This is a list of the world's largest armies, measured by the number of soldiers in uniform. This is not a list of the world's strongest armies, since military power is not simply a function of headcount.
Protocol is defined as the rules and customs of a group or a standard procedure. An example of protocol is the method by which a learning center must document their students' progress. YourDictionary definition and usage example.
All communications between devices require that the devices agree on the format of the data. The set of rules defining a format is called a protocol. In addition, protocols can include sophisticated techniques for detecting and recovering from transmission errors and for encoding and decoding data.