05/02/2023

Medium Access Control Protocols For wireless Sensor Network

By: Ahmed Shamel Noori

supervised by:Dr.En. Muhammed Najm Al-Salam

Outline

Introduction Background Performance Requirements

MAC Protocols : Contention-based Schedule-based Hybrid Conclusion

IntroductionWireless Sensor Networks are typically composed of a large number of low-cost, low-power, multifunctional wireless devices deployed over a geographical area in an ad hoc fashion and without careful planning. sensing devices are resource constrained and therefore are only capable of a limited amount of processing and communication.

The choice of the medium access control protocol is the major determining factor in WSN performance

the MAC protocol functionalities are provided by the lower sublayer of the data link layer (DLL). The higher sublayer of the DLL is referred as the logical link control (LLC) layer.

Background

The MAC sublayer resides directly above the physical layer. It supports thefollowing basic functions:

• Framing – Define the frame format and perform data encapsulation anddecapsulation for communication between devices.

• Reliability – Ensure successful transmission between devices. (by sending acknowledgement (ACK) messages and retransmissions when necessary).

• Flow Control – Prevent frame loss (swamping) through overloaded recipient buffers.

• Error Control – Use error detection or error correction codes to control theamount of errors present in frames delivered to upper layers.

• Medium Access – Control which devices participate in communication at any time. Medium access becomes a main function of wireless MAC protocols since broadcasts easily cause data corruption through collisions.

Why do we need MAC?● Wireless channel is a shared medium.

● Radios transmitting in the same frequency band interfere with each other.

The role of Medium Access Control● Controls when and how each node can transmit in the wireless channel.

● Solves the contention and collision.

Performance RequirementsIn trying to determine the performance requirements of MAC protocols, the scope

of research has been very broad, issues such as :

Delay: refers to the amount of time spent by a data packet in the MAC layer

before it is transmitted successfully.

Throughput: typically defined as the rate at which messages are serviced by a

communication system. It is usually measured either in messages per second or

bits per second.

Robustness: defined as a combination of reliability, availability, and

dependability requirements, reflects the degree of the protocol insensitivity to

errors and misinformation.

Performance Requirements Scalability: refers to the ability of a communications system to meet its

performance characteristics regardless of the size of the network or the number

of competing nodes.

Stability: refers to the ability of a communications system to handle

fluctuations of the traffic load over sustained periods of time.

Fairness: A MAC protocol is considered to be fair if it allocates channel

capacity evenly among the competing communicating nodes without unduly

reducing the network throughput.

Energy: a sensor node is equipped with one or more integrated sensors,

embedded processors with limited capability, and short-range radio

communication ability.

Major Sources of Energy Wastes● Control Packet Overhead E.g., RTS/CTS

● Collision (RTS: Request To Send)

Retransmission (CTS: Clear To Send)

● Overhearing The receiver of a packet is not the intended receiver of that packet

● Idle Listing Listening to possible traffic that is not sent

Type of Multiple Access protocol

Fixed-Assignment Protocols ( Channelized protocol) In fixed-assignment strategies, each node is allocated a predetermined fixed amount of the channel resources. his category include frequency-division multiple access (FDMA), time-division multiple access (TDMA), and code-division multiple access (CDMA).

Random Assignment Protocols In fixed-assignment schemes, each communicating node is assigned a frequency band in FDMA systems or a time slot in TDMA systems. This assignment is (static)

The ALOHA protocol (dynamic), also referred to as pure ALOHA, was one of the first such media access protocols. improve the performance of pure ALOHA lead to the development of several schemes, including carrier sense multiple access (CSMA), carrier-sense multiple access with collision detection (CSMA/CD), and carrier-sense multiple access with collision avoidance (CSMA/CA)

Type of Multiple Access protocol

PURE ALOHA

SLOTED ALOHA

Every node senses the carrier before transmitting If the carrier is not clear, the node defers transmission for a specified period

Otherwise, transmits. While transmitting, the sender is listening to carrier and sender stops

transmitting if collision has been detected.

CSMA/CD (carrier sense multiple access/ collision detection)

Classification of MAC Protocols

Classification of MAC Protocols Contention-based protocols ( S-MAC , B-MAC )

1. S-MAC Basic Idea

Trades energy efficiency for lower throughput and higher latency

Main Components

Periodic Listen and Sleep

Collision Avoidance

Overhearing Avoidance

Message Passing

Periodic Listen and Sleep● Nodes periodically sleep● Turn off radio when sleeping● Reduce duty cycle to ~10%● Trades energy efficiency for lower throughput and higher latency

Classification of MAC Protocols

Collision Avoidance● Similar to IEEE 802.11

● Virtual Carrier Sense

● NAV (Network Allocation Vector)

● Physical Carrier Sense

● Four-way(steps) handshake

● RTS/CTS/DATA/ACK

Classification of MAC Protocols

Overhearing Avoidance● The Basic Idea a node can go to sleep whenever its neighbor is talking with

another node.

● Who should sleep?

The immediate neighbors of sender and receiver.

● How do they know when to sleep?

By overhearing RTS or CTS.

● How long should they sleep?

NAV (Network Allocation Vector).

Classification of MAC Protocols

Message PassingHow to transmit a long message?

● Transmit it as a single long packet (Easy to be corrupted).

● Transmit as many independent packets (Higher Control Overhead & Longer Delay).

● Divide into fragments, but transmit all in burst.

Classification of MAC Protocols

Classification of MAC Protocols2. B-MAC B-MAC is implemented in TinyOS.

Major Feature: reconfigurable.

● Above B-MAC, one can implement an RTS-CTS scheme or a TDMS like

scheduling protocol.

A small core of media access functionality

● arbitration, reliability, low power communication

2. B-MAC (Overview)● Channel Arbitration

Clear Channel Assessment (CCA) & Backoffs

● Reliability

Link-layer acknowledgment

● Low Power Communication

Low Power Listening (LPL)

Classification of MAC Protocols

Classification of MAC Protocols Schedule-based MAC Protocols for WSNs

(Traditional TDMA MAC Protocols)

● Divide time into cycles

A cycle consists of several slots

● Advantages

Collision-Free, Low Idle Listing and Overhearing.

● Disadvantages

Synchronization, Low Channel Utilization

● An important Issue

Slot Assignment Strategy

Slot Assignment Strategy

A node should own a slot different from its one-hop and two-hop neighbors

Classification of MAC Protocols

Classification of MAC Protocols

Hybrid (TDMA/CSMA)

● Z-MAC

● Funneling-MAC

1. Z-MAC (Zebra MAC)● A hybrid TDMA and CSMA MAC scheme

● The main feature is its adaptability to the level of contention in the network

● under low contention, it behaves like CSMA, and

● under high contention, like TDMA

Classification of MAC Protocols

Funneling-MAC● The authors propose a localized, sink-oriented funneling-MAC

● Localized

Using local TDMA scheduling in the intensity region only

● Sink-oriented

Manage TDMA scheduling

Compute and maintain the depth of the intensity region

Classification of MAC Protocols

Conclusion

● MAC Protocols in WSNs● Energy Efficiency and Other Concerns● Contention-based/Schedule-based/Hybrid