Transcript chapter two lecture slides

Chapter 2
Introduction to the
Internet
Part 1: Data Communications in the Information Age
Learning Objectives
• Be able to distinguish between an internet, the Internet,
and an intranet
• Be able to trace the history of the Internet
• Identify and briefly describe important Internet
technologies
• Describe the distinctions between the Internet and the
World Wide Web
• Identify and briefly describe key TCP/IP protocols
• Identify and briefly describe the major text-based
Internet services
• Describe the different ways of gaining access to the
internet
• Discuss the roles of ISP’s in Internet Access
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What is the Internet?
• An internet is an interconnection of two or more networks
that makes them appear to be one continuous network
– A company may have an internet (or enterprise network) that
is not connected to the Internet
• The Internet is a “network of networks” linking commercial,
academic, and government computers in all but a handful of
countries worldwide
– It is a public network: individuals are able to gain access to the
Internet and use its resources in a variety of ways
• An intranet is a private network that uses Internet
technology such as hypertext documents and Internet
protocols to store and retrieve data
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Internet Browsers and
Hypertext
• Most Internet users utilize browsers such as
Internet Explorer or Netscape Navigator to
access Web pages and access hypertext links
– Browsers enable microcomputer, PDA, and Internetready cell phone users to “surf” the Internet
– Clickable hypertext links enable Internet users to move
effortlessly among Web pages. Hypertext is essentially
text in a document or Web page that contains links to
other documents or text
– Much of the text found on a browser screen is
hypertext, as illustrated in Figure 2-1
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Figure 2-1
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Internet History
• The Internet began as a concept in 1964 when
researchers at the Rand Corporation introduced
the concept of packet-switching networks
– Packet-switching networks (PSNs) break messages into
smaller packets for transmission over the network and
use switches to get messages to their destinations
• The physical implementation of the Internet
began in 1969 as a 4-node packet-switching
network called ARPAnet. ARPAnet was named for
and sponsored by the U.S. Defense Department’s
Advanced Projects Research Agency (ARPA)
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Internet History
(Continued)
• By 1984, over 1,000 computers were connected to
ARPAnet
• Until 1983, MILNET was part of the Internet; it
connected nodes in military organizations,
research organizations, and colleges and
universities involved in military-sponsored
research
• ARPAnet was officially shut down in 1984, but its
remaining nodes and subnets continued to
function
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Internet History
(Continued)
• During the 1980s, several regional networks such
as BITNET and CSNET joined the Internet
• In 1986, the National Science Foundation (NSF)
connected its five supercomputer networks, called
NSFnet, to the Internet. After this happened,
the resulting network of networks became known
as the Internet
• In 1987, the NSF assumed responsibility for
managing the backbone network and created the
NSF Network Service Center (NNSC)
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Internet History
(Continued)
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By 1989, over 80,000 hosts were interconnected via the Internet
backbone
In 1991, NFSnet lifted its restrictions on using the Internet for
commercial purposes
In 1992, the first Internet-based e-commerce applications
emerged
In 1993, NSF replaced the NNSC with InterNIC (Internet
Network Information Center)
NSFnet served as the major backbone network on the Internet
until 1995 when the NSF quit all direct support of the Internet in
order to return to its original status as a research network
By 1997, there were approximately 16 million Internet hosts
representing all but a few countries worldwide
By 2001, the number of Internet hosts surpassed 100 million
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The Internet Today
• Today’s Internet is best described as a highspeed backbone network (see Figure 2-2) to which
networks in businesses, education institutions, and
government agencies worldwide are attached
• The Internet remains a public, cooperative, and
independent network
• No single person, government, institution, or
company owns the Internet
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Figure 2-2
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Internet Governance
• Several organizations play a key role in the
ongoing evolution of the Internet through
the development of recommendations and
standards and by addressing other issues
• The major responsibilities of several of
the major organizations involved in
Internet governance are summarized in
Table 2-1
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Key Internet Advisory Groups
and Governance Organizations
Abbreviation
Full Name
W3C
World Wide Web Consortium
IAB
Internet Architecture Board
ICANN
Internet Corporation for
Assigned Names and Numbers
IESG
Internet Engineering Steering
Group
IETF
Internet Engineering Task
Force
ISOC
Internet Society
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Internet Fundamentals
• Each network attached to the Internet must contain at
least one host
• A network attached to the Internet may be subdivided into
smaller segments called subnets
• Routers are used to send packets across the Internet from
one network to another
• There may be multiple hops within the Internet backbone as
messages make their way from one network to another
• An organization may use internal routers to interconnect
subnets.
