• What does a network do - It lets us communicate.


• Start by thinking of a telegraph machine.

- a talker hits a key and a pulse is sent along a wire to a receiving station

- at the receiving station a listener hears the pulses

- the sequence of the pulses (morse code) determine the message

- the two take turns talking and listening to communicate


• Computer networks work exactly the same way (just a bit faster)

- instead of keying stations we have network cards and cables

- there are many talkers and listeners

- instead of morse code we use ASCII to transmit letters, numbers, etc.

- there are certain methods for determining who is listening and who is talking (eg, FTP)




• A small network is called a Local Area Network (LAN) and only connects a few computers for fast communication.


• We can connect smaller networks to larger networks that may just go across campus. These are Wide Area Networks (WAN).



• The Internet is just a lot of LANs and WANs connected together. If your computer is on one LAN that is connected to the Internet, you can reach computers on other LANs.


• The information that networks typically communicate includes,

email - text files, binary files (MIME encoded)

programs - binary, or uuencoded

web pages - (HTML) Hyper Text Markup Language


• To transfer this information we count on access procedures that allow agreement about when computers talk and listen, and what they say.

email - (SMTP) Simple Mail Transfer Protocol, POP3, IMAP

programs - (FTP) File Transfer Protocol

login sessions - Telnet

web access - (HTTP) Hyper Text Transfer Protocol






1.1.1 Computer Addresses


• Computers are often given names, because names are easy to remember.


• In truth the computers are given numbers.



• When we ask for a computer by name, your computer must find the number. It does this using a DNS (Domain Name Server). On campus we have two ‘’ and ‘’.



• The number has four parts. The first two digits ‘148.61’ indicate to all of the internet that the computer is at ‘gvsu.edu’, or on campus here (we actually pay a yearly fee of about $50 to register this internationally). The third number indicates what LAN the computer is located on (Basically each hub has its own number). Finally the last digit is specific to a machine.




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