This document provides an overview of various medium access control (MAC) protocols for wireless sensor networks. It discusses distributed and centralized MAC protocols, including DFWMAC, EY-NPMA, ISMA, RAP, RAMA, Zhang's and Acampora's proposals, and DTMP. It also covers hybrid access protocols like RRA, PRMA, RRA-ISA, DQRUMA, and MASCARA. Additionally, it summarizes MAC protocols like S-MAC, T-MAC, B-MAC, P-MAC, Y-MAC, and Z-MAC and discusses their key characteristics and performance results.

1. UNIT III
18CSE451T -Wireless Sensor
Networks
Prepared by
Dr.N.Noor Alleema
AP , SRM IST

2. • Distributed MAC Protocols
– Distributed Foundation Wirelesss MAC
(DFWMAC)
– Eliminate Yield – Non-Preemptive Priority
Multiple Access (EY-NPMA)
• Centralized MAC Protocols
– Random Access
• Idle Sense Multiple Acces (ISMA)
• Randomly Addressed Polling (RAP)
• Resource Auction Multiple Access (RAMA)
– Guaranteed Access
• Zhang’s and Acampora’s Proposals
• Disposable Token MAC Protocol (DTMP)

3. – Hybrid Access
• Random Reservation Protocols (RRA)
• Packet Reservation Multiple Access (PRMA)
• Random Reservation Access – Independent Stations
Algorithm (RRA-ISA)
• Distributed Queuing Request Updated Multiple Access
(DQRUMA)
• Moble Access Scheme based on Contention and
Reservation for ATM (MASCARA)

4. Distributed Wireless Network
• ad hoc network
• No central administration
• Multi-hop wireless networks
• Wireless Sensor Nets

5. Centralized Wireless Network
• Last Hop Network
• Very common
– Corporate, Academic, and Cellular uses.
• Has a controlling Base Station, with variable
intelligence
– Wireless Access Point
– Cellular Tower

6. Centralized Wireless Network
• Last Hop Network
• Very common
– Corporate, Academic, and Cellular uses.
• Has a controlling Base Station, with variable
intelligence
– Wireless Access Point
– Cellular Tower

7. Characteristics of MAC Protocols in
Sensor Networks
• Energy Efficiency
• Scalability
• Adaptability
• Low Latency and Predictability
• Reliability

8. MAC Protocols in Sensor Networks
• ALOHA
• CSMA
– Persistent
• L persistent
• P persistent
– Non Persistent

9. MAC Protocols in Sensor Networks
• CSMA
– CSMA/CD
• Truncated binary exponential back-off algorithm
– CSMA/CA
• Hidden-node problems
• Exposed-node problems

10. Hidden-node scenario in wireless
sensor networks

11. Exposed node scenario in wireless
sensor networks

12. Collision avoidance using RTS/CTS
handshake

13. Collision avoidance failure using
RTS/CTS handshake

14. Collision avoidance failure using
RTS/CTS handshake

15. Contention-Free MAC Protocols
• Traffic-Adaptive Medium Access
• Y-MAC
• Low energy Adaptive Clustering

16. Traffic-Adaptive Medium Access
• TRAMA assumes a time-slotted channel,
where time is divided into
– Periodic random access intervals (signaling slots)
• Neighbor Protocol (NP)
– Scheduled-access intervals (transmission slots)
• Schedule Exchange Protocol (SEP)

17. Overview
•Routing in WSNs is challenging due to distinguish
from other wireless networks like mobile ad hoc
networks or cellular networks.
•First, it is not possible to build a global
addressing scheme for a large number of sensor
nodes. Thus, traditional IP-based protocols may
not be applied to WSNs. In WSNs, sometimes
getting the data is more important than knowing
the IDs of which nodes sent the data.
•Second, in contrast to typical communication
networks, almost all applications of sensor
networks require the flow of sensed data from

18. 1
8
Overview
(cont.)
• Third, sensor nodes are tightly constrained in
terms of energy, processing, and storage
capacities. Thus, they require carefully resource
management.
• Fourth, in most application scenarios, nodes in WSNs
are generally stationary after deployment except for,
may be, a few mobile nodes.
• Fifth, sensor networks are application specific, i.e.,
design
requirements of a sensor network change with
application.
• Sixth, position awareness of sensor nodes is
important since data collection is normally based
on the location.
• Finally, data collected by many sensors in WSNs is
typically based on common phenomena, hence there
is a high probability that this data has some
redundancy.