• These fundamentals are illustrated in Figure 2-3
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Internet Hosts and Nodes
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In the early days of the Internet, only large computers
(mainframes or midrange computers) had the power needed to
attach to the Internet. Because these locally provided the
application processing services for multiple terminal users, they
were called “hosts”
Today it has become common to use host to refer to the
Internet’s large computers and servers that function as major
repositories of files or applications, and nodes to refer to the
microcomputers, terminals, and other computers in a network
To use the Internet, every host and node must have an IP address
(such as 128.191.17.15)
Internet hosts may also have an optional host name (such as
gsaix2.cc.gasou.edu)
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Subnets
• A subnet is a portion of a network
• A large network is often subdivided into multiple
interconnected, but independent, segments or domains in
order to improve network performance or security
• All the computers that make up a single LAN are typically
included in the same subnet
• Each IP address is made up of two major parts: network
address and node address. When subnets are created, part
of the node address is used to designate the subnet that
the node is in
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Routers
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Routers are data communication devices that are capable of
forwarding packets from a computer on one network to computers
attached to any other interconnected network
Routers make the Internet transparent to users; they make it look
like a single network rather than the like the set of
interconnected networks that it really is
Routers read the packets they receive and use the IP address of
the destination host or node to determine how to forward the
packet
The path that a packet takes across the routers in the Internet
(or an internet) is called its route
Most consumers and businesses gain access to the Internet via the
routers at ISPs (Internet service providers). This is illustrated in
Figure 2-4
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Figure 2-4
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The World Wide Web
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The World Wide Web is arguably the best known and most widely
used Internet service
According to the Internet User’s Guide, the Web can be defined
as “a hypertext-based, distributed information system created by
researchers at CERN in Switzerland”
Tim Berners-Lee is credited with developing the concept of a
worldwide collection of electronic documents that include
hyperlinks to other related documents to enable users to move
quickly from one document to another regardless of whether they
are stored on the same host or on hosts in different networks
By 2000, the Web was estimated to include at least 2 billion
unique Web pages and to be growing at the rate of more than 7
million pages each day
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WWW Fundamentals
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An electronic document on the Web is called a Web page
A collection of related Web pages that can be accessed from the
same starting location is called a Web site
Most Web sites have a starting point, and central reference point,
called a homepage
Each Web page at each Web site has a unique address or URL
(uniform resource locator). A URL specifies the protocol, domain
name, and path for the Web page (see Figure 2-5)
– HTTP (Hypertext transport protocol) translates a URL into the IP
address of the host on which a requested Web page is stored. Once
the host is contacted, HTTP uses the path to access the requested
page and transfer it to the user’s computer
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Figure 2-5
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Web Servers
• The Web pages that comprise a Web site are
stored on one or more servers called Web
servers. Each Web server must have:
– An IP address to uniquely identify it
– Hardware capable of being connected to the Internet
and handling visitor requests
– A link to the Internet with sufficient bandwidth to
ensure acceptable performance and responsiveness to
Internet user requests for Web pages
– Web server software (see Table 2-2)
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Table 2-2
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Browsers
• Internet users are able to access and view Web pages by
using browsers such as Netscape Navigator and Internet
Explorer
• The layout of the browser display is controlled by the
Hypertext Markup Language (HTML) standard that it
supports
• HTML uses tags to define the content and formatting of a
Web page (see Figures 2-6a and 2-6b)
• Browser plug-ins and helper applications may be needed to
display Web page multimedia content (see Table 2-3)
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Figure 2-6a
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Figure 2-6b
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Table 2-3
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Firewalls
• A firewall is software (or a
hardware/software combination) that
