Suppose you have a server called fred.bloggs.ac.uk at your institution and you have written some nice server which is listening on port 9999 and some nasty man suddenly in the middle of your course blocks port 9999. What do you do?
Luckily you can SSH onto fred.blogs.ac.uk
(1) Run you server as normal on fred.blogs.ac.uk listening on port 9999.
(2) then type: ssh -L4950:fred.bloggs.ac.uk:9999 fred.bloggs.ac.uk
(3) finally point your clients at your machine port 4950 and off you go!