Telegesis (UK) Limited
TG-ETRXn-UG-01-103
10
User Guide
1.04
ETRX1 and ETRX2
©2008 Telegesis (UK) Ltd
ETRXn User Guide (Rev 1.04)
Another scenario is that a node scans for an available network to join, and if no network is found
the node can choose to become a coordinator and start its own network as described above.
Remote nodes are then capable of finding this newly established network and joining it. As more
and more remote nodes join, the network grows from the inside out. If the network is spread over
a wide area, a new node may be out of range of the coordinator and will join the PAN via another
node, which will act as a router. Messages may then pass across the network in more than one
“hop”.
The Telegesis AT command driven software supports point-to-point messages travelling up to six
hops and broadcast messages travelling up to ten hops through the network.
In the examples of Section 3.3, the commands used to establish and maintain a network are
described. For a list of all available commands please refer to the AT-Command dictionary
document.
3.2 Device Types
A ZigBee
®
network can consist of three different device types:
ZigBee Coordinator (ZC)
ZigBee Router (ZR)
ZigBee End Device (ZED)
ZigBee Coordinators, Routers and End Devices were formerly known as Coordinators, Full
Function Devices and Reduced Function Devices. ZigBee End Devices can be further classified
as Sleepy End Devices (SED) and Mobile End Devices (MED).
A ZigBee Router can route messages between ZigBee
®
devices, whereas a ZigBee End Device
does not provide any routing capabilities. The primary difference between the two is that a ZR
needs to constantly be awake in order to fulfil its routing responsibilities, whereas a ZED can spend
its life in sleep mode as it has no routing responsibilities.
ZRs consequently consume more power than ZEDs, therefore you must evaluate which type of
device will suit your application best. See Section 10 for a list of example scenarios.
A Coordinator is effectively a Router which has started the network. Each network must have only
one coordinator node. With the meshing stack of EmberZNet a mesh will continue to function even
if the coordinator leaves the PAN.
A ZigBee End Device has no routing responsibilities and joins the network via a ZigBee Router (its
“parent”). The parent will buffer up incoming messages for its “child” while it is asleep. The child
should poll regularly to check if there are any new messages pending on the parent device to
prevent loss of messages due to buffer overflow. The parent will also act as a relay point for its
childrens' outgoing messages. For example when a child wants to send a broadcast it sends the
data to its parent and the parent in turn will initiate the broadcast.
There are two different types of ZigBee End Devices defined in EmberZNet:
sleepy end device
mobile end device
The sleepy end device will remain in its parent‟s child list permanently (or until the parent is reset
or leaves the network by itself). This implies that the sleepy end device should not physically move
away from its parent and join a new parent, as it will still block a child entry at its previous parent.
A mobile sleepy end device will time out and be erased from the parent‟s child table if it does not
poll its parent within 3 seconds. When a mobile end device cannot find its parent it assumes that it
has moved and will search for a new parent. A device need not be defined as “mobile” merely if it
