A Balanced Introduction to Computer Science, 3/E David Reed, Creighton University ©2011 Pearson Prentice Hall ISBN 978-0-13-216675-1History of InternetARPANetARPANet GrowthNSFNet"Internet"Internet SocietyInternet GrowthDistributed NetworksPacket SwitchingAdvantages of PacketsProtocols and AddressesTCP/IPRouters and DNSHistory of the WebWeb TimelineHow the Web WorksA Balanced Introduction A Balanced Introduction to Computer Science, to Computer Science, 3/E3/EDavid Reed, Creighton UniversityDavid Reed, Creighton University©2011 Pearson Prentice Hall©2011 Pearson Prentice HallISBN 978-0-13-216675-1ISBN 978-0-13-216675-1Chapter 3The Internet and the Web1History of Internetrecall: the Internet is a vast, international network of computersthe Internet traces its roots back to the early 1960sMIT professor J.C.R. Licklider published a series of articles describing a “Galactic Network” of communicating computersin 1962, Licklider became head of computer research at the U.S. Department of Defense’s Advanced Research Project Agency (ARPA)in 1967, Licklider hired Larry Roberts to design and implement his vision of a Galactic Network2the ARPANet (precursor to the Internet) became a reality in 1969it connected computers at four universities: UCLA, UCSB, SRI, and Utahit employed dedicated cables, buried undergroundthe data transfer rate was 56K bits/sec, roughly the same as dial-up services todaythe ARPANet demonstrated that researchers at different sites could communicate, share data, and run software remotelyARPANetthe ARPANet was intended to connect only military installations and universities participating in government projectsby 1971, 18 sites were connected; most used Interface Message Processors (IMPs) which allowed up to 4 terminal connections at the sitesites labeled with a T utilized Terminal Interface Processors (TIPs), which allowed up to 64 terminal connections at the site3ARPANet Growthby 1980, close to 100 sites were connected to the ARPANetsatellite connections provided links to select cities outside the continental U.S.4NSFNetin the early 1980s, the ARPANet experienced an astounding growth spurtapplications such as email, newsgroups, and remote logins were attractive to all colleges and universitiesby 1984, the ARPANet encompassed more than 1,000 sitesto accommodate further growth, the National Science Foundation (NSF) became involved with the ARPANet in 1984NSF funded the construction of high-speed transmission lines that would form the backbone of the expanding network5"Internet"the term “Internet” was coined in recognition of the similarities between the NSFNet and the interstate highway systembackbone connections provided fast communications between principal destinations, analogous to interstate highwaysconnected to the backbone were slower transmission lines that linked secondary destinations, analogous to state highwayslocal connections were required to reach individual computers, analogous to city and neighborhood roads6recognizing that continued growth would require significant funding and research, the government decided in the mid 90s to privatize the Internetcontrol of the network’s hardware was turned over to telecommunications companies and research organizations (e.g., AT&T, Verizon, Qwest, Sprint) research and design are administered by the Internet Societynote: Al Gore did not INVENT the Internet, nor did he ever claim tohe sponsored legislation in the late 1980s to support growth and expand accessInternet SocietyInternet Society is an international nonprofit organization (founded in 1992) it maintains and enforces standards, ensuring that all computers on the Internet are able to communicate with each otherit also organizes committees that propose and approve new Internet-related technologies and software7Internet Growthuntil recently, the Internet more than doubled in size every 1 or 2 years why has this trend slowed? will it continue?8(Internet Software Consortium, April 2010.)Distributed Networksthe design of the ARPANet was influenced by the ideas of Paul Baran, a researcher at the RAND InstituteBaran proposed 2 key ideas: distributed network and packet-switchingrecall: the ARPANet was funded by the Dept of Defense for communicationsas such, it needed to be resistant to attack or mechanical failure9Packet Switchingin a packet-switching network, messages to be sent over the network are first broken into small pieces known as packets these packets are sent independently to their final destination10Advantages of Packets1. sending information in smaller units increases the efficient use of connectionslarge messages can't monopolize the connectionanalogy: limiting call lengths at a pay phone to limit waiting2. transmitting packets independently allows the network to react to failures or network congestionrouters (special-purpose computers that direct the flow of messages) can recognize failures or congestion and reroute the packet around trouble areas3. breaking the message into packets can improve reliabilitysince the packets are transmitted independently, it is likely that at least part of the message will arrive (even if some failures occur within the network)software at the destination can recognize which packets are missing and request retransmission11Protocols and Addressesthe Internet allows different types of computers from around the world to communicatethis is possible because the computing community agreed upon common protocols (sets of rules that describe how communication takes place)the two central protocols that control Internet communication are:1. Transmission Control Protocol (TCP) 2. Internet Protocol (IP)12these protocols rely on each computer having a unique identifier (known as an IP address)analogy: street address + zip code provide unique address for your house/dormusing this address, anyone in the world can send you a letteran IP address is a number, written as a dotted sequence such as 147.134.2.84each computer is assigned an IP address by its Internet Service Provider (ISP) some ISPs (e.g., AOL, most colleges) maintain a pool of IP addresses and assign them dynamically to computers each time they connectTCP/IPTransmission Control Protocol (TCP) controls the method by which messages are broken down into packets and then reassembled when they reach their final destinationInternet Protocol (IP) concerned with
View Full Document