Servlet was designed to be used as an Interface to be implemented on any protocol.
Technically Servlet supports most of the commonly used protocols
Stated like that, this is really not correct. The request/response architecture of the servlet API limits it to those protocols that can reasonable be used that way, and many common protocols just can't. In practice, no servlet implementation exists that supports anything but HTTP/HTTPS and -more recently- SIP.
See where your hand is? Not there. It's next to this tiny ad: