Basics of zigbee protocol layers
This page on zigbee tutorial covers zigbee protocol stack. It includes zigbee protocol layers viz. PHY,MAC,network,security and application layer.
The following figure depicts zigbee protocol stack,which consists of four layers viz. PHY,MAC,network & security and application layer. The first two are covered in IEEE 802.15.4 WPAN standard and the later two are covered in documents published by zigbee alliance.
Application Layer:
Pl. refer our article on Basics of OSI and TCPIP to understand application layer in general. There are two profiles at this layer. 1. Manufacturer specific application profile- Operate as closed systems and also ensure that they can coexist with other zigbee systems. 2. Public application profile- for this to work interoperability between various zigbee devices is a must. A single zigbee node supports up to 240 application objects called end points. An end point specifies specific application, for example, 0 dedicated to ZDO (Zigbee device object), provides control and management commands. 6 used for control of light. 8 used for managing heating and air conditioning.
Network Layer:
Ad-hoc on-demand Distance Vector Routing protocol (AODV) is used at network layer. Refer zigbee AODV protocol for more.
Security Layer:
If security is enabled, zigbee device will start up using a 128 bit AES encryption key.
Devices having same security key can communicate on PAN.
How to obtain this key?
1. Pre-installation
2. Key is received over the air during joining.
MAC Layer
Each MAC frame consists of three fields MAC header, MAC payload and MFR (FCS).
Each MAC frame will contain Frame control field (16 bit), which carry frame type, addressing fields and other control flags.
This MAC control field contain frame type field, which is the main differentiating factor in identifying one MAC frame with the other. It is 3 bit in length.
The MAC frames are divided into following four major categories,
which is used by zigbee devices to establish connection to the PAN by exchanging system information.
1. Beacon
2. Data
3. Acknowledgement
4. MAC command
Refer Zigbee MAC frame formats which describes beacon, data, ack,frame and command frames.
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