Wireless Control That Simply Works
Gateways: Beyond the Sensor
Network Patrick Kinney Kinney Consulting LLC
[email protected] TM
Copyright © 2004 ZigBee
Alliance. All Rights Reserved.
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 Personal Area 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.
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Wireless Control That Simply Works
Overview External Connectivity: Why and How
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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. ZigBeeTM Alliance | Wireless Control That Simply Works Copyright © 2004. All Rights Reserved.
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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.
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Wireless Control That Simply Works
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.
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Examples of these formats include BACnet and LonWorks for building systems, SCADA and Modbus for industrial networks, and of course HTML and XML for Internet applications.
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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. Abstracted Messages
Gateway ZigBee
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Gateway Stack Diagram ZigBee Gateway
ZigBee Node
OEM APP (Java, et al) ZigBee Gateway Application Services ZigBee Gateway Transport Services SMTP Rijndael
Web Server TFTP
TCP, UDP
NET
NET
IP
LLC
LLC
MAC
MAC
PHY
PHY
Cellular
APP Support
WiFi
APP Support
Ethernet
SNMP DHCP
OEM APP (Embedded)
The IP stack is terminated at the Gateway as is the ZigBee Stack. The Gateway provides translation between the respective stacks ZigBeeTM Alliance | Wireless Control That Simply Works Copyright © 2004. All Rights Reserved.
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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. ZigBeeTM Alliance | Wireless Control That Simply Works Copyright © 2004. All Rights Reserved.
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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 Internet Laptop computer
Cable/ DSL Modem Home PC
Router Tower PC
Laptop computer
Wireless Access Point
Home Network
HVAC control via web browser from devices on the internet to typical home installations
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Remote Ability to Query ZigBee Device Status
PDA
Mobile Phone
IP
ZB Gateway
Laptop
WiFi Radio WiFi AP
Internet Cloud
Ethernet
ZigBee Radio ZigBee App. Server ZigBee Mesh Network
Workstation ZigBee Nodes
PCs, PDAs, or cellular handsets would have the ability to remotely query ZigBee device status ZigBeeTM Alliance | Wireless Control That Simply Works Copyright © 2004. All Rights Reserved.
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Building Automation Workstation HVAC/ Lighting Server
ZigBee Gateway
IP backbone
BACnet Server (optional)
ZigBee devices BACnet devices (optional)
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 of each device in the ZigBee Network ZigBeeTM Alliance | Wireless Control That Simply Works Copyright © 2004. All Rights Reserved.
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Wireless Control That Simply Works
Bridges i.e. ZEDs ZigBee Expansion Device
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ZED Usage Scenarios ZigBee Messages
ZED
ZED
ZigBee
ZigBee
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 WiFi types 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 ZigBee Messages
ZED ZigBee
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.
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ZED Stack Diagram
ZigBee Network Layer and above Layers
802.15.4 MAC
IP
802.15.4 PHY
Cellular
TCP, UDP
WiFi
Ethernet
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
PAN A
PAN A
Coordinator 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
PAN B
ZED
Coordinator 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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