How does the session ID differ from port number?

The difference between Session ID & Port Numbers:

Session ID keep data streams separate. Port numbers identifies the process of where a network message should be forwarded on a server.

A session ID is a unique number that a Web site's server assigns a specific user for the duration of that user's visit (session). A port number is a way to identify a specific process to which an Internet or other network message is to be forwarded when it arrives at a server.