sits between the Internet and an
enterprise network in order to
monitor and control the traffic
between them
– Firewalls are often used to protect and
maintain the privacy of intranets
– Firewalls help to protect networks from
hackers and virus infections
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Firewall Categories
• There are several types of firewalls
including:
– packet filter firewalls
– application firewalls
– proxy firewalls
• Border routers often include firewall
software, however, firewalls can also be
implemented in hosts (see Figure 2-7)
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Figure 2-7
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TCP/IP: The Internet
Protocol
• The TCP/IP protocol suite consists
of five relatively independent layers:
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Application
Transport (host-to-host)
Internet
Network access
Physical
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Internet Protocol (IP)
• The Internet Protocol (IP) is found at the
Internet layer of the TCP/IP protocol
suite
• It is responsible for routing data packets
across multiple interconnected networks
(such as the Internet)
• To work, it must be implemented in all
hosts, nodes, and routers, hence, each
must have an “IP address”
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Transmission Control
Protocol (TCP)
• TCP is the key communication protocol
found at the transport or host-to-host
layer of the TCP/IP protocol suite
• It is responsible for ensuring that data is
exchanged reliability between hosts
located in different networks
– This involves ensuring that all of a sender’s
data packets are delivered to the receiver in
same order in which they were sent
• TCP only needs to be implemented in hosts
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TCP/IP Operation
Figure 2-8
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Other Important TCP/IP
Protocols
• Important Application layer TCP/IP protocols
include:
– Hypertext Transport Protocol (HTTP) - transferring
Web pages
– File Transfer Protocol (FTP) - downloading/uploading
files
– Simple Mail Transfer Protocol (SMTP) - transferring email among TCP/IP hosts
– Simple Network Management Protocol (SNMP) collecting and reporting data traffic within a network
– Telnet (enables users to run applications on hosts in
other networks)
– Wireless Application Protocol (WAP) - enables cell
phones, PDAs, etc. to receive and display Web pages
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IPv6: Internet Protocol
Version 6
• IPv4 is the current version of IP; because it only
supports 32-bit addresses, we will run out of IP
addresses
• IPv6 supports 128-bit addresses (see Table 2-5)
and is being used on Internet2
• Other key upgrades in IPv6 include:
– header changes to improve quality of service, security,
and privacy
– interoperability with IPv4
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Internet Services
• Major Internet services include:
– search engines
– text-based applications
– chatting and instant messaging
applications
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Search Engines
• Search engines enable users to find Internet
resources by supplying keywords.
• Numerous search engines are widely used (see
Table 2-6)
• Search engines have three major parts (see
Figure 2-10):
– spider
– index
– search engine
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Figure 2-10
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Text-based Internet
Applications
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Archie
Gopher
Veronica
Jughead
Wide Area
Information
Server (WAIS)
• Usenet
• Internet Relay
Chat (IRC)
• Talk
• Instant messaging
(IM)
• Two-way messaging
and SMS
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Internet Access Options
• Individuals can access the Internet in a
variety of ways including:
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At work via networks with Internet access
In educational institutions
Through public services (e.g. public libraries)
Via freenets
ISP subscriptions
Via wireless networks
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Internet Service
Providers
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ISPs may be local, regional, national, or international in scope
Individuals should consider multiple factors when selecting an ISPs
(see Table 2-9)
ISP configurations often include multiple servers in addition to a
router for Internet access and modem banks (see Figure 2-11)
Some ISPs support multiple subscriber connection options (such as
DSL and cable modem connections) in addition to dial-in access
(see Figure 2-12). Some support wireless Internet access
Local ISPs typically gain Internet access via regional ISPs,
network access points (NAPs) or metropolitan area exchanges
(MAEs)--see Figures 2-13 and 2-14
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Local ISP Configuration
Figure 2-11
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ISP with Multiple Internet Access
Options
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Regional ISP
Configuration
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Major U.S. MAEs and
NAPs
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Chapter 2
Introduction to the
Internet
Part 1: Data Communications in the Information Age