We saw that a mailbox tied to a particular process on a system is called a port; each port is identified by a number. So, for example, the port to which to direct a request for a web page is number 80. What port numbers are used for:

a. ssh (secure shell logins)?

b. smtp (simple mail transfer protocol)?

c. ntp (network time protocol)?

Are these port numbers the same across standard Internet-connected systems?