October 5, 2011 Abstraction, Privacy, and the Internet

Agenda Team Project #1 due Monday  One per team  Presenting to the class Abstraction  Jeff Kramer’s “Is Abstraction the Key to Computing?” Internet Blown to Bits Chapters 2 & 3

Kramer’s Question “Why is it that some software engineers are computer scientists are able to produce clear, elegant designs and programs, while others cannot?”

Cognitive Development Jean Piaget ( ) - four stages of development  Sensorimotor  Pre-operational (infancy – 7)  Concrete operational (7-12)  Formal operational (12 to adulthood) 30%-35% of adolescents conquer fourth stage

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” Is abstraction only found in Computer Science?

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 Life

Abstraction in BYOB - Procedural

Abstraction in CS “Once you realize that computing is all about constructing, manipulating, and reasoning about abstractions, it becomes clear that an important prerequisite for writing (good) computer programs is the ability to handle abstractions in a precise manner.” - Keith Devlin

Abstraction and the Internet – IP Addresses  Four octets 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

Abstraction and the Internet – Domain Name Server Domains have a hierarchy  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 packets persistently 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 -

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

Wget Allows the user to download a file without using a browser

Privacy

Bits Behind the Scenes