want know about network protocol testing

Hi guys,
i want to know about network protocol testing.

  1. What is network protocol testing?
  2. Whats the role of network protocol tester?
  3. Is there good future scope in network protocol testing field?
  4. Just give me a example of protocol testing.
  5. How it relates to perl or unix?
    Thanks in advance
    Cheers,
    Ranga:-)