A24-HASM-450 Digi International/Maxstream, A24-HASM-450 Datasheet - Page 19

• Manufacturer Part Number: A24-HASM-450
• Description: ANT 2.4GHZ DIPOLE HALF-WAVE
• Manufacturer: Digi International/Maxstream
• Series: XPressr

Specifications of A24-HASM-450

• Antenna Type: Whip: 1/2 Wave, Swivel, Tilt (Right Angle)
• Number Of Bands: 1
• Frequency: 2.4GHz
• Vswr: 2
• Gain: 2.1dBi
• Termination: RP-SMA
• Mounting Type: Connector
• Height (max): 4.35" (110.5mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 70000340; Q2724499B

XBee/XBee‐PRO OEM RF Modules ‐ ZigBee ‐ v1.x1x [2007.06.01]
Chapter 3 ‐ ZigBee Networks
address that corresponds to a known 64-bit address. Once the 16-bit address is known, a route to
the destination device must be discovered. ZigBee employs mesh routing using the Ad-hoc On-
demand Distance Vector routing (AODV) protocol to establish a route between the source device
and the destination.
Network Address Discovery
Data transmissions are always sent to the 16-bit network address of the destination device.
However, since the 64-bit address is unique to each device and is generally known, ZigBee devices
must discover the network address that was assigned to a particular device when it joined the PAN
before they can transmit data.
To do this, the device initiating a transmission sends a broadcast network address discovery
transmission throughout the network. This packet contains the 64-bit address of the device the
initiator needs to send data to. Devices that receive this broadcast transmission check to see if
their 64-bit address matches the 64-bit address contained in the broadcast transmission. If the
addresses match, the device sends a response packet back to the initiator, providing the network
address of the device with the matching 64-bit address. When this response is received, the
initiator can then transmit data.
Mesh Routing
Mesh routing allows data packets to traverse multiple nodes (hops) in a network to route data
from a source to a destination. The route a packet can take in a mesh network is independent of
the parent/child relationships established during joining. Before transmitting a data packet from
source to destination nodes, a route must be established. Route discovery is based on the AODV
(Ad-hoc On-demand Distance Vector routing) protocol.
AODV (Ad-hoc On-demand Distance Vector) Routing Algorithm
Routing under the AODV protocol is accomplished using tables in each node that store in the next
hop (intermediary node between source and destination nodes) for a destination node. If a next
hop is not known, route discovery must take place in order to find a path. Since only a limited
number of routes can be stored on a Router, route discovery will take place more often on a large
network with communication between many different nodes.
When a source node must discover a route to a destination node, it sends a broadcast route
request command. The route request command contains the source Network Address, the
destination Network Address and a Path Cost field (a metric for measuring route quality). As the
route request command is propagated through the network (refer to the Broadcast Transmission),
each node that re-broadcasts the message updates the Path Cost field and creates a temporary
entry in its route discovery table.
When the destination node receives a route request, it compares the ‘path cost’ field against
previously received route request commands. If the path cost stored in the route request is better
than any previously received, the destination node will transmit a route reply packet to the node
that originated the route request. Intermediate nodes receive and forward the route reply packet
to the Source Node (the node that originated route request).
Retries and Acknowledgments
ZigBee includes acknowledgment packets at both the Mac and Application Support (APS) layers.
When data is transmitted to remote device, it may traverse multiple hops to reach the destination.
As data is transmitted from one node to its neighbor, an acknowledgment packet (Ack) is
transmitted in the opposite direction to indicate that the transmission was successfully received. If
the Ack is not received, the transmitting device will retransmit the data, up to 4 times. This Ack is
called the Mac layer acknowledgment.
In addition, the device that originated the transmission expects to receive an acknowledgment
packet (Ack) from the destination device. This Ack will traverse the same path that the data
traversed, but in the opposite direction. If the originator fails to receive this Ack, it will retransmit
the data, up to 2 times until an Ack is received. This Ack is called the ZigBee APS layer
acknowledgment.
Refer to the ZigBee specification for more details.
© 2007 Digi International, Inc.
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