Use a sequence diagram to describe the interactions among the participating processes.
Consider the Simple Mail Transfer Protocol (SMTP)4.An excerpt from the RFC for this protocol provides the following sample session.
```
R: 220 USC-ISI.ARPA Simple Mail Transfer Service Ready
S: HELO LBL-UNIX.ARPA
R: 250 USC-ISI.ARPA
S: MAIL FROM:
R: 250 OK
S: RCPT TO:
R: OK
S: DATA
R: 354 Start mail input; end with .
S: Blah blah blah...
S: ...etc. etc. etc.
S: .
R: 250 OK
S: QUIT
R: 221 USC-ISI.ARPA Service closing transmission channel
```
Computer Science & Information Technology