Wireless sensor networks -- ZigBee and 6LoWPAN

ZigBee topology

Three structures ： Stars 、 Tree and mesh topologies .

Star topology is the easiest topology to implement , But because of ZigBee Coordinator limitations , Not suitable for large-scale networks , Once the coordinator fails , Then the whole network will be affected

More flexible tree structure , Its deployment is not limited by the coordinator , You can also use ZigBee Routers use sub devices to expand the scope . It is easy to implement the routing protocol , Each device only needs to maintain a tree table, but there is no alternative route in case of node failure

Mesh topology is more flexible than tree topology , Each device can communicate directly , And when the halfway route fails , You can choose another route to replace .

In general ,ZigBee The network is a hybrid network structure , One ZigBee The terminal device of can only communicate with its parent node , It does not involve the forwarding function of network communication

ZigBee Address assignment scheme

1. Cskip：
   • Cm: The total number of child devices that each parent device can have
   • Rm: Each parent device can have a total number of routers
   • Lm： The maximum depth of the network
   • d： The actual network depth of the device

above 4 All parameters are stored in ZigBee In the network information base of the coordinator . The number of terminal devices that the router device can accept is calculated according to this formula ：
MaxEndDevices = MaxChildren - MaxRouters = Cm - Rm

The picture below is Cskip The method of calculating the total number of possible successor nodes in any branch of the existing network

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-LhP2HSLV-1656730641139)(C:\Users\14645\AppData\Roaming\Typora\typora-user-images\image-20220702094304486.png)]

In any ZigBee In the network , The maximum number of network nodes is 65535.

Cskip(d) It is usually assigned to the router and its terminal equipment as an address offset
Give the router Rn How to assign addresses ：Rn = R1 + （n - 1）x Cskip（d）

ZigBee Management mechanism

1. Address management

​ The management mechanism includes address management 、 Describe management 、 Discovery and binding of devices and services

​ ZigBee The network can be used 64 Bit extended address can be used 16 Bit network address , But in order to solve the problem that multiple objects share a physical address , Need to use the concept of endpoint addressing .

​ There are two in the figure below ZigBee equipment A and B,A Terminal in 1 adopt IEEE 802.15.4 Standard request device A and B Establish wireless communication channel , But there's a problem ,B How to identify the terminal 1 It communicates with the humidity sensor ,ZigBee The specification defines a child addressing mode — Endpoint , Therefore, the initiator of the communication specifies the endpoint with which it establishes communication ,ZigBee In the equipment ZigBee The protocol stack can easily determine the target object

2. Describe management

​ Description management is ZigBee Standardized communication basis , By the information 、 The protocol of information format and processing action constitutes , Define the processing action protocol to ensure cooperation within the system , Enable different components to create interoperable distributed applications .

As shown in the figure below , describe ID Long 8 position , Identify the attribute of the current description .

Public description ID For the range of 0x0000 - 0x7FFF, Private description ID The scope of the oxbf00 - 0xFFFF

3. ZigBee binding

   The logical relationship between two endpoints without devices .

   See why binding is needed through the following figure . In four cases , Some switches are one to many , Some are many to one , Using traditional methods to implement it will do a lot of repetitive work .

Use binding mechanism to improve efficiency . The coordinator is always working , So it is used to store binding tables , Record two items ：1. switch 1 Endpoint and original address of , And lights 1 And lamp 2 The endpoint of and the matching address ;2. switch 2 Endpoint and address of , And lights 3 The endpoint of and the matching address . If the switch 1 Need to start the light 1 And lamp 2, Then switch 1 Send instructions and its own address to the coordinator . The coordinator receives the instruction and searches the binding table , Find the lamp 1 And lamp 2 The address of , Then the coordinator replaces the target address of the instruction with a lamp 1 And lamp 2 The address of , And send it automatically , Finally switch 1 You can control the light 1 And lamp 2.

6LoWPAN And wireless sensor networks

​ 6LoWPAN send IPv6 Can be directly based on IEEE 802.15.4 Low power WSN Work on , Make it easier for wireless nodes to access the Internet

1. WSN The advantages of Internet Application ：

   • Using a IP Existing network architecture of the Protocol , Interoperability can be achieved
   • Wireless devices can easily connect to the Internet without a gateway
   • have access to HTTP、SNMP and DPWS And other established application protocols and data models
   • Use the transmission protocol to provide a certain degree of reliability for networks with unreliable connections

2. Protocol stack

   LoWPAN Layer in MAC Layer and the IPv6 Between , function ：IPv6 Compression of the head 、IPv6 Fragment of load 、UDP Compression of the head

   

3. Configure the instance

   Every LoWPAN By a border router , A number of LoWPAN Router and several hosts (H) form , There is also a remote server on the Internet

• LoWPAN Problems needing attention when connecting to the Internet
  • 6LoWPAN The application of should make the data packet as small as possible , Prevent the packet from being divided into several IPv6 package
  • End to end application protocols should take advantage of UDP And compact load format to accommodate 6LoWPA Use of nodes
  • Firewall and URL conversion
  • IPv4 interconnection
  • safety problem

Make the packet as small as possible , Prevent the packet from being divided into several IPv6 package

• End to end application protocols should take advantage of UDP And compact load format to accommodate 6LoWPA Use of nodes
• Firewall and URL conversion
• IPv4 interconnection
• safety problem