Libelium Waspmote 868LP, Сетевое руководство

Страница: 18 / 31

-18- v7.1
Networking methods
7. Networking methods
Note: It is important to keep in mind that XBee networks are defined by the networking parameters. Every XBee
module within a network must share the same networking parameters. In the case of the XBee 868, every node in a
network must have the same:
• PAN ID
• Channel mask
• Preamble ID
7.1. Topology
The XBee 868LP provides a star topology to create a star network has a central node, which is linked to all other
nodes in the network. The central node gathers all data coming from the network nodes.
Figure : Star Topology
7.2. Addressing
Every RF data packet sent over-the-air contains a Source Address and Destination Address field in its header. XBee
868LP supports long 64-bit addresses. A unique 64-bit IEEE source address is assigned at the factory and can be
read with the functions explained in the chapter related to MAC address.
XBee 868LP support Unicast and Broadcast transmissions:
•
Unicast: The unicast mode is the only mode that supports acknowledgements (ACKs). When a packet is sent
using unicast mode, the receiving module sends an affirmative response to the sending module. If the sending
module does not receive the ACK, it will re-send the packet up to ten times or until the ACK is received. To send
a unicast message, the 64-bit receiver’s address must be set correctly.
•
Broadcast: Used to transmit all modules in the same network. Any RF module within range will accept a
packet that contains a broadcast address. When a packet is sent using broadcast mode, receiving modules do
not send ACKs. All broadcast packets are automatically transmitted four times to ensure it is received. To send
a broadcast message, the receiver address must be set to 0x000000000000FFFF.