Transcript Lecture Slides - Lake Forest College

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 nonprofit Organization which evolved into ISOC
(Internet SOCiety). It's membership includes
researchers from major technology companies and
research universities around the world.
The World Wide Web is born
• 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 the
Internet.
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.
Summary of Internet layers up to this point.
Internetwork Layer -- Data can be lost. That is, the IP
protocol does not guarantee delivery of data packets
between networks.
Network Layer -- Networking protocols make sure
data makes it from one computer to another in a
network.
Physical Layer -- Data can be lost.
Transport Layer
The Transmission Control Protocol (TCP) coordinates
data transfer between two computers. This is the endto-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.
InterNetworking
End-to-end Transport (TCP) -- Two computers in different networks
talking to each other. Reliable data transfer.
InterNetworking (IP) -- Routing Between Networks. Potential data loss.
Networking
Networking protocols -- Two computers in the same network talking to
each other. Reliable data transfer.
Physical -- 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, ...
Client-Server Model
• Examples of Client Software: Web Browsers,
E-mail clients, FTP clients, Telnet Clients, …
• Examples of Server Software: Web Servers,
POP/IMAP servers, FTP servers, ...
Peer-to-peer Internet Applications
The World Wide Web
• The first domain names were registered in the Mid
1980s, well before the Web was born. Domain Name
Service is used for many things on the Internet, not
just the Web. But since domain names came into the
public eye in conjunction with the Web, we begin
there.
• It should be clear why something like
www.cknuckles.com
is far better for humans than
164.68.21.170
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 Locator
Three 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