ZigBee Overview

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ZigBee Overview

Sunghyun Choi, Associate Professor, Ph.D.

Multimedia & Wireless Networking Lab. (MWNL) Seoul National University

E-mail: [email protected] URL: http://mwnl.snu.ac.kr

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Talk Outline

ZigBee Architecture Overview

ZigBee Network Overview

Network Structure

ZigBee Device Types

Addressing

Message Routing

Link Symmetry

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The 802 Wireless Space

Data Rate (Mbps)

Range

ZigBee

802.15.4 802.15.3

802.15.3a 802.15.3c WiFi

802.11

10 100 1000

WPAN WLAN WMAN WWAN

0.01 0.1 1

Bluetooth 802.15.1

IEEE 802.22

WiMax IEEE 802.16

IEEE 802.20

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What IEEE 802.15.4 Addresses

IEEE 802.15.4

MAC and PHY only

IEEE 802.15.4 MAC Upper Layer Stack

IEEE 802.2 LLC Other LLC

IEEE 802.15.4 2400 MHz PHY IEEE 802.15.4

868/915 MHz PHY

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ZigBee Missions

Needed an organization with a mission to define a complete open global standard for reliable,

cost-effective, low-power, wirelessly networked products addressing monitoring and control

Alliance provides

Upper layer stack and application profiles

Compliance and certification testing

Branding

Result is a set of recognizable, interoperable solutions

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ZigBee Architecture Objectives

Enable low cost, low power, reliable

devices for monitoring and control based on IEEE 802.15.4 PHY/MAC standard.

Ensure interoperability through the definition of application profiles

Provide the framework to allow a separation of concerns for the

specification, design, and implementation

of ZigBee devices.

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The ZigBee Platform

IEEE 802.15.4

Public Application Profile

ZigBee Stack

Compliant Platform

Certified Product

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ZigBee Protocol Stack

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ZigBee Protocol Stack (1/2)

Application Framework

The manufacturer-defined application objects

Application Support Layer

Maintains tables for binding, which is the ability to match two devices together based on their services and their needs

Forwards messages between bound devices

Network Layer

Will be covered.

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ZigBee Protocol Stack (2/2)

ZigBee Device Object (ZDO)

Defines the role of the device within the network (e.g., ZigBee coordinator or end device)

Initiates and/or responds to binding requests

Establishes a secure relationship between network devices

Discovers devices on the network and

determining which application services they provide.

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ZigBee NWK Overview

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NWK Layer Details

ZigBee device types

Network management and addressing

Message routing

Route discovery and Maintenance

Security (not dealt in this material)

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Network Structure

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ZigBee Device Types (1/2)

ZigBee Coordinator (ZC)

Acts as IEEE 802.15.4 PAN Coordinator (FFD)

Initiates network formation

Channel, PANId, Stack profile

One extra function: acts as Bind Request Controller

ZigBee End Device (ZED)

Acts as IEEE 802.15.4 Device (RFD)

Shall not allow associating and participating in routing

Relies on its parent to let it sleep Î RxOnWhenIdle is off

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ZigBee Device Types (2/2)

ZigBee Router (ZR)

Acts as IEEE 802.15.4 Coordinator (FFD)

Discovers and associates with ZC or ZR

Extends the network coverage

Manages local address allocation/de- allocation

Look after its ZEDs when it comes to broadcast and routing messages

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Addressing (1/2)

CSkip based address assignment

Cm: nwkMaxChildren, Rm: nwkMaxRouters, Lm: nwkMaxDepth

( ) ( 1) 1, if -th child router

( ) , if -th child end-device

where 1 for router and 1 ( ) for end-device, respectively

parent skip n

parent skip m

m m m

A C d n n

A A C d R n n

n R n C R

+ ⋅ − +

= ⎨⎧⎩ + ⋅ +

≤ ≤ ≤ ≤ −

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Addressing (2/2)

Address determined from tree location

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Example

Cm=5: nwkMaxChildren, Rm=3: nwkMaxRouters, Lm=3: nwkMaxDepth

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Example (Cont ’ d)

Note that the addresses for Zigbee Router (a), (b), and (c) are not assigned via the rule by which those for ZED (e) ~ (j) are assigned. And ZED (e)

couldn’t associate with ZR (k) since ZR (k) exhausts its addresses for ZED.

ZC [Cskip=21, Addr=0]

j c

f i

g

h b

ZR [Cskip=6, Addr=1]

ZED [Cskip=6, Addr=64]

e X

a

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Message Routing

1.

