Internet History and Concepts

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Internet History and Concepts

• Internet trainning workshop
• 13-14th Bahman-1383

S.Habibi Ardabil university of medical
sciences Health Information Center
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Connect Computers

• 1958 After USSR launches Sputnik, first
  artificial earth satellite, US forms the Advanced
  Research Projects Agency (ARPA), the following
  year, within the Department of Defense (DoD) to
  establish US lead in science and technology
  applicable to the military
• 1969 ARPANET begins with 3 computers in
  California and one in Utah

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Protocol Development

• 1972-1974 Robert Kahn and Vint Cerf developed
  protocols to connect networks with different
  topology or specific characteristics of the
  underlying nets
• 1974 First full draft of TCP produced
• 1981 Term Internet coined to mean collection
  of interconnected networks
• 1983 ARPANET split into ARPANET and MILNET
  MILNET to carry defense related traffic

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Internet Concepts

• Network
• Protocol
• Client/server model
• TCP/IP
• Bandwidth

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Local Area Networks (LANs)

• A small network of computers in close proximity
  to each other.
• Roughly a single buildings worth of computers
  connected together
• Usually via ethernet, but other ways are possible
  (token ring, local talk, etc.)

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Wide Area Networks (WANs)

• Connect physically distant computers
• Often connect physically distant LANs
• Usually involve phone companies

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What is the internet?

• The internet is a collection of local area
  networks combined into one extremely large wide
  area network.

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Packet Switching

• Messages are broken into small pieces and then
  transmitted one at a time.
• Packets on the internet are usually 0.5-1.5
  kilobytes
• Each packet must have an address and some error
  correction information-its header

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Protocol

• A way for machines to talk to one another
• Hundreds of different protocols operate together
  to make the internet work properly

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Internet Protocol (IP)

• The most basic protocol of the Internet
• Designed to get a single packet from one computer
  to another
• Every computer on the Internet has one
• Represented by four numbers between 0 and 255
  (ie, four bytes)
• 216.132.81.61

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The problem with IP

• 32 bits long means that the maximum size of the
  Internet is 4,294,967,296 computers
• A new version called IPv6 is coming to augment
  the current IPv4
• 128-bit addresses

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Transmission Control Protocol (TCP)

• Almost always mentioned in the same breath as IP
  (TCP/IP)
• Fakes a reliable connection over an unreliable
  one
• Delivers an entire message to a particular
  destination

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How TCP Works

• Adds certain information to an IP packet
• Packet 1 of 10
• Error correction information
• Destination application (email, web, etc.)
• the port number
• The destination computer asks the original
  computer to resend any missing or corrupted
  packets
• Resorts the packets into the proper order

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Latency and Bandwidth

• Bandwidth
• Number of bits per time unit usually seconds
  (bps)
• Latency
• How long minimum communication takes in seconds
  (s)

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Client and Server

• User uses HTTP client (Web Browser)
• It has a URL (e.g. http//www.yahoo.com/)
• Makes a request to the server
• Server sends back data (the response)
• User clicks on the client side...

request (URL)
response (HTML, )
Client
Server
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Routers

• Connect two physically different networks
• an ethernet and a token-ring network
• a modem connection and an ethernet
• a LAN and a fiber optic cable
• Look to other computers like just another machine
  on the LAN
• Looks at all packets on the LAN and forwards
  those destined for the outside world
• Translate between the two addresses

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Proxies

• A proxy is an intermediary between a client and
  an origin server.
• To the client, the proxy acts like a server.
• To the server, the proxy acts like a client.

Client
Proxy
Origin Server
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Why Proxies?

• Can perform useful functions as requests and
  responses pass by
• Examples Caching, logging, anonymization

Client A
Origin Server
Proxy cache
Client B
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Typical Services

• File transfer (FTP)
• Remote login (telnet)
• Mail
• Gopher
• Web

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File Transfer Protocol

• Most basic file transfer application in the
  Internet
• One of the original client/server applications
  run on the ARPANET
• Requires that a host system run an FTP server
• Listens for incoming requests on a well known
  port (21)
• FTP is a two process model
• Control process which communicates with peer
  control process
• These processes communicate commands/responses as
  well as port information
• Data transfer process which actually transfers
  requested file

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File Transfer Protocol contd.