19. 1
9
Overview
(cont.)
• The task of finding and maintaining routes in
WSNs is nontrivial since energy restrictions and
sudden
changes in node status (e.g., failure) cause
frequent and unpredictable topological
changes.
• To minimize energy consumption, routing
techniques proposed for WSNs employ some
well-known routing strategies, e.g., data
aggregation and in-network processing,
clustering, different node role assignment, and
data-centric methods were employed.

20. Overview
• Data-centric communication
• Data is named by attribute-
value pairs
• Different form IP-
style
communication
• End-to-end delivery service
• e.g.
• How many pedestrians do
you observe in the
geographical region X?
Event
Sources
2
0
Sink Node
Directed
Diffusion
A sensorfield

21. 2
1
Overview(cont.)
• Data-centric communication (cont.)
• Human operator’s query (task) is diffused
• Sensors begin collecting information about query
• Information returns along the reverse path
• Intermediate nodes aggregate the data
• Combing reports from sensors
• Directed Diffusion is an important milestone in
the data centric routing research of sensor
networks

22. 2
2
HierarchicalRouting

23. 2
3
Overview
• In a hierarchical architecture, higher energy nodes
can be used to process and send the information
while low energy nodes can be used to perform
the sensing of the target.
• Hierarchical routing is mainly two-layer routing
where one layer is used to select cluster heads
and the other layer is used for routing.
• Hierarchical routing (or cluster-based routing),
e.g., LEACH, PEGASIS, TTDD, is an efficient
way to lower energy consumption within a
cluster and by performing data aggregation and
fusion in order to decrease the number of
transmitted messages to the base stations.

24. Y-MAC
• Y-MAC divides time into
– Frames
– Slots
• Each frame contains a broadcast period and a
unicast period
• Every node must wakeup at the beginning of a
broadcast period

25. Y-MAC

26. 2
6
LEACH
Low-Energy Adaptive Clustering Hierarchy

27. Low energy Adaptive Clustering
Hierarchy (LEACH)
• Setup Phase
• Steady-State Phase

28. Low energy Adaptive Clustering
Hierarchy (LEACH)

29. Low energy Adaptive Clustering
Hierarchy (LEACH)

30. 3
0
LEACH
• LEACH (Low-Energy Adaptive Clustering
Hierarchy), a clustering-based protocol that
minimizes energy dissipation in sensor
networks.
• LEACH outperforms classical clustering
algorithms by using adaptive clusters and
rotating cluster-heads, allowing the energy
requirements of the system to be distributed
among all the sensors.
• LEACH is able to perform local computation in
each cluster to reduce the amount of data that
must be transmitted to the base station.
• LEACH uses a CDMA/TDMA MAC to reduce
inter- cluster and intra-cluster collisions.

31. 3
1
LEACH(cont.)
• Sensors elect themselves to be local cluster-headsat
any given time with a certainprobability.
• Each sensor node joins a cluster-head thatrequires
the minimum communicationenergy.
• Once all the nodes are organized into clusters, each
cluster-head creates a transmission schedule forthe
nodes in itscluster
.
• In order to balance the energy consumption, the
cluster-head nodes are not fixed; rather
,thisposition
is self-elected at different timeintervals.

