• 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 ‘184.108.40.206’ and ‘220.127.116.11’.
• 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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