XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
©2014DigiInternationalInc. 131
The streaming limit (TT Command) is specified by the transmitting module as the maximum num-
ber of bytes the transmitting module can send in one transmission event. After the TT parameter
threshold is reached, the transmitting module will force a random delay of 1 to RN delay slots
(exactly 1 delay slot if RN = 0).
Subsequent packets are sent without an RF initializer since receiving modules stay synchronized
with the transmitting module for the duration of the transmission event (from preceding packet
information). However, due to interference, some receiving modules may lose data (and synchro-
nization to the transmitting module), particularly during long transmission events.
Once the transmitting module has sent all pending data or has reached the TT limit, the transmis-
sion event ends. The transmitting module will not transmit again for exactly RN delay slots if the
local (i.e. transmitting module’s) RN parameter is set to a non-zero value. The receiving module(s)
will not transmit for a random number of delays between 0 and (RN-1) if the local (i.e. receiving
module’s) RN parameter is set to a non-zero value. These delays are intended to lessen congestion
following long bursts of packets from a single transmitting module, during which several receiving
modules may have become ready to transmit.
Repeater Mode
Characteristics: Self-organizing - No route configuration is necessary
Self-healing / Fault-tolerant
Low power consumption and Minimized interference
Network throughput is determined by number of hops, not by number of
repeaters. Multiple repeaters within range of source node count as one hop.
Supports “transparent” multi-drop mode or addressed data filtering mode.
Duplicate RF packets are automatically filtered out.
All packets propagate to every node in the network (filtering rules apply).
Broadcast communications - each packet comes out every node exactly once.
Addressed communications - all radios see every packet. Only the module with
a matching address will forward it to the DO buffer (UART IN).
Data entering the network on any module is transmitted and forwarded through
every repeater module until it reaches the ends of the network.
Each repeater will repeat a packet only once.
Constraints: Requires that each module have a unique MY (Source Address) parameter.
System must introduce just one packet at a time to the network for
transmission (256 bytes max).
Each hop (H) decreases network throughput by a factor of 1/(H+1). Additional
repeaters add network redundancy without decreasing throughput.
Required Parameter Values (TX Module): MD = 3 or 4, MY = unique value (can be accomplished by
issuing the AM (Auto-set MY) and WR (Write) commands to all modules in the network).
Related Commands: Networking (MD, DT, MY, AM), Serial Interfacing (RN, PK, RO, RB).
Recommended Use: Use in networks where intermediary nodes are needed to relay data to
modules that are beyond the transmission range of the base module.
Theory of Operation
Integrators can extend the effective range and reliability of a data radio system by forwarding
traffic through one or more repeaters.
Instead of using routing tables and path discovery to establish dynamic paths through a network,
the repeater system uses a sophisticated algorithm to propagate each RF packet through the
entire network.
The network supports RF packets of up to 256 bytes. The repeater network can operate using
broadcast or addressed communications for multi-drop networks and works well in many systems
with no special configuration.
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