First Digital Computer -- ENIAC (Electronic Numerical Integrator And Calculator)

•1946 University of Pennsylvania

• Result of research to more quickly calculate trajectories for artillery shells in WW2

• 60,000 pounds• 18,000 vacuum tubes• Size of medium sized house (1,600 square feet)

By mid 1960's -- Minicomputers

• Multiple Terminals -- Different people using the computer at the same time.

• Time Sharing -- The computer could run more than one program at the same time.

• Only cost about $20,000 so most universities could afford one.

The First "Internet" -- ARPANET 1969• Funded by the US department of Defense• 4 Hosts at Universities in the Western USA• Original Plans call for 128 Hosts

There are 4 main things which cause the Internet to explode beginning in the late 1980s

• Desktop Computers Become Affordable in 1980s

• US Government Relinquishes Control of Internet starting in 1990

• Tim Berners-Lee Invents the World Wide Web in 1990

• Marc Andreessen creates Mosaic Web browser in 1993

First desktop Computers available around 1980

• 1977 Apple II -- Eventually Apple would be the first desktop computer to feature

– Floppy Disk Drives (1978)– Mouse (1983)– Windows Graphical User Interface (1983)

• 1981 IBM PC– Used Microsoft's DOS Operating System– Microsoft eventually patents the term Windows – Windows 1.1 (1985)

US Government releases control of the Internet

• 1990 -- First year internet access could be obtained without formal sponsorship from US Government

• 1992 -- Internet control formally transferred to non-profit Organization which evolved into ISOC(Internet SOCiety). It's membership includes researchers from major technology companies and research universities around the world.

• The internet is over 20 years old

• Tim Berners-Lee, while working at the CERN physics lab in Europe invents World Wide Web.

– Writes first Web browser and Web server software (UNIX platform).

– The goal is to enable physicists to be able to share abstracts of physics research papers over theInternet.

The World Wide Web is born

The Web as you know it is born

• 1990 -- Marc Andreessen, a graduate student in Illinois, creates Mosaic Web browser.

– Point-and-Click interface– Can render graphics.

• 1995 -- Netscape Communications releases Netscape Navigator 2 for all major platforms (Windows, Macintosh, Unix). Netscape was formed by Marc Andreessen and his buddies.

– Web traffic soon dominates e-mail traffic on Internet

The Internet uses a 5-layer networking model. This is sometimes called the Internet protocol stack.

Physical Layer

• Electrons whizzing through copper cables.• Visible light moving through fiber optic cables.• Non-visible wavelengths of electromagnetic radiation moving through the air for satellite transmissions and other wireless transmissions.• Protocols deal with physical properties -- voltage, amperage, wavelength, etc.

No delivery of data guarantee -- electrons slam into copper atoms, electromagnetic radiation dissipates.

Network Layer• Ethernet -- For linking computers into Local Area Networks (LANs). Typical examples -- a computer lab or all the computers in a small building.

• Wireless -- Similar idea to Ethernet, but no wires and usually slower. Examples: Wi-Fi, 4G

• Phone modem -- Point-to-Point Protocol (PPP). Link your computer to another at service provider.

• Cable Modem/DSL modem -- Point to point types of links, but faster than phone modems.

Comparison of network-level data transfer rates.

InterNetwork Layer

The Internetworking Protocol (IP) hooks various network types together into an Internetwork.

IP addresses

Example: 164.68.21.170

• Each number in the range 0-255• Around 4 billion different IP addresses• Class A IP license -- Example: 164.x.x.x• Class B IP license -- Example: 164.68.x.x• Class C IP license -- Example: 164.68.21.x

Other IP Features

• Data is segmented into small packets, each about 1 to1.5 K in size• Flow Control -- Packet routers try to pick the optimal path to destination based upon how busy neighboring routers are, not necessarily the shortest path. Different packets from same transaction might take same route. A busy router might just discard a given packet!• Time To Live -- A packet is only allowed a certain number of "hops" on the internet, after which it is dropped or killed by a router.

The design of IP is a major contributor to the success of the internet

• Flexible routing means that data is not bound to a set path. Thus, if one or more routers goes down, packets can simply take a different route. • Flow Control and Time To Live help to protect the routers from overload.

• Packet segmenting of data is ideal. It is far better to re-transmit a few lost or damaged packets than to retransmit a whole chunk of data.

Transport Layer

The Transmission Control Protocol (TCP) coordinates data transfer between two computers. This is the end-to-end service.

Here's how TCP works

When a file is requested from a server:

• It segments the file into packets and "stamps" each packet with a sequence number so that they can be reassembled later in the proper order.• It calculates a checksum for each packet and "stamps" that on. A checksum is basically a count of the bits comprising the packet. This is used on the other end to test for data loss.• It gives the packets to the IP layer for delivery.

When the IP layer on the client receives the packets, it passes them up to the TCP layer.

Here's how the TCP layer finishes the internet transaction. It re-calculates the checksum for each packet and sends a message back to the server with the packet's sequence number indicating whether or not it arrived intact. If it did not, the server will re-send it. Also, if no acknowledgement for a packet is received from the client within a certain period of time, the TCP layer on the server will assume IP has discarded it and re-send it. The TCP layer re-assembles the original data according to the sequence numbers of the packets.

The combination of IP and TCP are usually lumped together and referred to as the TCP/IP internet protocol suite. This enables data transfer between networks -- the internet.

NetworkingNetworking protocols -- Two computers in the same network talking to each other. Reliable data transfer.Physical -- Potential data loss.

InterNetworkingEnd-to-end Transport (TCP) -- Two computers in different networks talking to each other. Reliable data transfer.InterNetworking (IP) -- Routing Between Networks. Potential data loss.

Application Layer

• Interface with Humans.

• Pass data to TCP Layer (or save to local hard drive).

• Two major communication Models for Applications on the Internet:

– Client-Server -- Web, E-mail, File Transfer (FTP), Telnet, …

– Peer-To-Peer -- File trading software, Chat software, Networked games, ...

Domain Name Service

All internet routing is done with IP addresses. Domain Names are for Humans!

• Top-level domains• Virtual Domains• Named addresses

Domain names form a hierarchy and the DNS service can resolve domain names more efficiently using the hierarchical structure.

Virtual Hosting

• A service related to domain names provided by the Web server software.• Ultimately, a domain name used for a Web site is no more than a directory (folder) on a Web server. That is the (virtual) reality of it.

URL -- Uniform Resource LocatorThree parts:• Internet Protocol (how) -- We will see:

–http (HyperText Transfer Protocol) -- "Give me a Web page."– ftp (File Transfer Protocol) -- "Copy and transfer a file for me."– mailto -- "Send this e-mail for me."

• The address (where)– Can be a named address or numerical IP address

• The path to a particular Web page on the server (what)

Basic HTTP transaction: HTML file + two graphics = Web page