String that will be used to determine the type of source in use (file, remote/local interface).
This string will be prepended to the interface name in order to create a string that contains all the information required to open the source.
This string indicates that the user wants to open a capture from a network interface. This string does not necessarily involve the use of the RPCAP protocol. If the interface required resides on the local host, the RPCAP protocol is not involved and the local functions are used.