This is how a single machine can maintain 100s of Telnet sessions. This insures the uniqueness of each connection, while leaving port 23 open to answer future requests. These are also the unique ports to which each session is connected. TCP must have a set of commands that allow it to interact with Upper Level Programs. A Hierarchical Management structure for Host Names and IP numbers.
Host names can occur in several formats.
What DNS Does for us. Eliminates the need for Host tables on each machine. Central administration means single updates are seen by everyone and spread to other DNS servers. Eliminates single point of failure. Makes things like WWW work for real human beings.