1 Internet Technologies CSC457

2 Internet Internet is a communication technology. Like telephone it enables people to communicate. Telephones enabled voice communication. Internet enables data communication. Telephone services are available almost everywhere. Internet services are not available everywhere yet.

3 Evolution of the Internet What technological developments led to the development of the Internet? Communication conveys information thru a changing signal. Analog signals (cassette tape recorder) vs. digital signals (CD player). A-to-D & D-to-A Time when almost all signals were analog: early telephones.Telegraph was an exception. Morse Code. Telephones became digital.

4 ANALOG SIGNAL DIGITAL SIGNAL FOR “ ” MORSE CODE USED IN TELEGRAPH

5 Analog Phone wires Digital Phone wires

6 Evolution of the Internet Medium thru which signals travel: wires, optical fibers, atmosphere etc. Local communication: signals sent directly. Example: RS232. Long-Distance communication: signals modulated on to a carrier signal. MODEM: a modulator and demodulator. ASCII code: codes characters as binary (digital). Example ‘E’ is coded as

7 T R GG R T Minimum RS-232 Connection Device 1Device 2

8 DIGITAL SIGNAL CARRIER SIGNAL MODULATED SIGNAL

9 Evolution of the Internet Error detection: using parity bits or using a checksum. Example: character ‘E’ contains an odd number of bits so is assigned a parity bit 1, as the eighth bit. Example: if message contains digits a checksum digit of 9 is added. Receiver checks the sum of the received digits.

10 Evolution of the Internet: LANs Computers became cheaper and smaller, organizations started buying more & more computers, need to share data between computers arose. Provided motivation for communication. Data sharing thru (i) removable media is difficult (ii) communication… more convenient. Communication by direct connection between computers: two problems – cost & inconvenience.

11 Evolution of the Internet: LANs LAN is independent of the computers, computer needs NIC to connect to a LAN. Some LAN technologies: Ethernet, IBM Token Ring, ATM, etc. Different LAN technologies have different ways to connect computers, format data packets, data transmission rates, etc. So different LANs where incompatible with each other  one LAN could not be connected to the other.

12 Evolution: How Internet began? Late 1960’s  Many independent LANs & a few WANs but all incompatible with each other. Desirability of a single network  Enables resource sharing. The Dept. of Defense (DOD) had many networks and ARPANET…a WAN but incompatible. Problem faced was: how to connect the networks with each other? Late 1970’s  ARPA starts funding research on how to interconnect the networks.

13 Evolution: How Internet began? An inter-network called Internet is built with ARPANET as its backbone. Internet Software TCP/IP is created. ARPA made internet research public…the aim was to make the Internet an open system and not a closed system.  TCP/IP was made publicly available  prototype Internet was in place and TCP/IP technology had been tested.  US military adopts TCP/IP on its networks.

14 Evolution: How Internet began? Efforts made to Disseminate TCP/IP software. Unix was becoming popular. ARPA decided to give away TCP/IP with Unix. Late 1970’s  NSF project to connect CS departments proposed….TCP/IP used. Graduate students become interested in TCP/IP and did research to extend the TCP/IP software. Other US govt. agencies start using TCP/IP e.g. DOD and NASA.

15 Evolution: How Internet began? Mid-1980’s  NSF realizes importance of computer communication to science. NSF takes leadership role and decides to build NSFNET to connect five super-computer centers.  was smaller & slower than ARPANET  NSF involves IBM, MCI & MERIT  ANSNET backbone: first private network  MCI started building a WAN of an even higher capacity.

16 GROWTH OF THE INTERNET

17 Evolution: The Global Network. Other networks in other continents: BITNET (for IBM systems), FIDONET, JANET, EARN. Because it spans many countries Internet is called the global network. Electronic mail: first used in single, timeshared computers; later extended to users of networked computers.

18 Information Infrastructure. Internet provides a new infrastructure for communications like postal system, telegraph, and telephone did earlier. New infrastructure makes new industries and application possible, some of which cannot be foreseen.

19 The Underlying Technologies. What is inside the Internet? Or What are the key underlying technologies that make it work so successfully? –Packet Switching –Routers/Packet Switches –TCP/IP –Clients + Servers = Distributed Computing –Computer Names.

20 Applications Some applications of the Internet: –World Wide Web (WWW) –Electronic Mail ( ) –Bulletin Boards (Newsgroups) –Audio & Video Services