Transcript History of the Internet

History of the Internet
• Mid 1960’s During the Cold War – need for bomb proof
communications system.
• Government Agency and few Universities
• Emergency military communications system operated by
Department of Defense’s Advanced Research Project Agency
(ARPA) – ARPANET system
• Eventually all Universities with defense related projects
connected to ARPANET
• Military pipeline and 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
A Basic Guide to the Internet
What is the Internet ?
• Network of Networks
• Computers communicate over the internet using TCP/IP
(Transmission Control Protocol / Internet Protocol)
• Client / Server Architecture
Funding the Internet
• Funded through Agencies ( National Science Foundation,
Government agencies pay for some high speed backbones)
Who Runs the Internet – overseen by a variety of groups to
establish standards
• Internet Society (A private non-profit organisation)
• IETF (Internet Engineering Task Force) TCP/IP
• W3C (World Wide Web Consortium) MIT
• Private Companies oversee the registering of Internet
Domains.
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
How Computers Send Data
• TCP – breaks the data into packets
• 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 used to link groups of computers to one another and let
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 distances, the signal
sending the data can weaken over long distances, repeaters are
used to amplify the data at intervals
– Routers come into play when data is being sent between two
different networks. It examines packets for destination and
selects the quickest route taking into account traffic on the
internet.
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) ensure 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
contain addressing information telling the Internet where to
send the packet
• IP envelopes contain headers that contain information:
– Senders Address
– Destination Address
– Amount of time packet should be kept
– 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, Digital Subscriber
Line (DSL) line – needs a network card & hardware driver)
– Dialing connection (Modem)
• Serial Line Internet Protocol (SLIP)
• Point-to-Point Protocol (PPP)
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
Internet Addresses and Domain Names
The heart of how the Internet works 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
the 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.
Two types of IP address exist
– Static IP Addresses
– Dynamic IP Addresses
Dynamic IP Addresses
DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPPACK
DHCP
Server
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 but they officially registered.
.areo
.biz
.museum
.pro
for aviation industry
for business
for museums
for professionals
.info
.coop
.name
for general use
for cooperatives
for individuals
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 a
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 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).
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)
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 server’s directory
structure and how the page can be accessed.
http://www.computing.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.computing.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.
Protocols that may appear in URL’s
Protocols Names
Use
ftp://
File transfer
http://
Hypertext
https://
Hypertext Secure
Mailto:
Sending email
News:
Requesting news
telnet://
Remote login
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.
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 sends packet to another router closer to its final
destination. This router in turns forwards the packet on to a
router closer to the final destination (hops).
– Each router has to consider factors such as
• Traffic congestion
• Number of hops (IP packets carry a segment that holds the
max hop count)
• 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 – simpler 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))