Transcript Chapter 14 - Bilal A. Bajwa

Information Technology in Theory
By Pelin Aksoy and Laura DeNardis
Chapter 14
Internet Architecture
Objectives
• Become familiar with important Internet
technology milestones
• Understand fundamental Internet architectural
features such as Internet exchange points, the
Domain Name System, IP addresses, and Uniform
Resource Locators
• Understand the technology underlying popular
Internet applications
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Objectives (continued)
• Examine the centralized administrative functions that
keep the Internet running, including management of
domain names and Internet addresses
• Contemplate economic and social issues associated
with the Internet
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Internet History
• The cold war
• Launch of Sputnik in 1957
• ARPA founded within the Department of Defense
(DoD)
• ARPANET
• Packet switching by Paul Baran
• TCP/IP by Vinton Cerf and Robert Kahn
• The World Wide Web
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Internet History (continued)
• Web browser Mosaic by Marc Andreessen
• Wireless access
• Etc.
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Internet History (continued)
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Internet Architectural Components
• The Internet includes the following important
technological systems and components:
– Internet backbone and routers
– Internet exchange points (IXPs)
– The Internet Protocol (IP)
– The Domain Name System (DNS)
– Uniform Resource Locators (URLs)
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Internet Backbone and Routers
• Internet backbone: the global collection of highcapacity trunks
• Is not owned and operated by any single company or
government
• Rather, it is a collection of high-speed, interconnected
networks run by large network service providers
such as AT&T, British Telecom, France Telecom,
Qwest, and Verizon, etc.
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Internet Backbone and Routers
(continued)
• The foundation of the Internet’s architecture is an
enormous number of routers
• The router reads the destination IP address and uses a
routing table to look up information for how to
forward the packet
• A routing table is essentially a database on the router
that provides information for how destinations can be
reached most efficiently
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Internet Backbone and Routers
(continued)
• The routers in one service provider’s networks can
communicate with routers in other such networks
because they adhere to the same routing protocols
• These protocols enable routers to share network
changes that are reflected in updates to router tables
• An example of a routing protocol that provides this
service is Border Gateway Protocol (BGP)
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Internet Backbone and Routers
(continued)
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Internet Exchange Points
• Traffic from one network flows seamlessly to other
networks across the Internet through interconnection
locations called Internet exchange points (IXPs)
• The exchange point serves as a juncture at which
packets from different networks are exchanged and
routed toward their appropriate destinations
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Internet Exchange Points (continued)
• Peering agreements allow service providers to share
the costs of shared exchange points and provide
service-level agreements for characteristics such as
reliability and latency, the delay that packets undergo
en route to a destination
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Internet Exchange Points (continued)
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The Internet Protocol
• The Internet Protocol (IP) is a critical part of
TCP/IP and the circulatory system of the Internet in
many ways
• IP is the one protocol needed in almost every instance
of information sharing over the Internet
• The function of IP is to route blocks of information
from a source to a destination over a complex
network
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The Internet Protocol (continued)
• To perform this routing, IP uses a hierarchical
addressing scheme that assigns a hardwareindependent (logical rather than physical) address to
every device connected to the Internet
• Recall that the IP address is software defined; it is
distinct from a MAC address that is physically
associated with a LAN adapter such as an Ethernet
card
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IP Addresses
• Each device that communicates over the Internet must
use a unique address known as an IP address
• The traditional standard for IP addresses, called IPv4
(IP Version 4), specifies 32 bits for each address
• An IP address is a combination of 32 ones and zeros
such as the following:
01011110000101001100001111011100
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IP Addresses (continued)
• Industry convention dictates a shorthand method,
dotted decimal format, for discussing and managing
IP addresses
• For example, an IP address in dotted decimal format
might be 94.20.195.220
• The Internet address length of 32 bits theoretically
provides 4,294,967,296 (calculated as 232) unique
addresses
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IP Addresses (continued)
• As the Internet grew internationally and new
applications such as wireless Internet access and
Internet telephony emerged, the Internet Engineering
Task Force (IETF) identified the possibility that the
reserve of Internet addresses might be exhausted
• The need for more global Internet addresses was
recognized in the early 1990s
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IP Addresses (continued)
• The IETF engineered two initial technical approaches
to conserving Internet addresses:
– Classless Interdomain Routing (CIDR), which
eliminated the Class A, B, and C distinctions
– Network Address Translation (NAT), a technique
that allowed a network device such as a router to
share a limited number of public IP addresses
among many devices on a private network
• When a computing device on a private network
accesses the Internet, NAT dynamically allocates a
globally unique, temporary, public IP address for
transmission over the public Internet
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IP Addresses (continued)
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IPv6
• In addition to these address conservation strategies,
the IETF selected a new standard, now called IPv6
(Internet Protocol Version 6), to exponentially
expand the number of globally unique addresses
• Shorthand notation based on the Hex system
• Example of an IPv6 address in Hex shorthand
notation:
– FDDC:AC10:8132:BA32:4F12:1070:DD13:6921
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IPv6 (continued)
•
•
•
•
•
•
•
•
•
FDDC = 1111110111011100
AC10 = 1010110000010000
8132 = 1000000100110010
BA32 = 1011101000110010
4F12 = 0100111100010010
1070 = 0001000001110000
DD13 = 1101110100010011
6921 = 0110100100100001
IPv6 deployment is occurring more rapidly in Asia and other
countries than in the United States
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The Domain Name System
• Even the shorthand dotted decimal format, which was
designed to make IP addresses less unwieldy, is
difficult to remember and use
• Fortunately, Internet users do not have to remember
numeric IP addresses while using the Internet
– Instead, users can employ alphanumeric names that are
easy to remember, such as www.yale.edu.
