The server then tells the client the current time in a human readable format and then closes the connection. On the other hand the time protocol, specified in RFC 868, specifies a binary representation for the time that's legible to computers. Both daytime and time send the same information. However they use different formats and protocols to send it. There are as many different kinds of protocols as there are services that use them.
Lockstep protocols require one response for each request.
Some protocols like FTP use multiple connections. Most use only one. Some protocols like HTTP allow only one request and response per connection. Others, like FTP, allow multiple requests and responses over each connection. However the heart of the class are the methods that allow you to get an InputStream from a URL so you can read data from a server.