History of the Internet

1
History of the Internet

• Mid 1960s During the Cold War need for bomb
  proof communications system.
• Government Agency and few Universities
• Emergency military communications system operated
  by Department of Defenses Advanced Reserarch
  Project Agency (ARPA) ARPANET
• Eventually all Universities with defense related
  projects connected to ARPANET
• Military pipeline to communication tool for
  scientists ARPA transferred to National Science
  Foundation.
• Years later businesses began using the internet
  and the administrative responsiblilities were
  again transferred.
• No one party operates the internet, but there are
  several entities that oversee the system and the
  protocols involved

2

• A Basic Guide to the Internet
• What is the Internet ?
• Network of Networks
• Computers communicate over the internet using
  TCP/IP
• (Transmission Control Protcol / Internet
  Protocol)
• Client / Server Architecture
• Funding the Internet
• Funded through Agencies ( National Science
  Foundation, Government agencies pay for some high
  speed backbones)

3
Who Runs the Internet overseen by a variety of
groups to establish standardss

• Internet Society (A private nonprofit
  organisation)
• IETF (Internet Engineering Task Force) TCP/IP
• W3C (World Wide Web Consortium) MIT
• Private Companies oversee the registering of
  Internet Domains.

4
Underlying Architecture of the Internet

• We are going to look at the following
  Architectures
• How computers send data across the internet
• How TCP/IP works
• How Internet Addresses and Domain Names Work
• How Routers Work
• How Computers send data across the Internet
• TCP/IP
• Hubs
• Bridges
• Gateways
• Repeaters
• Routers

5
How Computers Send Data

• TCP breaks the data into packet
• Computer sends those packets local Network,
  Internet Service Provider (ISP), or On-Line
  Service
• Packets then travel through many levels of
  networks, computers, and communication lines
  before reaching their final destination.
• Variety of Hardware transmits the data between
  various networks. Five most important pieces of
  hardware are
• Hubs usesd to link groups of computers to one
  another and lets computers communicate with each
  other.
• Bridges Links one LAN with another LAN
• Gateways like Bridges but allow communication
  between different types of networks
• Repeaters - when data travels over long distance
  the signal sending the data can weaken over long
  distances, repeaters are used to amplify the data
  at interval
• Routers come into play when data being sent
  between two different networks, examine packets
  for destination and select the quickest route
  taking into account traffic on the internet.

6
How TCP/IP Works

• The Internet is a packet switched network
• Messages broken into a number of packets data
  to help the packet find its way through the
  Internet (TCP)
• Series of switchs called routers (IP) ensures
  that the packages arrive at their correct
  destination
• Packets are sent over many different routes at
  the same time
• Hardware restriction data broken into packets
  of 1,500 bytes each.
• Packet given header with order of packet
  checksum (based on the amount of data in packet)
• Each packet is put into separate IP envelopes,
  which contains addressing information telling the
  Internet where to send the packet
• IP envelopes contain headers that contain
  informations
• Senders Address
• Destination Address
• Amount of time packet should be kept

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• As packets sent across Internet Routers examine
  IP envelope destination addresses and determine
  the most efficient route for sending each packet.
  (Packets can arrive out of order)
• Packets arrive at their destination and TCP
  calculates the checksum for each packet (error
  checking)
• When all noncorrupt packets arrive at their
  destination TCP assembles them into their
  original form
• Winsock software (TCP/IP stack or Socket) serves
  as an intermediary between the Internet and PC
• Two ways to connect to the Internet and use the
  TCP/IP protocol
• Direct connection (via LAN, cable modem, DSL line
  needs a network card hardware driver)
• Dialing connection (Modem)
• Serial Line Internet Protocol (SLIP)
• Point-to-Point Protocol (PPP)

8
Sample Internet Connections
The basic idea of communication via the internet
is to have two remote sites or computers
connected together via a network or transmission
line
9
Internet Addresses and Domain Names

• The Heart of the Internet work is the Domain Name
  System (DNS), the way in which computers can
  contact each other and do things such as e-mail
  or display web pages. If a user wants to contact
  a specific location e.g. visit Web pages they
  type in the address (URL)
• www.computing.dcu.ie
• while numbers are convenient for machines, they
  are not for human beings, therefore humans use
  names for addresses and TCP/IP uses it DNS
  (Domain Name System) application (Name Servers)
  to provide name-to-address translation.
• The DNS translates the plain english address into
  a series of numbers called an IP address,
• 136.2.6.11.XXX
• An IP address marks the location on the internet
  similar to a house number and street address.
  All computers connected to the Internet must have
  an IP address.

