Internetworking

1
Internetworking

• Prof. Martins
• Department of Computer Science and Computer
  Information Systems

2
Goals

• In this chapter you will learn about
  internetworking
• The motivation
• The hardware
• The architecture

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The Motivation for Internetworking

• Each network technology is designed to fit a
  specific set of constraints
• LAN technologies provide high speed
  communications across short distances
• WAN technologies are designed to provide
  communications across large areas
• No single networking technology is best for all
  needs

4
The Concept of Universal Service

• A communication system that supplies universal
  service allows arbitrary pairs of computers to
  communicate. Universal service is desirable
  because it increases individual productivity.

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A Universal Service in A Heterogeneous World

• Although universal service is highly desirable,
  incompatibilities among network hardware and
  physical addressing prevent an organization from
  building a bridged network that includes
  arbitrary technologies.

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Internetworking

• Despite incompatibilities among network
  technologies, researchers have devised a scheme
  that provides universal service among
  heterogeneous networks, called Internetworking.

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Physical Network Connection with Routers

• The basic hardware component used to connect
  heterogeneous networks is a router.
• Routers resemble bridges (physically)
• Each router is a special-purpose hardware system
  dedicated to the task of interconnecting
  networks.
• The network treats the connection to a router the
  same as a connection to any computer.

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Physical Network Connection with Routers
Fig. 17.1 Two physical networks connected by a
router, which has a separate interface for each
network connection. Computers can attach to each
network.
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Internet Architecture
Fig. 17.2 An Internet formed by using three
routers to interconnect four physical networks.
Each network can be a LAN or a WAN
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Achieving Universal Service

• The goal of internetworking is universal
  service across heterogeneous networks
• Routers must agree to forward information from a
  source on one network to a specified destination
  or another.
• This task is complex because frame formats and
  addressing schemes used by the underlying
  networks can differ.

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Achieving Universal Service

• Protocol software is needed on computers and
  routers to make universal service possible.
• Internet protocols overcome differences in frame
  formats and physical address to make
  communication possible among networks that use
  different technologies.

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A Virtual Network

• Internet software provides the appearance of a
  single, seamless communication system
• The system offers universal service each
  computer is assigned an address, and any
  computer can send a packet to any other computer.
• Internet protocol hides the details of physical
  network connections, physical addresses, and
  routing information.

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A Virtual Network

• An internet is a virtual network system the
  communication system is an abstraction.
• Although a combination of hardware and software
  provides the illusion of a uniform network
  system, no such system exists.

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A Virtual Network
Fig. 17.3 The Internet concept (a) The
illusion of a single network that TCP/IP software
provides to users and applications, and (b) the
underlying physical structure in which a computer
attaches to one physical network, and routers
interconnect the networks.
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Protocols For Internetworking

• One suite stands out as the most widely used for
  internetworking The TCP/IP
• TCP/IP was the first set of protocols developed
  for use in an internet.
• TCP/IP origins ARPA, 1970s
• NSF and others mid-1980s

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Layering and TCP/IP Protocols
Figure 17.4 The five layers of the TCP/IP
reference model
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Layering and TCP/IP Protocols

• Layer 1 Physical corresponds to basic network
  hardware just as Layer 1 in the ISO 7-layer
  reference model
• Layer 2- Network Interface protocols specify how
  to organize data into frames and how a computer
  transmit frames over a network. Similar to layer
  2 protocols in the ISO reference model.

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Layering and TCP/IP Protocols

• Layer 3- Internet Specify the format of packets
  sent across an internet as well as the
  mechanisms used to forwards packets from a
  computer through one or more routers to a final
  destination.

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Layering and TCP/IP Protocols

• Layer 4- Transport Specify how to ensure
  reliable transfer (like layer 4 in the ISO model)
• Layer 5- Application corresponds to layers 6 and
  7 in the ISO model. Each layer 5 protocol
  specifies how one application uses an internet.

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To summarize

• TCP/IP protocols are organized into five
  conceptual layers. Although some layers of the
  TCP/IP reference model correspond to layers of
  the ISO reference model, the ISO layering scheme
  does not have a layer that corresponds to
  TCP/IPs Internet Layer.

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Host Computers, Routers and Protocol Layers

• TCP/IP defines the term host computer to refer
  to any computer system that connects to an
  internet and runs applications
• A host can be as small as a personal computer or
  as large as a mainframe.
• TCP/IP protocols make it possible for any pair of
  hosts to communicate, despite hardware
  differences.

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Host Computers, Routers and Protocol Layers

• Both hosts and routers need TCP/IP protocol
  software.
• A router does not need Layer 5 protocols for
  applications (such as FTP, since routers do not
  run such applications)

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Summary

• Physically, an internet is a collection of
  networks interconnected by devices called routers
• Conventional computers that connect to an
  internet are called hosts
• Logically, an internet appears to be a single,
  seamless communication system

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Summary

• The illusion of a single communication system is
  provided by internet protocol software.
• The most important protocols developed for
  internetworking are known as the TCP/IP Internet
  Protocols.
• TCP/IP protocol software works well and handles
  large internets.

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Summary

• In addition to being used on many private
  internets, TCP/IP is used on the global Internet
  that reaches over 82 million computers in 210
  countries.