User's Manual

Protocol Operation

Crescendo UHF Half-Duplex User Manual Page 35 of 78

6.3 Point-to-point Protocol

The point-to-point protocol establishes a connection between two end points. Both end points must have the

point-to-point protocol selected on the same serial port, and have the point-to-point destination set to the

remote radio modem address.

There are two operational modes configurable for the point-to-point protocol:

 Connection Based: This mode of operation provides a connection oriented link. It will report the

state of the connection via the RF link status parameter (either connected or not connected) and the

online LED will be solid green. If there is no data being transferred between the end units

background polling packets are sent to maintain the connection.

 Connectionless: This mode provides a packet oriented link. It does not maintain the state of the link

through background polling.

When operating in point-to-point mode, the radio will send all data to a fixed destination. Data inserted at

one end will appear at the other end. This is the simplest method of creating a wire replacement link.

Point-to-point applications are given in section 7.1 on page 44.

6.4 Point-to-multipoint Protocol

In a point-to-multipoint network, data transmitted by a unit is output by all the remotes and intervening

store-and-forward repeaters.

When using point-to-multipoint protocol, there are no acknowledgments on transactions. This is because

multiple units may be receiving the data, and if they were to all attempt to acknowledge the transmission,

they would interfere with each other.

Instead of acknowledgements, a unit will transmit each message a fixed number of times equal to the

broadcast retries parameter. For this reason, the number of retransmissions used in a point-to-multipoint

network should be configured to maintain a reasonable throughput.

Point-to-multipoint applications are given in section 7.2 on page 48.

6.4.1 Strict and Relaxed Addressing

The point-to-point and point-to-multipoint protocols can use strict or relaxed addressing. When strict

addressing is used:

 If point-to-multipoint protocol is selected, only data transmitted by a unit that is also in point-to-

multipoint protocol will be output on the serial port.

 If point-to-point protocol is selected, only data transmitted by the receiver’s destination will be

output on the serial port.

 If relaxed addressing is used, data will be output regardless of the source address or source

protocol mode. Data transmitted by a unit in point-to-multipoint mode will be output on units in

point-to-point and point-to-multipoint mode. Data transmitted by a unit in point-to-point mode will

be output on the destination, regardless of its point-to-point destination address, as long as it is in

point-to-point or point-to-multipoint mode.

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