1. Network overview
Forming a complete zigbee mesh network involves two steps: network initialization, and node joining the network. The node joins the network and includes two steps: connecting to the network through the coordinator and accessing the network through the existing parent node.
2. Network initialization preparation
The establishment of the Zigbee network is initiated by the network coordinator. Any zigbee node must meet the following two requirements to form a network:
(1) The node is an FFD node and has the capability of a zigbee coordinator;
(2) The node has not been connected to other networks. When the node is connected to other networks, this node can only act as a child of the network because there is one and only one network coordinator in a zigbee network.
FFD: Full FuncTIon Device fully functional node
RFD: Reduced FuncTIonDevice semi-functional node
3. Network initialization process
3.1 Determine the network coordinator:
First, it is judged whether the node is an FFD node, and then it is judged whether the FFD node has a coordinator in other networks or in the network. By active scanning, send a beacon request command (Beaconrequest command), and then set a scan period (T_scan_duraTIon). If no beacon is detected within the scan period, then the FFD is considered to have no coordinator in its pos, then this It is possible to build your own zigbee network and continue to generate beacons and broadcast them as coordinators of this network.
Note: There is one and only one coordinator in a network.
3.2 Perform the channel scanning process.
It includes two processes of energy scanning and active scanning: first, energy detection is performed on a specified channel or a default channel to avoid possible interference. Incrementally channel sort measured energy values, always such abandon energy value exceeds the allowable channel energy level, the energy level may be allowed to select a channel, and these channels are marked available channel. An active scan is then performed to search for network information within the communication radius of the node. The information in the form of beacon frames broadcast in the network node obtains the beacon frame by an active channel scan mode, and then based on that information, to find the best, relatively quiet channel, by the results recorded, selecting a channel, the channel should present minimal zigbee network, preferably no zigbee device. During active scanning, the MAC layer will discard all frames except the beacon received by the PHY layer data service.
3.3 Set the network ID.
After finding the appropriate channel, the coordinator will select a network identifier (PAN ID, value "=0x3FFF") for the network. This ID must be unique in the channel used and cannot conflict with other zigbee networks. Cannot be broadcast address 0xFFFF (this address is reserved and cannot be used). PAN ID can not select an ID conflict by listening to the network ID of another way to get, after the man may be designated channel scanning, PAN ID is determined not to conflict with other networks.
There are two address modes in the zigbee network: extended address (64 bits) and short address (16 bits), where the extended address is assigned by the IEEE organization for unique device identification; the short address is used for device identification in the local network, In a network, the short address of each device must be unique. When a node joins the network, it is assigned by its parent node and communicates by using a short address. For the coordinator, the short address is usually set to 0x0000.
After the above steps are completed, the zigbee mesh network is successfully initialized, and then waiting for other nodes to join. When the node enters the network, the parent node (including the coordinator) with the strongest signal in the selected range is added to the network. After successful, it will get a network short address and send and receive data through this address. The network topology relationship and address will be saved in their respective networks. In the flash.
4. The node joins the network through the coordinator
After the node coordinator determines, the node first needs to establish a connection with the coordinator to join the network.
In order to establish a connection, the FFD node needs to make a request to the coordinator. After receiving the connection request of the node, the coordinator decides whether to allow the connection according to the situation, and then responds to the node requesting the connection, and the node can establish the connection with the coordinator. Data is sent and received. The specific process of nodes joining the network can be divided into the following steps:
4.1 Find the network coordinator.
First will automatically scan for coordinators around the network, if a beacon is detected within the scanning period, it will get the information coordinator, then issues a connection request to the coordinator. After selecting the appropriate network, the upper layer will request the MAC layer to set the PIB attributes such as phyCurrentChannel and macPANID of the physical layer PHY and MAC layer accordingly. If not detected, the node re-initiates the scan after a period of time.
4.2 sends an association request command (Associaterequest command).
The node sends an association request command to the coordinator. The coordinator immediately responds with an acknowledgement frame (ACK) and sends a connection indication primitive to its upper layer, indicating that the node has received the connection request. But this does not mean that a connection has been established, only that the coordinator has received a connection request from the node. After receiving the upper layer coordinator mac connection indication primitive, the (storage space and energy) determines whether the resources according to their consent request to join this node, and then sends a response to the mac layer node.
4.3 Wait for the coordinator to process.
When the node receives the ACK of the coordinator joining the association request command, the node mac will wait for a period of time to accept the connection response of the coordinator. If a connection response is received within a predetermined time, it will advertise this response to its upper layer. When the coordinator sends a response to the mac layer of the node, a wait response time (T_ResponseWaitTIme) is set to wait for the coordinator to process the join request command. If the coordinator has sufficient resources, the coordinator will assign a 16-bit short to the node. The address, and a connection response command containing the new address and the connection success status, the node will successfully establish a connection with the coordinator and can begin communication. If the coordinator resources are insufficient, the node to be added will resend the request information and directly enter the network.
4.4 Send Data Request Command.
If the coordinator agrees to join the node within the response time, an association response command (Associateresponse command) is generated and the command is stored. When the response time elapses, the node sends a Datarequest command to the coordinator. The coordinator immediately responds with an ACK and then sends the stored association response command to the node. If, after the response time has elapsed, the coordinator has not decided whether to agree to join the node, the node will attempt to extract the association response command from the beacon frame of the coordinator. If successful, the network connection may succeed. Otherwise, the request information is resent until the network access is successful.
4.5 Reply.
After receiving the association response command, the node immediately replies with an acknowledgement frame (ACK) to the coordinator to confirm receipt of the connection response command. At this time, the node will save the coordinator's short address and extended address, and the node's MLME sends the connection to the upper layer. Confirm the primitive and notify the association to join the successful information.
5. The node joins the network through the existing node.
When the FFD node and the coordinator close to the coordinator are successfully associated, other nodes in the network range join the network with these FFD nodes as parent nodes. There are two ways to join the network, one is through association. The method is that the node to be joined initiates the joining of the network; the other is the direct mode, that is, the node to be joined is specifically added to that node as a child node of the node. The correlation method is the main way for new nodes to join the network in the zigbee network.
Only for a node is not a member of the network had to be added to the network. Some of these nodes have been added to the network, but have lost contact with their parent nodes (such as orphan nodes), while others are new nodes. When it is an orphan node, it stores the information of the original parent node in its neighbor table, so it can directly send the request information of joining the network to the original parent node. If the parent node has the ability to agree to join, then it directly tells its previously assigned network address that it enters the network successfully; if at this time its original parent node's network, the number of child nodes has reached the maximum, that is, the network Once the address has been allocated, the parent node cannot approve it to join, it can only rediscover and join the network as the new node.
For a new node, he first looks for a network that can be found by actively or passively scanning around the network it can find on one or more pre-defined channels, and has the ability to approve the parent node to join the network and find the parent that can be found. data is stored in its own node adjacent table. The data stored in the parent node of the adjacent table includes the version of the zigbee protocol, the specification of the protocol stack, the PAN ID, and information that can be added. Select one of the smallest nodes in the neighbor table and send the request information. If there are more than two parent nodes with the same minimum depth, then one send request is randomly selected. If there is no information about the appropriate parent node in the adjacent table, it means that the network access fails and the process is terminated. If the issued request is approved, the parent node will also assign a 16-bit network address. At this point, the network access is successful and the child node can start communication. If the request fails, the neighbor table is re-discovered and the request information continues to be sent until the network is joined.
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