Point-to-point/multipoint (P2MP)
XLR PRO Radio Frequency (RF) Modem User Guide
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Transparent mode uses the TO parameter as its default delivery method. For API transmissions, the TxOptions API
field is used to specify the delivery method. When the TxOptions API field is set to 0, the value in the TO parameter will
also be used by API transmissions.
The two delivery modes are described below.
Point-to-point/multipoint (P2MP)
P2MP delivery mode does not use a network header, only the MAC header. All messages are always sent directly to the
destination. There is no repeating of the packet by other nodes.
A P2MP unicast is only delivered directly to the destination radio, which must be in RF range of the sending radio. The
XLR PRO uses patented technology that allows the destination radio to receive transmissions directed to it, even
when there is a large amount of RF traffic. This works best when broadcast transmissions are kept to a minimum. A
P2MP broadcast transmission is repeated MT+1 times by the sending node, but is not repeated by nodes which
receive it, so like a unicast transmission, the receiving radio must be in range. All radios that receive a P2MP broadcast
transmission will output the data through the active serial interface.
Repeater/directed broadcast
Related parameters: CE, NH, NN, BH
Ethernet RF bridging does not support repeater/directed broadcast. All Ethernet frames are transmitted as point-to-
point or point-to-multipoint regardless of what the TO parameter is set to.
Directed broadcast transmissions will be received and repeated by all routers in the network. Because ACKs are not
used the originating node will send the broadcast multiple times. By default a broadcast transmission is sent four
times. Essentially the extra transmissions become automatic retries without acknowledgments. This will result in all
nodes repeating the transmission four times as well. Sending frequent broadcast transmissions can quickly reduce
the available network bandwidth and as such should be used sparingly.
The MAC layer is the building block that is used to build repeater capability. Repeater mode is implemented with a
network layer header that comes after the MAC layer header in each packet. In this network layer there is additional
packet tracking to eliminate duplicate broadcasts. In this delivery method, unicasts and broadcast packets are both
sent out as broadcasts that are always repeated. All repeated packets are sent to every radio. Broadcast data will be
sent out the active aerial interface of all radios that receive it.
When a unicast is sent, it specifies a destination address in the network header. Only the radio that has the matching
destination address then will send it out the serial port. This is called a directed broadcast. Any node that has a CE
parameter set to route will rebroadcast the packet if its broadcast hops (BH) or broadcast radius values have not been
depleted. If a repeated broadcast has already been seen, the node will ignore it. The NH parameter sets the maximum
number of hops that a broadcast will be repeated. This value is always used, unless a BH value is specified that is
smaller.
By default the CE parameter is set to not route broadcasts. Due to the long-range of the XLR PRO, it is advised to
evaluate on a per-radio basis which nodes should be configured as repeaters. This will provide a more reliable
network by limiting the amount of congestion and RF traffic being generated.