• These are known as domain names
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The Domain Name System (continued)
• Each domain name has an associated IP address
• Example of a domain name and an associated IP
address:
cnn.com 64.236.29.120
• The DNS is like a hierarchical tree; the suffix, which
is the component at the far right of any domain name,
is called the top-level domain (TLD)
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The Domain Name System (continued)
•
•
•
•
•
•
•
.com (for commercial businesses)
.org (for nonprofit organizations)
.edu (for educational institutions)
.gov (for the U.S. government)
.mil (for the U.S. military)
.net (for networks)
.int (for international entities)
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The Domain Name System (continued)
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The Domain Name System (continued)
• Within a domain name, the word to the left of the toplevel domain is called a second-level domain
• Domain names can also have third- and fourth-level
domains
• A method is needed to translate between
alphanumeric domain names and the associated IP
addresses required for routing information across the
Internet
• This translation is called address resolution and is
performed by the DNS
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The Domain Name System (continued)
• An important architectural component of the Internet
is its collection of root name servers, which are
usually just called root servers
• These servers maintain a master file, called the root
zone file, that lists the names and IP addresses of the
official DNS servers for all TLDs
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The Domain Name System (continued)
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Uniform Resource Locators
• A URL is a string of characters associated with a
specific information resource, such as www.ebay.com,
www.gmu.edu, and so on
• Many URLs relate to Web access via HTTP, but note
that URLs also apply to many other Internet protocols
and information resources
• Instead of “http,” the first part of a URL could
include “ftp” for File Transfer Protocol, “news” for
Usenet news, or other Internet resource types
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Uniform Resource Locators
(continued)
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Internet Applications
• At one point, the Internet primarily allowed file
sharing and electronic mail
• Over time, Internet applications have expanded to the
World Wide Web, text messaging, Internet telephony,
multimedia file sharing, and much more
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E-Mail
• E-mail is a store and forward system that does not
require the simultaneous online presence of senders
and receivers
• The de facto messaging protocol that historically has
supported Internet e-mail is SMTP, or Simple Mail
Transfer Protocol
• Today messages incorporate multimedia and include
attachments, thanks to newer messaging formats such
as MIME
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E-Mail (continued)
• The arrival of e-mail at a local server and its
transmission from the remote server to the recipient
are separate transactions that use different sets of
communications protocols, known as mail retrieval
protocols
– Post Office Protocol (POP)
– Internet Message Access Protocol (IMAP)
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E-Mail (continued)
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Messaging
• Unlike e-mail, text messaging generally requires both
users to be online or on their mobile phones
simultaneously
• When you send a text message to a recipient, a
window opens and displays the message on the
recipient’s computing device
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The World Wide Web
• The Web was a revolutionary advancement over
previous data-sharing tools for several reasons:
– It allows many users to simultaneously access the
same information
– It provides hyperlinked information—clicking a
textual link takes a user to another location
– It combines multimedia information such as video,
text, image, and sound
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The World Wide Web (continued)
• The Web was a revolutionary advancement over
previous data-sharing tools for several reasons
(continued):
– It allows access to anyone connected to the
Internet from any computing platform
– It provides searchable information
– Anyone can develop their own information site
and inexpensively make it available to millions of
people
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The World Wide Web (continued)
• The WWW uses a standard network protocol,
Hypertext Transfer Protocol (HTTP), to establish and
maintain communications over the Internet between a
computer user (client) and a Web site (server)
• Web interactions also require the encoding of
information in a standard format called Hypertext
Markup Language (HTML) or eXtensible Markup
Language (XML)
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The World Wide Web (continued)
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File Sharing and P2P
• The TCP/IP suite has historically provided a specific
protocol to enable file sharing over the Internet: FTP,
or File Transfer Protocol
• As Internet technologies have grown, file sharing has
expanded to include stored videos, audio files, and
images
• P2P file sharing was realized through music- and
video-sharing systems
• Rather than storing files on a server or large database
management system, P2P technologies distribute files
that are stored on the hard drives of individual users
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File Sharing and P2P (continued)
• P2P file sharing of any copyrighted information,
including music and movies, is illegal though
widespread
• A series of well-publicized lawsuits, especially those
brought by the Recording Industry Association of
America (RIAA), have attempted to curtail
downloading of copyrighted information
• However, countless applications of P2P network
technology are legal and hold great promise for
efficiently sharing information
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File Sharing and P2P (continued)
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Internet Telephony
• VoIP is a cost-effective alternative to traditional
telephone service and has quickly become a major
Internet application
• The main advantage of Internet telephony is that
telephone calls are virtually free to users who already
pay for an Internet connection
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Internet Broadcasting
• The advantage of “simulcasting” over the Internet is
that the broadcast has no physical or geographical
limitation
• A radio station can easily broadcast over the Internet
and reach a worldwide audience at very little cost
without having to contend with spectrum limitations
and regulations
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Internet Administration
• Does anyone run the Internet?
