3.1 NETWORKS

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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

3.1.1 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 `148.61.1.10' and `148.61.1.15'.

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.