• Client control process connects to server control
  process
• ftp// mirror1.cs.wisc.edu
• The client also starts a data transfer process
  which listens on a local port
• Communicates this port number to server via
  control process
• If client requests a file transfer, server
  initiates connection to clients data transfer
  port
• Server uses well known port for data transfer (20)

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gopher

• A menu-driven textual interface to a wide range
  of databases, text, images, FTP, sounds, etc.
• Pre-dates the Web outdated.
• But, some older databases, text, etc. still only
  accessible by gopher.
• gopher//gopher.loc.gov

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Telnet

• Internets most basic network virtual terminal
  application allowing users to log into a remote
  host
• Runs on top of TCP
• Requires authentication via user name and
  password
• Requires host system to run a telnet server
  (telnetd)
• Passes keystrokes to remote system and carries
  output back to users screen
• Clients TELNET process connects to servers
  TELNET
• telnet foo.cs.wisc.edu
• Server listens on well known port (23) for
  incoming connections

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Sending an Email

• SMTP Simple Mail Transfer Protocol
• Your email client talks to an SMTP server
• SMTP server routes the mail to other servers...
  until it reaches destination
• Destination server program
• Accepts mail, puts in mailbox of the user
• If user doesnt exist, then bounce!

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Receiving an Email

• POP Post Office Protocol
• Copies mail from server to local PC
• IMAP Internet Mail Access Protocol
• Mail remains on server
• GUI presents interface for interacting with server

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Electronic Mail mail servers

• Mail Servers
• mailbox contains incoming messages (yet to be
  read) for user
• message queue of outgoing (to be sent) mail
  messages
• smtp protocol between mail servers to send email
  messages
• client sending mail server
• server receiving mail server

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Mail access protocols
SMTP
POP3 or IMAP
receivers mail server

• SMTP delivery/storage to receivers server
• Mail access protocol retrieval from server
• POP Post Office Protocol RFC 1939
• authorization (agent lt--gtserver) and download
• IMAP Internet Mail Access Protocol RFC 1730
• more features (more complex)
• manipulation of stored msgs on server
• HTTP Hotmail , Yahoo! Mail, etc.

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World Wide Web

• World Wide Web is a user-friendly interface to
  the internet
• 1990-91 Developed by Tim Berners-Lee
• 1993 Mosaic (Web browser)
• HTML Hypertext Markup Language
• Simple computer language which can be used to
  create Web pages which include links, graphics,
  and multimedia components
• HTTP protocol that tells web browsers where to
  find Web pages and their components

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Web Browsers

• Mosaic, Netscape, and
• Internet Explorer (I.E.)

• A browser is an application program or software
  that request documents from computers connected
  to the internet (servers) around the world and
  then displays the information in the browser
  window. The browser displays the information
  according to HTML instructions.
• Lynx, is the first web browser. It is a TEXT
  based browser invented by Tim Lee.
• Mosaic is the first graphical Web browser which
  allowed you to view multimedia files (music,
  video, and graphical files) on the Web.
• Netscape
• Internet Explorer (I. E.) in 1995 by Microsoft

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Computer is running a web server
Your computer is running a web browser
Your browser requests a webpage
Server sends back the page or document
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HTML

• HTML (Hypertext Markup Language) is the set of
  "markup" symbols or codes inserted in a file
  intended for display on a World Wide Web browser.
  
• The markup tells the Web browser how to display a
  Web page's text, images, sound and video files
  for the user.
• The individual markup codes are referred to as
  elements (but many people also refer to them as
  tag).

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What is a URL?

• URL stands for Uniform Resource Locator. A URL
  identifies a particular Internet resource for
  example a Web page, a library catalog, an image,
  or a text file. For example, the URL
• http//www.company.com/freeware/home.htm
• the protocol used to access and transmit the
  resource is HTTP
• Not all URLs will have the directory and
  filename.
• Most browsers will assume http//

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URL
http//www.stanford.edu/class/cs193i/schedule.html
Protocol (Scheme)
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URL
http//www.stanford.edu/class/cs193i/schedule.html
Host Name
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URL
http//www.stanford.edu/class/cs193i/schedule.html
Path
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DNS Domain Name System

• A centralized database includes a complete lists
  of domain names and IP addresses which are
  distributed throughout the Internet.
• There is probably a DNS server within close
  geographic proximity to your access provider that
  maps the domain names in your Internet requests
  or forwards them to other servers in the
  Internet.

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Typical Top-level Domains

• For the USA and Canada
• com commercial organisation
• edu educational institution
• gov government
• org non-profit organisation
• Mil military

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Some International top-levels

• au Australia
• de Germany
• jp Japan
• nl The Netherlands
• ir Iran
• uk United Kingdom

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Some web statistics

• More than 9 billion pages
• Web languages
• 86.55 English
• 2.36 French
• 0.54 Dutch
• Today 8,085,000,000 web pages indexed by Google
  (http//www.google.com)