5. CONFIGURATION
2. First attempt for message transmitting, after initial time-out.
3. Second attempt for message transmission, after two times the initial time-out.
4. Third attempt for message transmission, after two times the latter time-out.
5. Quit of message transmission and failure indication, after the communication time-out exceeds (total time until the given
up: 300 + 600 + 1200 + 900 = 3000 ms).
6. It would be the fourth message transmission attempt, after two times the latter time-out but the communication time-out
configured inside the protocol was exceeded and the failure was indicated.
ACK sending delay: defines the maximum time waited by the interface for the TCP ACK transmitting. This ACK is
responsible for the message receiving conformation, in case of MODBUS, by the destiny device. The set of this field decreases
the amount of messages circling through the network. This mechanism is explained below:
All request messages, sent by a client to a server, need to be confirmed by the server through an ACK message transmitted
to the client.
All response messages, sent by a client to a server, need to be confirmed by the server through an ACK message
transmitted to the client.
If one of the parts does not receive the ACK message, within the time defined by the TCP time-out, the message will be
retransmitted by the origin address (see TCP number of tries parameter).
The ACK message does not need to be exclusive. The ACK needed to be sent by the server to the client, at the moment
it receives a request, can be included in the same answer message, and the ACK needed to be sent by the client to the
server, at the request moment, can be included in the same message including the next request.
The following pictures depict the difference between the sending of an immediate and a calibrated ACK:
Figure 44: Example of an Immediate ACK Sending (=0)
Figure 45: Example of a Calibrated ACK Sending
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