This chapter is from the book
This chapter is from the book
This chapter is from the book
2.7 ZigBee and ZigBee Pro Feature Sets
In October 2007, the ZigBee Alliance published two feature set specifications for ZigBee: ZigBee and ZigBee PRO. The ZigBee feature set is nearly the same as the ZigBee 2006 specification; however, it does offer a few new features. ZigBee PRO offers several significant improvements such as security and the capability to self-form and self-heal the network. It is targeted for use in building automation and environmental and industrial applications that contain more than 30 nodes. ZigBee PRO is based on a mesh topology and is a beaconless network. The following are its characteristics:
- Addressing: ZigBee PRO uses a mesh topology. Any device joining the network requires a network address. ZigBee PRO uses a stochastic addressing method, which means a ZigBee device randomly picks up an address when joining the network. Also, the device announces its address on the network by using the device-annc command. The ZigBee network layer provides address conflict resolution based on the MAC address if two nodes have the same network addresses. Stochastic addressing eliminates the need for the parent to maintain an address table for assignment to children.
- Link management: In a mesh topology, each node can communicate with its neighbor. The node has the ability to evaluate the quality of its neighbor's links and to select the best one for transmission of the packet.
- Frequency agility: ZigBee PRO selects the best available channel during startup of a network but, during network operation, if any node detects interference due to frequency conflict or noise, it will report the occurrence to the channel manager. (A channel manager can be a dedicated device or trust center.) When the channel manger receives the reports from several nodes on the network, it selects another channel for network operation and informs the nodes of the switch.
- Group addressing: ZigBee PRO provides group addressing; a single packet can reach a group of devices.
- Commissioning: It is a tool that is used by the ZigBee device installer to install ZigBee devices.
- Compatibility: The ZigBee PRO stack identifier is two and is advertised in its beacon frame. Any end device can join ZigBee PRO if it uses the standard security mode.
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Asymmetric link: The link between two nodes is usually asymmetric, meaning the quality of the link in both directions is not the same. The quality of the link is represented by the link cost. Figure 2.8 shows a ZigBee network. The link cost from node A to B is different from B to A (asymmetric link) because A and B do not have the same transmission powers and receiver sensitivities. When the nodes A and E use the same route B–D to exchange information, it is considered symmetric. In asymmetric routing, the destination node uses a different path to transmit to the source. In Figure 2.8, the source A uses the B–D path to send a packet to E, and E use the path C to send the packet to A.
Figure 2.8 Asymmetric link
- Fragmentation: ZigBee PRO provides fragmentation of large packets into smaller packets for transmission. The destination node will reassemble the packets.
- Power management: In ZigBee PRO, only the end devices are powered by batteries; the routers and coordinator use main power. ZigBee PRO allows end devices to go into sleep mode so that they consume less power. While the end device is in sleep mode, the node will miss any network key updates from the trust center. When the device wakes up, it uses its link key to send a message to the trust center to obtain an updated network key.
- Routing: ZigBee PRO offers two types of routing: many-to-one routing and multicast routing. Many-to-one routing is used for the network with a concentrator.
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Security: ZigBee PRO offers two security modes, as follows:
- Standard mode: In standard mode, the device is permitted to use the network key and link key. The network key is a standard key and all devices share the same key. In this mode, devices do not require authentication to join a network. The trust center, master key, and SKKE are optional. The trust center for ZigBee PRO standard security mode is used for transporting the network key.
- High-security mode: In this mode, three keys are permitted for use: the network, link, and master keys. The trust center and SKKE are mandatory. The trust center uses the transport key command to transport the link and network keys to the devices in the network. The device is required to perform authentication with its parent, and it is required to perform authentication between neighbors.
- Trust center: ZigBee PRO should have a trust center; the trust center can be a router, coordinator, concentrator, or specific device.
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Table 2.3 shows a comparison of ZigBee 2006, ZigBee, and ZigBee PRO feature sets.
Table 2.3. Comparison of 2006, ZigBee, and ZigBee PRO Feature Sets
|
ZigBee Features |
2006 Specification |
ZigBee Feature Set Specification |
ZigBee PRO Feature Set Specification |
|
Network coordinator selects best channel at startup. |
Yes |
Yes |
Yes |
|
During operation can detect interference and change channel operation. |
No |
Yes |
Yes |
|
Distributed address assignment. |
Yes |
Yes |
No |
|
Stochastic address assignment. |
No |
No |
Yes |
|
Supports group addressing. |
Yes |
Yes |
Yes |
|
Many-to-one routing. |
No |
No |
Yes |
|
128-bit Advanced Encryption Standard (AES) with message integrity code (MIC). |
Yes |
Yes |
Yes |
|
Trust center can be any device or coordinator in the network. |
Coordinator |
Coordinator |
Any device |
|
Network scale up limited to address assignment scheme. |
Yes |
Yes |
No |
|
Message fragmentation is permitted. |
No |
Yes |
Yes |
|
Supports buffering for message fragmentation. |
No |
Yes |
Yes |
|
Supports commissioning tool. |
Yes |
Yes |
Yes |
|
Device keeps information about its neighbor devices. |
No |
No |
Yes |
|
Offers high-security mode. |
No |
No |
Yes |
|
Network topologies. |
Tree and mesh |
Tree and mesh |
Mesh |