Broker vs bridge vs gateway

Hi All
Can you please help me to understand the difference in the terminology between broker vs bridge vs gateway from control point of view?
Different people use it in different way.

Please correct me if i am wrong : To me gateway is a hardware device which allows the data to flow between different protocols eg. modbus RTU and Modbus ASCII. Is software solution possible for the gateway at all? or does it depend if the protocols on both ends of the gateway are on the same physical layer (in which hardware solution is needed) or if the same protocol is used then maybe software solution is possible.

I am less clear on broker and bridge

Regards
 
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