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3.Medium Access Control

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Information about 3.Medium Access Control

Published on February 28, 2009

Author: sonalichauhan

Source: slideshare.net

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Chapter 3 : Medium Access Control

What is meant by transmission of signal? Medium Access is part of which layer in OSI?

What is meant by transmission of signal?

Medium Access is part of which layer in OSI?

Why is special MAC required? Hidden and Exposed Terminal Problem Near and Far Terminal Problem

Hidden and Exposed Terminal Problem

Near and Far Terminal Problem

Multiple Access Techniques Space Division Multiple Access:- used for allocating space to users Frequency Division Multiple Access:- comprises all algorithms allocating frequencies to transmission channel according to FDM Time Division Multiple Access:- comprises technologies which allocate time slots for communication i.e., controlling TDM FDMA + TDMA

Space Division Multiple Access:- used for allocating space to users

Frequency Division Multiple Access:- comprises all algorithms allocating frequencies to transmission channel according to FDM

Time Division Multiple Access:- comprises technologies which allocate time slots for communication i.e., controlling TDM

FDMA + TDMA

Algorithms in TDMA Fixed TDMA Time slots Fixed Delay Efficient for constant Data Rate Inefficient for bursty Data Rate

Fixed TDMA

Time slots

Fixed Delay

Efficient for constant Data Rate

Inefficient for bursty Data Rate

(Contd.) Classical Aloha TDM without control Invented at Hawaii University Neither co-ordinates medium access nor resolve contention No central arbiter and no co-ordination Simultaneous transmission leads to collision Light load Max. throughput for an 18% load

Classical Aloha

TDM without control

Invented at Hawaii University

Neither co-ordinates medium access nor resolve contention

No central arbiter and no co-ordination

Simultaneous transmission leads to collision

Light load

Max. throughput for an 18% load

(Contd.) Slotted Aloha Time Slots Transmission at the start of the load No control Max. throughput for an 36% load No transmission guarantee

Slotted Aloha

Time Slots

Transmission at the start of the load

No control

Max. throughput for an 36% load

No transmission guarantee

(Contd.) Carrier Sense Multiple Access (CSMA) Sensing carrier to avoid collision Hidden Terminals Problem Back-off algorithms Types Non-Persistent CSMA 1-Persistent CSMA p-Persistent CSMA CSMA/CA EY-NMPA

Carrier Sense Multiple Access (CSMA)

Sensing carrier to avoid collision

Hidden Terminals Problem

Back-off algorithms

Types

Non-Persistent CSMA

1-Persistent CSMA

p-Persistent CSMA

CSMA/CA

EY-NMPA

(Contd.) Demand Assigned Multiple Access Reservation + Fixed TDMA Reservation period+ Transmission period Satellite Transmission Reservation List Explicit Reservation Scheme

Demand Assigned Multiple Access

Reservation + Fixed TDMA

Reservation period+ Transmission period

Satellite Transmission

Reservation List

Explicit Reservation Scheme

(Contd.) Packet Reservation Multiple Access (PRMA) Similar DAMA Implicit reservation Collision during Reservation Ensures guaranteed data rate

Packet Reservation Multiple Access (PRMA)

Similar DAMA

Implicit reservation

Collision during Reservation

Ensures guaranteed data rate

(Contd.) Reservation TDMA N mini-slots for reservation N*k data slots Guarantees min. bandwidth and delay Free slots allocates using round-robin or uncoordinated.

Reservation TDMA

N mini-slots for reservation

N*k data slots

Guarantees min. bandwidth and delay

Free slots allocates using round-robin or uncoordinated.

(Contd.) Multiple Access with Collision Avoidance Request to send Hidden and exposed terminals No fixed access patter and co-ordinated

Multiple Access with Collision Avoidance

Request to send

Hidden and exposed terminals

No fixed access patter and co-ordinated

(Contd.) Polling Master station and slaves Round Robin, Random or reservation schemes used for polling List of stations during contention phase

Polling

Master station and slaves

Round Robin, Random or reservation schemes used for polling

List of stations during contention phase

(Contd.) Inhibit sense multiple access (Digital sense multiple access) Base station signals busy medium Base station acknowledges successful transmission Collision is detected by absence of positive acknowledge

Inhibit sense multiple access (Digital sense multiple access)

Base station signals busy medium

Base station acknowledges successful transmission

Collision is detected by absence of positive acknowledge

(Contd.) Code Division Multiple Access Orthogonal codes Protection against tapping Examples

Code Division Multiple Access

Orthogonal codes

Protection against tapping

Examples

(Contd.) Spread Aloha Multiple Access Aloha + CDMA Same orthogonal key High power, short period Phase difference Synchronization Max. throughput for 18% load Includes advantages of spread spectrum

Spread Aloha Multiple Access

Aloha + CDMA

Same orthogonal key

High power, short period

Phase difference

Synchronization

Max. throughput for 18% load

Includes advantages of spread spectrum

Thank-you

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