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Abstraction in Art “It is easy to make something simple sound complex, however it is more difficult to make something complex sound simple.”
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What is Abstraction?
“The act of withdrawing or removing something”
“The act or process of leaving out of consideration one or more properties of a complex object so as to attend to others”
Abstraction in Art
“It is easy to make something simple sound complex, however it is more difficult to make something
complex sound simple.”
Abstraction in CS
“Writing (good) computer programs is the ability to handle abstractions in a precise manner.”
- Keith Devlin
Abstraction and the Internet – IP Addresses 70.230.24.81
32-bit Each block is an 8 digit binary number
Dynamically assigned (DHCP – Dynamic Host Configuration Protocol) Laptop
Static IP address Web server
Abstraction and the Internet – IP Addresses
http://computer.howstuffworks.com/dns.htm
198.168.000.001
What is an IP Address? What does an IP address look like? What is its scheme? How many unique IP addresses could that scheme produce? What is IPv6?
Abstraction and the Internet – Domain Name Server Domains have a hierarchy
http://cs.ua.edu EDU – top-level domain
Accredited post-secondary educational US institutions UA – University of Alabama CS – Computer Science department
Information sent in Packets
Packet consists of two types of data Control information: source, destination, error
detection, sequence User data
Some systems send packetspersistently to avoid collisions
Delivery not guaranteed How is it sent?
Protocols
Networks speak the way people do Speaking has certain rules
Speak the same language (English, Spanish, …) One person speaks at a time Interruptions are disruptive Speak with the proper volume Don’t speak for too long
Pete Siemsen - http://nets.ucar.edu/nets/presentations/itn/
Protocols
By using a protocol, we know The syntax of a message
Fields/format The semantics of a message
Meaning; may illustrate error What actions required after receiving the
message If error received, the file may need to be resent
TCP/IP
Created by DARPA in 1970s Transmission Control Protocol and Internet
Protocol Also known as Internet Suite Protocol
IP moves packets of data from source to destination based on a four byte destination address
TCP verifies the correct delivery of data