitive unequal clustering algorithm. It makes local
decisions for determining competition radius and electing cluster-heads.
In order to estimate the competition radius for tentative cluster-heads, EAUCF
employs both residual energy and distance to the base station
parameters.
• EAUCF aims to decrease the work of the cluster-heads that are either
close to the base station or have low remaining battery power.
• A fuzzy logic approach is adopted in order to handle uncertainties in cluster-head
radius estimation.

THANK YOU

Schedule Based MAC Protocol

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