Blindly trusting the numbers from this stack overflow thread (as I'm not that deep in the TCP protocol typically): https://stackoverflow.com/questions/31378403/how-much-data-it-cost-to-set-up-a-tcp-connection

Without keep alive it would be opened and closed each poll, so 296bytes / poll. 24 * 3600 * 296 = 25574400 so maybe 25.5MB / day

But I would still encourage you to meter it if that overhead is important.

Not really a Mango question, and offhand I wouldn't expect it to have an easy answer other than 'a little'. I would imagine it to depend upon the size and frequency of the requests. I would encourage you to test! I would expect more savings as the polls got faster and to some extent larger, and expect it to consume more bandwidth if the polls were very infrequent (looks like > 2 hours by default) and TCP keep alive traffic composes most of the bandwidth usage.

• This stack overflow thread is relevant: https://stackoverflow.com/questions/1480236/does-a-tcp-socket-connection-have-a-keep-alive
• The use of keepAlive as a setting is in the TcpMaster: https://github.com/infiniteautomation/modbus4j/blob/master/Modbus4J/src/com/serotonin/modbus4j/ip/tcp/TcpMaster.java