32. LEACH
1 0 0 m
叢 集 區
觀 測 區 域
B a s e S t a t i o n
S e n s o r ( N o n C l u s t e r H e a d )
S e n s o r ( C l u s t e r H e a d )
I n i t i a l D a t a
A g g r e g a t e d D a t a
~ 1 0 0 m
1
2

33. LEACH:AdaptiveClustering
• Periodic independent self-election
• Probabilistic
• CSMA MAC used to advertise
• Nodes select advertisement with strongest signal
strength
• Dynamic TDM
A
cycles
All nodes marked with a given symbol belong to the same cluster, and
the cluster head nodes are marked with a ● .
3
3

34. 3
4
Algorithm
• Periodic process
• Two phases per round:
• Setup phase
• Advertisement: Execute election algorithm
• Members join to cluster
• Cluster-head broadcasts schedule
• Steady-State phase
• Data transmission to cluster-head using
TDMA
• Cluster-head transfers data to BS
(Base Station)

35. Algorithm(cont.)
15
Advertisement
phase
Cluster setup phase Broadcast schedule
Time slot
1
Time slot
2
Time slot
3
Setup phase Steady-state phase
Self-election of cluster
heads
Cluster heads compete
with CSMA
Members
compete with
CSMA
Cluster head Broadcast
CDMA code to members
Fixed-length cycle
1
5

36. Algorithm Summary(cont.)
• 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
1
6

37. 1
7
Algorithm Summary
(cont.)
• Steady-state phase
• All source nodes send their data to their cluster
heads
• Cluster heads perform data aggregation/fusion
through local transmission
• Cluster heads send aggregated data back to the BS
using a single direct transmission

38. An Example of a
LEACHNetwork
• While neither of these diagrams is the optimum scenario, the
second is better because the cluster-heads are spaced out and
the network is more properly sectioned
1
8
Node
Cluster-Head Node
Node that has been cluster-head in the last 1/P
rounds
Cluster
Border
X
Good case scenario Bad case scenario

39. 3
9
Conclusions
• 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

40. Contention-Based MAC Protocols
• Power Aware Multi-Access with signaling
• Sensor MAC
• Timeout MAC
• Data gathering MAC

41. Power Aware Multi-Access with
Signaling

42. Sensor MAC

43. Timeout MAC

44. Timeout MAC

45. Data gathering MAC
DATA GATHERING TREE

46. Data gathering MAC
CONVERGE CAST COMMUNICATION

47. Contents
• Basic Concepts
• S-MAC
• T-MAC
• B-MAC
• P-MAC
• Z-MAC

48. Basic Concepts
• Problem
• TDMA
• CSMA
• RTS / CTS

49. Hidden Nodes
A B C

50. MAC Challenges
• Traditionally
– Fairness
– Latency
– Throughput
• For Sensor Networks
– Power efficiency
– Scalability

51. S-MAC - Sensor MAC
• Nodes periodically sleep
• Trades energy efficiency for lower throughput
and higher latency
• Sleep during other nodes transmissions
Listen Sleep t
Listen Sleep

52. S-MAC
• Listen significantly longer than clock drift
• Neighboring nodes exchange SYNC msgs
• Exchanged timestamps are relative rather than
absolute
• RTS/CTS avoids hidden terminal
• Message passing provided
• Packets contain expected duration of message
• Every packet must be acknowledged
• Adaptive listening can be used so that potential
next hop nodes wake up in time for possible
transmissions

53. S-MAC Results
Latency and throughput are problems, but
adaptive listening improves it significantly

54. S-MAC Results
• Energy savings significant compared to
“non-sleeping” protocols

55. T-MAC - Timeout MAC
• Transmit all messages in bursts of variable
length and sleep between bursts
• RTS / CTS / ACK Scheme
• Synchronization similar to S-MAC

56. T-MAC Operation

57. T-MAC Results
• T-MAC saves energy compared to S-MAC
• The “early sleeping problem” limits the maximum
throughput
• Further testing on real sensors needed

58. B-MAC - Berkeley MAC
• B-MAC’s Goals:
– Low power operation
– Effective collision avoidance
– Simple implementation (small code)
– Efficient at both low and high data rates
– Reconfigurable by upper layers
– Tolerant to changes on the network
– Scalable to large number of nodes

