and an d Im Impl plementa ementation tion (01 0120 20442 - - PowerPoint PPT Presentation

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and an d im impl plementa ementation tion
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and an d Im Impl plementa ementation tion (01 0120 20442 - - PowerPoint PPT Presentation

Dec 25, 2023 185 likes •624 views

Net etwork work Ke Kerne nel l Ar Archi chitect tectures ures and an d Im Impl plementa ementation tion (01 0120 20442 4423) ) ) Me Medi dium um Ac Acce cess ss Con ontrol trol and WP an WPAN AN Te Tech chnologies

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SLIDE 1

Net etwork work Ke Kerne nel l Ar Archi chitect tectures ures an and d Im Impl plementa ementation tion (01 0120 20442 4423) ) ) Me Medi dium um Ac Acce cess ss Con

  • ntrol

trol an and WP WPAN AN Te Tech chnologies nologies

Chaiporn Jaikaeo chaiporn.j@ku.ac.th Department of Computer Engineering Kasetsart University

Materials taken from lecture slides by Karl and Willig

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2

Ov Overv rvie iew

Pr Prin incipal ipal optio ions ns and nd dif iffic icult ulties ies

Contention-based protocols

Schedule-based protocols

Wireless Personal Area Networks Technologies

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SLIDE 3

3

Di Diffi fficulties culties

Medium access in wireless networks is difficult, mainly because of

  • Half-duplex communication
  • High error rates

Requirements

  • As usual: high throughput, low overhead, low

error rates, …

  • Additionally: energy-efficient, handle switched
  • ff devices!
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SLIDE 4

4

Re Requirements quirements fo for r En Ener ergy gy-Ef Effic ficient ient MA MAC C Prot

  • toco
  • cols

ls

Recall

  • Transmissions are costly
  • Receiving about as expensive as transmitting
  • Idling can be cheaper but is still expensive

Energy problems

  • Collisions
  • Overhearing
  • Idle listening
  • Protocol overhead

Always wanted: Low complexity solution

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SLIDE 5

5

Mai Main n Opt Optio ions ns

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

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SLIDE 6

6

Cent ntralize ralized d Me Medi dium um Acc Access

A central station controls when a node may access the medium

  • E.g., Polling, computing TDMA schedules
  • Advantage: Simple, efficient

Not directly feasible for non-trivial wireless network sizes

But: Can be quite useful when network is somehow divided into smaller groups

Distributed approach still preferable

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SLIDE 7

7

Sch chedule dule- vs. . Cont ntention ention-Based Based

Sch chedul ule-bas based ed protocols

  • FDMA, TDMA, CDMA
  • Schedule can be fixed or computed on demand
  • Usually mixed
  • Collisions, overhearing, idle listening no issues
  • Time synchronization needed

Con

  • ntenti

ention

  • n-bas

based ed protocols

  • Hope: coordination overhead can be saved
  • Mechanisms to handle/reduce probability/impact of

collisions required

  • Randomization used somehow
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SLIDE 8

8

Ov Overv rvie iew

Principal options and difficulties

Cont ntention ntion-bas based ed proto tocol cols

Schedule-based protocols

Wireless Personal Area Networks Technologies

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SLIDE 9

9

A

Di Dist stribute ributed, d, Con

  • nte

tenti ntion

  • n-Based

Based MAC

Basic ideas

  • Receivers need to tell surrounding nodes to

shut up

  • Listen before talk (CSMA)

A)

  • Suffers from send

nder not knowing what is going on at re receiver ver

B C D Hidden terminal scenario: Also: recall exposed terminal scenario

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10

Ho How w To To Shu hut t Up S Up Send nders rs

Inform potential interferers during reception

  • Cannot use the same channel
  • So use a different one
  • Busy tone

e protocol

Inform potential interferers be befo fore reception

  • 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

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SLIDE 11

11

MA MACA CA

Multiple Access with Collision Avoidance

Sender B issues Request est to Send (RTS) S)

Receiver C agrees with Clear r to Send nd (CTS CTS)

Potential interferers learns from RTS/CTS

B sends, C acks

Used in IEE EEE E 802.11

A B C D

RTS CTS Data Ack NAV indicates busy medium NAV indicates busy medium

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12

Vi Virt rtual ual Car arri rier r Sens nsing ing

RTS CTS Data ACK

A B C D

NAV NAV

NAV  Network Allocation Vector (Virtual Carrier Sensing)

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13

Pro roblems blems Solv lved? d?

