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Copyright © 2004 ZigBeeTM Alliance. All Rights Reserved.

Wireless Control That Simply Works

Gateways: Beyond the Sensor Network

Patrick KinneyKinney Consulting [email protected]

Wireless Control That Simply WorksZigBeeTM Alliance |Copyright © 2004. All Rights Reserved.

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Biography

Patrick Kinney ([email protected]) is the president and CTO of an independent consulting company (Kinney Consulting LLC) specializing in Wireless Communications and serving both large and small companies for their wireless needs. Previously he was a Vice President of Communication Technologies at Invensys responsible for directing communication efforts throughout Invensys’s divisions. He received a Bachelors of Science in Electrical Engineering from the University of Notre Dame, Notre Dame Indiana. He has 28 years experience in the design, development, and deployment of communication systems and products. He is the co-Vice Chair and Secretary of the IEEE 802.15 Working Group for Wireless PersonalArea Networks and the chair of the IEEE 802.15.4a Task Group. He is also the Secretary of the ZigBee Alliance and its Gateway Working Group Chair. ZigBee is an association of companies working together to create a very low-cost, very low power consumption, two-way, wireless communications standard.



Copyright © 2004. All Rights Reserved.

OverviewExternal Connectivity: Why and How

ZigBeeTM Alliance | Wireless Control That Simply Works


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Why External Connectivity?

To unlock the full potential of sensor networks a method of communication with Industrial LANs and the Internet is needed. In this respect wireless sensor networks are no different than wired sensor networks.

Even though some wireless networks have value without external connectivity just about all wireless networks provide significantly more value with external connectivity.

It is also a strategic value to allow a wireless network the ability to use a wired line to help performance or to connect networks that are out of range.


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What Sort of Connectivity?

Gateways and Bridges are two different ways to provide connectivity.

In context of ZigBee, Gateways provide a more full featured connectivity and allow a greater diversity of devices and applications to connect to the ZigBee network.

Bridges are much simpler than Gateways and hence would be a lower cost to the user but serve a smaller application space.




Gateways

Full Featured Connectivity



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Gateways

A Gateway is a device that allows disparate networks to exchange information.

■ Gateways convert the wireless protocols and sensor data into the myriad of formats necessary for industrial, commercial, and residential systems.

■ Examples of these formats include BACnet and LonWorksfor building systems, SCADA and Modbus for industrial networks, and of course HTML and XML for Internet applications.

■ Gateways allow wireless sensor networks to use wireless protocols such as ZigBee that are well suited for the harsh RF environment as well as battery powered applications and allow them to be integrated into existing applications.


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ZigBee Gateway

A ZigBee Gateway is intended to provide an interface between ZigBee and IP devices through an abstracted interface on the IP side. The IP device is isolated from the ZigBee protocol by that interface. The ZigBee Gateway translates both addresses and commands between ZigBee and IP.

ZigBee

Gateway

Ab

stracted Messages


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Gateway Stack Diagram

PHY

MAC

LLC

NET

APP Support

OEM APP(Embedded)

ZigBeeNode

PHY

MAC

LLC

NET

APP Support

OEM APP(Java, et al)

ZigBeeGateway

ZigBee Gateway Transport Services

SNMPDHCP

SMTPRijndael

Web ServerTFTP

TCP, UDP

IP

Eth

erne

t

Cel

lula

r

WiF

i

ZigBee Gateway Application Services

The IP stack is terminated at the Gateway as is the ZigBee Stack. The Gateway provides translation between the respective stacks


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IP Command Translation

When working through a ZigBee Gateway, an IP device sends a command:

•“Turn on the light in the northeast corner of Room 123”

•Gateway translates this command to a packet that is compatible with the appropriate ZigBee lighting profile•Gateway also translates the logical address into a network address, and transmits the packet on behalf of the originator•Gateway acts as an agent on behalf of the IP device, isolating the IP device from the details of ZigBee operation and vice versa.


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Service Scenario

A collection of ZigBee devices sends data to a remote service over IP.

For example: A ZigBee security device is preconfigured to connect to a web service through a gateway.


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Typical Home Network

HVAC control via web browser from devices on the internet to typical home installations

Home Network

Laptop computer

Home PC

Tower PC

Laptop computer Wireless Access Point

Router

Internet

Cable/ DSL Modem


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Remote Ability to Query ZigBee Device Status

PCs, PDAs, or cellular handsets would have the ability to remotely query ZigBee device status

Ethernet

Workstation

Laptop

ZB Gateway

InternetCloud

IP

ZigBeeMesh Network

PDAMobilePhone

WiFi AP

ZigBeeRadio

WiFiRadio

ZigBee Nodes

ZigBee App. Server


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Building Automation

The HVAC/Lighting server communicates to ZigBee devices via the ZigBee Gateway. ZigBee devices send status updates on temperature, etc., to the HVAC/Lighting server via the Gateway. The server translates ZigBee packets and maintains the status ofeach device in the ZigBee Network

ZigBeeGateway

BACnetServer

(optional)

HVAC/LightingServer

BACnet devices (optional)

IP backbone

ZigBee devices

Workstation




Bridges i.e. ZEDsZigBee Expansion Device



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ZED Usage Scenarios

ZigBee ZigBee

ZED ZED

ZigBee Messages

A ZigBee ZED extends the ZigBee network over an IP based network. Since the specific PHY and MAC layers are not pertinent as long as the network layer is IP based, the ZED will work over Ethernet or WiFitypes of devices.

The ZigBee network layer is continuous among the ZigBee devices by overlaying it on the IP network’s transport layer. The ZED makes the IP connectivity transparent to the ZigBee devices.


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ZED Usage Scenarios

In an alternative configuration, a ZED may be used to communicate with IP devices that are executing the ZigBee stack and communicate through a ZigBee network layer. In this usage scenario, the IP device behaves like an extension of the ZigBee network.

ZigBee Messages

ZigBee

ZED


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ZED Stack Diagram

802.15.4 PHY

802.15.4 MAC

ZigBee Network Layer and above Layers

TCP, UDP

IP

Ethe

rnet

Cellu

lar

WiF

i

ZED Routing Layer

The ZigBee stack runs over the IEEE 802.15.4 MAC and is encapsulated to run over the TCP/IP stack


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Network Extensions

ZED ZED

Coordinator A

PAN APAN A

In this configuration geographically separated clusters of ZigBee devices may communicate with each other through an IP backbone using ZEDs. These networks may be separated by some distance, but they nonetheless share a single coordinator, PAN ID, and address space.


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Network Connectivity Enhancement

ZED ZED

Coordinator B

PAN B

A single cluster of ZigBee devices may utilize an IP backbone to provide low-cost routing within a PAN.

In the example on the right, in a multistory building it is possible to place a ZED on each story. Communication to nearby devices would occur through wireless links; but communication between floors would tend to occur through the IP backbone that provides fast and reliable wired links with low routing cost.


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Alarm Monitoring to a Central Site

Alarm monitoring would chose to use ZEDs due to their low cost and simplicity. The ZEDs would be pre-programmed with the alarm center’s address and would require no configuration. The alarm company would be able to configure such parameters as security and which devices are to be included in the network from the alarm center.


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Conclusion

ZigBee has concluded that total connectivity requires two types of devices; Gateways and ZEDs

Although both devices may accommodate some applications, upon reviewing each application’s requirements one of these devices will prove superior.

Standardization of these devices will permit multiple vendors to interoperate and provide a superior solution to ZigBee users.

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