Fundamentals of MAC protocols - Low duty cycle protocols and wakeup concepts – Contention based protocols - Schedule-based protocols - SMAC - BMAC - Traffic-adaptive medium access protocol (TRAMA) - The IEEE 802.15.4 MAC protocol - Zigbee protocol

1. WSN; IOT;V sem, GEHU by Dr. Vrince Vimal 1
Medium Access Control For Sensor
Network
9/21/2019
Dr. Vrince Vimal
Computer Science and Engineering

2. At the end of this unit, we would be able
to understand following
-Fundamentals of MAC protocols
- Low duty cycle protocols and wakeup concepts
– Contention based protocols
- Schedule-based protocols - SMAC - BMAC
- Traffic-adaptive medium access protocol (TRAMA) -
The IEEE 802.15.4 MAC protocol
- Zigbee protocol
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3. Classification Of MAC
• MAC are classified as follows
• Scheduled based MAC
• Contention Based MAC
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4. Scheduled based MAC
• Based on a-priory condition or scheduling
• Central authority or access point regulates medium
access.
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5. • Eg. TDMA
• Access point
• Node a
• Node b
• Node c
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Scheduled based MAC
Frame

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Contention Based MAC
▪ No open or fixed time lot is available
▪ Node has to content for access to the Medium
▪ Data transmitted in On-demand fashion

7. Contention Based MAC
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8. Why MAC for WSN
• Multi-hop Network
• Energy Constraint
• Ad-hoc deployment of 1000s of node. (Self Org)
• In WSN MAC must achieve two goals
• Create network infrastructure
• Allow fair and efficient sharing of resources.
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Energy Efficiency
• Reasons for waste of energy
➢ Idle Listening
➢ Collisions
➢ Overhearing
• Source of energy waste
➢ Protocol over head
➢ Traffic fluctuations

10. MAC Performance
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• For Efficient operations sensor network need to provide
certain operational guarantee to achieve benchmark.
• Following are the key features of MAC
➢Effective collision avoidance.
➢Scalability and adaptability.
➢Efficient Channel utilization
➢latency

11. MAC Performance
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➢ Throughput & fairness.
• Energy performance and trade-off
➢ Number of Physical channels used.
➢ Degree of Organization between nodes
➢ The method of notifying node of incoming
message,

12. MAC protocol for WSN
• Contention Based
• TDMA variants
• S-MAC and Variants
• Self Organizing MAC
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Contention Based MAC
• Preamble Sampling

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Contention Based MAC
• WISEMAC

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TDMA Variants
• EMACS
Time slots are divided into
➢ Contention Phase
➢ Traffic control section
➢ Data section
• LMACS
➢ Every sensor node has pre-allocated time slot,
➢ All sensor nodes have a time slot
• AI- LMAC
➢ Adaptive
➢ No. of slots vary according to traffic conditiond
➢ Allocation done locally on node level
➢ Upto 3 hops with no overlapping timeslots

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TDMA Variants
• Z-MAC
➢ Nodes are allocated some time slots but can utilize any
time slot using CSMA
• TRAMA (Traffic Adaptive Medium Access)
➢ Node broadcasts id of neighbours and traffic through
them.
➢ Each node is aware of its 2 hop neighbour.

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S-MAC
• Sensor Medium Access Control
• Designed specifically for WSN
• Primary goal: Energy efficiency
Disadvantages of existing Scheme
• TDMA: Useless in high node density app
• FDMA: Ineffective B/W utilization
• 802.11: idle listning

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SMAC & Variants
• S-MAC
➢ Assumes node have single operation and have long idle
periods.
➢ Virtual clustering to manage sync.
➢ Coarse –grained sleep/wakeup cycle to allow node to
sleep longer to save energy.

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SMAC & Variants
• Dynamic S-MAC
➢ Nodes assume dynamic duty cycle owing to traffic
conditions and energy conditions
• Timeout -MAC
➢ It uses timer to acknowledge end of active period
instead of relying on fixed duty cycle scheme.

