Appendix 3
Serial Port Data
It is not practicable for data to be sent over the network one character at a time. Therefore
Netiom-UDP packages the data for onward transmission.
As each character is received from the serial port it is placed into a 64 byte buffer. When a
packet is complete with either a carriage return / line feed pair or a break of transmission as
defined by the user it is packed into a UDP packet and transmitted.
If the package size reaches the buffer limit again it is packaged up and sent to the remote
end.
Inherent in this process is a transmission latency. Transmission at the remote end will not
commence until reception at the local end is complete (or the buffer is full). Systems using the
serial port must take this latency into account especially if retries and timeouts are employed.
Problems may also be encountered if large amounts of data is to be transmitted. Netiom-UDP
uses a strategy of acknowledgements and retries to minimise the effect of lost data packets.
However Netiom-UDP has limited storage for holding data for retransmission and if an
acknowledgement has not been received before another packet is ready for transmission the
new packet will be transmitted and the previous pack discarded. Normally this will not cause
problems as the data loss is relatively rare but critical data should be checked within the
receiving application.