RTS/CTS helps, but do not solve hidden/exposed terminal problems

A B C D

RTS CTS Data

A B C D

RTS RTS CTS RTS RTS CTS CTS Data Data Ack

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MAC MACA A Pro roble blem: m: Id Idle le li liste tening ning

Need to sense carrier for RTS or CTS packets

  • Simple sleeping will break the protocol

IEEE 802.11 solution

  • Idea: Nodes that have data buffered for

receivers send traff ffic c indica cato tors rs at prearranged points in time

  • ATIM - Announcement Traffic Indication

Message

  • Receivers need to wake up at these points, but

can sleep otherwise

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SLIDE 15

15

Sens nsor

  • r-MAC

MAC (S (S-MAC MAC)

MACA unsuitable if average data rate is low

  • Most of the time, nothing happens

Idea: Switch off, ensure that neighboring nodes turn on simultaneously to allow packet exchange

  • Need to also exchange

wakeup schedule between neighbors

  • When awake,

perform RTS/CTS

Wakeup period Active period Sleep period For SYNCH For RTS For CTS

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SLIDE 16

16

Listen for SYNC td

Sch chedule dule As Assig ignment nment

Synch chroniz ronizer

  • Listen for a mount
  • f time
  • If hear no SYNC,

select its own SYNC

  • Broadcasts its

SYNC immediately

Follower

  • Listen for amount
  • f time
  • Hear SYNC from A,

follow A’s SYNC

  • Rebroadcasts SYNC

after random delay td

Sleep Listen Go to sleep after time t Sleep Listen Broadcasts

A B

Broadcasts Go to sleep after time t- td

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17

S-MAC MAC Syn ynchronized chronized Is Isla lands nds

Nodes learn schedule from other nodes

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 E E E E

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18

Pre reamble amble Sam ampl pling ing

Alternative option: Don’t try to explicitly synchronize nodes

  • Have receiver sleep and only periodically sample the

channel

Use lon

  • ng preamb

mbles es to ensure that receiver stays awake to catch actual packet

  • Example: B-MAC, WiseMAC

Check channel Check channel Check channel Check channel Start transmission: Long preamble Actual packet Stay awake!

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19

B-MAC MAC

Very simple MAC protocol

Employs

  • Clear Channel Assessment (CCA) and backoffs

for channel arbitration

  • Link-layer acknowledgement for reliability
  • Low-power listening (LPL)
  • I.e., preamble sampling

Currently: Often considered as the defa faul ult t WSN N MAC AC protocol

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20

B-MAC MAC

B-MAC does not have

  • Synchronization
  • RTS/CTS
  • Results in simpler, leaner implementation
  • Clean and simple interface
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SLIDE 21

21

Cle lear ar Cha hanne nnel l As Assessment ment

"Carrier Sensing" in wireless networks

Thresholding CCA algorithm Outlier detection CCA algorithm

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22

Contik ntiki LP LPL and LPP L and LPP

Low-Power Listening (LPL)

  • Also known as ContikiMAC
  • Similar to B-MAC, but allowing packet-based

MAC such as IEEE 802.15.4

Low-Power Probing (LPP)

  • Receivers periodically broadcast a probe
  • Sender listens for probes from receivers before

transmitting

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SLIDE 23

23

Ov Overv rvie iew

Principal options and difficulties

Contention-based protocols

Schedu edule le-bas based ed proto toco cols ls

Wireless Personal Area Networks Technologies

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SLIDE 24

24

LE LEAC ACH

Low-Energy Adaptive Clustering Hierarchy

Assumptions

  • Dense network of nodes
  • Direct communication with central sink
  • Time synchronization

Idea: Group nodes into “cl clusters rs”

  • Each cluster controlled by cluster

terhe head ad

  • About 5% of nodes become clusterhead (depends on

scenario)

  • Role of clusterhead is rotated
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25

LE LEAC ACH H Clu luste terhead rhead

Each CH organizes

  • CDMA code for its cluster
  • 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
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26

LE LEAC ACH H ro round unds s

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

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27

TR TRAMA AMA

Tr Traffic Adaptive Medium Access Protocol

Assume nodes are time synchronized

Time divided into cycles, divided into

  • Random access period
  • Scheduled access period

Random Access Period Scheduled-Access Period

time cycle

  • Exchange and learn two-hop

neighbors

  • Exchange schedules
  • Used by winning nodes to

transmit data

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SLIDE 28

28

TR TRAMA AMA – Ada Adapt ptiv ive El Election ction

How to decide which slot (in scheduled access period) a node can use?