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S-MAC Features
▪ Periodic Listening
▪ Overhearing avoidance
▪ Collision avoidance
▪ Message Passing
▪ Trade- off
▪ Latency, fairness Energy efficiency

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S-MAC Design
▪ Idle listening wastes energy solution Periodic Listening
SleepListen Listen
T f
• Turnoff radio while asleep
• Reduced duty cycle by10%
• Preferably neighbouring nodes follow same duty cycle.

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Choosing and Maintaining Schedule
▪ Nodes exchange their schedule by periodically broadcasting
sync packets.
▪ Node select their schedule by following 2 steps.
▪ Listen for sync packet for fixed duration of time.
▪ Condition 1: No sync packet
▪ Condition 2: Sync packet received
▪ Condition 3: Multiple Sync received
▪ Schedule-1 Schedule-2

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S-MAC Design- Listen and Sleep
cycle
Receiver For sync For RTS For CTS
Listen
Sleep
Sender-1
Sender-2
CS Tx Sync
CS Tx CTS Got CS
Sending Data

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S-MAC Design; Adaptive listening
• Reduce multi-hop latency due to periodic sleep
• Neighbouring node wake up for short duration at
the end of each communication.
1 2 3 4
RTS
CTS CTS

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S-MAC Design; Escaping Overhearing
• All immediate neighbours are put to sleep on
x’mission of RTS and CTS
• Neighbouring node do not over hear data and
following acknowledgements
• Duration field in packet indicates sleep duration.
RTS
CTS
1 2 3 4

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S-MAC Design; Message Fragmentation
Data
Sync
Collision
1
2
3
Data/Ack Data/Ack Data/Ack Data/Ack
Contention for medium
• Large data is broken into small fragments of data.

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S-MAC Design
• S-MAC achieves better energy efficiency as compared
to always listening protocols.
• S-MAC efficiently elevates the network lifetime.
1
Source node
2
Sink

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T-MAC

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DS-MAC
• Good latency
• Collision

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Low duty Cycle and wake up concepts
• System Remains in sleep state
• Wakes up to trans-receive.
B
Sleep
Listen
T f
ListenA ➢ short beacon
➢ Frequent req
b
e
a
r
e
q
r
e
q
r
e
q
r
e
q

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Wake up concepts
• Simple low-power (power less) receiver wakes up
main receiver.

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Data Channels CS Other channel
idle channel → node xmitts rec id and channe id-→ rec
wakes up its transreceiver-→data trans mission starts
-→after wards transreceiver goes to sleep mode,
Bussy
Drawbacks
• No hardware available.
• Range
• Complexity

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STEM & B-MAC
Assingment-1

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IEEE 802.15.4
MAC
PHY
Network
Application IEEE802.15.4
IEEE802.15.4
IEEE802.15.4
IEEE802.15.4
IEEE802.15.4
ZigBee
6LoWPAN
WirelessHART
MiWi
ISA100.11a
Used by many IoT protocols:

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IEEE 802.15.4
• LR WPAN
• 2.4 Ghz; 16 channels of 5 Mhz.
• 250kbps PHY→ 50kbps
• Peak current depends on bits / symbol
• Like 802.11→ DSSS; CSMA CS; beacon; coordinator
• 64 bit EUI
1b- U/M 1b- G/L 22b- OUI 40 b Manufacturer

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• NO Segmentation / Reassembly
TOPOLOGIES
RFD
CO
FFD

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• FFD can become coordinator and route the data packets.
• RFDs can not become coordinator and can only be a leaf.
• FFD that starts a PAN become the coordinator.
• In star topology, all communication is to/from
coordinator.
• In P2P topology, FFDs can communicate directly.
• Each piconet has a PAN ID and is called a cluster.
• Nodes Join a cluster by sending association request to the
coordinator. Coordinator assign a 16-bit short address to
the device. Device can use either the short address or
EUI-64 address.
IEEE 802.15.4

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Super frame Structure

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THANKS