AeroComm ZB2430 manual F i g u r e 6 Z i g B e e R o u t e R e p l y

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T HE O R Y OF O P E R A TI O N

One of two things will happen when Nodes 1 and 2 receive the RREQ from Node 0:

•If a route is known or if they are the destination radio, they can send a Route Reply (RREP) back to Node 0.

•If they do not know the route and are also not the destination radio, they will rebroadcast the RREQ to their neighbors. The message keeps re-broadcasting until the lifespan (specified by the source radio) expires.

If Node 0 does not receive a reply within a set amount of time, it will rebroadcast the message, this time with a longer lifespan and a new ID number.

In the example, Node 1 does not have a route to Node 3 and therefore rebroadcasts the RREQ (see Figure 6: "ZigBee Route Reply" on page 18). Node 2 however, does have a route to Node 3 and therefore replies to the RREQ by sending out a RREP. Node 2 also sends a RREP to Node 3 so that it knows the route to Node 0.

F i g u r e 6 : Z i g B e e R o u t e R e p l y

C o o r d i n a t o r A d d r e s s i n g

Since the Coordinator’s NWK address is always 0x0000, it can be addressed using its 16-bit NWK address.

B r o a d c a s t T r a n s m i s s i o n s

Since ZigBee is targeted for large-scale applications in which all radios may not be in range of a single radio, broadcast packets are retransmitted throughout the network. Broadcast transmissions in ZigBee utilize a passive acknowledgement mechanism; meaning that the Coordinator and all Routers keep track of whether or not their neighbor(s) have relayed the broadcast packet and will re-broadcast the packet until all of their neighboring devices have received the packet. Any device can initiate a Broadcast transmission by programming its Destination Address with a Broadcast Address (see Table 4 on page 19). Subsequent broadcast transmissions occur every 500ms.