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• Two types of IP address exist
• Static IP Addresses
• Dynamic IP Addresses
• Dynamic IP Addresses

DHCP Server
DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPPACK
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• Domains can be organised in Hierarchy
• Major Domains and minor domains
• www.computing.dcu.ie
• .ie is the major domain
• .dcu is the Dublin City University Domain
• .computing is the computer applications server
• Some Common Major Domain Names in the United
  States are
• .edu for educational institution, usually a
  university
• .com for a commercial business
• .gov for a government department or agency
• .mil for a military unit
• .org for a non-profit organisation
• Following introduced to reduce the load on .com
  domain not all are in
• use yet as they officially registered.
• .areo for aviation industry .info for general
  use
• .biz for business .coop for cooperatives
• .museum for museums .name for individuals
• .pro for professionals

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• As networks in other countries were connected to
  the Internet, they were assigned their own domain
  names
• ie Ireland
• ca Canada
• au Australia
• uk United Kingdom
• de Germany
• In total there are more than 250 top-level domain
  names
• The IP address is a 32 bit number but is now
  being expanded to 128 bit number to allow for
  more IP addresses to be accommodated.
• Since networks vary in size, there are four
  different address formats or classes to consider
  when applying to NIC for a network number
• Class A addresses are for large networks with
  many devices.
• Class B addresses are for medium-sized networks.
• Class C addresses are for small networks (fewer
  than 256 devices).

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• The IP address is usually made up of two parts,
  1st part identifies the network, the 2nd the node
  (host or actual computer).
• An IP address is expressed as four decimal
  numbers (octets), each representing eight bits,
  separated by periods. The first few bits of each
  IP address indicate which of the address class
  formats it is using. The address structures look
  like this
• 130.5.5.25
• Each of the decimal digits represents a string of
  four binary digits. Thus, the above IP address
  really is this string of 0s and 1s
• 10000010.00000101.00000101.00011001
• Class A
• 0 Network (7 bits values 1-126) Local
  address (24 bits, 3 remaining octets used to
  identify host)
• Class B
• 10 Network (14 bits first octet 128-191
  second octet used to identify network) Local
  address (16 bits, 2 octets used to identify host)
• Class C
• 110 Network (21 bits, first octet 192-223, 1st ,
  2nd and 3rd octet identify network) Local
  address (8 bits, 1 octet identifies host)

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URL (Uniform Resource Locator)

• URLs uniquely identify each file on the web by
  specifying its name, what server it is on, and
  where it resides in the servers directory
  structure and how the page can be accessed.
• http//www.compapp.dcu.ie/NT_Software/index.html
•  
• The http// tells the browser which protocol to
  use to access the web page. In this case the
  protocol is hypertext transfer protocol. This
  protocol is the set of rules by which a HTML
  document is transferred over.
• Next www.comapp.dcu.ie is the name of the
  Internet host at which the resource is located.
• Following this you specify a path to a particular
  directory, in this case you start at the root
  directory and go down one level to the
  NT_Software directory.
• Finally index.html is the file holding the page
  you seek.
•  

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Protocols that may appear in URLs
Much of the power of browsers is that they are
multiprotocol. That is, they can retrieve and
render information from a variety of servers and
sources.
16
How Routers Work

• Routers are traffic cops of the Internet. They
  ensure that data gets to its final destination
  via the most efficient route.
• Routers check the IP envelopes for the
  destination address
• Calculate the best route and then send the
  package on its way
• Router send packet to another router closer to
  its final destination, this router in turns
  forwards the package on to a router closer to the
  final destination.
• Each router has to consider factors such as
• Traffic congestion
• Number of hops (IP packets carry a segment that
  holds the max hop count)

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• Routers have two or more physical ports
• Input port (routing process run, routing table)
• Output port (results from the routing process
  defines with output port the routes the packets
  should follow)
• Input queue (holding area for input port, queue
  capacity exceeded lost data)
• Routing Table
• Static simplier and specifies specific paths
  for packets
• Dynamic packets can have multiple routes to
  their final destination (table changes as
  network conditions change).
• Two broad type of routing protocols exist
• Interior (Gateway Routing Information Protocol
  (IGRP))
• Exterior (Exterior Gateway Protocol (EGP))