Chapter 3Fluency with Information Technology
4th editionby Lawrence Snyder
(slides by Deborah Woodall : [email protected])
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Network Defined
computer networkTwo or more computer systems that can communicate with each other over some communications media.
communications media may be classified as•wired - telephone lines, coax, fiber optic•wireless - microwave, satellite
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Far and Near
• LAN – Local Area Network
• WAN – Wide Area Network
• The Internet – A global network of Wide Area Networks
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Classifying Communication
Communication can be classified as either…
• asynchronous – sending and receiving occur at separate times
• synchronous – sending and receiving occur at the same time
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Classifying Communication
AlsoCommunication can be classified as either…
• broadcast – one sender, many receivers
• multicast – one sender, many selected receivers
• point-to-point – one sender, one receiver
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Communication Classifications
• In one way or another the Internet offers all of these forms of communication.
• The Internet is truly a universal communications medium.
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The Client/Server Structure
• Most encounters on the Internet reflect the client/server structure.
• client: (e.g. your browser) requests a service (like a Web page)
• server: (e.g. Web Server) provides a service (like sending a Web
page)
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The Client/Server Structure
• A client and a server have one or more BRIEF relationships.
• An advantage: The server can handle many clients in a short period of time.
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IP Addresses
• Every transmitted message on the Internet requires a destination address
• IP address – the address of a computer connected to the Internet
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IP Addresses
• Each IP address is a series of 4 numbers separated by dots, e.g.
234. 18. 45. 1
• Each of the 4 numbers takes up one byte of memory, so an IP address is a 4 byte address.
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IP Addresses
The IP address from the previous slide would look like this when stored in RAM
234. 18. 45. 1
11101010 00010010 00101101 00000001
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IP Addresses
• How many numbers will fit into one byte?
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IP Addresses
• What would be the range of one of the numbers in an IP address?
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IP Addresses
Why is each of the following an invalid IP address?
34.678.32.90
-89.53.244.32
34.23.67.89.145
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IP Addresses
• And finally, how many IP addresses are possible using the current scheme?
232 >4.3 billion
• There is an upgrade being planned for IPv4 called IPv6 – a 16 byte IP addressing scheme - e.g.
69DC:77AC:FF66:A1A2:BCDF:77AC:FF66:3459
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IP Addresses
• Your PC has an IP address when connected to the Internet– temporary if connected by modem– permanent (or temporary) if connected to a LAN
• Computers deal with numbers but humans don’t do very well remembering numbers.
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Domain Names
• A domain is a related group of networked computers.
• A domain name is a symbolic name for a 4-byte IP address, and thus a particular computer on the Internet.
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Domain Names
• An example: www.mc.edu
www is a specific computer
in the mc domain
of the edu domain
• A domain name reveals a hierarchy.
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Domain Names
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Domain Names
• Original top-level domains
– .edu– .org– .net– .mil– .gov– .com
• Newer top-level domains
– .biz (businesses)– .info (information)– .museum (museums)– .name (individuals)– .pro (credentialed
professionals)– country codes
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Domain Names
The purpose of a top level domain name is to indicate
• Function, or• Location
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The Domain Name System
• We like www.jvim.com• Computers like 198.160.140.235
• Where does your browser get the IP Address for a domain name?
DNS Servers
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TCP/IP
• Once the address of the computer is found, how is the message actually sent over the Internet?
TCP/IP• TCP/IP protocol specifies that the message is
broken into pieces and each piece goes into a packet.
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TCP/IP
• Each packet contains– A piece of the message being sent
– The destination address for the packet
– The source address of the packet
– A collating number
• Each packet is independent.24
Ethernet
• How is a message sent over a LAN?Ethernet Protocol
• Ethernet also uses packets.
• Ethernet is a true broadcast medium.
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Connecting to the Internet
How are computers connected to the Internet?
• Connect to an Internet Service Provider (ISP) e.g. bellsouth.net, comcast.com, earthlink.net– 56K dial-up modem– DSL – Cable modem– Satellite– Cell phone
• Connect through a campus or enterprise network.26
The World Wide Web
• The WWW is not the same as the Internet.
• The WWW is a subset of the Internet.
• The WWW is made up of Web servers and their files (Web pages and associated files).
• Web pages are NOT stored as bytes of pixel data but as a description of the page.
• The WWW is organized hierarchically.27
http://www.mc.edu/campus/clubs/acm/members.html
http://
• stands for Hypertext Transfer Protocol
• tells the computer how to handle the file
• indicates this is a Web page
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http://www.mc.edu/campus/clubs/acm/members.html
www.mc.edu
• the domain name
• represents the IP address of the server (a computer)
• specifies a hierarchy from specific to general(www is a computer in the mc domain of the
edu domain)
• not case sensitive
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http://www.mc.edu/campus/clubs/acm/members.html
campus/clubs/acm/members.html
• the path name telling which page and where it is on the server
• specifies a hierarchy from general to specific(in the campus folder is a clubs folder containing an acm folder containing a Web page file called members.html)
• may be case sensitive
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Wrap Up
• mc.edu vs. www.mc.edu
• http://www.mc.edu/faculty/woodall
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