  • For node id x and time slot t, compute p = h (x  t)
  • h is a global hash function
  • Compute p for next k time slots for itself and all two-

hop neighbors

  • Node uses those time slots for which it has the highest

priority t = 0 t = 1 t = 2 t=3 t = 4 t = 5 A 14 23 9 56 3 26 B 33 64 8 12 44 6 C 53 18 6 33 57 2

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29

Ov Overv rvie iew

Principal options and difficulties

Contention-based protocols

Schedule-based protocols

Wi Wirel eless ess Pe Perso sonal nal Area ea Ne Netwo works rks Techn hnologi logies

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IE IEEE EE 802 802.15 15.4

IEEE standard for low-rate WPAN (LR-WPAN) applications

  • Low-to-medium bit rates
  • Moderate delays without too strict requirements
  • Low energy consumption

Physical layer

  • 20 kbps over 1 channel @ 868-868.6 MHz
  • 40 kbps over 10 channels @ 905 – 928 MHz
  • 250 kbps over 16 channels @ 2.4 GHz

MAC protocol

  • Single channel at any one time
  • Combines contention-based and schedule-based schemes
  • Asymmetric: nodes can assume different roles
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31

868MHz / 915MHz PHY

2.4 GHz 868.3 MHz

Channel 0 Channels 1-10 Channels 11-26

2.4835 GHz 928 MHz 902 MHz 5 MHz 2 MHz

2.4 GHz PHY

802 02.15 15.4 4 PHY Ove HY Overv rview iew

Operating frequency bands

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32

802 02.15 15.4 4 De Devic ice Cla lasses

Full function device (FFD)

  • Any topology
  • Network coordinator capable
  • Talks to any other device

Reduced function device (RFD)

  • Limited to star topology
  • Cannot become a network coordinator
  • Talks only to a network coordinator
  • Very simple implementation
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33

802 02.15 15.4 4 Ne Netw twork rk To Topo pologies logies

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802.15 02.15.4 .4 Be Beaco acone ned d Mo Mode de

Superframe structure

GTS assigned to devices upon request

Active period Inactive period Contention access period Guaranteed time slots (GTS) Beacon

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SLIDE 35

802 02.15 15.4 4 GT GTS Da Data ta Tr Tran ansfe fer

Device  coordinator

  • If having allocated GTS,

wake up and send

  • Otherwise, send during CAP
  • Using slotted CSMA

Coordinator  device

  • If having allocated GTS,

wake up and receive

  • Otherwise, see picture

Coordinator Device Beacon Data request Acknowledgement Data Acknowledgement

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36

IE IEEE EE 802 802.15 15.4 4 Ado Adopt pters rs

ZigBee

  • Requires battery life of at least two

years be certified

  • Applications: Industrial control,

embedded sensing, home automation

  • ZigBee RF4CE (Radio Frequency for

Consumer Electronics) 

Nest (acquired by Google)

  • Learning thermostats,

Smoke and CO alarms

  • WiFi- and ZigBee-enabled

https://nest.com

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37

Bl Bluet uetooth

  • oth Sma

mart rt

Formally Bluetooth Low Energy (BLE)

  • Part of Bluetooth 4.0 Specification

Based on Nokia's Wibree technology

First smartphones to support  iPhone 4S

  • Now supported by most recent smartphones

http://redbearlab.com/blenano/

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38

Bl Bluet uetooth:

  • oth: Cla

lassic ic vs. Sm . Smar art

Source: Bluetooth SIG

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SLIDE 39

39

Bl Bluet uetooth

  • oth Comp

mpatibility atibility

http://blog.laptopmag.com/just-what-is-bluetooth-4-0-anyway

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40

Bl Bluet uetooth

  • oth Sma

mart rt: : De Devic ice Ro Role les

Central device

  • Serves as a hub to one or more peripheral devices
  • Two central devices cannot directly communicate
  • Similar to IEEE 802.15.4's FFD

Peripheral device

  • Must be connected to a central device
  • Two peripheral devices cannot directly communicate
  • Similar to IEEE 802.15.4's RFD
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41

AN ANT T / ANT ANT+ / NI NIKE+ E+

Primarily used for fitness monitoring devices

ANT / ANT+

  • pen access multicast

wireless sensor network

NIKE+

  • Proprietary protocols on

2.4 GHz band

http://developer.sonymobile.com Nike.com

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42

Wi WiFi Fi/Zig ZigBe Bee/Bluetooth /Bluetooth Coe

  • exist

istence ence

They all employ 2.4 GHz spectrum

http://www.digikey.com/en/articles/techzone/2011/aug/comparing-low-power-wireless-technologies

WiFi vs. Zigbee WiFi vs. Bluetooth

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Sum ummary mary

Many different ideas exist for medium access control in MANET/WSN

Comparing their performance and suitability is difficult

Especially, clearly identifying interdependencies between MAC protocol and other layers/applications is difficult

  • Which is the best MAC for which application?

Nonetheless, certain “common use cases” exist

  • IEEE 802.11 DCF for MANET
  • IEEE 802.15.4 for some early “commercial” WSN variants
  • B-MAC for WSN research not focusing on MAC