User's Manual

Radio Operation
Crescendo VHF Half-Duplex User Manual Page 25 of 74
Broadcast retransmissions: The number of retries to use on data that is destined for multiple
radios. This is applied to any transmission when using the point-to-multipoint protocol, or to any
packet addressed to the broadcast address when using the datagram protocol.
When a unit is broadcasting data, the transmission cannot be acknowledged, as collisions would occur
between the acknowledgements. Instead, a broadcasting unit will transmit all data a fixed number of times
equal to the broadcast retransmissions parameter, and receiving units will discard any duplicate data
received.
Two parameters determine how long the Crescendo will wait for an acknowledgement after transmission
before retrying. These parameters are:
Repeaters in Network: The maximum number of repeaters through which a packet must go before
reaching its destination. Note that this may be less than the total number of repeaters in the network.
This parameter should be set the same for all units in the network. The repeaters in network setting
can be configured between 0 and 65535.
Max Packet Size: This is the maximum number of bytes of payload a packet will have. This
parameter should be set the same for all units in the network. The max packet size can be
configured between 0 and 4096 bytes.
5.4 Network Architecture
5.4.1 Network Topology
The Crescendo has few restrictions on network topology, as there are no time division synchronisation
requirements. An example of a tree network topology is given below to help illustrate network concepts.
TREE NETWORK
A Crescendo network consists of a set of sub-networks (subnets). Each subnet has a single base or repeater
and any number of remotes.
1.
Base subnet: The root node of the tree, containing a unit not configured as a store-and-forward
repeater.
2. Repeater subnet: A branch node of the tree, containing a unit configured as a store-and-forward
repeater.
These two types of subnet are shown in Figure 5.