IEEE 802.15.4 Overview

2007/11/28

Chia-Hung Tsai

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IEEE 802.15 working group

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Comparison between WPAN

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ZigBee/IEEE 802.15.4 market feature Low power consumption Low cost Low offered message throughput Supports large network orders (<= 65k nodes) Low to no QoS guarantees Flexible protocol design suitable for many appli

cations，

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ZigBee/802.15.4 architecture

ZigBee Alliance Defining upper layers of protocol stack: from network to ap

plication, including application profiles First profiles published mid 2003

IEEE 802.15.4 Working Group Defining lower layers of protocol stack: MAC and PHY

PHY Layer

MAC Layer

Network & Security

Application Framework

Applications

802.15.4

ZigBeeSpecification

Hardware

ZigBee stack

Application

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IEEE 802.15.4 device types There are two different device types :

A full function device (FFD) A reduced function device (RFD)

The FFD can operate in three modes by serving as Device Coordinator PAN coordinator

The RFD can only serve as: Device

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Star topology

Full Function Device (FFD)

Reduced Function Device (RFD)

Communications Flow

NetworkNetworkcoordinatorcoordinator

Master/slave

NetworkNetworkcoordinatorcoordinator

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Tree topology

Communications Flow

Full Function Device (FFD)

Tree

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Device addressing Two or more devices communicating on the same

physical channel constitute a WPAN. A WPAN includes at least one FFD (PAN coordinator) Each independent PAN will select a unique PAN identifier

All devices operating on a network shall have a unique 64-bit extended address. This address can be used for direct communication in the PAN

A device can also have a 16-bit short address, which is allocated by the PAN coordinator when the device associates with its coordinator.

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Superframe

A superframe is divided into two parts Inactive: all station sleep Active:

Active period will be divided into 16 slots 16 slots can further divided into two parts

» Contention access period» Contention free period

0 10987654321 14131211 15

GTS 0

GTS 1

Beacon Beacon

CAP CFP

Inactive

SD = aBaseSuperframeDuration*2SO symbols (Active)

BI = aBaseSuperframeDuration*2BO symbols

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Superframe

Beacons are used for starting superframes synchronizing with other devices announcing the existence of a PAN informing pending data in coordinators

In a beacon enabled network, Devices use the slotted CAMA/CA mechanism to

contend for the usage of channels FFDs which require fixed rates of transmissions c

an ask for guarantee time slots (GTS) from the coordinator

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Superframe The structure of superframes is controlled by two par

ameters: beacon order (BO) and superframe order (SO) BO decides the length of a superframe SO decides the length of the active potion in a superframe

For a beacon-enabled network, the setting of BO and SO should satisfy the relationship 0 SO BO 14 ≦ ≦ ≦

For channels 11 to 26, the length of a superframe can range from 15.36 msec to 215.7 sec (= 3.5 min).

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Superframe Each device will be active for 2-(BO-SO) portion of the time,

and sleep for 1-2-(BO-SO) portion of the time In IEEE 802.15.4, devices’ duty cycle follow the

specification

BO-SO 0 1 2 3 4 5 6 7 8 9 ≧10

Duty cycle (%) 100 50 25 12 6.25 3.125 1.56 0.78 0.39 0.195 < 0.1

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Starting and Maintaining PANs

Scanning Through Channels Energy scan Active scan

Devices are instructed to begin a channel scan through MLME-SCAN.request primitive

The scan results shall be returned via the MLME-SCAN.confirm primitive

During the scan, device shall suspend beacon transmission

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Starting a PAN

A PAN shall be started by an FFD only after an active channel scan and a suitable PAN ID has been selected

An FFD uses the MLME-START.request primitive to begin operating a PAN

The MAC sublayer shall set the logical channel in phyCurrentChannel and the PAN identified in macPANId

Then this FFD can begin operating as a PAN coordinator

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Beacon Generation An FFD shall use the MLME-START.request

primitive to begin transmitting beacon BeaconOrder SuperframeOrder

The FFD may either begin beacon transmission as The PAN coordinator of a new PAN A device on previously established PAN

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Association procedures (1/2) A device becomes a member of a PAN by associating

with its coordinator Procedures

Beacon (pending address)

ACK

Association req.

Coordinator Device

Data req.

ACK

Association resp.

ACK

Scan channel

Wait for response

Make decision

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Association procedures (2/2) In IEEE 802.15.4, association results are announced in an

indirect fashion A coordinator responds to association requests by

appending devices’ long addresses in beacon frames Devices need to send a data request to the coordinator to

acquire the association result

After associating to a coordinator, a device will be

assigned a 16-bit short address.

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Association

A device shall only attempt to associate after having completed either an active channel scan or passive channel scan The results of channel scan would have then bee

n used to choose a suitable PAN

A coordinator shall only allow association if macAssociationPermit is set to TRUE

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Association The device shall set the necessary values for

association phyCurrentChannel shall be set to an appropriate

channel macPANId shall be set to the identifier of the PAN

with which to associate macCoordShortAddress or macCoordExtendedA

ddress, depending on which is knowing from the beacon frame of the coordinator

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Association An unassociated device shall initiate the association

procedure by sending an associate request command to the coordinator of an existing PAN

The coordinator that successfully receives this request will reply an acknowledgment frame

The ACK frame to an request command does not mean that this device has associated. The coordinator needs time to determine whether the

resource available on the PAN are sufficient

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Association If sufficient resources are available, the coordinator

shall allocate a short address to the device and generate an association response command containing the

new address and a status indicating a success association If sufficient resources are not available, the

coordinator shall generate an association response command containing the

status indicating a failure association The association response command frame shall be

added to the list of pending transaction stored on the coordinator

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Association After receiving the ACK, the device shall wait

for at most aResponseWaitTime symbols for the decision

The device attempt to track the beacon for the association response command

If the device does not extract the response after timeout, the association attempt shall be deemed a failure The device shall terminate any tracking of the bea

con

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Association

On receiving the association response command, the device shall send an ACK frame

If successfully associated, the device shall store the short address and extended address of coordinator

If unsuccessfully associated, the device shall set macPANId to the default value (0xffff)

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Lab report

Analyze the WUART application Trace code Sniffer - TestUtility.bin

Hand in a lab report Due day 12/11 Describe the procedure of building a 802.1

5.4 network in WUART applicationInclude the log analysis about sniffer