Transcript Document

Many Independent Networks
•
By late 1970s, many
organizations began installing
Local Area Networks because
they:
– Were inexpensive.
– Were easy to install
– Could operate them
independently of a central
administration.
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The Proliferation of LANs
• Advantages
– An organization
can:
• budget funds
• decide who has
access
• devise policies for
use
• Disadvantages
– Independent
groups can:
• Encourage
proliferation of
different LAN
technologies
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Facts About LANs
• Engineers have devised many
LAN technologies
• LAN performance determines
cost.
• LAN technology may only work
with specific computers.
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LANs Are Incompatible
• Various LAN technologies are
completely incompatible.
– Connecting multiple LANs is not
possible
• Engineered to operate over limited
distance
• May be electrically incompatible
• Encoding information may not make
sense to another LAN
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Wide Area Technologies Exist
• WAN technology includes an
additional special-purpose
computer at each site that:
–Connects to the transmission
lines
–Keeps communication
independent of the computer
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Few WANs, Many WANs
• WANs cost much more than
LANs.
–Require more planning
–Require more hardware
• Only a few companies build
their own WAN.
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WANs And LANs Are
Incompatible
• Many Wide Area Networks and
Local Area Networks exist.
–Cannot connect a WAN to a
LAN
–Cannot interconnect the wires
from two different networks
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The Desirability Of A Single
Network
• Users should not have to:
– Transfer data manually between one
network and another.
– Move from one computer to another
to access different resources.
• The best solution is for a computer
to have access to all resources.
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The Department Of Defense
Had Multiple Networks
• The Defense Department became
interested in networks by the late
1960s.
• ARPA realized that each network:
– Connected a set of computers.
– Formed an isolated island with no
path between the islands.
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Connecting Disconnected
Machines
• ARPA started with a few basic
ideas.
– Awarded grants to researchers in
both industry and academia
– Arranged for cooperation in solving
problems
• Discussed findings
• Generated new ideas at regular
meetings
• Built a prototype to test their ideas
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The Internet Emerges
• ARPA funded research
to investigate ways to
solve the problem of
incompatible networks.
– Became known by the
name Internet
The Internet Emerges by Melissa Lee
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The ARPANET Backbone
• The ARPANET:
–Served as a standard network to
move data
–Allowed researchers to evaluate
new network software and
applications.
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Internet Software
• Software makes it possible to
interconnect networks.
–Consists of many programs that
interact in complex ways
–Formed an integrated system
–Resulted in a smooth, almost
seamless design
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The Name Is TCP/IP
• Two pieces of Internet software
stand out as important and
innovative.
– The Internet Protocol (IP)
• Provides basic communication
– Transmission Control Protocol (TCP)
• Provides additional facilities
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The Shock Of An Open
System
• ARPA made the research public.
– Asked researchers to:
• Document results in a report.
• Document all experience installing and
using the software.
• Maintain an open system of compatible
technology.
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Open Systems Are Necessary
• A large organization needs an
open system because it:
–Acquires computers from multiple
vendors.
–Does not restrict computers that
connect to the network.
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TCP/IP Documentation Is
Online
• Initially researchers planned to
issue report in two steps:
– Available for comment
• Request for Comments (RFC)
– Finalized version
• Internet Engineering Note (IEN)
• Eventually RFC reports became the
official record.
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The Military Adopts TCP/IP
• By 1983, ARPA expanded the
Internet to include all military sites
connected to the ARPANET.
– Marked a transition for the Internet
– Changed the Internet from an
experiment to a useful network
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Glossary
• ARPA
•
– Abbreviation for Advanced Research
Projects Agency.
Backbone Network
– Used to refer to a central network to
which many routers connect.
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Glossary
• Internet
•
– The collection of networks and
routers that use the TCP/IP protocol
suite and function as a single, large
network.
Open System
– A non-proprietary technology or
system: any vendor can use the
specifications of an open system to
build products and services.
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Glossary
• RFC
•
– Abbreviation for Request For
Comments.
TCP/IP
– Literally, the name of protocols that
specify how computers communicate
on the Internet.
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Glossary
• TCP/IP Software
•
– The name of the software that
implements the protocols.
Wide Area Network (WAN)
– Any network technology that can
span long geographic distances.
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