Chapter 3Fluency with Information Technology

4th editionby Lawrence Snyder

(slides by Deborah Woodall : woodall@mc.edu)

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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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