Chapter 17' Internetworking: Concepts, Architecture, and Protocols

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Chapter 17. Internetworking Concepts,
Architecture, and Protocols

• Jing Wang
• Towson University

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Motivation for internetworking

• No single networking technology is best for all
  needs

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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.
• 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

• internetwork (internet)
• Internet (global Internet)

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Physical Network Connection With Routers

• Router
• A special-purpose system dedicated to the task of
  interconnecting networks.
• Can interconnect networks that use different
  technologies, including different media, physical
  addressing schemes, or frame formats

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• Figure 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

• An internet consists of a set of networks
  interconnected by routers.
• The internet scheme allows each organization to
  choose the number and type of networks, the
  number of routers to use to interconnect them and
  the exact interconnection topology.

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• Figure 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

• Task is complex because of the differences in
  underlying networks
• Frame formats
• Physical addresses
• Universal service
• Each computer is assigned an address, and any
  computer can send a packet to any other computer

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A Virtual Network

• An internet is a virtual network
• Because the communication system is an abstraction

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• Figure 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

• The TCP/IP Internet Protocols (TCP/IP)

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Layering And TCP/IP Protocols

• TCP/IP layering model (Internet Layering Model or
  Internet Reference Model)
• 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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• Figure 17.4. The five layers of the TCP/IP
  reference model.

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The five layers of the TCP/IP reference model.

• Layer 1 Physical
• basic network hardware
• Layer 1 in ISO 7-layer reference model
• Layer 2 Network Interface
• Specify how to organize data into frames and how
  a computer transmits frames over a network
• Layer 2 in ISO 7-layer reference model
• Layer 3 Internet
• Specify the format of packets sent across an
  internet as well as mechanisms used to forward
  packets from a computer through one or more
  routers to a final destination
• Layer 4 Transport
• Specify how to ensure reliable transfer
• Layer 4 in ISO 7-layer reference model
• Layer 5 Application
• Specify how one application uses an internet
• Layers 6 and 7 in ISO 7-layer reference model

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Host Computers, Routers, And Protocol Layers

• Host computer
• Any computer system that connects to an internet
  and runs applications
• TCP/IP protocols make it possible fro any pair of
  hosts to communicate, despite hardware
  differences.
• Router
• Do not use protocols from all layers
• e.g. a router does not need Layer 5 protocol for
  applications like file transfer

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Summary

• Routers
• Hosts
• A single, seamless communication system internet
  
• The illusion is provided by internet protocol
  software
• TCP/IP Internet Protocols (TCP/IP)
• Reaches 82 million computers in 210 countries