Chapter 3 Fluency with Information Technology 4th edition by Lawrence Snyder (slides by Deborah Woodall : woodall@mc.edu)

Network Defined computer network Two 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

Far and Near LAN – Local Area Network WAN – Wide Area Network The Internet – A global network of Wide Area Networks

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

Classifying Communication Also Communication can be classified as either… broadcast – one sender, many receivers multicast – one sender, many selected receivers point-to-point – one sender, one receiver

Communication Classifications In one way or another the Internet offers all of these forms of communication. The Internet is truly a universal communications medium.

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)

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.

IP Addresses Every transmitted message on the Internet requires a destination address IP address – the address of a computer connected to the Internet

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.

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

IP Addresses How many numbers will fit into one byte?

IP Addresses What would be the range of one of the numbers in an IP address?

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

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

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.

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.

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.

Domain Names edu mc www sandbox oak

Domain Names Original top-level domains Newer 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

Domain Names The purpose of a top level domain name is to indicate Function, or Location

The Domain Name System DNS Servers 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

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.

TCP/IP Each packet contains Each packet is independent. 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.

Ethernet How is a message sent over a LAN? Ethernet Protocol Ethernet also uses packets. Ethernet is a true broadcast medium.

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.

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.

stands for Hypertext Transfer Protocol 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

represents the IP address of the server (a computer) 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

the path name telling which page and where it is on the server 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

Wrap Up mc.edu vs. www.mc.edu http://www.mc.edu/faculty/woodall