See if the destination is in the Neighbor Table

2.

Check for a Routing Table Entry

3.

Finally resort to Tree Routing

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Tree Routing

The address tells you where the destination is

Simple equation gives ‘route up’ or ‘route down’

If , route down

Else route up

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Neighboring Routing

A ZC or ZR maintains a table of devices in its neighborhood.

If the target device is physically in range it

can send message directly.

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Mesh Routing

A ZC or ZR maintains a routing table of next hop addresses

If the target device has a routing table

entry then the message can be sent using

this routing

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Routing: Route Discovery (1/2)

A device wishing to discover a route

issues a route request command frame (RREQ)

Specialized broadcast frame transmitted throughout the network

Nodes relay the route request with new

accumulated path cost if it is new or better route request

Path cost is computed by intermediary nodes upon reception

Path cost = sum of link costs

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Routing: Route Discovery (2/2)

Intended destination responds to the

RREQ with a route reply command frame (RREP) if it is new or better route request

Unicast fame, returns along the reverse path

Reports the path cost

Intermediate nodes relay the route reply and update their routing tables

Mesh Routing is adopted from AODVjr[4]

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Routing Information Tables (1/2)

Routing table

Route status values

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Routing Information Tables (2/2)

Route discovery table

Only used for the transmission of RREP

Route discovery table entries last only during a single route discovery operation

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Command Frame Formats (1/2)

Route request command frameRREQ

Route request identifier:

sequence number in AODV or AODVjr

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Command Frame Formats (2/2)

Route reply command frame (RREP)

Originator: originator of corresponding RREQ

Responder: originator of this RREP

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Route Discovery Example

RREQ is originated and broadcast to neighbors.

src dest

RREQ

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1-hop neighbors

broadcast RREQ with accumulated path cost.

Referring to the same route identifier, 1-hop neighbors discard RREQ from its 1-hop neighbor.

However, less expensive path cost makes a

neighbor relay that RREQ.

(1) RREQ Broadcast

src dest

RREQ

Discarded RREQ

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Route Discovery Example

According to the rules that a node relays

newer or better RREQ, RREQ is gradually

propagating to the destination.

src dest

RREQ

Discarded RREQ

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The final destination also responds to

newer or better RREQ with a RREP.

RREP is forwarded to the originator of the RREQ by unicasting.

(1) RREQ Broadcast

src dest

RREQ

Discarded RREQ RREP

RREP

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Route Discovery Example

Because of the less expensive path cost, the RREP is generated and unicast though

one has been already unicast.

The originator

receives two RREPs, and selects one route to deliver data

packets.

(2) RREP Propagation and

RREP

route

Less expensive path is found later!

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Flow Chart: Basic Routing

Algorithm (1/2)

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Flow Chart: Basic Routing

Algorithm (2/2)

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Flow Chart: Receipt of RREQ

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Flow Chart: Receipt of RREP

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Link Symmetry

Assume that links are symmetrical

Establish reverse routes at the same time the forward route is established

Devices that do not assume symmetry

should not establish reverse automatically

nwkSymLink (TRUE of FALSE) The current route symmetry setting TRUE means that routes are considers to be comprised of

symmetric links. Back ward and forward routes are created during one route discovery and they are identical. FALSE indicates that routes are not consider to be comprised of symmetric links. Only the forward route is stored during route discovery

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Conclusion

Missions of ZigBee Alliance and

architecture of ZigBee protocol stacks are introduced.

Network layer functions and routing algorithm are speculated.

ZigBee standards provide more convenient way to turn 802.15.4 into a low power

multi-hop mesh network.

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Reference

1. Ian Marsden, “Network Layer Overview,” Open House

presentation materials, Mar. 16, 2006, available online at http://www.zigbee.org/en/events/OpenHousePresentations_

2006-03-16.asp.

2. Don Sturek, “ZigBee Architecture and Specifications

Overview,” Open House presentation meterials, Mar. 16, 2006. available at the above webpage.

3. ZigBee Document 02130r10, Network Specification Revision 10, Version 1.00, ZigBee Alliance, Dec. 14, 2004.

4. Ian D. Chakeres and Luke Klein-Berndt, “AODVjr, AODV Simplified, “ACM SIGMOBILE Mobile Computing and

Communications Review, vol 6, number 3, pp. 100 – 101, July 2002.