Packet filtering in operation
Packet filtering is an optional feature of the ZigBee PRO stack that is applied by the IEEE 802.15.4 MAC layer. It is useful during network joining, route discovery and normal network operation to optimize the processing of received packets.
Network joining
During network joining, a form of packet filtering is applied to the results of the network discovery phase. Any potential parents that have been discovered are filtered such that nodes with link costs greater than 5 (low LQI values) are discarded. This feature aids the formation of networks with strong links between neighbors and is most effective in dense networks. For more information about this process during network joining, refer to the ZigBee specification.
Parent topic:Packet filtering in operation
Route discovery and normal network operation
In a large network, traffic levels are high during both route discovery and normal operation, and a node is likely to receive many data packets. There is, however, limited storage capacity on a node to hold these packets until they can be processed. To restrict the number of received packets that are submitted to the receive queue, the following filtering system is applied:
All unicast packets are queued (without filtering) provided that sufficient space is available in the receive queue.
Broadcast packets are queued provided that at least 50% of the receive queue capacity is free, otherwise the packet filtering mechanism is applied and only packets with a link cost of 5 or less are queued.
During route discovery, this filtering prevents nodes with low associated LQI values from being entered into the Neighbor table, allowing reliable routes to be established. For example, it may be more desirable to establish a route comprising multiple hops with good LQI values than a single hop with a poor LQI value.
Parent topic:Packet filtering in operation
Parent topic:Filtering packets on LQI Value/Link cost