• Who is in charge of the many administrative
functions and standards setting that keep the Internet
up and running?
• The success of the Internet as an interoperable,
universal communications medium requires common,
compatible standards
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Administration of Internet Names and
Numbers
• If connecting to the Internet requires an IP address,
and if each address must be globally unique, someone
has to be responsible for allocating and administering
these resources
• The IANA, under the auspices of the Internet
Corporation for Assigned Names and Numbers
(ICANN), still has centralized responsibility for the
IP address space, including both IPv4 and IPv6
• The IANA, in turn, allocates large blocks of
addresses to regional Internet registries (RIRs) and
national Internet registries (NIRs)
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Administration of Internet Names and
Numbers (continued)
• In 1998, the U.S. Department of Commerce issued a
white paper calling for the creation of a private,
nonprofit corporation to administer these names
• This new entity became ICANN
• The greatest controversy over ICANN has involved
the questions of who should make these policy
decisions and have the authority to allocate IP
addresses
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Internet Standards Setting
• The IETF establishes common network technical
specifications and standards for the Internet
• The Internet standards process is complex, and
involves the proposal of a draft standards
specification followed by a period of iterative
revision by a “working group” that anyone can join
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Internet Standards Setting (continued)
• Technical specifications step through a progressive
approval process that begins with the designation of a
proposed standard, evolves to a draft standard, and
culminates in a standard
• The World Wide Web Consortium (W3C) develops
Web specifications
• The Institute of Electrical and Electronics Engineers
(IEEE) establishes Internet-related LAN standards
such as the Wi-Fi specifications
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Internet Open Issues
• The Internet has been accompanied by a host of
economic and social policy questions:
– Should online sales be taxed?
– Should voice services that use Internet telephony
(VoIP) be regulated and taxed, like other more
traditional services?
– How might a major Internet outage or
cyberterrorist attack affect nations economically?
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Internet Open Issues (continued)
• Some countries restrict or prohibit Internet access for
political or religious reasons
– Whose laws should apply, and how should they apply
to a network that transcends national boundaries?
– In what ways will the Internet intersect with politics?
– What are the ramifications of the international digital
divide, in which some countries have widespread
Internet access and computing resources, and others
have limited resources?
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Net Neutrality
• Net neutrality is a phrase that has received a great
deal of attention in the early twenty-first century
• Net neutrality has several meanings, but it generally
refers to the principle of nondiscrimination on the
Internet
• According to the Net neutrality principle, a cable
company that controls a residential broadband
connection should not be able to serve as a gatekeeper
that makes certain content more readily available to
consumers
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Net Neutrality (continued)
• Those who oppose Net neutrality legislation argue
that the Internet’s architecture is not neutral already,
because of how content is presented by search
companies and because of the tiered service-level
pricing offered by service providers
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Net Neutrality (continued)
• Opponents also note that engineering quality of
service (QoS) prioritization is necessary on an
application basis so that latency-sensitive applications
such as video and voice are given a higher
transmission priority than information that is not as
time sensitive, such as data
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Summary
• The Internet is not a single network or technology, but
a collection of systems that can interconnect because
they use common TCP/IP and routing protocols and
common architectural approaches such as packet
switching
• Different service provider networks interconnect at
locations called IXPs
– Peering agreements dictate how they share
costs and provide acceptable performance
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Summary (continued)
• The use of IP is arguably the defining architectural
characteristic of being “on the Internet”
• Devices that are connected to the Internet require an
Internet address—either a 32-bit address under the
IPv4 standard or a 128-bit address under the newer
IPv6 standard
• The DNS is a hierarchical, distributed database
management system that performs the important task
of address resolution
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Summary (continued)
• Internet applications are constantly evolving, but they
fall into the broad categories of e-mail, messaging,
the Web, file sharing, telephony, and Internet
broadcasting
• The Internet requires centralized administrative
coordination, such as managing the IP address space
and establishing standards
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