59. B-MAC’s Features
• Clear Channel Assessment (CCA)
• Low Power Listening (LPL) using preamble
sampling
• Hidden terminal and multi-packet mechanisms
not provided, should be implemented, if needed,
by higher layers
Sleep
t
Receive
Receiver
Sleep
t
Preamble
Sender Message
Sleep

60. B-MAC Interface
• CCA on/off
• Acknowledgements on/off
• Initial and congestion backoff in a per packet
basis
• Configurable check interval and preamble
length

61. B-MAC Lifetime Model

E  Erx  Etx  Elisten  Ed  Esleep
Erx  trxcrxbV
Etx  ttxctxbV
Elisten  Esample
1
ti
Ed  tdcdataV
Esleep  tsleepcsleepV
• E can be calculated if hardware constants, sample rate, number
of neighboring nodes and check time/preamble are known
• Better: E can be minimized by varying check time/preamble if
constants, sample rate and neighboring nodes are known

62. B-MAC Results
• Performs better than the other studied
protocols in most cases
• System model can be complicated for
application and routing protocol developers
• Protocol widely used because has good results
even with default parameters

63. P-MAC - Pattern MAC
• Patterns are 0*1 strings with size 1-N
• Every node starts with 1 as pattern
• Number of 0’s grow exponentially up to a threshold  and then linearly up to N-1
• TR = CW + RTS + CTS + DATA + ACK
• N = tradeoff between latency and energy

64. Patterns vs Schedules
Local
Pattern Bit
Packet to
Send
Receiver
Pattern Bit
Local
Schedule
1 1 1 1
1 1 0 1-
1 0 * 1-
0 1 1 1
0 1 0 0
0 0 * 0

65. P-MAC Evaluation
• Simulated results are better than SMAC
• Good for relatively stable traffic conditions
• Adaptation to changes on traffic might be
slow
• Loose time synchronization required
• Needs more testing and comparison with
other protocols besides S-MAC

66. Z-MAC - Zebra MAC
• Runs on top of B-MAC
• Combines TDMA and CSMA features
CSMA
 Pros
 Simple
 Scalable
 Cons
 Collisions due to
hidden terminals
 RTS/CTS is
overhead
TDMA
 Pros
 Naturally avoids
collisions
 Cons
 Complexity of
scheduling
 Synchronization
needed

67. Z-MAC Initialization
• Neighborhood discovery through ping messages
containing known neighbors
• Two-hop neighborhood used as input for a
scheduling algorithm (DRAND)
• Running time and message complexity of DRAND is
O(), where  is the two-hop neighborhood size
• The idea is to compensate the initialization energy
consumption during the protocol normal operation

68. Z-MAC Time Slot Assignment
2a1
 Fi  2a
1
l2a
 si ( for: l  0,1,2...)

69. Z-MAC Transmission Control
The Transmission Rule:
• If owner of slot
– Take a random backoff within To
– Run CCA and, if channel is clear, transmit
• Else
– Wait for To
– Take a random backoff within [To,Tno]
– Run CCA and, if channel is clear, transmit

70. Z-MAC HCL Mode
• Nodes can be in “High Contention Level” (HCL)
• A node is in HCL only if it recently received an
“Explicit Contention Notification” (ECN) from a two-
hop neighbor
• Nodes in HCL are not allowed to contend for the
channel on their two-hop neighbors’ time slots
• A node decides to send an ECN if it is losing too many
messages (application ACK’s) or based on noise
measured through CCA

71. Z-MAC Receiving Schedule
• B-MAC based
• Time slots should be large enough for
contention, CCA and one B-MAC packet
transmission
• Slot size choice, like in B-MAC, left to
application

72. Z-MAC Results
• Z-MAC performs better than B-MAC when load is high
• As expected, fairness increases with Z-MAC
• Complexity of the protocol can be a problem

73. Conclusions
• Between the protocols studied, B-MAC still
seems to be the best one for applications in
general
• Application developers seem not to use B-
MAC’s control interface
• Middleware service could make such
optimizations according to network status